Geology Lab Final

Lab 4 Slide 8: Great Sand Dunes National Park

A dune looks like a ripple only it's much larger. If you examined the side of a sand dune layer up close, you would see a fine layering or laminations of the sand grains inclined at an angle to the main sedimentary layer or bedding. I've drawn them in on the top photo of a dune at the Great Sand Dunes. These laminations are called cross-bedding. Cross-bedding forms as the sand dune migrates in the direction the wind is blowing. Grains of sand blown by the wind along the top of the dune tumble down the steeper side of the dune. In this way, the internal cross-bedding is tilted or leans in the direction that the wind is blowing.

Lab 3 Slide 10: Types of Volcanoes

A volcano is a mountain or hill with a crater or vent through which lava, rock fragments, hot vapor, and gas are ejected. Volcanoes can be grouped into the following three basic types. Shield volcanoes like those on Hawaii form by non-explosive eruption of flowing basaltic mafic lava. Lavas flow along the earth's surface gradually building up to form a broad, gently sloping volcanic shape that resembles a warrior's shield. These are the largest of the volcano types. In contrast, medium sized stratovolcanoes like, Mt. St. Helens, build from both explosive and flowing eruptions. Alternating layers of blown out material and lava flows create the steep-sided, often symmetrical cones that we think of as the classic volcano shape (e.g. Mt. Fuji in Japan). Since the magma in these volcanoes are so explosive, when it is extruded as lava it cannot flow far. Magma that forms stratovolcanoes is derived from the partial melting of the subducting slab at subduction zones. Lastly, there are the small cinder cones—the smallest of the three volcano types—cinder cones primarily form from the explosive eruption of basaltic lava. They occur on continents in areas of rifting (e.g., southwestern US, Sunset Crater), or on the flanks of shield and stratovolcanoes. The erupting lava is blown into fragments called cinders, which fall from the air after eruption and accumulate in the shape of a cone around the volcano's central vent.

Lab 8 Slide 10: Seismic-hazard risk map of the US

Accurate prediction of earthquakes would help reduce catastrophic losses. However, fault movement does not occur predictably on short timescales of days, months, or even decades. And precursors to earthquakes, like foreshocks and ground level changes, are unreliable. But based on the average time between large earthquake events, earthquakes can be predicted over the long term based on their probability (or likelihood) to occur over a certain time-span. By documenting the history of past earthquakes, seismologists can produce seismic risk maps, which express the probability of an area experiencing a large earthquake. This type of information is useful for land-use and disaster planning, as well as, for developing appropriated building codes. Not surprisingly, seismologists estimate that the west coast of the US has a greater probability of experiencing a larger earthquake than much, but not all of, the rest of the US. What is surprising is the high risk bullseye region of the New Madrid area between St. Louis, Missouri and Memphis, Tennessee. The largest historical earthquake in the lower 48 states occurred in Missouri - it was in the New Madrid region (the large pink area in the central US), which is why this region is designated as a very high seismic-risk hazard. Another seismic hotspot in the east is the smaller bullseye related to the 1886 Charlotte earthquake. These seismic risk hotspots are surprising because they occur in the middle of the North American plate far from any tectonic plate boundary. These earthquakes are referred to as intraplate earthquakes.

Lab 9 Slide 2: Topographic Maps and their elements

All topographic maps contain certain basic elements, such as, location, direction, and scale. Location is depicted broadly by the maps title and specifically by a grid system - typically latitude/longitude. Latitude is the angular position above or below the equator (0 degrees). Longitude is the angular position east and west of the Prime Meridian, a line drawn from the North Pole to the South Pole through Greenwich, England. Identification of latitude and longitude define a unique point on the surface of the earth. For instance Kent State University's Kent Campus location, or coordinates, are 41.15 degrees North and 81.34 degrees West. Direction on a map is given by a north arrow which is typically located to the left of the scale bars. Most maps are oriented so that north is straight up. The arrow with the star denotes true north, and the arrow with the MN symbol is magnetic north (the north direction the compass points to). Map scales allow us to determine the distance between points on the map and they represent the distance relative to the actual ground distance. Scales are represented in two ways: 1) proportionally and 2) graphically. The proportional scale, such as 1:24,000, tells us that one inch on the map equals 24,000 inches on the ground. The graphic scales (3 bars shown here) represent distance in miles, feet, and kilometers. Contour lines are used to depict the topography of the land surface - they are typically brown lines on physical maps. A contour connects all points of the same or equal elevation. If you walked along one contour line you would never go up or downhill. Numbers printed along a contour indicate the elevation of the line - typically in feet above sea level. Below the scale bars, the contour interval is indicated in this image as 40 feet. To make maps easier to read, every fifth contour line is bolded. On this map, the elevation change between the bolded contours is 200 feet (the 5000, 5200, and 5400 feet bold contours). When reading topography, one important aspect of an area is the difference in elevation between the highest and the lowest points on a map - that is known as the maps relief. Rugged areas have high relief

lab 1 slide 2: Atomic Structure

An orderly atomic structure means that the elements making up the mineral are fixed in a specific, orderly pattern that give the mineral a crystal shape. Think of soldiers lined up in rows or scaffolding for a building. The arrangement of atoms in a geometric pattern gives the mineral its crystal shape - which are often pleasing to look at, such as this single crystal of quartz on the left. A crystal then is a solid material whose atoms are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, large single crystals are usually identifiable by their geometrical shape. Snowflakes, diamonds, and table salt are examples of large crystals. Solids with atoms that are not aligned in an orderly pattern (think students lounging around at a party) are noncrystalline, glass being an excellent example of a noncrystalline solid. You may be surprised to learn that crystals, minerals that display flat external surfaces or faces, are quite rare in nature because they form best in open spaces or cavities. This is why minerals that form in the hollow interior cavity of geodes often exhibit excellent crystal forms - the mineral grows into an open space and is therefore free to take on its complete crystal form. Most minerals form in contact with other minerals or in a melt - and as such many minerals in rocks do not exhibit such spectacular 3D crystal shapes.

Lab 4 Slide 9: Cross bedding

Ancient sand dunes in the sedimentary rock record can preserve large internal cross-bedding (the slightly curved layers shown here). Knowing how sand dunes and cross-bed form today, we can not only say that the Navajo Sandstone in Zion National Park represents a desert environment, we can even know the primary direction the wind was blowing 180 million years ago when these dunes were forming. I've outlined the main bedding planes for one bed which has cross-bedding in it that's tilted to the right-so that's the direction the wind was blowing at the time this bed was forming.

Lab 4 Slide 10: Graded bedding features

Another sedimentary structure that occurs in some beds is graded bedding. A graded bed exhibits a gradual change in grain size from the bottom of the bed to the top of the bed, as shown on the left diagram for a single bed. Normally grain size is largest at the bottom and decreases gradually upward toward the top. The photo on the right shows seven different graded beds deposited one on top of the other about 1 billion years ago in British Columbia. I've outlined the thickest of the graded beds (#4) shown with a solid line at the base of the bed and a dashed line at the top of the bed. The lighter portions of each bed are coarser sand which is overlain by finer dark clay. Each graded bed formed by the settling out of a quickly moving underwater avalanche. Larger grains in the avalanche sink faster through a fluid than do finer grains, so when the avalanche slows down, the coarsest sediment settles out first. Progressively finer grains accumulate on top, with the finest clay sediment settling out last.

Lab 2 Slide 5: Rates of plate motions from the size of oceans

Another way to determine past rates of geologic plate motions, is by examining the size and age of growing oceans like the Atlantic Ocean. Growing oceans are bordered by continents with passive or quiet margins such as what we presently see along the margins of the Atlantic Ocean. Since the supercontinent Pangea started to break-up around 200 million years ago, the Atlantic Ocean has been slowly expanding and the Americas have been getting further and further away from Africa and Europe. The Mid-Atlantic Ridge (MAR) is a mid-ocean ridge, a tectonic plate boundary located along the floor of the Atlantic Ocean, and part of the longest mountain range in the world. The tectonic plates on either side of the ridge are moving away from each other. Rifting at the MAR continues today, gradually expanding the Atlantic Ocean, which means that slowly but surely the Atlantic Ocean is getting bigger. By measuring the size of the Atlantic Ocean and by knowing how old it is (in millions of years), we can determine the average rate of sea-flooring spreading in the geologic past.

Lab 9 Slide 5: Making contour lines

Any 3-D surface can be contoured and then easily visualized in 3-D, if you know how to read contour maps. For instance, water tables below ground are often mapped (contoured) by hydrogeologists to evaluate which way ground water is flowing in an area. Such information is vital for predicting where contaminated water might end up in the subsurface. On the left are points of known elevation in an area and on the right is the same map contoured every 25 units (starting at 225). The contour map shows the 3-D shape of the feature which can be visualized quickly and interpreted correctly. The highest contour around the two peaks is the 325 elevation and the lowest contour is the 225 elevation. All points outside of the 225 contour must be less than 225 units and all elevation points between the 225 and 250 contour must be between 225 and 250 units, etc.

Lab 8 Slide 7: How do Earthquakes cause damage?

At 9:40 am local time, November 1, 1755 a great earthquake (likely 9.0 Richter magnitude) destroyed Lisbon, Portugal. The fact that it occurred on the holy day of All Saints' Day when many where attending Church, likely contributed to it being one of the deadliest earthquakes in history. Ground shaking led to the collapse of many buildings, but shaking is only one part of how earthquakes cause damage. Historically fires have played a huge role in earthquake damage as have tsunamis, especially recently with the increased global population in coastal regions. More locally the sudden collapse of sediment and the sudden triggering of landslides are two other important components of earthquake-related destruction.

Lab 1 Slide 4: Common rock forming minerals - Quartz

Before we go any further, let's take a quick look at some common rock forming minerals. Pay attention to how I describe these few minerals - what physical properties I mention. Let's start with quartz, which is essentially pure Silicon and Oxygen (SiO2) plus some minor impurities. Quartz is the most familiar of the rock forming minerals - and it makes up around 25% of Earth's continental crust. It has a glassy luster, and a six sided prism form ending in a six-sided pyramid. It's also the hardest of the common minerals, being number 7 (out of 10) on the mineral hardness scale.

Lab 4 Slide 13: Chemical Sedimentary Rocks

Chemical sedimentary rocks are precipitated directly from water. Salt deposits form by precipitating halite or salt crystals directly out of evaporating saltwater. Deposits that form from evaporation of water are called evaporates. Chert is formed by precipitation of silica or quartz directly from water. Chemical sedimentary rocks that precipitate directly out of water have a crystalline texture.

Lab 4 Slide 3: How would you describe these two sed rocks?

Clastic sedimentary rocks consist of fragments of other rocks cemented together. Because of this, they tend to break easily and are relatively soft. How would you describe these two clastic sedimentary rocks? What characteristics would you mention in describing them? We know that all rocks within a rock group are classified on the basis of: 1) composition and 2) texture. Clearly these two rocks have very different textures-so let's start with the most obvious part of rock texture— that is, grain size. Rock A has a variety of grain sizes, some of which are quite coarse, much larger than 2 mm in diameter, some intermediate sized sandy grains, and many that are fine grained, that is, they are less than 1/16 mm in diameter. Rock B consists of mostly all intermediate sized grains that are about the size of sand. Another visible feature is the angularity or absence of roundedness of the coarse clasts in rock A. Overall the clasts have sharp edges with pointy intersections; they are not very circular or rounded. The angularity of grains is hard to see in intermediate to fine grained rocks, but I do know that the grains in rock B are quite rounded. What about the composition of the grains? The variety of grain colors in rock A suggests that they are composed of many different compositions. The large grains are rock fragments, also known as lithic fragments. In contrast again, rock B is composed mostly of quartz sand grains. The felsic minerals quartz and feldspar are very common in intermediate and fine grained sedimentary rocks because they resist weathering and disintegration. In contrast, the mafic minerals weather and break down or fall apart more easily. This is why fine-grained muds are commonly made of quartz, and feldspar minerals, and some clay, and sandstones are often composed primarily of quartz grains and minor feldspar.

Lab 5 Slide 5: Recrystallization of a biochemical limestone

Contact metamorphism often results in recrystallization of the original grains or crystals making up the rock. Heating provides energy to the rock which enable crystals to break bonds and reform as larger crystals of the same composition. In recrystallization, the rock maintains its original composition or mineralogy but with a new texture. A great example of recrystallization occurs when fossiliferous limestone (on the left) is baked or contact metamorphosed to form large calcite crystals in marble (on the right). Both of these rocks are made up of the mineral calcite (CaCO3); the fossiliferous limestone is the sedimentary protolith that has been completely recrystallized into the metamorphic rock marble. Likewise quartz sandstones often get baked into quartzite by contact metamorphism.

Lab 11 Slide 2: Porosity

Contrary to popular belief, only a very small proportion of groundwater occurs in caves. There are gasoline storage tanks below gas stations, but for groundwater and oil and gas for that matter, there are no big tanks! (Except in rare cases). Just as for a sponge, groundwater resides within small open spaces between grains of sediment or rock, and within cracks in rocks. Such empty spaces are called pores and the total amount of pore space is called porosity. Geologists specify porosity as the percentage of open or pore space in a rock. Despite the well-known saying "solid as rock", you may be surprised to learn that some rocks have 20-35% porosity, meaning that 20-35% of the rock consists of open space. Incredible!

Lab 7 Slide 2: Convergent Boundaries

Convergent boundaries are places where two plates in contact are moving toward one another, they are converging, as shown by the arrows on this block diagram. Here, one plate dives or sinks back into the mantle, a process called subduction. When oceanic and continental lithosphere converge, the down-going plate, which is ultimately destroyed and disappears, is always the more dense oceanic lithosphere. Subduction recycles oceanic lithosphere - which is why oceans are so young. Subduction also results in melting and formation of magma that rises to form volcanoes. Examples of this are volcanoes in the Andes mountain range in South America and the Japanese islands.

Lab 1 Slide 10: Fracture and cleavage; density

Different minerals fracture (break) in different ways, depending on the internal arrangement of atoms. Some minerals break along one or more distinct planar surfaces that have a specific orientation in relation to the crystal structure. Such planes are called the cleavage planes. Mineral cleavage planes form along planes across which the chemical bonds holding the atoms together in the crystal are the weakest. Some minerals produce only one such set of cleavage planes, while some produce multiple sets of cleavage planes as shown here. For instance, muscovite mica has weak bonds in one direction. Hence it easily splits into parallel sheets. Calcite, on the other hand, has weak chemical bonds in three different directions. So it breaks along three different planes, which are not parallel to each other. In absence of any cleavage planes, minerals can break along irregular fracture planes. Quartz does not have any cleavage so it breaks in a characteristic fashion forming wavy fracture planes. Such fractures are described as 'conchoidal' fracture. Specific gravity represents the density of a mineral. It is the ratio of the density of a volume of mineral divided by density of equal volume of water. Minerals that are made up of heavy elements have high specific gravity while those made up of lighter elements have low specific gravity.

Lab 10 Slide 4: Fault contact

Discovering and extracting mineral and energy resources requires knowing something about geologic structures. Specifically it requires us to know how to read and interpret the Rock Record. Now the three rock groups are only one part of the rock record. The entire rock record includes the three rock groups, their contacts (how they are in contact with each other that is), and their geometry. Fortunately, there are only three types of contacts - only three ways that rocks can be in contact with each other. They are: 1) intrusive, 2) depositional, and 3) faults. This is an aerial photo of sedimentary rocks in Nevada that have been faulted. The fault plane is depicted with a white dashed line. Faults are fractures or large breaks in rocks across which movement has occurred. We can see that movement has occurred because the rocks on either side of the fault don't match up. Note how the thinly bedded grey layers labeled A don't line up across the fault. We would say that the rocks on either side of the dashed line are in fault contact with one another. In summary, these are sedimentary rocks that were first deposited and then faulted.

Lab 8 Slide 8: Ground shaking

Earthquakes start suddenly and may last from a few seconds to several minutes. The severity of ground shaking and damage at any given location depends on four factors: 1) the magnitude of the earthquake, because greater magnitude earthquakes release more energy 2) the distance from the epicenter, because energy decreases away from the source 3) the duration and frequency of the vibrations, and 4) the nature of the sediment and rock beneath the ground surface. Strong bedrock can transmit waves quickly resulting in less damage, whereas, weaker material in the subsurface (such as soft sediments) amplify the seismic waves and increase the ground shaking.

Lab 1 slide 1: Minerals are

Everything we live on is composed of minerals and rock, or the weathered remains of rock. Minerals are the building blocks of rocks. They make up all of the rocks and sediments on Earth. So understanding How the Earth Works requires understanding minerals. In the next few labs we will explore minerals and rocks, the primary Earth Materials, we will discuss some of their properties and how to identify them. What is a mineral by definition? First, it's a solid material formed by geologic and sometimes biologic processes - in other words, it's a naturally occurring solid. Second, it has an orderly atomic structure which gives it a crystal form and a specific chemical composition, and lastly, its mostly inorganic. Now, solid and naturally occurring are self-explanatory terms, so we know that water and homemade ice cubes are not minerals, but that naturally occurring ice is a mineral. But what do we mean by an orderly atomic structure?

Lab 3 Slide 11: Volcanic Hazards

Explosive volcanoes can pose many hazards, and not just in the immediate vicinity of the eruption. Volcanic ash can be a threat to aircraft, in particular those with jet engines where ash particles can be melted by the high operating temperature. Large eruptions can affect temperature as ash and droplets of sulfuric acid obscure the sun and cool the Earth's atmosphere. Historically, so-called volcanic winters have caused catastrophic famines. The serious hazard to aviation posed by invisible ash clouds has prompted development of methods to predict where the ash clouds will travel following an eruption. Many of the world's busiest air traffic corridors pass over hundreds of active volcanoes capable of sudden explosive eruptions. Here's a great satellite image of the 2011 Chile eruption which shut down airports hundreds of kilometers away in Argentina and affected air travel as far away as New Zealand. The reason this happened was because ash is gritty and can abrade airplane engines. In the United States, aircraft carry thousands of passengers and millions of dollars of cargo over active volcanoes every day. In this exercise you will do some simple calculations about the impact of the 1980 Mt. St. Helens eruption.

Lab 10 Slide 11: Faults in block diagrams

Faults are planes of breakage in rocks across which there has been movement. These four block diagrams show four very common faults that geologists map in the field over and over again in different parts of the world. Faults are classified according to their orientation (typically their dip) and how the blocks on either side of the fault moved. For instance, a normal fault (upper left block) is typically steep and the hanging wall block (the block above the fault) has moved down with respect to the other side (typically called the footwall block). Strike-slip faults (upper right) are typically oriented vertically and the blocks move sideways. The two lower blocks show faults that have hanging walls which moved upwards relative to the other block. See how the arrow above the fault points upwards? When a hanging wall up fault is steep it's called a reverse fault because it's the reverse motion of a normal fault. And when a hanging wall up fault dips gently, it's called a thrust fault. The Google image shows faulted layers in eastern Iran, most of which are oriented east-west. See how many separate faults you can find in this beautiful photograph

Lab 10 Slide 1: Geologic structures

Geologic structures, such as faults and folds, are produced when rocks break or bend due to the great forces typically associated with plate tectonic movement. The response to stress is called rock deformation. Before deformation, the crust typically consists of crystalline basement rocks overlain by horizontal strata or layers of undeformed sedimentary rocks. When these crustal rocks are pulled-apart or extended, they are typically faulted into blocks which are tilted, as shown in the middle diagram. Topographic basins and ranges commonly form into which sediment is deposited. Faulting results in tilted beds and in a jumbling of the initial stratigraphic order of sedimentary units. When crustal rocks are compressed by continents colliding, shortening of the rocks also results in faulting as well as folding, as seen in the lower crosssection. In this lab, you will learn about the different types of contacts and the different types of faulting and different geometries of folding. Importantly, you will learn about how geologists use maps of deformed regions to construct cross sections of deformed regions in the subsurface

Lab 4 Slide 4: What does clast size relate to?

Grain size refers to the diameter of a clast or grain. Names used for clast size, from largest to smallest, are boulders, cobbles, pebbles, sand, silt, and clay (or mud). What does clast size relate to? The farther sediment has been transported, the smaller the grains. Why? Well large blocks of rock that tumble off cliffs slam into other blocks and break apart, and those blocks break into even smaller clasts as they travel and are carried downstream in a river. As the stream loses energy at low elevations, it's not able to carry boulders, cobbles, and pebbles so only smaller sand, silt, and clays continue to move downstream. So clast size can indicate how far the sediment was transported away from the source as shown in this diagram.

Lab 1 Slide 12: Moh's Hardness scale

Hardness is the ability to resist scratching and geologists use the Moh's hardness scale shown on the right to help them identify minerals. The softest mineral on earth with a hardness of 1 is talc, which talcum powder is made from. Gypsum, which is used for drywall, is 2, calcite is 3, quartz is 7 which I mentioned earlier, and diamond is 10, the hardest mineral on earth. Since a harder material always scratches a softer material, we can use common materials with known hardness to test an unknown minerals hardness. For instance, your fingernail, which has a hardness of 2.5, will scratch gypsum, but not calcite. And a steel file will scratch orthoclase but not quartz.

Lab 10 Slide 10: More fold shapes in block diagrams

Here are some colored block diagrams of different fold shapes. Spend a few minutes looking at the three different views provided for each block. The top two blocks show folds that do not plunge, the middle two show plunging folds with their V-shape in map view, and the bottom two blocks show a dome-shaped fold on the left (like an upside down bowl) and a basin-shaped fold on the right (like a right-side up bowl). The two Google images on the right show a large scale dome in Morocco (top) and basin in Iran (below). Note how the photos look like the geologic maps of the bottom block diagrams on the left. Very cool!

Lab 6 Slide 8: A more complicated history depicted in block-diagram

Here's a block-diagram of an area with a more complicated geologic history. The relations illustrated here can be used to give structures a relative age. Let's summarize these events in order using the letters A through F for ease of explanation. A represents folded rock strata cut by a fault labeled X. B is a large intrusion which cuts through A and fault X. C is an angular unconformity which cuts off A and B on which rock strata were deposited. D is an igneous dike which crosscuts A, B, and C. E is a younger sedimentary rock unit that overlies C and D. And finally F is a fault cutting through A, B, C, and E. We are going to return to this shortly after a brief introduction to numerical age dating using radioactivity.

Lab 3 Slide 8: Igneous rock classification chart

Here's a cool chart that you will use in this lab to identify and name most igneous rocks that you will ever see. Rock composition is divided into felsic, mafic, intermediate (which is in between felsic and mafic) and ultramafic or super magnesium and iron rich rocks. The first row of rock names, rhyolite, andesite, and basalt are the finegrained igneous rocks and the second row are the names of coarse grained intrusive rocks, granite, diorite, gabbro, and peridotite (which is mantle rock). The minerals and their relative abundances in each rock are shown in the lower half of the chart. We can see that the felsic rocks rhyolite and granite consist primarily of the felsic minerals quartz and both feldspars and small amounts of mica. The intermediate rock, Andesite, is fine-grained and consists of feldspar (most), mica, amphibole, pyroxene, and possibly quartz.

Lab 5 Slide 8: Metamorphic Rock Identification Chart

Here's a metamorphic rock ID chart that you will use in this week's lab. To ID a metamorphic rock, work from left to right starting with whether or not the rock is layered or foliated, then looking at grain size (fine, medium, or coarse), and considering mineral composition. From your observations and with proper descriptions, and practice, you can then learn to identify these beautiful rocks.

Lab 9 Slide 7: Shaded relief digital elevation map of the US

Here's a really great map of the US published by the US Geological Survey. The nation's varied topography is easily seen on this shaded relief image. Note the 'rough' texture (topographic relief) in the west and the 'smooth' regions in the central and eastern US. The starkly different landscape of the United States is a product of tectonic age. The western third of the US stands tall and rugged because of its tectonic youthfulness compared to the older more mature Appalachians in the east and especially the ancient Precambrian interior of North America in the center.

Lab 4 Slide 14: Sedimentary rock classification

Here's a simple classification table for clastic and chemical sedimentary rocks-the ones we have discussed. First, determine if the sedimentary rock is clastic, biochemical, or chemical. Then, use its grain size and other diagnostic properties such as roundness, sorting, and composition to determine the appropriate rock name. Note that grain size is the most important criteria and that there are even simple field tools, like the ruler shown, that can be used to accurately determine grain size in the field or in the lab.

Lab 10 Slide 9: Plunging anticline, Iran

Here's a spectacular oblique Google Earth image of a plunging anticline in Iran. Note how the sedimentary layers dip away from the middle of the fold (making it an anticline) and how the fold wraps around in a V shape indicating that it is plunging in the direction that the V points.

Lab 10 Slide 8: Block diagrams of folds

Here's what the fold structure looks like in a 3-D block diagram. Note how the top surface looks just like the map above. Then note how the front surface shows an anticline fold with the left limb dipping to the left and the right limb dipping to the right. Then note how the side surface shows units B, C, and D which look horizontal because we are looking at the fold from the side. That's it! Now deformed regions can have complex geometries both in map view and in block diagram. The block diagram on the right from geologycafe.com shows two anticline (up-arched) folds separated by a syncline (down-arched) fold with the noses of the folds plunging northward into the subsurface. Note how the map geometry looks different from the simpler fold on the left. See how the strikes on the map change direction around the fold? Also, note the V pattern of the geologic units on the map. That's a result of the folds plunging downward toward the north. Finally, note how the side view shows the two anticlines with the syncline in between. Kind of like a stretched out letter M.

Lab 3 Slide 4: Melt cools and hardens to form igneous rock

Hot melt that exists in the crust or upper mantle beneath the earth's surface tends to rise up and eventually cool and harden by crystallization to form igneous (or fire) rock. Magma in the surface that rises and cools and hardens in the subsurface forms an intrusive or plutonic rock. Sometimes, melts breach the earth's surface to form lava which can flow or erupt as volcanoes and form extrusive igneous or volcanic rocks. Lava at the earth's surface cools quickly and mineral grains that form are tiny because they haven't had time to grow. In contrast, magma that hardens in the subsurface cools more slowly, giving mineral crystals time to grow into larger grains. So it's largely the cooling rate that controls grain size of an igneous rock. Now note how the lava on the top left is blackish and the rock on the bottom left is a light colored granite. What makes some igneous rocks lighter and some darker?

Lab 1 Slide 8: : Minerals can be identified by

How did I identify these few minerals? What physical properties did I use to describe the minerals? Color is an obvious physical property and some minerals are easily identified by their distinct color, such as olivine (which was named after its green color). But color alone is not a good diagnostic property as many minerals come in a variety of colors. Here we have four different colored variations of quartz, for instance. Other properties I used were crystal form, hardness, density, luster (which is how a mineral reflects light), and the number of fractures or cleavage planes. Other special properties can sometimes be used for individual minerals. Magnetite is strongly magnetic, halite or salt tastes like salt, and calcite fizzes by releasing CO2 with the application of a weak acid.

Lab 8 Slide 2: Generating Earthquake energy

How does faulting generate earthquakes? What actually happens before, during, and after an earthquake? One hundred-year-old studies of fences built across faults in California were key to recognizing how earthquakes occur. Consider a white picket fence built across an active fault (this is represented by the offset yellow lines across the fault). When solid objects are initially stressed, they don't break immediately, they bend slightly. In fact, if the stresses where removed, the object would unbend, or rebound to its original shape. This is called elastic deformation - similar to what happens with a stretched rubber band. In a sense a stretched rubber band stores energy, which can be felt when the stretched rubber band breaks. Rocks are a little bit elastic and store energy and bend under applied stresses. But at some point the stresses get too high, the strength of the rock is exceeded, and the rock ruptures, releasing the stored energy as seismic waves. The energy released radiates outward in all direction. After rupture, the rocks on either side of the fault rebound to their former un-deformed state. You can see this in diagram c where the broken fence on either side of the fault is straight again. This process tends to be cyclical. With time, the initial geometry of the rocks change again as stress builds up again. Eventually rupture occurs by movement along the fault, the rocks rebound, movement stops due to friction, and the cycle starts over again. The elastic-rebound theory suggests that faults move in quick jumps, separated by periods of no-movement. Geologists call this 'stick-slip' behavior, given that faults appear to stick for certain periods and then slip briefly before sticking again.

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Lab 10 Slide 3: Structural traps

In addition to their beauty and historical significance, geologic structures like folds and faults are also important for practical reasons - they often form traps which capture and store natural resources such as oil and gas. In some places sedimentary beds are no longer horizontal as they were when they were originally deposited. An anticline is a fold with an arch-like shape like the fold shown here. If the rock layers in the anticline include an oil rich layer that is overlain by a seal rock, then, voila, we have the recipe for an oil reserve. Sometimes movement or displacement from faulting creates a fault contact between rocks with different permeability. Because the oil rich rock was tilted, oil and gas migrate upwards until it is trapped between impermeable seal rocks.

Lab 10 Slide 6: Depositional contact

Lastly, this photo shows a light grey laminated sedimentary rock deposited on top of a conglomerate. Both of these rocks formed at the earth's surface. Here, the younger sedimentary rock was laid down initially as sediment on top of the older conglomerate, making this a depositional contact. So the three types of contacts are: 1) a fault contact, 2) an intrusive contact, and 3) a depositional contact.

Lab 7 Slide 5: Transform Plate Boundaries

Lastly, transform plate boundaries occur when two lithospheric plates move sideways with respect to each other, sliding past one another horizontally. In this case, lithosphere is not being created or destroyed, so there is no associated volcanism along this boundary zone and earthquakes that occur because of breaking and sliding along the fault zone are all shallow, extending only as far down as the thickness of the plate. Most commonly transform boundaries appear to offset oceanic ridge segments. There are a few transform faults that cut through continental lithosphere, perhaps the best known being the famous San Andreas fault in western California. Okay, with this brief overview of plates and their boundaries, you should be able to do this week's lab assignment without further instruction. If you feel you need more information, I suggest you google Plate Tectonics and Plate Boundaries or go to geologycafe.edu or another cool geology website. There's a ton of awesome information at your fingertips these days and I encourage you to use any resource available. Most importantly, have fun!

Lab 6 Slide 7: Putting sequences of events in relative order

Let's do a couple more relatively easy reconstructions of geologic events. The simple crosssection on the left depicts a fault (labeled E), three sedimentary rock units (A, B, and C), and an igneous dike (labeled D). We want to put these in their correct relative order, from oldest to youngest. You should recognize that the three sedimentary units are older than the dike and the fault by the principal of cross-cutting relations. And the oldest sedimentary rock is C based on the law of superposition. Which is older, the fault or the dike? Since the fault offsets the dike, we can say with confidence that the dike is older. So, the short answer of events is C, B, A, D, E (oldest to youngest). The longer answer using the geologic terms is: 1) deposition of sedimentary units C, B, and A in that order, intrusion of dike D, and faulting. What about the geologic history of the structure at Pismo Beach on the right? Here we see that the light grey sedimentary rocks have been folded and are overlain by dark grey sedimentary rocks. The sequence of events would then be: 1) deposition of the light grey sedimentary rocks, 2) folding (into a syncline), 3) uplift and erosion of the fold structure, 4) deposition of the dark grey sedimentary rocks, and finally 5) uplift and erosion to expose this wonderful outcrop today. Cool. What type of contact exists between the light grey and dark grey sedimentary rock units? Hopefully you recognize that the contact is depositional and specifically that it's an angular unconformity.

Lab 6 Slide 5: Two cross-sections with unconformities

Let's reconstruct the geologic history of these two cross-sections both of which preserve an unconformity. On the left, we have an older sequence of three sedimentary rocks - shale (the oldest), sandstone, then limestone (the youngest). We see that a second sandstone above the limestone has clasts of the limestone in it which indicates erosion of the limestone before deposition of the second sandstone - that's represented by the disconformity surface (#4). And the youngest unit to be deposited is the modern alluvium. On the right, we see an older sequence of four units that were subsequently tilted and eroded and then buried by deposition of sandstone 3 and lastly the modern alluvium. The unconformity represented here is an angular unconformity.

Lab 3 Slide 5: Common igneous minerals are grouped

Light and dark colored rocks reflect the mineral composition of the rock. Let's take a look at some common igneous minerals lumped into two categories: dark and light. It turns out that naturally dark minerals, such as olivine, pyroxene, and biotite mica, are dark because they are rich in the heavy magnesium and iron elements. Minerals rich in magnesium and iron are called mafic (m-a-f-i-c) minerals, the 'ma' part standing for magnesium and the 'fic' part standing for iron (with its Fe, iron, abbreviation). And the light colored minerals quartz, muscovite mica, and feldspar, which do not contain magnesium and iron, we call the felsic (f-e-l-s-i-c) minerals: Fel being short for feldspar and Sic being short for Silica rich or quartz. So lighter colored igneous rocks have more felsic minerals in them and dark colored igneous rocks have more of the mafic minerals in them.

Lab 5 Slide 3: Textures of Metamorphic Rocks

Like sedimentary and igneous rocks, metamorphic rocks are classified on the basis of texture (including grain size) and composition (mineral content). Cooking and/or squeezing (or adding pressure) results in the formation of two classes or two types of metamorphic rocks based on texture, or the arrangement of minerals. For rocks that have only been heated or cooked, the new minerals that recrystallized have no preferred orientation or layering, they are non-foliated or massive because heat acts the same in all directions. Fine-grained non-foliated rocks are called hornfels. Rocks that have been squeezed or pressurized during heating transform into metamorphic rocks that are foliated or banded. When the minerals in a rock are lined up in planes, we say the rock has a foliation.

Lab 8 Slide 4: Finding distance from lag time

Locating where earthquakes occur, whether in populated land areas or in the unpopulated deep ocean, is possible because seismic waves travel through rock at different speeds. In fact, P-waves travel about 1.75 times faster than S-waves. To understand how this key body-wave property is useful for locating epicenters, consider two cars that start from the same spot at the same time but travel at different speeds. Early on, the gap between the cars is small, indicating they are not far from where they started. Over time, however, the gap between the cars increases, reflecting the fact that they are both farther from where they started. In the same way, the difference in time between first arrival of the P-waves and of the S-waves represents how far the seismograph station is from the earthquake's epicenter. Here's a graph showing how the PS lag time (the difference in time between P and S wave arrivals) increases with distance away from the epicenter. The red curve represents the velocity of the S (or shear wave) and the blue curve represents the velocity of the P (or compressional wave). The yellow bracket is the PS lag time at 2,000 km, 6,000 km, and 10,000 km away. Note how the lag time increases with increasing distance from the earthquake depicted by the red explosion.

Lab 2 slide 4: Hawaiian Ridge-Emperor Seamounts Chain

Looking at the world ocean floor map, we can see that the Hawaiian island chain actually continues underwater as seamounts for hundreds of kilometers. The Hawaiian ridge is a line of extinct underwater volcanoes that formed over the last 22 million years. What's really interesting is that the seamounts chain continues for another 23 million years as the Emperor Seamount Chain but with a very different orientation. Why did the orientation of the seamounts change direction about 22 million years ago? Remember that the seamounts formed above a stationary hotspot, so their orientation represents the direction of Pacific plate motion over the past 45 million years. So geologists infer that the Pacific plate was moving almost due north between 45 million years and 22 million years ago, and that it changed direction at about 22 million years and started moving toward the northwest and has continued moving in that direction right up to today. You will determine the overall rate of motion in this week's lab exercise.

Lab 9 Slide 1: Mapping Earth's Surface

Maps are the bread and butter of Geology - they are important means of providing information. Fortunately, it is easier to study Earth's surface today than at any time in the past. In fact, there are a variety of images that can now be used to study Earth's surface including: topographic maps, aerial photographs, Landsat images and digital elevation models. You already know that Google Earth provides satellite and 3-D images of the entire globe. Each of these image types are helpful for different types of study. Topographic maps are a special kind of map that not only show the positions of towns, buildings, roads, and other human built features, they also provide a very accurate picture of topography, the position and shape of hills and valley as well as rivers, lakes, and swamps. Reading topographic maps is simple and requires knowing only a few key points. The best way to study landforms is to look at them from above, like Google Earth does. How does a 2- dimensional topographic map depict a 3-dimensional landform? How do we 'see' 3-D? The image above (image A), from study.com, shows a cross-section of an asymmetric hill with equal elevation lines or contours drawn on it. Map B (below) shows these same contours viewed from the air. Note how Outlook Hill is represented by a closed contour (the 600 elevation) and how the contours are closer together to the right of the peak and farther apart to the left of the peak. By comparing the map B with the image A you can see that closely spaced contours represent steeper slopes and more widely spaced contours represent more gentle hillsides. This, in essence, is how to 'read' or visualize a 2-D topo map. The lesson here of course is to stay away from areas with very closely spaced contours because they are very steep!

Lab 5 Slide 2: Metamorphism

Metamorphism is the process of changing an existing rock (called the proto-lith or early rock) into a new rock by changing its environment without melting it. New minerals and new texture forms as a result of metamorphism. Many new minerals and the strong metamorphic layering, like the red garnets and the foliation in this rock on the right, give metamorphic rocks a certain beauty. All metamorphic rocks started as something else, either a sedimentary rock, an igneous rock, or even an older metamorphic rock (if it was metamorphosed again). There are then 3 questions to ask about any metamorphic rock: •What is the rock now? For instance, what is its metamorphic grade? •What was it before it was metamorphosed? That is, what was its protolith? •What caused the protolith to change? What causes metamorphism? The two primary ways to change an existing rock, whether it's an igneous, a sedimentary, or even an already metamorphosed rock is to heat it and to increase its pressure, say by burying it. That is, cook it and squeeze it-just don't melt it. Metamorphism can also happen during deformation - when pressure is greater in one direction-and when hot fluids like water are added to rocks. By definition, metamorphic rocks are those that have been altered by physical and chemical processes mostly in response to heat, pressure and reaction with hot metamorphic fluid. It's important to realize that these changes occur solely in the solid-state, without melting. If melting does occur, then the resulting rock would be an igneous rock.

Lab 3 Slide 1: Minerals combine to form rocks

Minerals are the 'stuff' of rocks - what rocks are made of. But what is a rock? And how do rocks form? A rock is a coherent, naturally occurring solid consisting of a collection of minerals or of glass. Because of their coherence, rocks form cliffs or can be carved into sculptures. How are rocks grouped or classified? How are the minerals on the left combined to form gneiss, or granite, or sandstone on the right? And how do Earth Scientists describe these different rocks? That's the topic of the next three labs.

Lab 6 Slide 4: Different types of depositional contacts

Most depositional contacts are simply normal, or conformable contacts, formed by continuous deposition of sediment over time with little or no break in time between the layers. A stack of 7 conformable sandstone beds is shown in the photograph all of which were likely deposited continuously. The rock layers can have the same composition, like the layers in the photograph, or they can show a gradual change in composition say from sandstone to shale as shown in the lower right diagram of a conformable contact. Conformable contacts result in sequences of beds that are parallel to one another. In contrast to conformable contacts, unconformable depositional contacts indicate significant breaks or gaps in time between the younger and older rock layers, typically due to periods of erosion. There are three major types of unconformities commonly preserved in the rock record, one of which you saw in the previous frame, the nonconformity. A nonconformity is a depositional contact separating older igneous or metamorphic rock below from younger sedimentary rock above. In the upper left example here the Flathead sandstone is deposited on top of Precambrian metamorphic rocks as seen in the area of Dubois Wyoming. Nonconformities represent large missing gaps in time (in the rock record) because the crystalline rock had to be brought up to the surface by erosion and then buried again by deposition of sediments that are much younger than the basement rocks. An angular unconformity like the one shown in the upper right, separates tilted or folded rock layers (below) from overlying rock units above. It is important to note that an angular unconformity also represents a significant amount of time during which originally horizontal beds were tilted and eroded. Lastly, a disconformity is an unconformity that separates parallel sedimentary layers. Because the layers below and above the unconformity are parallel, this particular unconformity can be difficult to distinguish in the rock record from a normal conformable depositional contact.

Lab 4 Slide 11: Mudcracks

Mudcracks are sedimentary structures formed as muddy sediment dries and contracts as a result of a reduction in water content. Mudcracks are generally polygonal and v-shaped in side view. Naturally occurring mud cracks form in sediment that was once saturated with water. Abandoned river channels, floodplain muds, and dried ponds are localities that form mudcracks. Ancient mudcracks in the rock record look similar to modern mudcracks except that the cracks are filled with sediment.

Lab 11 Slide 1: 97% of liquid freshwater resides underground

Of Earth's liquid freshwater, an astounding 97% resides underground. In addition, groundwater occurs almost everywhere beneath the land surface. In effect, the upper part of the land surface behaves like a giant sponge that soaks up water. This makes groundwater a self-service resource accessible to nearly everyone, instead of just the favored few who live near a river or canal. In essence, groundwater is a democratic resource.

Lab 6 Slide 3: Determining relative age from two simple cross-sections

Okay, let's go through the relative ages of rock formation for these two cross-sections, starting with the left one. The left diagram shows 5 horizontal sedimentary layers and a granite intrusion. The law of superposition indicates that the shale is the oldest sedimentary layer, followed by the first sandstone above it, followed by the overlying limestone, and then the second sandstone, and finally the modern alluvium or sediment deposited by rivers. But when did the granite intrude? Using cross-cutting relations, we can say with confidence that the granite intruded the first four sedimentary units, so it must be younger than sandstone 2. But it does not intrude the alluvium. Very good. The right cross-section shows four rock units from bottom to top - granite, shale, sandstone, and alluvium. The alluvium is youngest because it's modern, but what about the relative ages of the granite, shale and sandstone? Namely, is the granite older or younger than the shale? The key line of evidence that this granite is older than the shale is that pieces of the granite occur as clasts within the shale where the shale is in contact with the granite. That key observation indicates that the shale was deposited on top of the granite after the granite formed and was eroded. Very cool. Sediment deposited on top of crystalline basement following erosion form a special type of depositional contact called a non-conformity (labeled number 2 here). There are actually four different types of depositional contacts in the rock record.

Lab 9 Slide 6: Let's see what you know

Okay, let's see if you can answer some basic questions about this map shown on the left. Note that the contours get higher and higher toward the middle of the map (look at the elevations) and that the final contour closes around the letter B, which would indicate a high point on the map. The other thing to note is how the contours have a V shape to the west of peak B with the contours pointing toward B. Lastly, note how the spacing of the contours vary with the most widely spaced contours occurring to the east of peak B. Now here are some questions. Could the peak elevation of B be 1405 meters? Well the contour interval is 100 m which makes the contour around B equal to 1300 meters. This means that the peak must be higher than 1300 meters but lower than 1400 meters (since there is no 1400 meter contour line). Got it? Question 2: what's the elevation at E? Even though there is no elevation marked on the E contour, by counting the contours down from the highest 1300 meter contour we see that E is at an elevation of 400 meters. What's the elevation difference between A and B? If A is at 750 meters (right between the 600 and 800 meter contours) and B is at 1350 meters (50 meters above the highest contour), then the elevation difference is about 600 meters. Yikes! Could the elevation at F be 475 meters? Absolutely not, since F lies in a broad area between the 700 m contours and the 800 m contour. Here's a good question: if you walked a straight line from D to C, would you go over a ridge or down into a valley? Between D and C is the V-shaped contours and since the V points up elevation, we know that there's a valley between D and C. Finally, would it be easier to head down from the peak going east or going north? Clearly going east would be easier since the contours are wider in that direction and, therefore, the slope is more gentle.

Lab 8 Slide 5: Locating an Epicenter

Okay, so one seismogram can be used to determine how far away the seismometer is from the earthquake epicenter. If the seismometer is 500 km away from an earthquake's epicenter, then a 500 km radius circle drawn around the seismometer would indicate all of the possible earthquake locations. Drawing two circles around two different seismometers would narrow the earthquakes location down to two possible locations. And a third seismometer would pinpoint the true location (that point where all three circles intersect)

Lab 2 Slide 1: Geologic Rates

One of the most fundamental aspects of understanding geology is to have a solid understanding of geological time or 'deep time', which is almost unfathomable. The Earth is 4.6 billion years old and the rocks that we see around us are very old too, often tens of millions of years or hundreds of millions of years old. Hence, natural phenomena that appear to us to be very slow and almost static. For instance, like the growth of mountains, the opening of oceans, or sideways migration of a river channel, are indeed happening at rapid rates of 'geologic' time when you look at it from the perspective of the 'deep time'. One way to comprehend 4.6 billion years is to compress it into a single calendar year. If Earth's birthday was January 1, the oldest rocks still around would have formed in mid-February and the oldest fossils in early March. The first dinosaurs, which lived about 230 million years ago would come on the scene on December 11 and they go extinct 65 million years ago on December 26. The mighty Himalayan mountain range started forming Dec. 27 in the last 50 million years, only 5 days ago in this compressed time-frame. This is why geologists describe the Himalayas as a 'young' mountain range that formed 'very recently'.

Lab 4 Slide 5: The texture of a clastic rock reveals its journey from source to deposition

Other aspects of a clastic texture also reveals the sediments journey from source to depositional environments where sediment accumulates. During transport, clasts get not only smaller but more rounded and sphericall, as shown here. The angular edges break off during transport and the grain shapes can change from quite angular to very rounded depending on how far they have traveled. So grain size and grain shape both change during transport. Sorting, which is the uniformity of grain size, is another property that changes during transport of sediment. In high source regions, sediment tends to be very poorly sorted, a mish-mash of grain sizes, but during transport a natural hydraulic winnowing process makes grains become uniform in size or very well sorted.

Lab 2 Slide 6: GPS tracks rate of plate motions today

Past motions of plates are largely determined from the geologic record, using hotspot tracks, age of growing oceans, and other measurements. With today's advanced technology, we can use GPS, Global Positioning System satellite data, to precisely measure the motion of the plates today. Such measurements are being continuously made today around the world to monitor potential volcanic activity and to track movement along major highly populated plate boundaries such as along the San Andreas fault in western California and the islands of Japan. So what is the rate of plate motion today? About 1-2 centimeters per year. But how fast is that? And how does this current motion compare with rates of geologic motion in the past? In this week's lab you will determine rates of past plate tectonic motions and compare these rates with rates of slow moving objects that we experience today. This exercise will help you grasp these 'deep time' and 'geological rate' concepts and also refresh your memory about different systems of units and conversions between different systems of units. To compare geologic rates of plate motion (typically measured in kilometers per million years), with rates of things that move slowly over days (growth of grass in spring time, growth of finger nails, motion of turtles), we have to use the same units of measurement, typically meters or centimeters over days or years, for everyday slow rates.

Lab 2 slide 2: Rates of plate motions from hotspot tracks (Hawaiian Island Chain)

Recall that rates of motion, or velocity, are determined by the distance measured (D) divided by time (T). (V=D/T). The earth's tectonic plates are always moving over geologic time (millions of years). One way to measure past geologic rates is by measuring the track of volcanoes that formed over a stationary 'hotspot' such as exists in Hawaii today. The line of islands making up Hawaii are formed by a deep-seated hot spot that has seared through the middle of the Pacific oceanic plate. Active volcanism occurring today on the big island is depicted by red. As lithospheric plate migrates over the hot spot, a volcano develops directly above the hotspot. When the plate slides on, the volcano that was over the hotspot becomes dormant and over time it migrates many kilometers from the hotspot. Meanwhile, a new volcano arises as new lithosphere passes over hotspot. This results in a string, or chain, of volcanoes with one end of the line located over the hotspot and quite active, and the other end distant and inactive. In between there is a succession of volcanoes that are progressively older with distance from the hotspot (toward the northeast) - with the oldest Hawaiian island having formed about 5 million years ago.

Lab 10 Slide 2: Spectacular structures

Rock deformation produces some really visually spectacular structures. Folds in ancient limestone on the beautiful island of Crete are shown on the left and large-scale faults along the coastline of southwest England are shown in the right photograph. In both these regions, the structures shown formed millions of years ago in older collisional and extensional belts. Knowledge of these structures is useful for reconstructing the geologic history of Earth.

Lab 3 Slide 2: There are only 3 ways to form rocks

Rocks are classified on the basis of how they form and there are only three ways to form a rock as summarized in this diagram. Using this simple idea, there are only then three rock types: Igneous: a rock that forms by crystallization from a melt (either lava or magma). Sedimentary: a rock that forms from the consolidation of sediment. Metamorphic: a rock that has been transformed by temperature and pressure. Classification schemes help us organize information and recognize similarities and differences among earth materials. A genetic rock classification, like this one, emphasizes the importance of rock-forming processes in producing earth materials, including crystallization for igneous rocks, deposition, burial, and lithification for sedimentary rocks, and recrystallization in the solid state for metamorphic rocks.

Lab 11 Slide 3: Rocks exhibit a wide range of porosity

Rocks exhibit a wide range of porosity, but it's the sedimentary rocks that have the highest porosity, ranging between five and thirty percent. Igneous and metamorphic rocks, overall, have very low primary porosity because of their interlocking crystal texture. There is quite a range of primary porosity in sedimentary rocks though, from fine-grained shales with only 5% porosity to coarse conglomerates and well-sorted sandstones that have porosities of 30-35%.

Lab 4 Slide 1: Sedimentary Rocks

Sedimentary rocks form by the cementing of fragments or grains of broken off pre-existing rocks or by the precipitation of mineral crystals like salt out of water solutions at or near the Earth's surface. The particles or clasts that make up a sedimentary rock first accumulated as sediment. These sediments are often transported and deposited within bodies of water forming lake or marine ocean sediments or they are deposited on land by rivers, glaciers, or even wind. Sedimentary rocks are typically deposited in layers or strata as bedding. Beautiful layers of horizontal bedding are exposed in the ancient sedimentary rocks that have been carved out by the Colorado River in the Grand Canyon of Arizona. Since sedimentary rocks form at the earth's surface (either on land or under water), they form a thin veneer of rock that caps or covers a crust consisting mainly of igneous and metamorphic 'basement' rocks. Three out of four rocks that people see or come across are sedimentary rocks, yet sedimentary rocks make up less than 10% of the total volume of the crust. We just see them more because we live at the earth's surface where sedimentary rocks form. Note the strong horizontal layering or bedding in this photo of the Grand Canyon and the stair stepped topography produced by the erosion of alternating layers of different types of sedimentary rock. These are layers of alternating shale and sandstone that were deposited in extensive shallow ocean seas that once covered much of the North American continent. Clastic sedimentary rocks like these form by cementation of clasts or weathered rock fragments and grains broken off of pre-existing rocks. Unlike igneous rocks, clastic sedimentary rocks cannot be dated using standard radiometric techniques because they consist of a mumbojumbo of fragments of older broken-up and weathered rocks. Instead, many sedimentary rocks are given a depositional age based on the fossils found in them. Of the three rock types (igneous, sedimentary, and metamorphic), sedimentary rocks are the only ones with preserved pristine fossils in them

Lab 4 Slide 7: Sedimentary features that we see today

Sedimentary rocks often contain interesting structures that formed when the original sediment was deposited. Here's one. Ripples in sand are familiar features that form by water flowing over loose sediment today. Ripples are commonly preserved in ancient sedimentary rocks like these in 100 million year old sandstones in Colorado.

Lab 8 Slide 3: Seismometers and the record of an earthquake

Seismometers record and measure the ground shaking at a certain spot on the earth's surface. Before an earthquake, the pen on a seismometer traces a straight line; but during an earthquake, squiggles are produced as the ground moves. The resulting seismogram contains a wealth of information that tells the seismologist: 1) how far away the earthquake was from the seismometer, and 2) the amount or magnitude of ground motion at that distance from the earthquake. Let's consider an earthquake starting at some depth below a building with a seismometer in it. All the energy waves are generated at the same time and place but as the waves move upwards they start to separate from one another since they travel at different speeds. The first set of waves to arrive at the station are the fastest P waves, followed later by the first arrival of a set of S waves, and lastly by the slowest surface waves. How are these waves recorded on the seismogram? The horizontal axis represents time (typically in secs or minutes) and the vertical axis represents the amplitude or the size of the seismic waves. The first squiggle on the seismogram represents the first arrival of a P wave because they travel the fastest. Next comes the S wave, and finally the surface waves. The real important measure is the difference in time between the arrivals of the P and S waves. Let's call this the PS lag time - since it represents how much the S wave arrival lags behind the P wave.

Lab 6 Slide 6: Siccar Point, Scotland - a geologic mecca

Siccar Point, in Scotland, is a rocky promontory on the east coast of Scotland that played a significant role in the early history of the development of Geology as a science. Hutton, the father of geology, recognized the major angular unconformity here annotated with the dashed line and he was the first to correctly interpret that the unconformity represented a significant gap in time missing from the rock record - 65 million years based on the age difference between the underlying and overlying sedimentary rock units. How did this form? What are the sequence of geologic events recorded here in the rocks? Note that there are two separate tilting events recorded based on the law of original horizontality.

Lab 6 Slide 10: Adding numerical ages to relative dating

Since igneous rocks form by a single process, crystallization, that happens rather quickly, these are the rocks that are easiest to date radiometrically. In this block diagram, there are two igneous rocks that can be dated, rocks B and D. Let's say that you successfully date these rocks in the lab and come up with the following numerical ages: rock B is 100 million years old and dike D is 88 million years old. Knowing this and the relative age relations we determined previously for this block, how old is unit C in millions of years? Now sedimentary rocks basically can't be dated radiometrically, since they consist of grains of a variety of older rocks that were transported and deposited to this location. But we can use cross-cutting relations with the now dated igneous rocks to determine an age range over which unit C was deposited. Here's how. Note that sedimentary unit C must be younger than rock B because it is deposited on top of B along the unconformity at location Z. Also note how dike D cuts across unit C, making unit C older than the dike. Therefore, we know that unit C was deposited between 100 and 88 million years ago. So that's a sweet example of how numerical ages obtained from igneous rocks can be used to bracket the age of deposition of sedimentary rock units. And that's essentially how numerical ages were added to the geologic time scale after Madam Curie's discovery of radioactivity.

lab 3 Slide 6: Examples of common igneous rocks

So what do igneous rocks look like up close? Here are four common igneous rocks up close, two of which you might be familiar with. Granite in the upper left and basalt in the lower right. Two other common igneous rocks are gabbro in the upper right and rhyolite in the lower left. What differences do you observe between these four igneous rocks? Can you describe how they look different from one another? Conversely, how are they all the same? Do you see anything unusual in any of them? They are all similar in that they don't have any type of layering or orientation to them. They look massive with no layering or alignment of minerals in them. You for sure noticed that they differ in color - the ones on the left are reddish/pinkish and the ones on the right are blackish/greyish. They also have different crystal or grain sizes. The two on top are coarse grained (you can see individual small crystals with the naked eye), and the two on the bottom are fine-grained with no visible crystals. Lastly, you probably noticed the different sized holes in the basalt sample, which is kind of unusual. These physical features are what geologists use to determine what the rock is and to interpret how the rock formed. The two features that geologists use to describe all rocks are: 1) its composition (what minerals it's made of) and 2) its texture - namely the size, shape, and arrangement of minerals and grains making up the rock.

Lab 3 Slide 9: Magma Melt factories

So where does melting and crystallization of igneous rocks occur? Where are the magma melt factories? We know from plate tectonics that igneous rocks form at two plate tectonic boundaries: 1) At subduction zones which are convergent boundaries where two plate are moving toward each other and 2) at oceanic ridges which are divergent boundaries where two plates are moving apart. We have also seen that magmas are produced far away from plate boundaries at hotspots which originate from deep in the mantle. Examples include Hawaii and Yellowstone. Melting occurs at these three types of places, the melts rise, and often reach the earth's surface to produce volcanoes.

Lab 1 Slide 11: The Fizz Test: Special properties of some minerals

Some minerals have distinctive properties that readily distinguish them from other minerals. For instance, calcite (CaC03) reacts with dilute hydrochloric acid to produce carbon dioxide gas as a result of which visible bubbles are created on the surface of the mineral where the acid is poured.

lab 1 slide 3: Specific Chemical Composition

Specific chemical composition simply means that a chemical formula can be written for a mineral. Some minerals are composed of only one element. Diamond and graphite are both made up entirely of Carbon (with a formula of C). Most minerals are compounds of two or more elements. Quartz contains the elements Silicon and Oxygen in a 1 to 2 ratio - so its chemical formula is SiO2. And some minerals such as biotite have a more complex composition. Related to this, is the rule that a mineral cannot be 'organic'; it doesn't consist of molecules of carbon and hydrogen that form from living organisms. Sugar is an organic compound, so although it is a solid, has a specific chemical formula, and structure, it is not a mineral by definition.

Lab 1 Slide 9: Streak and Luster

Streak is the color of the mineral in its powdered form. The streak can be different from the color of the mineral and tend to have less variability. Hence it is a relatively more reliable property for mineral identification. Streak is usually obtained by scraping the mineral against an unglazed ceramic plate. Photo A shows that the silver grey hematite mineral leaves a brown streak as does rusty red hematite (photo B). Gold colored pyrite has a black streak and pink colored rhodocrosite leaves a white streak. Luster refers to the way a mineral surface scatters light, or more simply how it shines. For example, the mineral pyrite, an iron ore, has a metallic luster, whereas quartz has a non-metallic vitreous or glassy luster. Other examples of luster, are earthy or dull appearance, and pearly or greasy luster. A few minerals, like gypsum even have a silky or satiny luster with its parallel arrangement of extremely fine fibers. Clear minerals that allow light to pass through them are transparent; clear quartz crystals being a good example of transparency.

Lab 6 Slide 9: Numerical age dating

The discovery of radioactivity by Madam Curie gave scientists the ability to date the crystallization of igneous rocks using decay 'clocks'. Madam Curie was a Polish and naturalizedFrench physicist and chemist who conducted pioneering research on radioactivity, a term that she coined. She was the first woman to win a Nobel Prize, the first person and only woman to win twice, and the only person to win a Nobel Prize in two different sciences. Numerical age dating is based on the fact that radioactive elements found in some minerals (parent elements) decay to form new stable elements (daughter elements) at a fixed rate regardless of the conditions. The amount of time it takes for half of the parent atoms in a mineral to decay to an equal number of daughter atoms is called the half-life. The graph on the left illustrates the 'decay' of parent atoms over 5 half-lives. Initially, when the mineral crystallizes in an igneous rock, it start with 100% of the radioactive parent element (depicted by the green dots). After one half-life (say 1 billion years for example), the mineral contains an equal number of parent and daughter elements since 50% of the parent atoms have decayed to daughter atoms (note the equal number of red and green dots in that mineral). The parent-daughter ratio is now 1:1 or equal. After another half-life (2 billion years total now), 25% of the atoms remain, and for every 1 parent atom there is now 3 daughter atoms. In another billion years, only 12.5% parent atoms remain and the parentdaughter ratio is 1:7. This continues on the graph for two more half-lives when only 3.1% of the parent atoms are remaining. To calculate the numerical age of an igneous rock, geologists crush the rock to separate out minerals containing radioactive elements. Then a mass spectrometer determines the parent-daughter ratio and an equation is solved to calculate the age. Voila! For this lab, we will simply use whole numbers of half-lives to make the age determination easy. Let's say that an igneous mineral contains a radioactive element with a half-life of 50 million years. If you determine that the amount of parent remaining now is 12.5%, how old is the igneous rock? Well, we know that the mineral has gone through 3 half-lives with only 12.5% parent remaining, so simply multiply the half-life time period that is 50 million years by 3 to get the age. So, the rock is 150 million years old. Here's another example. If an element with a halflife of 30,000 years in a mineral is determined to have an equal number of parent and daughter atoms, how old is the mineral? The answer is 30,000 years since the mineral has gone through only one half life. Last one: let's say you determine that the parent-daughter ratio is 1:31 of an element with a half-life of 300 million years. Since this ratio is the P/D ratio expected after 5 half-lives we know the rock must be 1500 million or 1.5 billion years old. Very cool. Keep these percentages and ratios in mind as you do this week's lab.

lab 1 Slide 5: Orthoclase feldspar

The feldspars are the most common mineral family in the crust - making up about half of all minerals. There are two types of feldspar: the orthoclase feldspar shown here is rich in potassium and aluminum. The potassium rich variety is also called K-spar. Orthoclase feldspar is one of the 10 defining minerals for hardness (it's a six). It tends to break along 2 planes at right angles. It's generally light colored (white, pink, grey, green, orange), and its light weight or low density.

Lab 5 Slide 1: Metamorphic Rocks

The further down we go into the earth, the hotter it gets. With sufficient burial, the heat can become great enough to change or metamorphose rocks without melting; whereas other rocks will completely melt and become igneous plutons. Because metamorphic rocks often reside in the middle and lower crust, buried by a veneer of sedimentary rocks, students tend to be less familiar with them, especially here in Ohio where the basement rocks are completely blanketed by sedimentary rocks. Metamorphism is a process that occurs below the surface where rocks are under pressure and warm. However it's important to know that metamorphic change occurs solely in the solid state with no melting involved. New minerals grow not by crystallization from a melt, but by recrystallization of existing minerals. Metamorphic rocks, which are commonly layered, can exhibit beautiful features such as folds and large crystals that grew by recrystallization during metamorphism.

Lab 5 Slide 7: Increasing temperature and pressure, grain size and prominence of foliation

The grade or degree of metamorphism of rock during mountain building events increases with increasing temperature and pressure. The rock samples shown here represent the different foliated rocks that form with increasing metamorphism of a typical shale protolith (the red rock on the left). The images at the bottom represent drawings of microscopic views of rock texture with increasing metamorphic grade from left to right. The drawings and the rock samples show how grain size and foliation layering increase significantly with metamorphic grade. Low grade slate forms by the initial growth and alignment of tiny mica crystals. With higher temperatures and pressure the mica crystals grow in size and the foliation becomes pronounced as the slate first becomes a phyllite and then a schist. Finally, at high temperatures and pressure the rock takes on a banded appearance characteristic of a gneiss. A general rule of thumb then is that grain size increases with increasing degree (or grade) of metamorphism and the foliation tends to become more and more prominent. Lastly, metamorphic grade change is also characterized by the growth of new minerals which replace earlier formed minerals. The platey shiny micas tend to form first at lower metamorphic grade, whereas, the red gem mineral garnet starts to grow at medium metamorphic grade. At higher grade the micas start to break down and feldspars start to grow as the foliation becomes banded. This banding is nicely visible in the gneiss (g-ne-i-s-s) sample on the right.

Lab 8 Slide 9: A different way to measure size

The great Alaska earthquake in 1964 killed 131 people because of the remoteness of the area, whereas, the great Sumatra earthquake killed almost ¼ million people. So instead of simply measuring the energy released it may perhaps be more informative to use a different type of measure when estimating the size of an earthquake. With the exploding growth in human population and built structures, Mercalli, an Italian seismologist, suggested that the amount of damage caused by an earthquake might be used as a measure of the earthquakes intensity or its impact on the human built environment. This intensity scale uses Roman numerals assigned to different descriptive levels of damage. For instance, an intensity of II would be felt by a few stationary people and would cause chandeliers to sway. An intensity V would wake people up and break dishes and windows. An intensity VII would frighten people and cause chimneys to topple. The maximum intensity of XII would be total destruction. This kind of measurement can then be used to produce informative maps (like the one shown here) indicating how the various regions of eastern US were affected by the 1886 Charleston SC earthquake. This likely 7.3 M earthquake caused considerable damage in Georgia and South Carolina and woke up most of the population of the surrounding states of Ohio, Kentucky, Alabama, Virginia, and Florida.

Lab 1 Slide 7: Pyroxene

The mineral pyroxene is typically black to dark green in color and has two planes of breakage that are at right angles to one another. Pyroxene is a dense Mg (Magnesium) and Fe (Iron) rich mineral common in volcanic rocks.

Lab 4 Slide 6: Common Clastic Sedimentary Rocks

The names of clastic sedimentary rocks are based largely on grain size. Very fine to fine-grained mud or clay hardens into shale, intermediate-grained sand hardens into sandstone, and coarse sediment with pebbles and cobbles hardens into a conglomerate. So grain size is related, in part, to distance of transport, with conglomerates forming in high-energy environments, perhaps mountainous regions near the source, and shales forming in low-energy quiet water environments where fine grains of sediment settle out slowly to form mud.

Lab 8 Slide 6: How big was that earthquake?

The other important piece of information that seismograms tell us, is the magnitude or size of the earthquake - that is, the amount of energy released. To determine this, we pay attention to the vertical axis on a seismogram labeled here with the words 'up down'. Since surface waves cause the most ground shaking, they show up on seismograms with the highest amplitude, or highest amount of up down motion. Seismologists look at the tallest squiggle (which represents the maximum seismogram motion) and use that as a measure of the magnitude of the earthquakes. This makes sense because a large magnitude seismogram shook up and down a lot and probably experienced a strong earthquake. Except for one problem, an earthquakes energy dissipates, or weakens, as its spreads out from the epicenter. So, a station farther away from an epicenter will be shaken less than one that's closer to the epicenter - see the problem? The thing to do then is to normalize (or correct for distance) using a graphical device known as a nomogram shown on the right. On the diagram the horizontal dotted line represents the "standard" Richter magnitude earthquake, which is 100 km away from the epicenter and produces 1 mm amplitude on the seismogram. It's given a magnitude of 3 and all other earthquakes are then compared to this standard reference. For comparison, a magnitude 4 earthquake would produce a 10 mm amplitude and a magnitude 5 earthquake would produce a 100 mm amplitude (shown by the solid lines). Note how a 1 unit increase in magnitude is equal to a 10 fold increase in ground motion. That makes magnitude scales logarithmic - a Richter 5M earthquake is 10 times larger than a Richter 4M earthquake, etc.

Lab 5 Slide 6: Deformation produces foliation

The other main type of metamorphism in the rock record is called regional metamorphism which occurs over large regions because it forms in mountain building events. Tectonic collisions deform huge regions forming thick mountains. Regional metamorphism creates foliated or layered metamorphic rocks that form by both increased heat and increased pressure during deformation. Rocks caught up in mountain building get hotter when they are deeply buried and come into contact with melts which also form during collision. During collisions pressure is often greater in one direction as depicted by the black arrows in the diagram on the left. Squeezing of rocks in this manner shortens the crust and causes minerals in the rock to be oriented parallel to one another, creating a foliation in the rock as depicted schematically in the center diagram and shown in this photograph of schist which has sheety mica crystals oriented in planes parallel to one another.

Lab 9 Slide 3: Reading a topographic map

The patterns of contour lines on a topographic map represent familiar surface features like hills, valleys, slopes, plains, and depressions. For instance, figure A shows concentric patterns of closed contours representing a hill (note how the elevations get higher towards the center). Figure B represents depressions (note how the topographical elevations get lower towards the center and note that there are hachure lines that point inwards). Contours do not cross or intersect one another; closely-spaced contours indicate steep slopes, whereas, widely-spaced contours indicate gentle slopes. Finally, when contours cross rivers or streams, they bend into V-shaped patterns that point upstream (as shown in figure C), so you can tell the direction of stream flow just by examining which way the V's point on the map. Thus, if the V's point northwest on the map, then the stream is flowing southeast. You can also tell the stream flow by noting which direction elevation is decreasing since 'water flows downhill' as they say! Benchmarks are points on maps where the exact elevation is known and marked with a brass or aluminum plate.

Lab 1 Slide 6: Plagioclase feldspar

The plagioclase feldspar is Na and Ca rich and is somewhat more dense than orthoclase feldspar. It's commonly whitish or grey in hand sample, has a glassy luster, and breaks along two separate planes. It's common to see parallel lines on crystal faces called striations in plagioclase - due to crystal's twinning or sharing part of their crystal lattice.

Lab 6 Slide 1: Rules for determining relative age

The rock record consists of the three rock types and their contacts. Geologists use the rock record to reconstruct the geologic history of a region which can include events such as: faulting, folding, igneous activity, and erosion. Before the discovery of radioactivity and the ability to numerically date igneous rocks, geologists simply put the geologic history of events into a relative order; this happened first, then that happened, etc. Here are some of the simple principles which allow scientists to put rock formation and geologic events in a relative order. The first two relate to the formation of sedimentary rocks. The Law of Original Horizontality states that sediments settle out from water under the influence of gravity and are deposited in approximately horizontal layers, roughly parallel to the Earth's surface. So, tilted beds indicate folding or faulting. The Law of Superposition states that younger sediments are deposited on top of older sediments. In an undisturbed sequence of sedimentary layers, the youngest layer is on the top and the oldest on the bottom; each layer being younger than the one beneath it and older than the one above it. The third law relates to structures that form during geologic events. The Law of CrossCutting Relationships states than an intrusion or fault that cuts across a rock unit must be younger than the rocks being intruded or displaced. Similarly, folding of rocks must be younger than the youngest rock involved in the folding. We will go through examples of these important rules, which might seem obvious, but do require practice in order to reconstruct the geologic history of an area.

Lab 7 Slide 4: Divergent plate boundaries

The second plate boundary type, called divergent boundaries, are places where two plates in contact are moving away from one another as shown by the arrows on this block diagram. All oceanic ridges are divergent boundaries because they are locations where sea-floor spreading causes plates to move apart. In these regions new subsurface melt or magma rises up and fills in the gap and quickly cools into basaltic rock that becomes part of each plate. Hence these zones are where new crust is formed. Because the plates are quite thin at the ridges, only very shallow earthquakes occur along divergent boundaries. Since these are areas on the earth's surface where plates are moving away from each other, these are also sometimes called rift zones (r-i-f-t) and also extensional zones, or areas where the lithosphere is extending horizontally. Most rifting along divergent boundaries is occurring along the oceanic ridges today, but there are a few places where continental lithosphere is rifting such as the Great Rift Valley in northeast Africa.

Lab 7 Slide 1: Plate Tectonics

The three main types of plate boundaries This week's lab topic is on plate tectonics - which most students know about somewhat, at least conceptually. Plate tectonics is the idea that Earth has an outer rocky shell that is broken into only a few large, plus a few small, strong or rigid plates that move. The plates interact with each other where they are in contact at their boundaries (that's where the action is!) and the motion between two bounding plates describes or defines the type of boundary it is. And thankfully there are only three types of plate boundaries - yahoo! What are the tectonic plates made of? Many people incorrectly think the tectonic plates are made of the outermost crust of the oceans and continents. Argh.. Tectonic plates are not made up of just crust!! In reality each plate is a piece of brittle or breakable lithosphere (where 'lith' means rock and 'sphere' means world) consisting of crust plus a part of the mantle layer beneath it. The lithosphere moves or floats, in a sense, on top of a soft, more plastic portion of mantle that we call the asthenosphere (where 'astheno' means flowing) - so this is a weaker softer part of the mantle. There are two types of lithosphere: 1) oceanic lithosphere, which is made up primarily of basalt and gabbro and 2) and continental lithosphere (made up primarily of granitic rocks which form much of continents). This diagram is a cross-section view through both thicker continental lithosphere and thinner oceanic lithosphere (with its thinner crust). During motion, tectonic plates sometimes collide with each other causing subduction zones, sometimes moves away from each other forming mid-ocean ridges, and sometimes slide sideways past each other forming transform faults. In this diagram subduction of oceanic lithosphere is occurring on both sides of the cross-section and sea-floor spreading is occurring at an oceanic ridge. Small block diagrams at the top show the three types of plate boundaries known as transform (on the left), divergent (in the middle) and convergent (on the right). These boundary types are defined by the relative motion of the two plates on either side of the boundary zone. Let's go over these three types of plate boundaries in some detail.

Lab 5 Slide 4: Contact (Local) Metamorphism

The two main types of textures in metamorphic rocks correspond to the two main types of metamorphism in the rock record: 1) Contact (or local) metamorphism and 2) Regional metamorphism. Contact metamorphism occurs when heat from a shallow igneous intrusion bakes the surrounding country rocks. The rock directly in contact with the hot magma experiences the highest temperatures. We say it has the highest-grade of metamorphism. The rocks further away from the magma also get cooked but at lower temperatures, so they are lower grade metamorphic rocks. A zone of contact metamorphic rocks forms around the pluton from high-grade near the pluton to lowgrade farther from the pluton. The contact metamorphism occurs only around the pluton so this type of metamorphism is often referred to as local metamorphism because of its limited scale. A zone of contact metamorphism associated with the intrusion of a black dike is visible in this photo of a road cut in the Death Valley area of California. The brown zone of rock consists of baked volcanic rock heated by the underlying dike.

Lab 3 Slide 7: Obsidian and pumice

There are some very fast cooling volcanic rocks that have a glassy texture which are called obsidian. Essentially, these are igneous rocks that formed from a quenched lava. The cooling was so fast that no crystals formed, leaving a glassy rock like this hand sample. Then there's pumice, a fine grained felsic volcanic rock with many tiny vesicles or gas bubbles preserved in it. Pumice is a very low density rock because of all the tiny air pockets preserved in it. Pumice can look like a sponge and sometimes specimens can float on water. Pumice forms from quickly cooling, gas rich frothy lava much like the foam in a glass of beer.

Lab 6 Slide 2: Law of Inclusions

There's one more very important law that is perhaps not as intuitive as the others but nonetheless just as important. The law of Inclusions states that the components of rock must be older than the rock itself. For instance, the grains or clasts making up a sedimentary rock must be older than the time when the rock was deposited. The rounded quartz pebbles in the conglomerate on the right must be older than the conglomerate itself. Likewise, inclusions in igneous rocks are older than the igneous rock containing them. The dark blob inside the granite shown on the left must be older than the granite itself, because the blob got there by falling or stooping into the magma just before the magma crystallized in the granite. Got it?

Lab 10 Slide 5: Intrusive contact

This is a photo of pink massive granite intruded into grey metamorphic rock in the Sierra Nevada of California. We would call this an intrusive contact with the younger granite intruding into or cutting across the grey older metamorphic rocks.

Lab 2 Slide 3: Hotspot trail

This slice or cross-section through the Hawaiian Islands shows how the hotspot, currently beneath the big island, has left a trail of volcanic islands that initially formed above the hotspot and then became inactive as the Pacific plate moved over and away from the rising plume. The orientation of the islands represents the direction of plate motion, from the youngest to the oldest islands. We can easily measure distance between the islands and determine time by knowing the age of the volcanic rocks making up the Hawaiian Islands. From this we can determine a rate of plate tectonic motion over the past 5 million years when the Hawaiian Islands formed.

Lab 8 Slide 1: Defining the focus and epicenter of an Earthquake

Throughout recorded history, earthquakes have constituted an ever-present, natural hazard to human civilization. Indeed, many written accounts dating from as far back as the classical GrecoRoman world document the catastrophic loss of life and property attributed to earthquakes. One such casualty was the Colossus of Rhodes Greek statue, one of the Seven Wonders of the Ancient World. At the time, it was the tallest statue in the world, about the height of the Statue of Liberty. It was destroyed during the earthquake of 226 BC, and never rebuilt. Today, many of the world's 7 billion people live in earthquake-prone areas including Japan, China, India-Pakistan, Indonesia, and California. The Indian Ocean tsunami of 2004, which affected millions of people in western Indonesia and environs, was actually triggered by a major earthquake. Here in relatively stable Ohio, far from lithospheric plate boundaries, we need not give much thought or worry to earthquakes. However, if you were to take a job in California you would be well-served to gain some practical knowledge about earthquakes. Most, although not all, earthquakes are associated with faulting in the crust related to movement of adjacent lithospheric plates. When faulting occurs, it commonly begins at a point of rupture kilometers beneath the surface (which is called the earthquake focus) and the energy released at the focus spreads rapidly outward in all directions - much like concentric waves generated in a glassy pond, when you throw in a stone. News reports on earthquakes usually specify the location of a point on the earth's surface directly above its focus, which is called the earthquake epicenter. News reports also usually include the Richter magnitude for a given earthquake, which is a measure of the amount of energy released at its focus.

Lab 10 Slide 7: Describing orientation of geologic features

To identify geologic structures in the rock record, we have to be able to describe how rock layers, like bedding, are oriented. Let's look at a block diagram of some tilted sedimentary rock layers that are cropping out in a lake. The block diagram gives us the 3-D appearance of the dipping layers. Okay, we can see that the bedding planes are oriented at an angle to the north arrow. If we measure that angle, we can see that its 40 degrees to the west of north as shown by the north arrow. We call the line that shows the orientation of the bedding planes the strike line. For this case we can see the bed strikes northwest or north-40 degrees west to be exact. We also see that the beds are tilted about 30 degrees down from horizontal toward the lake. The angle of tilting is called the dip angle or simply the dip of the beds. The dip of beds is always oriented perpendicular to the strike line. On a map like the one to the right of the block diagram, geologists can use the strike and dip map symbol to show the orientation of the beds. The longer line represents the strike direction and the little tick mark represents the dip direction. A number next to the tick mark represents the amount of tilt which is 30 degrees on this simple map. As a geologist, I look at the map symbols and know that the rock layers are tilted down into the earth at about 30 degrees in this map area. Let's look more at the geologic map on the right. We know it's a map because there's a north arrow. Note that there are three sedimentary rock units, B, C, and D. The units are oriented north-south and the units dip 30 degrees. But note that the units on the left dip to the left (or west) and the units on the right dip toward the right which is east - see how the tick marks point in opposite directions. Also note that units C and D are repeated on either side of B. What structure is this? What might this structure look like in a 3-D block diagram?

Lab 9 Slide 4: Constructing a Topographic Profile

Topographic profiles are cross-sections, or side views, of topography. Profiles provide valuable information for assessing a region's relief in specific directions and are used by surveyors and scientists interested in studying the evolution of landscapes among other things. There are great programs these days that can generate profiles quickly, but it's important to know how profiles are constructed by hand. Once the direction of the profile is selected (A-B in this case), a strip of paper with elevation lines is placed along the line of profile. Whereever a contour line crosses the strip of paper, the corresponding elevation point is marked with a dot (see the dashed lines). The dots along the profile line are then simply connected to construct a continuous profile. Voila! Now this particular topo map and profile shows an important rule of contour lines on maps. Contour lines form closed circles around the tops of hills or mountains. There are two hills on this topo map, one slightly lower than the other (based on the contour number). Note also how the 30 contour between the two peaks is repeated because of the saddle or small valley between the peaks. The contouring indicates that the region between the two peaks dips below the 30 elevation slightly.

lab 7 Slide 3: Intermediate and Deep Earthquakes

Tremendous forces between two converging plates cause earthquakes along convergent plate boundaries. You can imagine the oceanic lithosphere moving along the ocean floor and starting to subduct underneath continental lithosphere. An earthquake's point of initial rupture is called its focus or hypocenter. Why do the majority of earthquakes occur at convergent plate boundaries where subduction occurs? At the region of contact between the two plates, the down going plate starts to bend and break under great stress and shallow earthquakes occur. However, the entire plate continues to break along the subduction zone, because the plate is still cool and rigid there. So intermediate and deep seated earthquakes occur all along the subduction zone - because so much more area of plate is deforming. How are these deep earthquakes related on two-D world maps? Seismologists define the location of earthquakes on maps by their epicenters, or the place on the surface directly above its origin point (or focus). Just imagine drawing vertical lines straight up to the surface from the deep earthquakes in this diagram. These epicenters would all occur together in a narrow region where most volcanoes are also located.

Lab 4 Slide 2: Recipe for Clastic Sedimentary Rocks

Unlike igneous rocks, which form by a single process of crystallization from a cooling melt, clastic sedimentary rocks form by a sequence of processes at the earth's surface. Take a sandstone for instance. Sandstone feels gritty, like sand because it mostly made of sand size grains of quartz cemented together. Sandy-sized or intermediate size grains, are grains that have diameters of 1/16 mm up to 2 mm. Forming an accumulation of sand that then transforms into a clastic sedimentary rock, is a five-step process that begins in one place, called the Source area, and ends possibly very far away at the site of deposition. The five steps are: 1) weathering which is the breakdown of the rock source and 2) erosion or removal of the weathered material away from the source. Then, 3) transport of the sediment most commonly by rivers, and 4) its deposition into low lying regions. Finally, 5) lithification or hardening of the deposited sediment into a rock.

Lab 11 Slide 4: Permeability is the ease of water flow due to pore connectedness

Water that is trapped in isolated pore spaces below ground is inaccessible and therefore of not much use. For groundwater to flow, conduits, or connections, must exist between pores. The ability of a material to allow fluids to pass through interconnected pores is called the material's permeability. Groundwater flows easily through highly permeable material such as loose gravel. If you pour water into a gravel-filled jar, it quickly trickles down to the bottom, and fills the pores. Groundwater flows slowly through low-permeability materiallike shale, in which it must follow a tortuous path through narrow, crooked conduits. A material's permeability depends on three factors: 1) the number of conduits, 2) the size of the conduits, and 3) the straightness of the conduits. Traffic flow is a great analogy that might help you better understand permeability. Traffic can flow quickly in a city with many straight, multilane boulevards, whereas traffic is slow in a city with only a few narrow, crooked streets.

Lab 10 Slide 12: Geologic map and cross-section of Ohio

We don't have spectacular structures like faults and folds at the surface here in Ohio. But I want to show you the Ohio Geological Survey's geologic map of Ohio and the cross-section. This map represents the bed rock that's just below the young glacial deposits and the overlying soil. From the map, we can see that the bedrock geology of Ohio consists of nearly flat-lying sedimentary rocks between 450-250 million years old. The oldest rocks are in the west and the bedrock gets younger progressively toward the east. The cross-section is oriented west (left) to east (right) across the state. It nicely shows the relatively undeformed geology which is largely a reflection of the state's location in the ancient continental interior of North America.

Lab 4 Slide 12: Biochemical Marine Rocks

We've mostly been covering the formation of clastic sedimentary rocks-those rocks derived from the disintegration of other rocks and which are made up of fragments or clasts of those rocks or their minerals. Biochemical sedimentary rocks are those that form from biological processes. When the organisms die, the solid material in their shells survive. This material, when lithified, then becomes what's referred to as biochemical marine rocks. The shells of most marine organisms are made of calcium carbonate (CaCO3), or calcite, which when hardened into rock is known as limestone. The beautiful coral reefs of the world today are biochemical limestones of the future. Coquina is a biochemical rock formed almost completely of broken shell fragments cemented together. Because it consists of broken pieces, or clasts geologists refer to the texture of a coquina as bioclastic.

Lab 3 Slide 3: How do we describe rocks?

You may recall from lecture that rocks are described generally by two criteria: 1) their composition (that is, the minerals that make up the rock) and 2) by their texture (the size, shape, and arrangement of the crystals or grains in the rock). So when someone hands me an igneous rock, I start with color. Roughly - is it light or dark colored? Which gives a hint about mineral composition. Next I look at the texture, and generally grain size is the most important characteristic of texture in any rock. So what controls the grain size of an igneous rock?