Geology Final

Flood recurrence intervals: what is meant by a "100-year flood?"

"100-year flood" means that there is a 1% probability for a flood of that size in any given year • A "25-year flood" would be much smaller but four times more likely to occur than a "100-year flood" • There could be more than one 25-year flood (or 100-year flood) in a given year, especially if tropical storms or hurricanes occur • If the frequency of large floods increases through time, then the volume of a 100-year flood, etc., would need to be recalculated

Debris Flow

- A very rapid flow of soil and regolith saturated with water (called a mudflow if the rock material is fine grained) - Tends to follow stream channels in mountainous regions • Saturated with water during heavy rainfall or snow-melt ex. Lahar - Debris flow composed mostly of volcanic ash - Can occur during a volcanic eruption or when a volcano is quiet if there is a large amount of loose ash on the slopes

Fires

- Can start when gas or electrical lines are destroyed - Broken water lines make fire control nearly impossible

Coastal hazards - what are the main types?

- Coastal land loss • Erosion of beach sand by waves and storms • Dams on rivers prevent sediment from reaching the coast and feeding beaches → beaches shrink • Compaction and subsidence of land created by relatively young sediments may lead to encroachment of the sea upon the land (ex. abandoned deltas in southern Louisiana) - Mass wasting • Ocean waves directly undercut cliffs, leading to collapse and destruction of property - Tsunamis - Storms - especially hurricanes!

Rock falls, debris falls

- Detached material falls off of a steep slope

Earthquakes or volcanic eruptions

- Earthquakes or eruptions can dislodge loose rock materials • Rock falls, debris falls and flows are common • 1994 Northridge earthquake in California triggered 11,000 landslides - Liquefaction induced by earthquakes • During periods of ground shaking, watersaturated rock materials behave as fluid-like masses that can flow, even on very gentle slopes - Lahars are commonly triggered when volcanic ash deposits are saturated by rainfall or snowmelt.

Fjord (fiord)

- Fjords (or fiords) are deep, steep-sided inlets of the sea • Typically represent glacial troughs that are submerged when sea level rises • Very common along Scandinavian coastlines

Wave Characteristics

- Height, length, and period of a wave depend on: • Wind speed • Length of time wind has blown • Fetch (the distance that the wind has traveled across open water) - As a wave moves through water, the water passes the energy along by moving in a circle • called circular orbital motion - Normal wave motion dies out at a depth equal to about half the wavelength, called wave base

Alpine-type mountain building (and 2 examples)

- Large mountain chains formed by compressional stresses associated with continental convergence • Large-scale thickening and deformation of continental crust • deformation of a thick sequence of sedimentary rocks into a fold-and thrust belt • deep igneous and metamorphic activity, but little or no volcanism • a suture zone where the two continents meet - Typically contains slivers of oceanic lithosphere that are remnants of a subducted oceanic basin formerly between the continents - May also include fragments of islands or continental crust trapped in between the colliding continents - Ex. Alps in Europe, Himalayas in India, Appalachians in the U.S. Alpine-Type Mountain Building: The Himalayas - India collided with Asia after subduction of oceanic lithosphere - Collision began about 50 million years ago and continues today Prior to the collision, India was approaching Asia from the south. During collision, large thrust faults and folds shortened, thickened, and uplifted the crust.

Island arc-type mountain building

- Mountainous volcanic chain of islands - Volcano growth is triggered by partial melting in the mantle wedge above the subducted slab • Lavas are mostly andesitic, but may be more basaltic - Trench forms where subducted slab descends into the mantle • Typically a site of thrust faulting, where sediments and slices of oceanic crust are scraped off • Earthquakes follow the subducted slab

What are the differences between body waves and surface waves?

- P waves • first to arrive at recording station • lowest amplitude - S waves • second to arrive at recording station - Surface waves • slowest velocity • last to arrive at recording station • highest amplitude • cause the greatest property damage

Removal of Vegetation

- Plants protect against mass wasting by binding soil particles together • Plants also shield the soil surface from the impact of rain - Removal of vegetation can lead to mass wasting - Vegetation can be removed by humans or natural processes • Ex. Wildfires, which are common in the western United States - Intense rainfall after a fire can trigger hazardous mass wasting

Slope steepness in mass wasting

- Steeper slopes promote mass wasting - Slopes may be oversteepened by human or natural processes • construction along mountainsides - ex. cutting a vertical cliff across a mountain to build a road or house • waves or streams can erode at the bottom of a cliff or bluff

What are the main factors that affect rock deformation?

- Temperature: higher temperature deformation tends to promote more ductile deformation, and cooler temperatures → more brittle - Confining pressure: higher confining pressure tends to make rocks stronger and promotes more ductile deformation - Time (strain rate): stresses applied more quickly tend to result in more brittle behavior; stresses applied very slowly tend to result in ductile deformation - Specific rock textures and compositions also play a role

What is base level, and how do streams respond to changes in base level?

- The base level is the lowest point to which a stream can erode its channel • Ultimate base level is sea level • Local or temporary base level includes lakes or larger rivers - A change in base level changes the potential energy of a stream, causing readjustment of stream activities • Lowering base level causes increased erosion (ex. drop in sea level, or tectonic uplift) • Raising base level causes increased deposition (e. rise in sea level, or building a dam)

What are the main features of a typical coastal zone?

- The shoreline is the contact between land and sea. - The shore extends between the lowest tide level and the highest elevation affected by storm waves. - The coast extends inland from the shore as far as ocean-related features are found.

How do glaciers move? How rapidly do they move?

- Under the pressure of overlying ice, ice deeper than about 50 meters behaves as a ductile material and flows plastically - the entire ice mass slides by basal slip along meltwater at the bottom of the glacier -the upper 50 meters of a glacier is brittle and called the zone of fracture - Ice within a single glacier does not move at the same rate

What is elastic rebound theory?

- earthquakes are caused by the sudden release of accumulated strain energy in rocks position • As tectonic plates move, frictional resistance inhibits fault slip • The rocks deform elastically as strain energy builds up • When the fault finally slips, the accumulated elastic strain energy is suddenly released (earthquake), then the rocks snap back to their original shapes

Deltas

- form when sediment-rich streams enter a relatively still body of water (ex. lake, ocean) • The water velocity decreases → sediment particles settle out • Coarse sediments are deposited close to the river mouth • Fine sediments are deposited farther out, at the edges of the delta ‒ River deltas build new land at the edge of a continent The main channel divides into several smaller channels in the delta, called distributaries The Mississippi River Delta, Southern Louisiana - the 7th largest river delta on earth

Natural Levees

- long narrow ridges of coarse sand and gravel deposited along the top edge of a river bank during flooding - as water rises above the river banks, it spreads out across the floodplain and loses velocity instantly - coarse sediment particles are deposited near the banks

What is an earthquake?

- sudden, violent shaking of the ground caused by slip along a fault

What are the 3 types of unconformities and how are they significant?

1. Angular unconformity • Tilted strata are eroded, and flat- lying strata are deposited on top • The older strata were deformed before being eroded (or during erosion) • Implies tectonic activity before deposition of the younger strata 2. Disconformity • Sedimentary strata above and below the erosional surface are parallel • Common in marine sediments • Implies a drop in sea level, erosion, then a rise in sea level with resumed deposition 3. Nonconformity • Sedimentary strata overlie eroded metamorphic or igneous rocks • Implies very long-term erosion and significant amounts of rock eroded All three types of unconformities can be seen in the Grand Canyon

Crustal subsidence and rebound, sea level changes, etc.

1. Crustal Subsidence - Massive ice sheets cause downwarping of the continental crust • After the glacier melts, the crust gradually rebounds isostatically 2. Sea-Level Change - Because glacial ice stores a large amount of water in the hydrologic cycle, sea level drops during an ice-age (and rises as glaciers retreat) 3. Changes to regional stream drainage systems - The advance and retreat of the North American ice sheets changed the routes of rivers and modified the sizes and shapes of many valleys

What are characteristics of submergent vs. emergent coasts?

1. Emergent Coasts - Develop because of uplift of land or drop in sea level • Examples: - California coast (tectonically uplifted) - Hudson Bay (isostatically uplifted) - Features of an emergent coast are mainly erosional • Narrow continental shelf • Wave-cut cliffs • Wave-cut platforms • Marine terraces 2. Submergent Coasts - Caused by subsidence of land or a rise in sea level • Ex. U.S. Atlantic Coast - Features of a submergent coast • Wide continental shelf • Estuaries (drowned river mouths) • Highly irregular shorelines

What are the main points of the following groundwater-related issues? How many of these issues face Texas?

1. Groundwater supply 2. Subsidence 3. Contamination 4. Salt water intrusion

What is the difference between earthquake intensity and magnitude?

1. Intensity: a descriptive assessment of the amount of ground shaking at a particular location based on observed property damage (ex. Modified Mercalli Scale) 2. Magnitude: a calculated, quantitative assessment of ground motion based on data from seismograms, used to estimate of the amount of energy released (ex. Moment Magnitude, Richter Magnitude)

What are the 5 principles of relative geologic dating?

1. Principle of Superposition: - In an undeformed sequence of sedimentary rocks, layers are older at the bottom and get younger toward the top - Proposed by Nicolas Steno in 1669 2. Principle of Original Horizontality: - Layers of sediment are typically deposited in a roughly horizontal position - Rock layers that are folded or tilted must have been deformed after deposition 3. Principle of Lateral Continuity:Sedimentary beds originate as continuous layers that extend in all directions until they eventually thin out or grade into a different sediment type - If a river carves a canyon, we can infer that similar strata on either side were once connected across the canyon 4. Principle of Cross-Cutting Relationships:Younger features cut across older features • Ex. this fault must be younger than the sedimentary strata it cuts across 5. Principle of Inclusions: - Inclusions are fragments of one rock unit that are enclosed within another rock unit - The rock containing the inclusion is younger than the rock in the inclusion

What are the two approaches to long-range forecasting?

1. Seismic gaps are tectonically quiet zones along a fault where strain is currently building up • The stored strain will be released in a future earthquake • Strain can be estimated using known rate of plate movement • By identifying seismic gaps along active faults, seismologists can estimate the probability of a future earthquake in that area 2. Paleoseismology - the study of prehistoric earthquakes • By digging trenches across a fault zone, scientists look for evidence and timing of ancient earthquakes • Using the frequency of past earthquakes, scientists can estimate the probability of future earthquakes over a time span

Streams erode their channels and the landscape, transport sediment, and deposit sediment. What controls which of these processes takes place?

1. Stream Erosion - The erosional power of a stream is related to its slope, discharge, and the type of rock material that makes up the channel • Bedrock vs. different sediments erode at different rates • Grain size and cohesiveness of sediments are also important 2. Transport of Sediment by Streams - Sediment load is transported in three ways: • Dissolved load - mineral matter carried in solution • Suspended load - fine sand, silt, and clay suspended in the water column • Bed load - larger particles that move along the channel bottom 3. Deposition of Sediment by Streams - Sediments are deposited from a stream when the water velocity drops below the settling velocity of the rock particles The Work of Running Water - Particles of the same size tend to be deposited at the same time in a process called sorting • Larger particles settle out first as the water velocity drops - Sediments deposited by streams are called alluvium

Flows

A flow occurs when material moves downslope as a viscous fluid (ex. debris flow, mud flow)

Hanging valleys

A glacier in the main valley typically erodes more deeply than tributary glaciers, creating hanging valleys perched along the sides of the main valley

what is a glacier?

A glacier is a thick mass of ice that forms on land by the accumulation, compaction, and recrystallization of snow - Individual glaciers exist for 100's-10,000's of years - Show evidence of internal flow

What is a radioactive half-life?

A half-life is the amount of time required for half of the radioactive isotope to decay (determined statistically) • When the ratio of parent to daughter is 1:1, one half-life has passed • When the ratio is 25%:75%, two half-lives have passed - Multiply the number of half-lives by the length of a half- life for a specific isotope to get the age in years

Tsunami

A series of large ocean waves generated by slip on a submarine fault or by a coastal volcanic eruption - Can travel across the ocean at 800 km/hr (500 mph) - In open water, the wave height is less than 1 meter, making it difficult to detect, but close to shore, the water "piles up" and may reach heights greater than 30 meters

Slumps

A slump is a rotational slide in which a mass of rock or debris moves as a unit along a curved surface • Can involve a single mass or multiple blocks

What are characteristics of a stream that is actively downcutting?

A steep gradient and a channel far above base level leads to downcutting of the channel and deepening of the valley V-shaped valleys with steep sides are the result • Rapids and waterfalls are prominent features • Typical of youthful streams in mountain regions

What is a stream?

A stream is any channelized body of flowing water, regardless of size (ex. brook, creek, river, bayou) - A river is a stream that carries a large amount of water and has many tributaries - Streams are usually initiated by runoff, as tiny channel (rills) merge and grow to form gullies, then larger bodies of water - As streams grow, they tend to accumulate more water from the surrounding landscape - Streams erode and sculpt the landscape, transport sediment, and deposit sediment

What is alluvium?

Alluvial channels form in sediment previously deposited in a valley • Channels change shape as material is eroded from the banks • Channel patterns reflect the stream's ability to transport load at a uniform rate while expending the least amount of energy • More typical of mature stream systems • Types of alluvial channels: meandering and braided

Eskers

An esker is a narrow, sinuous ridge composed of sand and gravel deposited by a stream flowing through a tunnel in the bottom of the glacier

Define an unconformity

An unconformity is a buried surface of erosion (or non- deposition) in a rock sequence • Represents a gap in the rock record

What are anticlines, synclines, domes, and basins?

Anticlines are upfolded or arched rock layers • Limbs dip away from each other • Oldest strata are in the core of the fold - Synclines are downfolded or trough-like rock layers • Limbs dip toward each other • Youngest strata are in the center - Domes are upwarped circular or oval structures • Oldest rocks are in the center - Basins are downwarped circular or oval structures • Youngest rocks are in the center • Can form from subsidence of large sedimentary basins

What types of areas are prone to flash flooding?

Areas prone to flash floods • Mountainous areas • Steep-walled canyons • Coastal areas subject to torrential rains Many Texas cities are prone to flash floods that affect low-lying roads, underpasses, and roads along streams

Drift, Till, and Stratified drift

As glaciers melt, sediments are deposited as glacial drift (any sediment of glacial origin) • Till - Rock debris that is deposited directly by the ice - Dropped where the ice melts - Unsorted mixture of many grain sizes; the matrix is often finegrained - No sedimentary bedding features - Glacial erratics - boulders in the till or dropped on the ground • Stratified drift - Sediments deposited by glacial meltwater (often by streams) - Sorted and bedded

What are the main characteristics of bedrock stream channels?

Bedrock channels are cut into the underlying rock • Typical in the headwaters region where youthful mountain streams have steep gradients (but there are exceptions) • Tend to carve narrow V-shaped valleys • Rapids, steps, and pools are common features • Channel pattern is controlled by the underlying geology

What are body fossils vs. trace fossils?

Body fossils - whole or partial body parts of organisms Organisms preserved in ice, tar, or amber (dried tree sap) • Preserved bones, teeth, and shells of organisms • Permineralized remains - minerals such as chert precipitate from groundwater into porous wood or bone material • Molds and Casts ‒ A mold is created when a shell is buried in sediment and then dissolved, preserving the shape of the shell's surface ‒ A cast is created when the hollow spaces of a mold are filled with sediment or mineral matter • CarbonizedImpressions ‒ Carbonization occurs when an organism is buried and compressed, and partial decay leaves behind a thin film of carbon • Ex.fossilleaves,insects,andsoft-bodiedanimals ‒ Impressions remain in the rock when the carbon film is lost ‒ Ex.petrifiedwood • Trace fossils - features left by an organism as it passed by Indirect evidence of ancient organisms ‒ footprints, trails ‒ burrows ‒ coprolites (fossil dung) ‒ gastroliths (stomach stones)

How does groundwater dissolve rock like limestone?

Carbonic acid promotes dissolution of calcite in limestone as groundwater moves through pores and fractures Dissolution occurs at several levels, often as the water table drops

In what geologic environments do isostatic adjustments take place?

Changes in elevation and glacier ice As a mountain belt is worn down by erosion, the crust rises isostatically in order to maintain flotational balance. Another example of isostatic adjustment is associated with thick glacial ice: The weight of glacial ice depresses the crust, causing it to sink (or subside). After the ice melts, the crust slowly rebounds isostatically.

What are the main components of differential stress?

Components of differential stress - Compressional stress tends to squeeze a rock body and shorten it - Extensional stress tends to pull apart a rock body and lengthen it (tension is a special case of extension) - Shear stress acts parallel to the surface of a rock body, and tends to produce a motion similar to slippage between playing cards

Mountain building in divergent margins

Continental rifting is typically the initial phase in development of a divergent plate margin. • Normal faulting in such extensional settings can produce fault-block mountains • The mountains are residual blocks (horsts) standing higher than the down-dropped grabens Substantial displacement and tilting along normal faults can produce mountains with significant topographic relief. The Basin and Range Province in North America - Very large region of crustal extension and fault-blockmountains • Encompasses Nevada and parts of surrounding states, continuing into Mexico - Tilted half-grabens have produced nearly parallel linear mountain ranges and valleys - Extension began about 20 million years ago, stretching the crust twice its original width

What are the two main mechanisms of heat flow within Earth's interior?

Convection is the transfer hot materials to replace cold material (or vice versa) - Primary means of heat transfer within Earth - Typically occurs in flowing cycles similar to a pot of boiling soup - Convection cycles occur within the mantle and outer core • Mantle plumes may be the upward flowing arm of the cycle in the mantle • Separate convection cells may operate in the asthenosphere Conduction is the transfer of heat through a material - Through the collision of atoms or the flow of electrons - Materials conduct heat at different rates • Metals are better than rocks at conducting heat • Most rocks are poor conductors of heat Conduction is not an efficient way to move heat through most of Earth, but it is important in the solid inner core

Define correlation; how is correlation used?

Correlation involves matching rock layers from two or more different locations based on characteristics of the rocks or fossils - Helps in establishing age relationships among geologic strata - May be accomplished by noting the layering relationships among specific beds in a sequence of strata - Used in developing the Geologic Time Scale Correlation of distinctive strata in different locations has been used to put together the complete sedimentary sequence across the Colorado Plateau. • The Use of Fossils in Correlation - Principle of Faunal Succession • Based on observations by William Smith, British canal builder • States that fossils succeed one another in a definite and determinable order; therefore any time interval can be recognized by its fossil content. • Ex.: Age of Trilobites, Age of Reptiles, Age of Mammals - Index Fossils and Fossil Assemblages • Index fossils - specific fossil organisms that can be used to pinpoint a specific span of geologic time - tend to be widespread geographically, and their occurrence is limited to a short period of geologic time • Fossil assemblages - groups of different fossils that existed during similar or overlapping time spans

What are crevasses?

Crevasses are steep cracks in the ice in the zone of fracture

What are the most likely causes of ice ages?

Cycles of extensive glaciation have occurred throughout the history of Earth - Notable glaciation occurred during the Precambrian, the Permian Period, and the Quaternary Period (most recent) • Evidence of tillite (sedimentary rock formed from glacial till) in the geologic record - The most recent Ice Age cycles began in the Northern Hemisphere 2 - 3 million years ago

Define deformation

Deformation refers to all changes in the size, shape, or position of a rock body in response to stress - Mostly associated with plate tectonic boundaries

What are the three types of sediment load transported by streams?

Dissolved load - mineral matter carried in solution • Suspended load - fine sand, silt, and clay suspended in the water column • Bed load - larger particles that move along the channel bottom

Define drainage basin and divide

Drainage Basins - A stream drains an area of land called a drainage basin or watershed Divides - The imaginary line that separates adjacent drainage basins is called a divide • Sometimes a high ridge in a mountainous region • Sometimes hard to determine in areas of gentle topography - A continental divide splits a continent into different drainage basins In North America, the eastern and western continental divides follow mountain ranges

Define stream gradient and discharge

Factors affecting the velocity of water flow in a stream - The slope, or gradient, of the stream • A steeper gradient has more gravitational energy to drive water flow - Channel size, shape, and roughness - Discharge • the volume of water flowing past a certain point on a stream in a given time interval Discharge = Area of the stream channel X Velocity of the water • If discharge (volume) increases, the channel area and/or flow velocity must increase ‒ If discharge exceeds the channel's capacity, then flooding will occur ‒ If discharge is excessive, floodwaters will rise to cover higher and higher floodplains (ex. 100-yr floodplain)

What are faults? What are the characteristics of faults?

Faults are fractures along which displacement has occurred - We typically think of faults as being planar surfaces, but this is not always true - Fault planes may be vertical, horizontal, or inclined at some other angle - Sudden movements along faults are the cause of most earthquakes Faults are classified by the orientation of the fault surface and the sense of slip along that surface.

Fossil preservation: what normally happens to an organism when it dies?

Fossil Preservation • When an organism dies, what normally happens to its remains? ‒ Eaten by other organisms ‒ Broken up, dissolved, or decayed ‒ Buried in sediment and preserved • The odds are against fossil preservation ‒ There is not a complete record of all types of organisms that have ever lived • Two special conditions are necessary for most fossil preservation: ‒ Rapid burial by sediment (or lava) ‒ The possession of hard parts (ex. bones, shells, teeth)

What are fractures and what are their basic characteristics?

Fractures (joints) - roughly planar cracks in rock - no slip along the joint surface - produced by tensional or extensional stress in brittle rock - many joints appear in parallel groups - very common

What is long-range earthquake forecasting?

Gives the probability of large earthquakes occurring during a future time span of 10-100 years • Helps residents be prepared • Useful guide for building codes, dams, roadways, etc. - Observations suggest that many large faults slip in a cyclical manner, producing large earthquakes over roughly similar time intervals - Earthquakes tend to cluster spatially and temporally • Slip on one section of a fault tends to increase the stress on nearby faults, leading to future earthquakes to relieve the built-up strain

Glacial striations and grooves

Glacial abrasion also can produce long grooves and striations (scratches) in the bedrock

Cirque, Arete, Horn

Glacial erosion of cirques along opposite sides of a ridge can form arêtes and horns ‒ An arête is a sharp-edged ridge ‒ A horn is a pyramid-like peak Glaciers typically form high in the mountains, carving out bowl-shaped depressions called cirques

How do glaciers form?

Glaciers form in areas where more snow falls in winter than melts during the summer • Snowflakes initially compact and become smaller, thicker, and more spherical • Snow is recrystallized into a much denser mass of small grains called firn • Once the thickness of the ice and snow exceeds 50 meters, firn fuses into a solid mass of interlocking ice crystals — glacial ice

What are recharge areas and discharge areas?

Groundwater is replenished in recharge areas, and flows out at the surface in discharge areas

What is groundwater and where does it exist underground?

Groundwater is water that occupies the pores and fractures in rock, soil, and sediment underground - Contrary to popular belief, there are not widespread underground rivers or caverns filled with water - Permeable rocks act like sponges, gradually soaking up water (ex. sandstone coasters used to soak up water from drinking glasses

Liquefaction - what is it and why is it significant

Groundwater may be mobilized during an earthquake, saturating loose sediment and making it behave like a fluid, similar to quicksand.

What is the general nature of groundwater flow?

Groundwater tends to flow slowly under the influence of gravity and subsurface pressure differences, seeking equilibrium.

Efforts to stabilize the shore from erosion (pros & cons)

Hard Stabilization - structures built to protect the coast from erosion - Jetties or groins are built perpendicular to the shoreline and extend into the ocean • Trap sand transported by the longshore current, depriving unprotected areas of sand - Erosion occurs down the beach • No longer a preferred method to stop beach erosion -A breakwater is built offshore, parallel to shore • Creates a protected region of sand accumulation between the breakwater and the shoreline • Deprives other sections of the beach of sand - A seawall is built near the edge of the shore • Designed to protect property from breaking waves • Causes severe erosion seaward of the seawall, causing the beach to become narrower -Beach nourishment involves adding large quantities of sand to the beach • Expensive and not a permanent solution • The same processes that eroded the beach initially will also erode the new sand

Hurricanes - how do they form, what are their characteristics, and what types of destruction do they cause?

Hurricanes are the greatest storms on Earth - Called typhoons in the western Pacific and cyclones in the Indian Ocean - Form in summer and early fall

What is an artesian groundwater system?

If a confined aquifer and the surrounding strata are inclined, an artesian system may develop • In an artesian system, groundwater under pressure is capable of rising above the level of the aquifer, typically in a well or spring Some artesian systems transmit water long distances • Ex. South Dakota

Where are areas of greatest earthquake risk in the U.S.?

In the U.S., the greatest earthquake risk lies near - Modern plate boundaries along the western coast (ex. San Andreas Fault, Cascadia subduction zone). - The Basin and Range region (site of modern crustal extension) - Ancient faults near ancient tectonic boundaries in mountain belts of the western US (ex. The Rocky Mountains) - Ancient faults scattered across the central and eastern parts of the country (ex. New Madrid fault zone along the Mississippi River) Ancient faults can be reactivated in the modern stress environment

Ground rupture

Includes fracturing and displacement of roads, bridges, and other structures

Landslides and ground subsidence

Landslide associated with the Mag. 9.0 Alaska earthquake in 1964 Vibrations from the earthquake caused cracks in the rock above the Bootlegger Cove clay in the Turnagain Heights area.

Drumlins

Long, streamlined asymmetrical hills composed of till - 15 to 50 meters tall, and up to 1 kilometer long • The steep side of the hill faces the direction from which the ice advanced • The gentler, longer slope points in the direction the ice moved

What are the characteristics of meandering stream channels, and how do they change through time?

Meandering Channels • Have broad, winding bends called meanders • Relatively deep, smooth channels that tend to transport finegrained sediments (ex. silt and mud) • Early in development, the channel has gently curving meander bends • Meander curves become more pronounced as the channel shifts through time

Lateral, medial, and end moraines

Moraines - elongate mounds of glacial till - A lateral moraine is till that is transported and deposited along the sides of a glacier - Medial moraines are transported along the middle of the glacier surface after two glaciers merge • Medial moraines are rarely preserved after the glacier melts An end moraine is a mound of till that forms at the terminus of a glacier • End moraines that form as the ice front occasionally stabilizes during retreat are called recessional end moraines • The end moraine that signifies the farthest advance of a glacier is called a terminal moraine

In what types of geologic environments do earthquakes occur?

Most earthquakes originate along faults associated with tectonic plate boundaries - Global areas of greatest seismic risk include the circum-Pacific belt ("Ring of Fire"), followed by the Alpine - Himalayan belt.

How does groundwater originate?

Most groundwater soaks into the ground from rainfall Distribution of Groundwater - Water percolates downward, saturating the deepest pores first - The zone where all of the open spaces in rock or regolith are filled with water is the zone of saturation - The upper surface of this zone is the water table - Above the water table, pore spaces are filled with mostly air and small amounts of water (unsaturated zone)

In general, most of Earth's mountain belts have been produced by what?

Most of Earth's mountain belts have been produced by plate tectonic activity - Subduction zones - Continental collision zones - Divergent margins (extensional settings)

How do we know the characteristics of Earth's internal layers?

Most of our knowledge of Earth's interior comes from the study of earthquake-generated seismic waves

What are normal, reverse, thrust, and strike-slip faults? With what types of stress and tectonic settings are they associated?

Normal Fault The hanging wall moves down relative to the footwall (It's normal for a block to slide down an inclined surface under the pull of gravity) associated with extensional stress (or tensional stress) as the rocks pull apart, stretching the crust • typical of divergent plate margins Large-scale normal faults may produce fault-block mountains. Ex. Basin and Range Province (Nevada, Arizona) • Down-dropped blocks are called grabens • Adjacent mountain blocks are called horsts Reverse Fault The hanging wall moves up relative to the footwall • hanging wall moves up relative to the footwall • associated with compressional stress as the crust shortens • typical of convergent plate margins Thrust faults • reverse faults that have dip angles less than 45º, (typically ≤15º, so the HW moves almost horizontallyover the FW). Example Thrust Fault in Glacier National Park, Montana Strike-slip faults • displacement is horizontal and parallel to the strike of the fault • fault is typically vertical (or almost vertical) Sense of slip is described as: • Right-lateral—As you face the fault, the opposite side of the fault moves to the right • Left-lateral—As you face the fault, the opposite side of the fault moves to the left Large strike-slip faults that cut through the crust to accommodate plate motion are called transform faults. Ex. San Andreas Fault, California; note sense of motion

oceanic crust vs. continental crust

Oceanic crust Forms at mid-ocean ridges structure Averages 7 km thick Composed of basalt and gabbro Average density of 3.0 g/cm3 Continental crust Heterogeneous and composition (generally granitic) Averages 40 km thick Average density of 2.7 g/cm3

mantle

Over 82% of Earth's volume is in the mantle • Nearly 2900 km thick - Solid rocky layer composed of mafic silicate minerals The upper mantle extends from the Moho to 660 km depth • Composed of peridotite, a mafic silicate rock composed of olivine and pyroxene • The lithospheric mantle is the uppermost sliver of the mantle that lies at the base of the crust - This layer plus the crust make up the rigid lithosphere The lower mantle extends from the transition zone to the liquid outer core (2900 km deep) • Earth's largest layer, occupying 56 percent of Earth's volume • Mafic silicates undergo another phase change at the top of this zone, increasing their density - The boundary zone between the rocky lower mantle and the liquid outer core is called the D" layer

How do P-waves and S-waves reveal information about Earth's interior?

P-waves and S-waves travel fastest in stiff, high-density rocks S-waves cannot travel through liquids The boundary between the crust and the mantle is called the Mohorovicic Discontinuity (The Moho) - Seismic waves refract as they cross the Moho - P-waves increase in velocity

What is permeability, and why is it important for groundwater flow?

Permeability is the ability of a material to transmit a fluid • Depends on the connectivity between pores

What are the characteristics of primary waves and secondary waves?Primary (P) waves

Primary (P) waves - fastest waves - alternating pulses of compression and expansion - can travel through solids, liquids, or gases • Secondary waves (S-waves or Shear waves) - slower waves - sine wave style of motion - cannot travel through liquids or gases

How is Earth's magnetic field generated?

Produced by convection of liquid iron in the outer core - A geodynamo is the magnetic field caused by spiraling columns of rising electrically charged fluid in the outer core • Patterns of convection change rapidly enough so that the magnetic field varies noticeably over our lifetimes

Numerical Dating: define isotope and radioactive isotope

Radioactive isotopes - naturally unstable isotopes that spontaneously change (decay) into other elements or other isotopes of the same element Isotopes - varieties of the same element that have different atomic masses • Same number of protons • Different numbers of neutrons • Different atomic masses

What are the useful aspects of Carbon-14 dating?

Radiocarbon dating uses the radioactive isotope carbon-14 to date geologically recent events • The half-life of carbon-14 is 5730 years - Can be used to date events from the historic past to events as old as 70,000 years • Carbon-14 is produced in the upper atmosphere from cosmic- ray bombardment, and is incorporated into carbon dioxide - absorbed by plants and animals through photosynthesis or respiration - useful only for dating organic matter

What are the two main types of magnitude calculations?

Richter magnitude (ML - local magnitude) • Concept introduced by Charles Richter in 1935 for California earthquakes • The Richter scale is a numerical scale based on the height of the largest seismic wave recorded on a seismogram (i.e. a calculation, not a device) Moment Magnitude (MW) • Developed in 1979 to take advantage of waveform analysis of modern seismic data • Based on the area of the rupture, the amount of slip, and the force needed to cause fault slip • Calculates total energy released during an earthquake • More accurate, especially for the largest earthquakes

What are rip currents?

Rip currents are relatively strong, narrow currents of backwash flowing oceanward through the surf zone

Why are sedimentary deposits associated with streams significant?

Sediments deposited by streams form significant landforms, sedimentary rock strata, and important reservoir rock for groundwater and petroleum. • Types of deposits associated with streams include sand and gravel bars, river deltas, natural levees, and alluvial fans • Sediments deposited by streams are described as fluvial or fluviodeltaic

What happens as seismic waves pass through layers having different physical properties?

Seismic waves change velocity and direction when they pass through layers having different physical properties When a seismic wave hits a boundary between different layers, some of the waves are reflected and some are refracted (bent)

What is seismology? What are seismographs and seismograms?

Seismology is the study of earthquake waves Seismographs (or seismometers) - instruments that record the ground shaking of earthquakes - Record the movement of Earth in relation to a stationary mass, based on the principle of inertia - Earthquakes cause vertical and horizontal ground movement in different directions • More than one type of seismograph is needed to record and accurately describe the shaking • Seismogram - the graphical record of ground shaking

What are short-range earthquake prediction efforts, and are they successful?

Short-Range Earthquake Prediction Efforts - The goal is to provide a warning of a large earthquake within a short time frame (minutes, hours, days) - Research has concentrated on monitoring possible precursors of major earthquakes: • changes in ground elevation • deformation in the rocks • changes in groundwater level • frequency of foreshocks • odd behavior by animals??? To be reliable, a precursor must be consistent and not produce false alarms Currently, there is no reliable method for making short-range earthquake predictions

Rockslides

Some rockslides can involve the movement of huge volumes of rock, such as the Gros Ventre rockslide in Wyoming.

What are speleothems and how do they form (in general)?

Speleothem is the general name for all dripstone features - Includes stalactites (hanging from the ceiling) and stalagmites (form on the floor of a cavern) - These may join together to form a column

Define stress, confining pressure, and differential stress

Stress = the amount of force applied to a given area • Two types act on rocks - Confining pressure • Equal in all directions, associated with the weight of the overlying rocks • Does not change the shape or orientation of a rock body • Acts on all rocks in the subsurface - Differential stress • Not equal in all directions • Associated with tectonic activity • Includes components of compression, tension/extension, and shear stress that act in different directions on the rock body

Andean-type mountain building

Subduction beneath a continent (ex. Andes Mountains, S. America) - Long-lasting igneous activity and crustal thickening -Volcanic mountain growth is triggered by partial melting in the mantle wedge and lower continental crust • Lavas are mostly andesitic, but may be more felsic. • Most felsic magma crystallizes underground as huge granitic batholiths in the core of the volcanic arc, thickening the crust. • Eventually, uplift and erosion expose the batholiths - Ex. The Sierra Nevada in California - Crustal thickening may be supplemented by thrust faulting caused by the compressional stresses of convergence - Trench sediments and slices of oceanic crust are scraped off and thrusted upward to form an accretionary wedge • Prolonged subduction may cause the accretionary wedge to thicken and grow above sea level, forming new islands or mountains - A forearc basin lies between the volcanic arc and the trench • Accumulation of thick sediment and volcanic rock Ex. A huge Andean-type subduction zone complex built most of central California during the Jurassic Period

Geologic time scale - what are eons, eras, and periods?

The Geologic Time Scale covers all of Earth's history • originally created using relative dating techniques • numerical dates were applied in the twentieth century • arranged so that older time units are at the bottom, and younger are toward the top An eon represents the greatest expanse of time"The Precambrian" (oldest 88% of Earth's history) • Phanerozoic eon ("visible life") - the most recent eon, having the most abundantly preserved rocks and fossils. • Proterozoic eon - ("before life") • Archean eon - includes the oldest rocks on earth • Hadean eon - the oldest eon, before the oldest rocks Eons are divided into eras - The Phanerozoic eon is divided into three eras • Cenozoic era ("recent life") - the youngest era • Mesozoic era ("middle life") - Dinosaurs ruled • Paleozoic era ("ancient life") - the oldest era The younger eras are divided into periods - Ex. Cambrian, Permian, Jurassic, Cretaceous Periods are divided into epochs

In which period do we now live?

The Holocene epoch, The Quaternary period, The Cenozoic era

Water in mass wasting

The Role of Water - If a small amount of water is added to sediment pores, the material tends to become more cohesive (ex. sand castles) and resists downslope movement - Large amounts of water in pores can force the grains apart, making sediment susceptible to downslope movement - Water also adds weight to a mass of loose material

asthenosphere

The asthenosphere is the weak, flowing layer beneath the lithosphere and has slower wave velocities • Below the asthenosphere is the transition zone (between 410 and 660 km depth) The lower mantle extends from the transition zone to the liquid core

Cordilleran-type mountain building (and 1 example in North America)

The collision of volcanic island arcs or small slivers of continental crust with the edge of a continent to form mountainous regions - These crustal fragments that originated elsewhere are called terranes (or "exotic terranes") • Ex. microcontinents (similar to Madagascar), volcanic island arcs, or oceanic plateaus - Most terranes are carried to a continental margin by subduction of intervening oceanic lithosphere. - The addition of "exotic" crustal material to the edge of a continent is called accretion.

What are stream terraces and incised meanders

The flat, higher remnants of old floodplains are called stream terraces These meandering channels in bedrock are called incised meanders

Inner core

The inner core is a solid, dense sphere • Has a density of 13 g/cm3 • As Earth cools, the inner core grows at the expense of the outer core • Rotates faster, and moves independently of, the crust and mantle • Has a radius of 1216 km • Temperature is about 5500°C

What are point bars, a cut bank, and oxbow lakes?

The inner curve of a meander bend is a zone of sediment deposition (point bar) The outer curve of a meander bend (cut bank) is a zone of active erosion, so the channel tends to migrate in the direction of each cut bank Eventually, adjacent meander bends may intersect, cutting off a whole loop. The abandoned meander curve is called an oxbow lake.

When was the most recent major glacial maximum? How has Earth's climate changed since then?

The last major ice age cycle peaked about 18,000-20,000 years ago • Known as the Last Glacial Maximum • Since that time Earth has been in a natural phase of global warming

What is the significance of reversals of the Earth's magnetic field?

The magnetic field randomly reverses, and north and south poles swap direction • Reversal takes only a few thousand years, but during that time, the magnetic field, which protects Earth from solar wind, significantly decreases—to about 10% of normal • Provide evidence that convection patterns in the outer core change over relatively short time spans • The discovery of reversals has been extremely important to the foundation of the theory of plate tectonics

What happens if accumulation and wastage are not balanced?

The mass balance (glacial budget) is the balance between accumulation and loss of ice • If accumulation exceeds loss, the glacier grows and the glacial front advances • If ablation exceeds accumulation, the glacier will melt back from the toe region (glacial retreat)

Is there a complete fossil record of all types of organisms that have ever lived?

The odds are against fossil preservation ‒ There is not a complete record of all types of organisms that have ever lived

outer core

The outer core is liquid, based on the absence of S-waves traveling through the core • The outer core has a density of 9.9 g/cm3 • Composed mostly of iron, with some nickel and lighter elements • Outer core is 2270 km thick

What is porosity?

The percentage of pore spaces in a rock or sediment is called porosity

Define the geothermal gradient

The profile of Earth's temperature at each depth is called the geothermal gradient • Varies within Earth's interior - Crust: 30°C per kilometer of depth - Mantle: 0.3°C per kilometer » Exception is the D" layer • Temperature at the base of the lithosphere is about 1400º • Temperature at the base of the mantle is roughly 2500º • Temperature at Earth's center is estimated to be 5500º

Define hydraulic gradient, aquifer, and aquitard

The slope of the water table is the hydraulic gradient An aquifer is a permeable body of rock or sediment that transmits groundwater freely • Ex: sands, gravels, sandstone • An aquifer is consideredconfined if it is overlain by low-permeability rock An aquitard is a lowpermeability layer that hinders or prevents groundwater flow • Ex: clay or shale • Sometimes called a confining unit

What are the characteristics of Earth's gravity field near the surface?

The value of gravity near Earth's surface varies at different positions around the globe - Variations in gravity are caused by: • Earth's rotation • Earth's shape, which is an oblate ellipsoid (bulges at the equator), resulting in weaker gravity at the equator • Topography (mountains vs. areas at sea level) • Density and thickness of rock bodies

What happens in the zone of accumulation and the zone of wastage in a glacier?

The zone of accumulation is the uphill part of the glacier, where snowfall adds mass to the glacier • located above the snowline - The zone of wastage is the downslope part of a glacier where there is a net loss of glacial ice through ablation

What are tides, and what causes them? What other factors influence the tides?

Tides are daily changes in the elevation of the ocean surface -Except for polar regions, any position on Earth rotates through two tidal bulges per day -When the Sun and Moon are aligned with Earth, their gravitational fields combine to produce higher and lower tides - called spring tides - occur during new and full moons • When the Sun and Moon are at right angles to each other, a smaller tidal range results - called neap tides -A diurnal tidal pattern is characterized by a single high tide and a single low tide each tidal day - A semidiurnal tidal pattern is characterized by two high tides and two low tides each tidal day - A mixed tidal pattern is also characterized by two high tides and two low tides each tidal day • Large inequality in high or low water heights

How do rocks deform (elastic, brittle, ductile deformation)

Under the right conditions, rocks can fracture, bend, or flow like silly putty. When stress is initially applied gradually, rocks may initially respond by deforming elastically Elastic deformation = reversible strain - The rock returns to its original size and shape when the stress is removed • Ex. Try gently bending (but not breaking) a long pencil; when you release the stress, the pencil returns to its original shape • Ex. Stretch a rubber band, then release the stress; the rubber band returns to its original size and shape After the elastic limit of a rock is reached, the rock may fracture (brittle deformation), bend, or flow (ductile deformation)

What are valley glaciers and ice sheets, and what are their characteristics?

Valley (Alpine) Glaciers • Glaciers that occupy pre-existing stream valleys in mountainous areas are called valley or alpine glaciers - Flow down slope under the influence of gravity Ice Sheets (continental glaciers) - Very large glaciers that occupy significant portions of continents in polar regions - Ice flows out in all directions from the thickest accumulation centers • Ex. Greenland and Antarctica ice sheets • The Greenland ice sheet is 5,000 ft thick and covers ~80% of the landscape (1.7 million sq. km) • The Antarctic ice sheet covers 13.9 million sq. km • Note that the North Pole is covered with ocean, therefore any ice in the area issea ice not glacial ice Along parts of Antarctica, glacial ice flows into the sea, creating ice shelves (still attached to main glacier) - In shallow water, the ice touches bottom and is grounded - In deep water, the ice shelf floats • Some ice shelves are unstable and break apart

Glacial troughs (U-shaped valleys)

Valley glaciers widen and deepen stream valleys, creating U-shaped glacial troughs

Earth Flows

Viscous flow of water-saturated soil and regolith along hill slopes (instead of stream valleys) - Commonly clay- and silt-sized particles of soil - Move at slower rates than debris flows or mudflows - Range in size from a few meters to several hundred meters

What are the main processes of erosion and sediment transport along the beach?

Wave Erosion - Breaking waves exert a great force against the shore • Atlantic winter waves average 10,000 kg/m2 • The force during storms is even greater! In addition to wave impact, rock fragments carried in the water abrade the shore • Very intense in the surf zone

What are the main types of shoreline features produced by erosion, and how are they formed?

Wave-cut cliffs, wave-cut platforms, and marine terraces • Wave-cut cliffs originate by the cutting action of the surf against the base of the coast. • Wave-cut platforms are flat, bench-like surfaces left behind by the receding cliff. • A tectonically uplifted wave-cut platform is a marine terrace.

What happens to waves in the surf zone?

When waves approach shallower water, wave base eventually interacts with the sea floor - As waves "feel bottom," the seafloor interferes with water movement and the wave begins to slow down The waves become asymmetrical as water piles up • As the wave gets higher, it becomes too steep and eventually collapses or "breaks" → breakers • Surf is the turbulent water created by breaking waves

What causes typical ocean waves?

Wind-generated waves provide most of the energy that shapes and modifies shorelines

Define strain

a change in size or shape of a rock mass as the result of stress

What is karst topography, and what are common features found in karst landscapes?

a landscape that has been shaped mainly by the dissolving power of groundwater - forms in moist regions underlain by limestone Common features include: • Sinkholes - round depressions formed by collapse or subsidence above a cave • Solution valleys formed by the merging of sinkholes • Disappearing streams - surface streams that are diverted underground into a cave system • Karst towers - residual conical or steep-sided hills left behind after dissolution, collapse, and erosion have removed much of the original landscape Karst topography is characterized by irregular terrain and a lack of integrated stream systems

Flooding is the most common and deadly natural hazard in the U.S., but it is a natural part of stream behavior.

a natural part of stream behavior, when discharge increases and a stream overflows its banks

Alluvial Fans

fan-shaped deposits of coarse sediment at the foot of a mountain range, where a stream enters a flat valley floor • As a mountain stream emerges onto a flat lowland, the water velocity drops, and sediment is deposited • More common in arid climates

Define mass wasting

is the downslope movement of loose rock material (rock, regolith, and soil) under the influence of gravity - Often follows or occurs concurrently with weathering - Rapid mass wasting events are often called "landslides" - The combined effects of weathering, mass wasting, and erosional processes produce many natural landforms, including large stream valleys, cliffs, and canyons

Earth's oldest rocks (what, where, how old?)

metamorphic rocks located in the shield regions of continents • All continents have rocks ≥ 3.5 billion years old

Define isostasy

the principle that the crust floats in gravitational balance with the mantle below - Ex. A thick block of styrofoam would float higher in a swimming pool than a block of dense wood. - If weight is added to or removed from the crust, isostatic adjustment will take place as the crust sinks or rises in response.

How does numerical dating work?

the ratio between parent and daughter isotopes in a rock is used to determine its numerical age

Can any rock deform in a brittle or ductile manner?

yes

What are the main types of depositional features along a shoreline, and how are they formed?

• A spit is an elongated ridge of sand extending from the land into the mouth of an adjacent bay. • A baymouth bar is a spit that extends across a bay and closes it off from the ocean. • A tombolo is a ridge of sand that connects an island to the mainland or another island (typically perpendicular to shore).

What are the main characteristics of braided stream channels?

• Complex network of converging and diverging channels that interconnect among islands or gravel bars • Most of the load is coarse rock material • Discharge is highly variable - Commonly form at the toe of a melting glacier

Creeps

• Creep - the slowest form of mass wasting - Gradual movement of soil and regolith downhill • Acts on most sloping landscapes, even gentle slopes • Aided by the alternate expansion and contraction of the soil • Can be caused by freezing and thawing or wetting and drying • Causes fences, trees, and walls to tilt

Define the focus and epicenter of an earthquake

• Focus (Hypocenter)-the site on the fault surface where rupture and energy release begin • Epicenter-the point on the earth's surface vertically above the focus

Properties of the rock material

• Sand, clay, rock debris, and specific soil types have differences in cohesiveness and frictional properties that affect the stability of the material along a slope • Small amounts of clay can promote cohesiveness, but most clays have sheetlike crystal structure with weak bonds, allowing slippage • Some clays absorb water and swell, becoming weaker • Different types of rock materials have different angles of repose

Folds - typically form under what type of stress?

• Typically result from compressional stresses that shorten and thicken the crust • Each rock layer is bent along a hinge line, which is the site of maximum curvature - Fold hinges can be horizontal or inclined • The axial plane is an imaginary surface that connects all hinge lines of the folded strata