Geology 2

P waves

Primary Waves Arrives first b/c moves faster Moves 6-7 km/s Moves through solids, liquids, gases

primary waves

Primary waves are seismic waves from an earthquake that travel quickly and arrive first

under oceanic lithosphere

When a divergent boundary occurs beneath oceanic lithosphere: 1. The rising convection current below lifts the lithosphere producing a mid-ocean ridge. 2. Extensional forces stretch the lithosphere and produce a deep fissure. 3. When the fissure opens, pressure is reduced on the super-heated mantle material below. 4. It responds by melting and the new magma flows into the fissure. 5. The magma then solidifies and the process repeats itself.

subduction

When oceanic crust converges with continental crust, the denser oceanic plate plunges beneath the continental plate. This process is called subduction. Subduction is the process of an oceanic plate plunging below a continental plate, occurring at the oceanic trenches. The entire region is known as a subduction zone.

The Cenozoic Era

"new life" 70 mya - present

The Pleistocene

(5.3- 1.8 mya) The glaciers recede ~18,000 years ago. Rising seas leave a ridge above water- the modern barrier islands.

Continental drift evidence

1. The continents appear to fit together. 2. Ancient fossils of the same species of extinct plants and animals are found in rocks of the same age but are on continents that are now separated 3. Identical rocks, of the same type and age, are found on both sides of the Atlantic Ocean. Wegener said the rocks had formed side by side and that the land had since moved apart. 4. Mountain ranges with the same rock types, structures, and ages are now on opposite sides of the Atlantic Ocean. 5.5. Grooves and rock deposits left by ancient glaciers are found today on different continents very close to the equator. 6. Coral reefs and coal-forming swamps are found in tropical and subtropical environments, but ancient coal seams and coral reefs are found in locations where it is much too cold today.

continetal volcanic arc

A continental volcanic arc is a series of volcanoes associated with convergent plate boundaries where an oceanic plate plunges beneath a continental plate

this thing

A given volcanic landform will be characteristic of the types of material it is made of, which in turn depends on the prior eruptive behavior of the volcano.

lahar

A high-speed pyroclastic flow, which melted snow and created a volcanic mudflow known as a lahar

rift valley

A rift valley is a lowland region that forms where Earth's tectonic plates move apart, or rift. Rift valleys are found both on land and at the bottom of the ocean, where they are created by the process of seafloor spreading.

what plate creates most volcanoes

A subducting plate creates most volcanoes. Locations with converging in which at least one plate is oceanic at the boundary have volcanoes

techtonic plate

A tectonic plate is a large, thin, relatively rigid plate that moves relative to others on the outer surface of the Earth.

intraplate quakes

About 5% of earthquakes take place within a plate, away from plate boundaries and are caused by stresses within a plate. Since plates move over a spherical surface, zones of weakness are created. Intraplate earthquakes happen along these zones of weakness. The earthquakes may take place along ancient faults or rift zones. In 1812, a magnitude 7.5 earthquake struck near New Madrid,

nearly 95 percent take place on these boundaries

About 80% of all earthquakes strike around the Pacific Ocean basin because it is lined with convergent and transform boundaries About 15% take place in the Mediterranean-Asiatic Belt, where convergence is causing the Indian Plate to run into the Eurasian Plate. The remaining 5% are scattered around other plate boundaries or are intraplate earthquakes.

ocean stuffon

According to Hess, the Atlantic Ocean was expanding while the Pacific Ocean was shrinking. As old oceanic crust was consumed in the trenches, new magma rose and erupted along the spreading ridges to form new crust. In effect, the ocean basins were perpetually being "recycled," with the creation of new crust and the destruction of old oceanic lithosphere occurring simultaneously.

contiental drift

Alfred Wegener's Theory was known as Continental Drift, and was not exactly the same as Plate Tectonics One of the largest issues with Wegener's idea being accepted by the scientific community was that he couldn't provide the mechanism by which the continents could move.

intraplate volcanoes

Although most volcanoes are found at convergent or divergent plate boundaries, intraplate volcanoes are found in the middle of a tectonic plate. These volcanoes rise at a hotspot above a mantle plume. A hotspot is a volcano found in the middle of a tectonic plate where magma rises through the mantle away from a subduction zone Melting at a hotspot is due to pressure release as the plume rises through the mantle

earthquakes

An earthquake is ground movement caused by the sudden release of energy stored in rocks.

island arc

An island arc similarly is a chain of volcanic islands that results from subduction of one oceanic plate underneath another ocean plate

hotspots

As the plate over a mantle plume moves over time, the hotspot may create a series of islands. Earth is home to about 50 known hotspots. Most of these are in the oceans because they are better able to penetrate oceanic lithosphere to create volcanoes. But there are some large ones in the continents. Yellowstone is a good example of a mantle plume erupting within a continent.

How does divergent plate boundaries create volcanoes

At divergent plate boundaries hot mantle rock rises into the space where the plates are moving apart. As the hot mantle rock convects upward it rises higher in the mantle. The rock is under lower pressure; this lowers the melting temperature of the rock and so it melts. Lava erupts through long cracks in the ground, or fissures.

stuff

At the center of the Earth lies the core, which is nearly twice as dense as the mantle because its composition is metallic (iron-nickel alloy) rather than stony. Unlike the yolk of an egg, however, the Earth's core is actually made up of two distinct parts: a 2,200 km-thick liquid outer core and a 1,250 km-thick solid inner core. As the Earth rotates, the liquid outer core spins, creating the Earth's magnetic field.

Transform

At transform plate boundaries two slabs of lithosphere are sliding past each other in opposite directions. The boundary between the two plates is a transform fault.

vicous magma

Because it is more difficult for dissolved gas to escape from more viscous magma, higher silica magmas generally erupt more explosively.

magnetic striping and polar reversals

Beginning in the 1950s, scientists, using magnetic instruments adapted from airborne devices developed during World War II, began recognizing odd magnetic variations across the ocean floor. This finding, though unexpected, was not entirely surprising because it was known that basalt - the iron-rich rock making up the ocean floor- contains a strongly magnetic mineral (magnetite) and can locally distort compass readings.

mantle

Below the crust is the mantle, a dense, hot layer of semi-solid rock approximately 2,900 km thick. Mantle is the part of the earth's interior between the metallic outer core and the crust The mantle, which contains more iron, magnesium, and calcium than the crust, is hotter and denser because temp and pressure inside the Earth increase with depth.

body waves

Body waves are seismic waves that travel through the Earth's interior.

caldera shape

Caldera - large basin-shaped volcanic depression with a diameter many times larger than included volcanic vents; may range from 2 to 50 km (1 to 30 mi) across. Commonly formed when magma is withdrawn or erupted from a shallow underground magma reservoir.

Cinder cone

Cinder cone - A conical hill, often steep, formed by accumulation of solidified fragments of lava that fall around the vent of a single basaltic or andesitic eruption.

cinder cone shape

Cinder cones are small volume cones consisting predominantly of tephra that result from strombolian eruptions. They are actually fall deposits that are built surrounding the eruptive vent. Slopes of the cones are controlled by the angle of repose (angle of stable slope for loose unconsolidated material) and are usually between about 25 and 35o.

compressional stress

Compressional stress - stress that has the effect of squeezing and shortening the terrain, happening at convergent plate boundaries where 2 plates move toward each other.

modern plate techtonic theory

Continental Drift provided the template for the modern Plate Tectonic Theory - there was plenty of evidence that the continents had moved, but the discovery of new evidence allowed for a mechanism by which this could have happened These pieces of evidence included: Ocean floor mapping that revealed mid ocean ridges Magnetic striping and polar reversals Sea floor spreading and recycling of ocean crust Concentrations of earthquakes

felsic vs mafic

Continental crust is felsic and oceanic crust is mafic.

contiental crust

Continental crust is made up of many different types of igneous, metamorphic, and sedimentary rocks. The average composition is granite, which is much less dense than the mafic rocks of the oceanic crust. Because it is thick and has relatively low density, continental crust rises higher on the mantle than oceanic crust, which sinks into the mantle to form basins. When filled with water, these basins form the planet's oceans.

heat flow: mantle

Convection currents within Earth's mantle form as material near the core heats up. As the core heats the bottom layer of mantle material, particles move more rapidly, decreasing its density and causing it to rise. The rising material begins the convection current. When the warm material reaches the surface, it spreads horizontally. The material cools because it is no longer near the core. It eventually becomes cool and dense enough to sink back down into the mantle. At the bottom of the mantle, the material travels horizontally and is heated by the core. It reaches the location where warm mantle material rises, and the mantle convection cell is complete

convection earth's mantle

Convection within the Earth's mantle causes the plates to move. Mantle material is heated above the core. The hot mantle rises up toward the surface . As the mantle rises, it cools. At the surface, the material moves horizontally away from a mid-ocean ridge crest. The material continues to cool. It sinks back down into the mantle at a deep sea trench. The material sinks back down to the core. It moves horizontally again, completing a convection cell.

Convergent

Convergent plate boundaries are locations where two tectonic plates meet and move towards each other When two plates converge, what happens depends on the types of lithosphere that meet. The three possibilities are: oceanic crust to oceanic crust oceanic crust to continental crust continental crust to continental crust If at least one of the slabs of lithosphere is oceanic, that oceanic plate will plunge into the trench and back into the mantle. The meeting of two enormous slabs of lithosphere and subduction of one results in magma generation and earthquakes.

3 main layers of earth

Crust Mantle Core

crust

Crust - the outermost major layer of the earth, ranging from about 10 to 65 km in thickness worldwide.

more crust

Crust - the outermost major layer of the earth, ranging from about 10 to 65 km in thickness worldwide. The crust, the outermost layer, is rigid and very thin compared with the other two. Beneath the oceans, the crust varies little in thickness, generally extending only to about 5 km. The uppermost 15-35 km of crust is brittle enough to produce earthquakes. The thickness of the crust beneath continents is much more variable but averages about 30 km; under large mountain ranges, such as the Alps or the Sierra Nevada, however, the base of the crust can be as deep as 100 km.

dikes

Dikes - tabular or sheet-like bodies of magma that cut through and across the layering of adjacent rocks. They form when magma rises into an existing fracture, or creates a new crack by forcing its way through existing rock, and then solidifies. Hundreds of dikes can invade the cone and inner core of a volcano, sometimes preferentially along zones of structural weakness.

divergent

Divergent plate boundaries are locations where plates are moving away from one another. This occurs above rising convection currents. The rising current pushes up on the bottom of the lithosphere, lifting it and flowing laterally beneath it. This lateral flow causes the plate material above to be dragged along in the direction of flow. At the crest of the uplift, the overlying plate is stretched thin, breaks and pulls apart. This results in a mid-ocean ridge - aka oceanic ridge is an underwater mountain range, formed by plate tectonics.

concentration of quakes

During the 20th century, improvements in seismic instrumentation and greater use of seismographs worldwide enabled scientists to learn that earthquakes tend to be concentrated in certain areas, notably along the oceanic trenches and spreading ridges.

paleomagnetism

Early in the 20th century, paleomagnetists recognized that rocks generally belong to two groups according to their magnetic properties. (Paleomagnetism - is the 'frozen' orientation of iron-bearing magnetic minerals recording the location of the Earth's magnetic poles and the latitude of the rock at the time of cooling.) One group has normal polarity, characterized by the magnetic minerals in the rock having the same polarity as that of the Earth's present magnetic field. This would result in the north end of the rock's "compass needle" pointing toward magnetic north. The other group has reversed polarity, indicated by a polarity alignment opposite to that of the Earth's present magnetic field. In this case, the north end of the rock's compass needle would point south. How could this be?

can earthquakes be predicted

Earthquakes cannot be predicted currently and it is not expected to developed any time in the foreseeable future. However based on scientific data, probabilities can be calculated for potential future earthquakes.

elastic rebound theory

Elastic rebound theory states that as tectonic plates move relative to each other, elastic strain energy builds up along their edges in the rocks along fault planes. Since fault planes are not usually very smooth, great amounts of energy can be stored (if the rock is strong enough) as movement is restricted due to interlock along the fault. When the shearing stresses induced in the rocks on the fault planes exceed the shear strength of the rock, rupture occurs.

pyroclastic material

Erupted rock fragments are called tephra. Ash and gas also explode from the volcano. Scorching hot tephra, ash, and gas may speed down the volcano's slopes at 700 km/h (450 mph) as a pyroclastic flow. Pyroclastic flows knock down everything in their path. The temperature inside a pyroclastic flow may be as high as 1,000oC (1,800oF).

explosive eruptions

Explosive eruptions are caused by gas-rich, felsic magmas that churn within the magma chamber. When the pressure becomes too great the magma breaks through the rock above the chamber and explodes, just like when a cork is released from a bottle of champagne. Magma, rock, and ash burst upward in an enormous explosion

fault

Faults - a location in which blocks of rock of a fracture move. Sudden motions along faults cause rocks to break and move suddenly. The energy released is an earthquake.

The triassic

First mammals and crocodilia appeared. As soon as they had formed, the Appalachians began to erode.

fracture

Fracture - a break in rock that occurs when it is under stress.There may or may not be movement along the fracture.

how convection moves plate

Hot mantle from the two adjacent cells rises at the ridge axis, creating new ocean crust. The top limb of the convection cell moves horizontally away from the ridge crest, as does the new seafloor. The outer limbs of the convection cells plunge down into the deeper mantle, dragging oceanic crust as well. This takes place at the deep sea trenches. Material sinks to the core and moves horizontally. Material heats up and reaches the zone where it rises again.

EEw

However, the USGS and other scientists are working on an earthquake early warning (EEW) system for the US.

mountain formation

If both plates meet with continental crust, there will be mountain building.

normal fault

In a normal fault, the hanging wall drops down relative to the footwall.

reverse fault

In a reverse fault, the footwall drops down relative to the hanging wall.

focus

In an earthquake, the initial point where the rocks rupture in the crust is called the focus.

joint

Joint - If there is no movement on either side of a fracture, the fracture is called a joint. These rocks in Spain show horizontal and vertical jointing. These joints formed when the confining stress was removed from the rocks

Uniformatism

Law of Uniformitarianism - the idea that the same processes we see occurring now also occurred in the past. "The present is the key to the past."

liquefacation

Liquefaction - process by which water-saturated sediment temporarily loses strength and acts as a fluid, which can be caused by earthquake shaking.

effusive eruptions

Mafic magma creates gentler effusive eruptions. Although the pressure builds enough for the magma to erupt, it does not erupt with the same explosive force as felsic magma. Magma pushes toward the surface through fissures. Eventually, the magma reaches the surface and erupts through a vent. Effusive eruptions are common in Hawaii, where lavas are mafic.

how does that work

Melting at convergent plate boundaries has many causes. The subducting plate heats up as it sinks into the mantle. Also, water is mixed in with the sediments lying on top of the subducting plate. As the sediments subduct, the water rises into the overlying mantle material and lowers its melting point. Melting in the mantle above the subducting plate leads to volcanoes within an island or continental arc.

shield volcanos shape

Most shield volcanoes have a roughly circular or oval shape in map view. These volcanoes are the largest of any volcanoes on Earth, despite their gentle shape.

crater

On young cones, a depression at the top of the cone, called a crater, is evident, and represents the area above the vent from which material was explosively ejected. Craters are usually eroded away on older cones.

fault and boundaries

Normal faults are associated with divergent plate boundaries. Reverse faults are associated with convergent boundaries. Strike-slip faults are associated with transform plate boundaries.

lithosphere

Not surprisingly, the Earth's internal structure influences plate tectonics. The upper part of the mantle is cooler and more rigid than the deep mantle; in many ways, it behaves like the overlying crust. Together they form a rigid layer of rock called the lithosphere (from lithos, Greek for stone). The lithosphere is the outer solid part of the earth, including the crust and uppermost mantle. The lithosphere is about 100 km thick, although its thickness is age dependent (older lithosphere is thicker). The lithosphere below the crust is brittle enough at some locations to produce earthquakes by faulting, such as within a subducted oceanic plate. The lithosphere is composed of both the crust and the portion of the upper mantle and behaves as a brittle, rigid solid.

liquefacation demo

Notice that things built on top tend to sink and under the ground tend to rise. Observe the latter in the video on the next page

oceanic crust

Oceanic crust is composed of mafic magma that erupts on the seafloor to create basalt lava flows or cools deeper down to create the intrusive igneous rock gabbro.

upper mantle

Our knowledge of the upper mantle, including the tectonic plates, is derived from analyses of earthquake waves (see figure for paths); heat flow, magnetic, and gravity studies; and laboratory experiments on rocks and minerals. Between 100-200 km below the Earth's surface, the temp of the rock is near the melting point; molten rock erupted by some volcanoes originates in this region of the mantle. This zone of extremely yielding rock has a slightly lower velocity of earthquake waves and is presumed to be the layer on which the tectonic plates ride.

plate techtonics

Plate Tectonics- the theory supported by a wide range of evidence that considers the earth's crust and upper mantle to be composed of several large, thin, relatively rigid plates that move relative to one another.

Seafloor spreading

Seafloor spreading is the formation of new seafloor, taking place as plates move apart from each other at a mid-ocean ridge.

s waves

Secondary Waves Arrives second b/c moves slower Moves at 3.5 km/s More damage Moves through solids

secondary waves

Secondary waves are seismic waves that travel more slowly.

seismic waves

Seismic waves are just one type of wave. Sound and light also travel in waves. Every wave has a high point called a crest and a low point called a trough. The height of a wave from the center line to its crest is its amplitude. The horizontal distance between waves from crest to crest (or trough to trough) is its wavelength

shear stress

Shear stress - stress that is experienced at transform boundaries where two plates are sliding past each other, a frictional stress.

Shield volcanoes

Shield volcanoes - broad shield-shaped volcano that is built up by successive, mostly effusive, eruptions of low-silica lava.

Stratovolcano

Stratovolcano - aka a composite volcano, steep, conical volcanoes built by the eruption of viscous lava flows, tephra, and pyroclastic flows.

stratovolcano shapes

Stratovolcanoes (aka composite volcanoes) have a steep slope near the summit - due partly to thick, short viscous lava flows that do not travel far down slope from the vent.

strike slip fault

Strike-slip fault - a fault in which the dip of the fault plane is vertical. Strike-slip faults result from shear stresses. Imagine placing one foot on either side of a strike-slip fault. One block moves toward you. If that block moves toward your right foot, the fault is a right-lateral strike-slip fault; if that block moves toward your left foot, the fault is a left-lateral strike-slip fault

surface waves

Surface waves are seismic waves that travel along the ground surface.

tensional stress

Tensional stress - stress that has the effect of pulling and elongating, happens at divergent plate boundaries where 2 plates are moving away from each other.

Paleozoic (cambrian)

The Cambrian (570-542 mya) "Cambrian Explosion" - major diversification of life. Most modern phyla — the broadest groupings of animals and plants — appeared, including first chordates (ancestors of vertebrates). Trilobites, worms, sponges, brachiopods, and others flourished, as did some predators much larger than other life.

the cascades

The Cascades have been active for 27 my, although the current peaks are no more than 2 myo. The volcanoes are far north and are in a region where storms are common, so many are covered by glaciers.

Cretaceous

The Cretaceous Flowering plants proliferated,

Eocene

The Eocene (65.5-55.8 mya) First grasses appeared. First modern families of mammals emerged, and primitive whales diversified.

Mezozoic

The Mesozoic Era "middle life" 245 - 70 mya Triassic,Jurrasic, Cretaceous

Miocene

The Miocene (33.9-23 mya) Modern mammal and bird families became recognizable. Grasses spread across the globe, and the first apes appeared.

Ogliocene

The Oligocene (55.8-33.9 mya) Animals, especially mammals, evolved rapidly and became more diverse. Modern types of flowering plants evolved and spread.

seismograph

The P and S waves (body waves) and surface waves can be seen on a seismogram - a visualization of the intensity of earthquake waves recorded by a seismometer or seismograph.

Paleocene

The Paleocene (70-65.5 mya) Early mammals diversified, and first large mammals appeared.

paleozoic

The Paleozoic Era "old life" 570 - 245 mya The Paleozoic is characterized by: development of diverse sea life emergence of the first land plants first insects first amphibians first reptiles Cambrian, Carniforous, permian

permian

The Permian (286-245 mya) By 260 mya, the Appalachian mountains were complete.

The pilocene

The Pliocene (23-5.3 mya) Homo habilis, the first species of the genus Homo to which humans belong, appeared. The land surfaces of the Blue Ridge and Piedmont now appeared essentially as they do today.

Precambrian

The Precambrian Era 4.5 billion - 570 mya By 4.4 bya,Earth had a stable crust with oceans and a primitive atmosphere Simple single-celled life emerged as early as 3.8 bya The first oxygen-producing bacteria emerged Prior to this, Earth's atmosphere had much CO₂ and little O₂. The oldest microscopic fossils that have been found are ~3.5 byo. The landmass of North America began to form. Erosion by the first glaciers. Tectonic plates developed ~1.3 bya: 1st mountains formed in NC. ~1 bya: the land under NC was pulled apart, and inland seas emerged. Island volcanoes developed along the NC-VA border and in an arc from VA to GA.

usgs

USGS - United States Geological Survey, government agency that studies landforms, natural resources, and hazards.

athenosphere

The asthenosphere is the ductile part of the earth just below the lithosphere, including the upper mantle. The asthenosphere is about 180 km thick. The asthenosphere is partially molten upper mantle material and behaves plastically and can flow.

Moho

The boundary between the crust and mantle is called the Mohorovicic discontinuity (or Moho); it is named in honor of the man who discovered it, the Croatian scientist Andrija Mohorovicic.

core

The core - innermost part of the earth. The outer core extends from 2500 to 3500 miles below the earth's surface and is liquid metal. The inner core is the central 500 miles and is solid metal The core was the first internal structural element to be identified.

epicenter

The epicenter is the point on the land surface that is directly above the focus Shallower earthquakes generally cause more damage.

Jurassic

The first birds and lizards appeared. Ichthyosaurs and plesiosaurs were diverse in the oceans. As the North American continent drifted to the northwest, its trailing edge sank under water, and the Atlantic Ocean formed between North America and Africa. The shore was located near the present Outer Banks.

lower mantle

The lower mantle lies between 660-2,891 km (410-1,796 miles) in depth. Temps in this region of the planet can reach over 4,000 °C (7,230 °F) at the boundary with the core, vastly exceeding the melting points of mantle rocks. However, due to the enormous pressure exerted on the mantle, viscosity and melting are very limited compared to the upper mantle. Very little is known about the lower mantle apart from that it appears to be relatively seismically homogeneous.

visocsity

The speed at which lava moves across the ground depends on several factors, including (1) type of lava erupted and its viscosity; (2) steepness of the ground over which it travels; (3) whether the lava flows as a broad sheet, through a confined channel, or down a lava tube; and (4) rate of lava production at the vent. Viscosity - the extent to which a fluid resists a tendency to flow

Inner core

The temp of the inner core is estimated to be about 5,700 K (~5,400 °C; 9,800 °F). The only reason why iron and other heavy metals can be solid at such high temps is because their melting temps dramatically increase at the pressures present there, which ranges from about 330 to 360 gigapascals. Because the inner core is not rigidly connected to the Earth's solid mantle, the possibility that it rotates slightly faster or slower than the rest of Earth has long been considered. By observing changes in seismic waves as they passed through the core over the course of many decades, scientists estimate that the inner core rotates at a rate of one degree faster than the surface.

forces of plate techtonics

There are three forces that produce the motions of plate tectonics Convection is the most influential, and involves the rising and fall of hot and cool mantle material, creating new crust and pulling along other crust like a conveyer belt Gravity, aka slab pull, is the force that pulls crust down at plate boundaries Ridge push is the outward push of new seafloor as hot material fills in gaps at a divergent plate boundary

richter scale

Used to measure intensity of earthquakes, but largely out of favor in the scientific community. Moment Magnitude Scale is more widely used.

vent

Vent - any opening at the Earth's surface through which magma erupts or volcanic gases are emitted. Volcanoes may emit lava, gases, rock, and ash. Lava is the molten material that escapes the Earth during an eruption. Magma is the term used to refer to lava when it is below the Earth's crust.

lava domes

Volcanic or lava domes are formed by relatively small, bulbous masses of lava too viscous to flow any great distance; consequently, on extrusion, the lava piles over and around its vent.

volcanic soils

Volcanic rocks make some of the best soils on earth because they not only have a wide variety of common elements, but are readily chemically separated into elemental components. These soils are highly fertile and great for growing a variety of crops.

break

almost there

Volcanic gases

are dangerous and deadly and cause numerous enviromental problems

break

do it

The carboniferous

he Carboniferous (360-300 mya) In wetland forests, ferns thrived and primitive trees called scale trees grew more than 100 feet high. Their decayed remains became coal. The portions of the Appalachian region where coal is mined today were then covered in such forests. ~320 mya, the North American and Euro-African continents collided, resulting in the last period of Appalachian mountain building. Land under the Piedmont and Coastal Plain was also pushed upward. The continents were united in a "supercontinent" that geologists call Pangaea. Amphibians common, and reptiles began to branch off Insects grew to enormous sizes

Outer core

he outer core, which has been confirmed to be liquid (based on seismic investigations), is 2300 km thick, extending to a radius of ~3,400 km. In this region, the density is estimated to be much higher than the mantle or crust, ranging between 9,900 and 12,200 kg/m3. The outer core is believed to be composed of 80% iron, along with nickel and some other lighter elements. Denser elements, like lead and uranium, are either too rare to be significant or tend to bind to lighter elements and thus remain in the crust. The outer core is not under enough pressure to be solid, so it is liquid even though it has a composition similar to that of the inner core. The temp of the outer core ranges from 4,300 K (4,030 °C; 7,280 °F) in the outer regions to 6,000 K (5,730 °C; 10,340 °F) closest to the inner core.

cascades earthquake

pacific northwest are at risk for a massive earthquake that hasn'e happned since 1700

chart look at last

pl

caldera

very large composite volcano collapsed after an explosive period frequently associated with plug domes

flood or platea basalt

very liquid lava flows very widespread emitted from fractures

plug dome or volcanic dome

very viscous lava relatively small can be explosibe commonly occurs adjacent to craters or composite volcanos

u did it!

yes