Geo _ Unit 30 - 33

Which type of tectonic boundary is the result of two tectonic plates colliding with each other?

Convergent boundary **Convergent boundaries form as a result of compressional forces pushing two plates together.

Which term best characterizes up-welling in the Asthenosphere?

Diffuse

Which tectonic boundary results when two tectonic plates pull apart from each other?

Divergent boundaries **Divergent boundaries form because of tensional stress.

Which of the following statements about Earth's magnetic field is most accurate?

Earth's magnetic field switches polarity at irregular time intervals.

Along the seafloor, the youngest ocean rocks are found near continents. T or F

False

The temperature of ocean rocks is coolest near midocean ridges and increases as rocks get closer to continental margins.

False

An earthquake can only occur where plate boundaries exist. T or F

False.

What is a plume?

A plume is a zone of up-welling material originating at the outer core-mantle boundary.

In general, what is our best evidence that the orientation of Earth's magnetic field has changed over time?

A record of Earth's magnetic field is recorded in oceanic rocks, which show a clear pattern of changes in Earth's magnetic polarity.

Why are volcanoes NOT found at transform boundaries?

Volcanoes are not found at transform boundaries because they do not cause changes to the pressure, temperature, or composition of the mantle.

What evidence supports that the glaciers on the southern continents were once part of a single, massive ice sheet?

Striations **Striations are scratches or grooves created by glacial debris as it moves. The striations found on the southern continents all radiate from the center of the south part of Pangaea.

A volcano that has erupted in recorded history is said to be:

active.

All are ways in identifying suspect terranes from host continents EXCEPT:

age of rocks are similar

Shaking accounts for just a fraction of the damage caused by earthquakes. Damage may also be caused by:

all of the above : fires, tsunami, landslides

Earthquakes, volcanoes, and mountains are characterized by the following

all of the above.

What processes explain the thickening of the lithosphere?

all of the above: -collision of lithospheric plates -as time progresses, sediments build up making the lithosphere thicker -subduction of oceanic crust beneath continental crust

Although a 7.0 magnitude earthquake measures the same amount of ground motion despite the location, certain areas experience more destruction than others. Reason(s) that may explain this are:

all of the above: -the area is more heavily populated -the ground to which the earthquake travels through may experience more shaking -structures are not built to withstand earthquakes

Earthquakes are caused by movement along lithospheric plates. Lithospheric plates move by

all of the above: diverging plates, converging plates, side-by-side motion

Cold, old oceanic crust can be found:

along convergent plate boundaries near subduction zones

Volcanoes are NOT found at this location

along plains with thick deposits.

The East African rift is a divergent plate boundary that is splitting the continent of Africa into two pieces. What will eventually form around this divergent boundary?

an ocean

How old are the oldest continental rocks?

approximately 2.5 to 3.5 billion years old.

New oceanic crust can be found

at mid-ocean rift zones

Shaking is felt stronger near the epicenter of an earthquake and lessens to areas moving farther away. This effect is called:

attenuation

Lahars may be caused by

both (a) and (b): intense rainfall rapid snowmelt

The mechanism used to describe the spreading of oceanic crust is:

both (a) and (c)

Isostasy, the condition of equilibrium between floating landmasses and the denser rock beneath them, can best be explained by

both (a) and (c): -greater crustal thickness extending below sea level -a low density root system caused parts of the crust to stand much higher

Why did the 9.2 magnitude in Alaska's 1964 earthquake result in only 131 deaths, while the 7.0 magnitude in Haiti's 2010 earthquake result in over 300,000 deaths?

both (a) and (c): because Alaska is built on loose sediment and buildings moved with the shaking because of low population density near the epicenter in Alaska's earthquake

Thickening of lithospheric plates is best explained by understanding that:

collision of continental plates pushes rocks of the same density together.

A type of volcano that's mostly associated with subduction zones along convergent plate boundaries are:

composite cones.

The Himalayan Mountains are an example of:

continent-continent convergent boundary

The process of upwelling magma at divergent boundaries with subsequent movement away from those boundaries, and the return flow of cooled rock to deep in the mantle form cycles of slowly moving rock may be explained by:

convection currents

Subduction zones are associated with this type of plate boundary.

convergent boundaries

The largest earthquakes that have been recorded typically occur along:

convergent boundaries

Which type of plate boundary is most closely associated with the formation of new ocean floor?

divergent

As stress is imposed on a rock, it will deform until the stress is greater than the strength of the rock causing a(n):

earthquake?

On earth's surface, directly above the location where an earthquake originates is called a(n):

epicenter

Mountain ranges undergo weathering, erosion and deposition on adjacent low-lying plains. As sediment deposits accumulate on the plains, the plains will:

eventually re-adjust to its original level.

How often does the Earth's magnetic field switch polarity?

every 100,000 to several million years

After studying the ages of continental and oceanic rocks, the oldest continental rocks found on Earth are approximately 3 billion years old while the oldest oceanic rocks are approximately 180 million years old. Which statement best explains this discrepancy in ages between continental and oceanic crust

evidence of seafloor spreading explains how old, oceanic rocks are constantly being destroyed

When a volcano shows no signs of life and exhibits evidence of long-term erosion, it would be classified as a(n):

extinct.

When one fault block moves up relative to a block on the opposite side, the exposed fault plane is called a(n):

fault scarp

A ____ is the leading edge along a fault of the lower fault block.

fault trace.

A fracture in the earth's crust is called a joint. It is called a _____ when there is displacement of rocks on either side of the fracture.

fault.

The Columbia Plateau located in southern Washington and parts of eastern Oregon was formed by:

fissure eruption

As fluid basaltic lava pours out of linear cracks, or fissures, ___ form large sheets of lava rather than a typical cone-shaped volcano.

flood basalts

Which statement is NOT true with regard to lavas that are high in silica?

flows out of fissures

The following is true regarding continental shields

have constantly grown and have become progressively younger moving away from core shields.

With regards to magma viscosity, which of the following has the lowest viscosity?

high iron and magnesium content.

Gases cannot escape from _____ magma easily; therefore, they produce _____ eruptions

high-silica; explosive

Hawai'i, Yellowstone, and the Snake River Plain form on or near:

hot spots

It is recommended that if you feel an earthquake and are near the coastline, you should make it to high ground without waiting for an official tsunami warning because:

if you are near the epicenter, there is not enough time to receive an official warning

How an earthquake is felt by others and the amount of damage an earthquake creates is determined by its:

intensity.

Earthquakes that do NOT occur along a plate boundary occur in this zone.

intraplate

A condition of equilibrium between a floating landmass and the denser rock beneath is called:

isostasy.

All are true about plate boundaries EXCEPT

life does not exist along boundaries

The amount of energy that is released from an earthquake is its _____

magnitude

A zone where earthquakes occur but are generally less frequent and less severe is the:

mid-ocean ridge belt

Educating the public about the causes of earthquakes and their potential hazards may help to alleviate death and destruction should an earthquake occur, but a country also needs _____ to help prepare for the likelihood of such an event.

money

As mountain ranges, such as the Appalachian Mountains, erode, the:

mountain peaks are standing at or near their original elevation

Hot, fast, down-slope, turbulent flow of pyroclastic material mixed with gas is called

nuee ardente

Which evidence did Alfred Wegener NOT use to support his hypothesis of one large supercontinent named Pangaea and its subsequent break up?

ocean floor drilling exposing remnants of similar continental rocks of two separate continents

The area characterized by continental arcs and nearby deep sea trenches occurs along:

ocean-continent convergent boundaries

Mount St. Helens, Mount Rainier, and other active volcanoes along the Cascade Ranges are examples of:

ocean-continent convergent boundaries.

Where would you expect to see alternating bands of rock with different magnetic polarities?

on both sides of the mid-ocean ridge

Violent eruptions caused by the introduction of water into superheated magma is called:

phreatic eruption.

Solid fragments ejected from a volcano are called:

pyroclastics.

As ice sheets retreat, the underlying landmass will readjust and undergo isostatic ____

rebound

The San Andreas Fault system is an example of:

rift movement along divergent boundary.

Young rocks are created along spreading centers and old rocks are destroyed along deep ocean trenches. This phenomenon is called:

seafloor spreading.

The _____ is the instrument that measures an earthquake's moveme

seismograph

A type of volcano that erupts fluid basalt is called:

shield volcanoes

Which statement is true with regard to cinder cones?

single eruption of cinders made of basalt.

The majority of continental and island-arc volcanoes are in or near:

subduction zones

Ice sheets may exert significant weight on the surface of the Earth causing the surface to undergo isostatic _____.

subsidence

It is difficult for scientists to understand the evolution of ancient volcanoes (stratovolcanoes). Many times researchers can determine the degree of explosiveness and the height of the eruption column by studying the size of pyroclastic material and the distance they travelled. It can be inferred that the larger the fragments erupted, the more explosive the eruption; the more explosive the eruption, the farther the distance volcanic fragments travel; and:

the farther pyroclastic material travel, the higher the eruption column

Geophysicist Charles Richter developed the Richter Scale to measure an earthquake's magnitude. An increase from 4.0 magnitude to 5.0 magnitude means:

there is 10 times more physical force of ground motion

The two factors that determine how high or low the surface topography will be are ____ and _____ of the lithosphere relative to sea level.

thickness; density.

Crust is neither created nor destroyed at this boundary.

transform plate boundaries

Island arcs are volcanoes that have risen above sea level.

true.

In 2011, over 20,000 people died in Japan's 9.2M Tohoku earthquake. The worst damage and loss of life were caused by

tsunami

The theory that describes the depression and rebound of continental crust due to adding or removing weight is called:

-isostasy

A magnitude 4 earthquake causes 10 times more ground motion than a magnitude 3 earthquake and ______ times more ground motion than a magnitude 2 earthquake.

100.

Using the figure above, when was the last time the Earth had a magnetic reversal?

700,000 years ago

How are normal polarity and reverse polarity of Earth's magnetic field different?

A compass points toward the North Pole during normal polarity and to the South Pole during reverse polarity.

Which scientist developed the idea of Continental Drift?

Alfred Wegener

Alfred Wegener proposed that there was once a giant supercontinent he called Pangaea. He used the following evidence to support his hypothesis:

All of the above: -matching similar rock types across distant continents -matching fossils across distant continents -geographic fit of continents

What is convection?

Convection is a cycle of moving material formed by the rise of less-dense material and the sinking of denser material.

The greatest concentration of earthquakes occurs along the:

Circum-Pacific belt

In a collision between two continental plates, can a continental plate subduct? Why or why not?

Continental plates are too buoyant to subduct. **Continental lithosphere has a density of 2.7 grams per cubic centimeter, making it unlikely to subduct.

What statement best describes Wegener's idea of continental drift?

Continents were formerly in different positions on the Earth and have shifted to their present locations over time. **Wegener believed that the continents had once been part of a supercontinent that he named Pangaea.

Which part of the Earth is responsible for generating the planet's magnetic field?

Core **The field is generated in the outer part of the core, which is believed to be a liquid iron alloy.

What accounts for most tectonic plate motion?

Forces at subduction zones account for most tectonic plate motion.

After studying a region in the Northwestern part of the United States, observations and laboratory studies show that a mountain belt juxtaposed to a low-lying area are compositionally and structurally different and hundreds of thousands of years apart in age from each other. Which statement best explains this anomaly?

Foreign mountain ranges are accreted onto continental shields bringing unrelated rock types next to each other

How was the fossil record of ancient life used to support Wegener's hypothesis about Pangaea?

Fossils of identical organisms were found on several continents, indicating the continents were once joined. **When organisms are separated into two smaller groups by a physical barrier (i.e., the Atlantic Ocean), then they follow different evolutionary paths. The organisms Wegener cited were identical on both continents.

What features at the surface provide evidence of plumes?

Hot spots provide evidence of plumes.

In general, where do volcanoes form in subduction zones?

In general, volcanoes form on the overriding plate, away form the convergent boundary.

What is the relationship between temperature and density?

In general, warmer materials are less dense, and colder materials are more dense.

In general, where do earthquakes AND volcanic eruptions occur?

In general,earthquakes and volcanic eruptions occur at both divergent plate boundaries AND convergent plate boundaries.

How is information about magnetic fields recorded in rocks?

Iron particles in magnetically susceptible minerals within basaltic lava align with the magnetic field of the Earth while the lava is still liquid and then freeze in position when the lava solidifies. **Particles of iron will align while the material is still molten, but are locked into place once the lava hardens.

Alfred Wegener hypothesized that there was once one large supercontinent named Pangaea that was comprised of two major parts. These two parts were called:

Laurasia and Gondwana

What forms at divergent plate boundaries?

New oceanic lithosphere

Crustal rifting is currently occurring in East Africa. Which feature would you expect to find there?

Normal Faults, long-wide vallies, and lava flows **All of these physical features are evidence that the landscape is experiencing tensional stress from rifting.

The _____ Plate meets the Pacific Plate along California's San Andreas Fault.

North American

Depending on the type of plate convergence, different features could result. Examples of these features include volcanic island arcs, continental volcanic arcs, and a collisional mountain chain.

Once the volcanoes become completely dormant, they can be called mountains. Similarly, when the volcanic activity in the volcanic arc islands stops, they would appear and have the characteristics of islands.

The city of Los Angeles can be found on which tectonic plate?

Pacific Plate

The chain of explosive volcanoes that lie along the circumference of the Pacific Ocean is sometimes referred to as the

Pacific Ring of Fire

What is the name of the supercontinent proposed by Alfred Wegener?

Pangaea

Why are volcanic chains associated with convergent boundaries?

Partial melting occurs due to subduction. **Partial melting is triggered by water loss in the plate. This melts mantle material, which rises to the surface.

Plate A has oceanic lithosphere on its leading edge that is 10 million years old. Plate B has oceanic lithosphere on its leading edge that is 200 million years old. Which plate will be subducted if they collide with each other, and why?

Plate B will subduct because it is older—and therefore colder—and more dense. **The older an oceanic plate is, the colder it is, making it more dense.

The Hawaiian Islands formed over a stationary hot spot...By understanding that the Hawaiian Islands formed over a stationary hot spot, the youngest rocks are found on the actively-erupting Hawai'i island, and that rocks become progressively older as you move northwest helps support what theory?

Plate Tectonics Theory

How do plates move at divergent plate boundaries?

Plates move apart at divergent plate boundaries.

How do plates move at convergent plate boundaries?

Plates move toward one another at convergent plate boundaries.

How do plates move at transform plate boundaries?

Plates slide past one another at transform plate boundaries.

Identify each type of convergent plate boundary.

Since oceanic plates are denser than the continental plates, they will subduct to great depths when they converge with continental plates. When two oceanic plates converge, the denser of the two will subduct; whereas when two continental plates converge, neither will subduct. Therefore, the resulting geologic feature depends on the types of plates that converge.

How were scientists able to determine the date of the magnetic reversals during seafloor spreading?

Small marine fossils in deep-sea sediments give the age of the portions of the seafloor **Fossils are very useful in determining geologic ages.

____ is an example of a feature associated with an oceanic-continental convergent plate boundary?

The Cascade Mountain Range

____ is an example of a transform plate boundary.

The San Andreas Fault

Late Paleozoic sedimentary rocks often contain extensive coal seams that were used to support the existence of Pangaea. What would the climate have been at that time and at the location where the coal deposits were formed, and what would it indicate about the continent's past latitude?

The climate would have been a warm, humid climate near the Equator. **Swamp vegetation needs a lot of moisture and plenty of warm temperatures to thrive. The conditions would have been (and are today) present near the Equator.

When matching up once-joined continents such as South America and Africa, the coastlines do not fit together as nicely as the continental shelves. Why might this be the case?

The continental shelves are the edges of the continent. The shoreline simply shows where the sea level is in relation to topography. **Depending on sea level, continental shelves are often underwater and below the erosive effects of wave action.

The continental drift hypothesis was not accepted by the scientific community because:

The correct answer was: b. Alfred Wegener could not provide a plausible mechanism explaining how continents drifted.

At a subduction zone where oceanic lithosphere meets continental lithosphere, which would subduct and why?

The oceanic lithosphere would subduct because it has a higher density at 3.0 grams per cubic centimeter. **Oceanic lithosphere, which is basaltic, has a higher density than continental lithosphere.

The following statement is true with regard to the Atlantic Ocean

The oldest oceanic crust is found near continents

The following statement is true with regard to the Atlantic Ocean:

The oldest oceanic crust is found near continents

Which statement about the theory of plate tectonics is correct?

The rigid lithosphere plates overlay the hotter and weaker asthenosphere.

When George Everest took his gravity measurements by dropping a plumb line along the flank of a mountain range, he expected the mountain to attract the plumb line from vertical toward the range due to density differences. Instead, calculations later done by John Pratt showed that the plumb line experienced far less attraction toward the mountain than expected. It was concluded that:

The rocks under the mountain range have far less density beyond its base than its surrounding rocks

Divergent boundaries are not one, smooth ridge of separation. Instead, they are broken into a series of segments, with different segments of fault offset from others. What features allow for the offset of divergent boundaries?

Transform faults **Transform faults account for the lateral offset that is seen along divergent boundaries.

The higher the mountain, the deeper its root. T or F

True

Typically, the closer to an earthquake's epicenter, the more shaking is felt.

True

Which factor determines whether a volcano will have an explosive, violent eruption?

a. how high the temperature b. how long ago its last eruption occurrence c. the amount of dissolved oxygen d. the amount of magma in the volcanic chamber - NNOOO

Which of the following has the highest magma viscosity?

a. none, all magma have the same viscosity b. high silica content (rhyolitic) c. low silica content (basaltic) - NNOOO d. high iron and magnesium content

When unrelated landmasses and continental shields are juxtaposed next to each other, they are usually brought together by this process:

accretion.