Chapter 6 Science

Rhyolitic magma is created by melting continental crust. What is the direct source of heat for this process? The earth's core Rising andesitic magma The sun Friction

Rising andesitic magma

What type of volcano is typically very large, composed of low-viscosity lava, and has gently sloping sides? Stratovolcano Shield Cinder cone

Shield

Why does a higher silica content in a magma result in higher viscosity? Silica combines with other elements to form long molecular chains that get tangled. More silica molecules lower the temperature of the magma. Silica molecules are inherently "sticky."

Silica combines with other elements to form long molecular chains that get tangled.

Select all that apply Choose the three most common gases found inside magma. Sulfur dioxide Water vapor Hydrogen sulfide Carbon dioxide Ozone

Sulfur dioxide Water vapor Carbon dioxide

Why is the crust thicker underneath the Himalayas as compared to the Andes Mountains? The Himalayan mountains are older and have more time to grow. The Himalayas are the site of active volcanism, which is continually adding to the crustal thickness there. The Himalayans are formed from two overlapping continental crusts.

The Himalayans are formed from two overlapping continental crusts.

Select all that apply The volcanic explosivity index, or VEI, is based on ______. the atmospheric height of the erupted ash the volume of material erupted the length of the eruption event how loud the eruption was the horizontal diameter of the erupted ash

the atmospheric height of the erupted ash the volume of material erupted the length of the eruption event

Different plate boundaries produce different types of_____________ because each setting melts a different source rock.

magma

Which of these best describes a caldera? A large crater formed from the collapse of a volcano The central vent of a volcano A plateau of basaltic lava

A large crater formed from the collapse of a volcano

Which of these best describes a caldera? A plateau of basaltic lava The central vent of a volcano A large crater formed from the collapse of a volcano

A large crater formed from the collapse of a volcano

The emission of volcanic gases can affect the climate differently: ______dioxide in the atmosphere leads to warming, while ______dioxide leads to cooling.

Blank 1: carbon Blank 2: sulfur

The Himalayas are higher in elevation than the Andes because they are the result of ____________collision rather than the subduction of ocean crust under continental crust.

Blank 1: continental

Scientists were concerned that Mount St. Helens was going to erupt in early 1980 because the number of __________increased dramatically and the mountain________ nearly 500 feet in elevation.

Blank 1: earthquakes Blank 2: grew, increased, or rose

An impending volcanic eruption commonly is preceded by changes in the volcano's shape, an increase in volcanic________ emissions, and an increase in frequency __________.

Blank 1: gas Blank 2: earthquake

The oceanic ridge system is actually an underwater mountain range caused by the addition of __________from the upwelling magma

Blank 1: heat

The breakup of Pangaea led to the drastic ___________ of the climate because of increased volcanic activity and carbon dioxide emissions at ocean spreading centers.

Blank 1: heating or warming

This two-word term is used to describe the creation of magma from a source rock that does not completely melt.

Blank 1: partial Blank 2: melting

The violence of volcanic eruptions is dependent on magma ________ , which in turn is determined by magma ___________ .

Blank 1: viscosity Blank 2: composition

How often are lava flows stopped though the use of techniques such as explosives and cold water? Rarely On a regular basis Occasionally

Rarely

What type of magma has the highest silica content and is the most viscous? Rhyolitic Andesitic Basaltic

Rhyolitic

Lava plateaus are found across the globe and represent enormous eruptions of _______ lava. viscous basaltic rhyolitic

basaltic

Whereas mountain erosion rates are typically 1 kilometer every 5 to 10 million years, the resulting elevation change occurs over a ______ time period because of isostasy. longer shorter

longer

The preferential erosion of mountains in stream valleys can result in higher mountain peaks because _________ elevates the whole mountain range due to the material lost.

isostasy

The relatively high _________of the small amount of magma associated with the Mount St. Helens' eruption resulted in lava flows not posing much danger.

viscosity

What type of plate boundaries create mountains, which in turn are the locations of the thickest continental crust? Transform Convergent Divergent

Convergent

True or false: Volcanic activity releases more carbon dioxide in the atmosphere annually than human activities do. True False

False

Within your lifetime, how much mountain erosion would you notice? Quite a lot, since it would easily be over 10 meters Hardly any, since it might equal 10 millimeters A bit, since it would be close to 0.5 meters

Hardly any, since it might equal 10 millimeters

At convergent plate boundaries, continental crust thickens as reverse faults pile blocks of rock on top of each other. What is the primary result of this thickening? The crustal roots get thicker. The roots get thicker and the elevation gets higher equally. The land elevation gets higher.

The crustal roots get thicker.

This one-word term is used to describe a volcano that might erupt. Fifteen hundred of these currently exist.

Active

After the Himalayas, the tallest mountains in the world are found in the ______. Rockies Andes Alps Cascades

Andes

What role do the Himalayas play in the monsoon? Cool, moist air has to rise because of the mountains, which causes it to condense and create heavy rains. The monsoon rains are not influenced by the Himalayas. Cold air drops down the mountain range, picks up moisture from the glaciers, and then condenses once over the Indian plains.

Cool, moist air has to rise because of the mountains, which causes it to condense and create heavy rains.

What would eventually happen to the elevation of a mountaintop that lost 500 meters of material through erosion? (Let us assume that this takes some time to accomplish.) It would lose 1000 meters in elevation. It would lose 500 meters in elevation. It would lose about 100 meters in elevation. It would not change in elevation.

It would lose about 100 meters in elevation.

The Himalayan Mountains were formed about 50 million years ago in a continental collision. These are the tallest mountains on Earth, indicating that mountains ______. are short-lived features always get shorter with age are long-lived features

are long-lived features

Lava plateaus are related to ______ global temperatures because they released a lot of carbon dioxide. increased decreased

increased

When continental crust thickens due to collision, the land adjusts by ______. equally increasing the crustal root and land elevation mostly increasing the size of the crustal root mostly increasing the elevation of the land surface

mostly increasing the size of the crustal root

Why do the dissolved gases in magma come out of solution when magma rises to the surface? Pressure decreases. Temperature decreases. Pressure increases. Temperature increases.

pressure decreases

Approximately how many active volcanoes, those that might erupt, currently exist? 300 25 10,000 1,500

1,500

The eruption of Mount St. Helens in ______ was one of the United States' most destructive natural disasters. 1944 2011 1900 1980

1980

How many of the approximately 1,500 active volcanoes in the world have a complete network of instruments for monitoring seismic and volcanic activity? 20 1,240 710

20

The low-viscosity lava flows from Hawaiian volcanoes and Nyiragongo in Congo are good examples of how far lava can flow away from a volcano; in these cases, the lava has moved up to ______ kilometers. 50 500 5

50

The volcanic explosivity index has _______levels, each of which is a tenfold increase in the volume of material erupted.

8

What is viscosity? The relative amount of gas in a magma Mass per unit volume A liquid's resistance to flow The temperature at which a rock becomes liquid

A liquid's resistance to flow

What is a volcanic bomb? A piece of microscopic, volcanic glass A type of tephra that is formed from an airborne blob of lava Volcanic ash that has been pushed together in a spherical shape

A type of tephra that is formed from an airborne blob of lava

What type of magma is intermediate in composition (i.e., silica content) and viscosity? Andesitic Basaltic Rhyolitic

Andesitic

Select all that apply Choose all of the phrases that describe basaltic magmas. Have a low silica content Have a high viscosity Created though decompression melting at divergent plate boundaries Created at oceanic hot spots

Have a low silica content Created though decompression melting at divergent plate boundaries Created at oceanic hot spots

Choose the descriptors that are true of andesitic magma. It has a high enough viscosity to create explosive eruptions. It has a very high silica content. It is created due to decompression. It is created at convergent plate boundaries.

It has a high enough viscosity to create explosive eruptions. It is created at convergent plate boundaries.

Select all that apply Choose the descriptors that are true of andesitic magma. It is created at convergent plate boundaries. It is created due to decompression. It has a very high silica content. It has a high enough viscosity to create explosive eruptions.

It is created at convergent plate boundaries. It has a high enough viscosity to create explosive eruptions.

Select all that apply Choose the ways in which volcanic ash is dangerous. It is highly conductive. It starts forest fires. It is bad for soil quality. It can block sunlight in the atmosphere. It is slippery.

It is highly conductive. It can block sunlight in the atmosphere. It is slippery.

How does the continental crust vary in thickness? It does not vary. It is thick below mountain belts and thin at the margins. It is thickest on the edges and thinnest in the middle. The thickness varies randomly.

It is thick below mountain belts and thin at the margins.

What term is defined as mass per unit volume?

density

As magma rises to the surface, ______, which in turn changes the composition and results in different types of rocks. gases are lost gases are gained

gases are lost

Mountains can be found in areas of thin continental crust as _______ causes the rocks in the area to expand. density differences water heat

heat

A magma with a high viscosity likely has a ______. high amount of dissolved gases low silica content high silica content high temperature

high silica content

The melting temperature of silica-poor minerals is ______ that for silica-rich minerals. lower than the same as higher than

higher than

Shield volcanoes are typically found above ocean ______ and divergent plate boundaries, whereas stratovolcanoes are formed through subduction at ______ plate boundaries. plateaus; transform hot spots; convergent rifts; divergent

hot spots; convergent

Select all that apply Rhyolitic magma ______. is low in silica content is formed through partial melting of continental crust is so viscous it rarely makes it to the surface is produced at oceanic rifts

is formed through partial melting of continental crust is so viscous it rarely makes it to the surface

The eruption of a volcano in a sideways or horizontal direction is called a __________blast.

lateral

The Siberian Traps and the Deccan Traps in India are example of ______. shield volcanoes cinder cones lava plateaus

lava plateaus

A block of water that floats in water has a density that is ______ 1gm/cm3. less than greater than equal to

less than

Select all that apply Higher elevation areas result from either ______ or ______. more-dense rocks less-dense rocks thinner crust thicker crust

less-dense rocks thicker crust

The varying compositions of magma found at different plate boundaries result from ______. melting different source rocks a large variety of melting processes

melting different source rocks

The gases within a low-viscosity magma will escape ______ compared to those within a high-viscosity magma. more easily in the same fashion less easily

more easily

A lahar is a volcanic __________composed of ash and water, moving quickly down the side of a volcano. Lahars carry a tremendous volume of material and are capable of causing destruction by completely altering a downgradient landscape.

mudflow

A low-viscosity magma flows ______, whereas a high-viscosity magma flows ______. quickly; slowly slowly; quickly

quickly; slowly

Mount St. Helens was visibly ______ after it erupted in 1980. . wider hotter shorter

shorter

The silica chains within a silica-rich magma get _____________ , resulting in a high viscosity.

tangled

The 12-million-year-old ash layer in Nebraska that preserved hundreds of animal skeletons was create from a mantle plume ______. that was in Idaho but now is in Wyoming that was located underneath Yellowstone

that was in Idaho but now is in Wyoming

The eruption of Nyiragongo in 2002 was particularly dangerous because ______. the lava flows moved very quickly a powerful earthquake occurred at the same time of a massive mudflow that came after

the lava flows moved very quickly

Water vapor, carbon dioxide, and sulfur dioxide are ______ in magma. found rarely never occur the most common gases

the most common gases

Driving west on I-80 through the Great Plains of the United States, you eventually come to Denver and can't help but notice the great elevation change with the Rocky Mountains in front of you. Understanding the concept of isostasy, you correctly assume that the continental crust under the Rockies is ________than that under the Great Plains.

thicker

There are ______ common types of magma that are classified according to ______. five; viscosity two; color three; composition

three; composition

Thick continental crust with mountain belts is typically found near convergent plate boundaries; this is where ______. lava flows on the surface add significantly to the crust plate pull apart thrust faults push pieces of crust on top of one another

thrust faults push pieces of crust on top of one another

What type of magma has a low viscosity, low silica content, and is created at divergent plate boundaries? Rhyolitic Basaltic Andesitic

Basaltic

A fast-moving, dangerous flow of hot gas, ash, and volcanic debris down the side of a volcano is called a _________ flow.

Blank 1: pyroclastic

Andesitic magmas are created in subduction zones through the addition of _________ from the descending plate, which ___________ the melting temperature of the mantle rocks in the overlying plate.

Blank 1: water Blank 2: lowers

What volcanic feature is located in Yellowstone National Park and is responsible for a massive eruption about 640,000 years ago? Shield volcano Cinder cone Lava plateau Caldera Stratavolcano

Caldera

Select all that apply Choose all of the following that describe the geologic activity on Mount St. Helens preceding its eruption in May 1980. Animals deserted the mountain. Earthquakes increased in frequency to as many as 100 per day. The volume of sulfur dioxide emitted increased dramatically. Lightning strikes on the mountain quadrupled in number. The mountain grew nearly 500 feet (150 meters) in elevation.

Earthquakes increased in frequency to as many as 100 per day. The volume of sulfur dioxide emitted increased dramatically. The mountain grew nearly 500 feet (150 meters) in elevation.

The 12-million-year-old ash bed in Nebraska that preserves hundreds of animal skeletons came from the eruption of a supervolcano in present-day Idaho. Where is this supervolcano now? It is under the Cascade Mountains. It has disappeared. It is still under Idaho. It is under Yellowstone National Park.

It is under Yellowstone National Park.

Select all that apply Which of the following describe a typical shield volcano? Large Formed from low-silica lava Gently sloping Low in elevation Formed from high-viscosity lava

Large Formed from low-silica lava Gently sloping

How many of the approximately 1,500 active volcanoes in the world are monitored with instruments? None About half Less than 200 Nearly all

Less than 200

Do gases escape more easily from high-viscosity or low-viscosity magma? Low-viscosity Neither High-viscosity

Low-viscosity

Select all that apply Which of the following describe stratovolcanoes? Made of viscous lava Small Steep Erupt violently

Made of viscous lava Steep Erupt violently

Select all that apply Geysers, hot springs, and mud volcanoes are created by the indirect association of which two features? Volcanic gases Lava Magma Ground water

Magma Ground water

Select all that apply Which of the following describe the 1985 eruption of Nevado del Ruiz? Many people could have been saved had there been a warning and evacuation. The major cause of death was a hot lava flow. This particular type of volcanic eruption was unknown for this volcano. Over 23,000 people were killed.

Many people could have been saved had there been a warning and evacuation. Over 23,000 people were killed.

Select all that apply What events presaged the eruption of Nyiragongo in 2002 months before it occurred? More frequent earthquakes A change in the shape of the crater Increased gas emissions Animals abandoning their habitats on the mountain

More frequent earthquakes A change in the shape of the crater Increased gas emissions

What type of disaster is associated with the 1991 eruption of Mt. Unzen in Japan? Phreatic explosion Lava flow Ash fall Pyroclastic flow

Pyroclastic flow

How is the breakup of Pangaea 120 to 80 million years ago linked to a 10°C (18°F) rise in global temperatures? The breakup was associated with exaggerated volcanic activity at oceanic divergent plate boundaries. The breakup of the supercontinent released more heat from the core of Earth. The breakup of Pangaea released sulfur when the crust was broken, which then readily combined with oxygen to form atmospheric sulfur dioxide.

The breakup was associated with exaggerated volcanic activity at oceanic divergent plate boundaries.

Why do viscous magmas erupt more violently than less-viscous magmas? Viscous magma are higher in temperature. Viscous magmas contain a much higher amount of dissolved gases. The gases cannot escape as easily from viscous magmas, so gas pressure can get very high.

The gases cannot escape as easily from viscous magmas, so gas pressure can get very high.

Which of the following best describes what happens to the dissolved gases in magma as it rises to the surface? The gases come out of solution and form bubbles that help to push the magma to the surface. Some of the gases come out of solution, while others stay completely dissolved. They stay dissolved in the magma

The gases come out of solution and form bubbles that help to push the magma to the surface.

Given a few million years, what is the end result of a mountain loosing elevation due to erosion? The net change in elevation is less than that due to erosion because the crust rises. The net change in elevation is exactly that due to erosion. The net change in elevation is more than that due to erosion because the crust sinks.

The net change in elevation is less than that due to erosion because the crust rises.

What is isostasy? The relationship between Earth's topography and the thickness of the underlying crust The elevation of a mountain The process of convergence that creates mountains

The relationship between Earth's topography and the thickness of the underlying crust

Select all that apply Choose the three most common indicators of an impending volcanic eruption. The volcano changes shape. More volcanic gases are emitted. Earthquakes occur more frequently. Magma leaks down the volcano flanks. Animals act strangely.

The volcano changes shape. More volcanic gases are emitted. Earthquakes occur more frequently.

Select all that apply Why were lava flows not a primary hazard during the eruption of Mount St. Helens in May 1980? There wasn't very much magma. The lava flowed into a nearby basin that was completely unpopulated. There was no magma associated with the eruption. The magma had a high viscosity.

There wasn't very much magma. The magma had a high viscosity.

How are lava plateaus related to global climate change? They are found only in polar regions, suggesting that their formation leads to global cooling. They are created from enormous outpourings of lava, which added a lot of carbon dioxide to the atmosphere, leading to warming. They are not related to global climate change.

They are created from enormous outpourings of lava, which added a lot of carbon dioxide to the atmosphere, leading to warming.

Select all that apply Why are pyroclastic flows so dangerous? They are fast. The timing of these flows are completely unpredictable. Geologists do not understand where they occur. They are hot.v

They are fast. They are hot.

What is the primary goal of the Volcano Disaster Assistance Program? To save lives and reduce losses from impending volcanic eruptions To help people relocate following a disastrous volcanic eruption To prevent volcanic eruptions

To save lives and reduce losses from impending volcanic eruptions

Where is the continental crust the thickest? In the continent's interior Along the margins Under lake basins Under mountain ranges

Under mountain ranges

The word we use to describe a liquid's resistance to flow is ________________

Viscosity

What happens to the viscosity of a liquid as temperature increases? Viscosity doesn't change due to temperature change. Viscosity increases. Viscosity decreases.

Viscosity decreases.

What is the relationship between silica content and magma viscosity? Viscosity is not affected by silica content. Viscosity increases with more silica. Viscosity decreases with more silica.

Viscosity increases with more silica.

What is the difference between volcanic and plutonic igneous rocks? Volcanic rocks are light in color and plutonic rocks are dark. Volcanic rocks are made of felsic magma, whereas plutonic rocks are made of basaltic lava. Volcanic rocks form from lava at Earth's surface, and plutonic rocks form from magma within Earth.

Volcanic rocks form from lava at Earth's surface, and plutonic rocks form from magma within Earth.

Select all that apply What two ingredients are needed to make a lahar? Water Volcanic bombs Fine-grained tephra Lava Volcanic gases

Water Fine-grained tephra

The supervolcano that was responsible for the 12-million-year-old ash layer in Nebraska is associated with the mantle hot spot that is currently underneath___________ in Wyoming.

Yellowstone

What US National Park is underlain by a caldera? Arches Yellowstone Grand Tetons Sequoia

Yellowstone

The 1985 eruption of Nevada del Ruiz is infamous due to the deaths of 23,000 people because of ______. ashfall lava a mudflow

a mudflow

The three common types of magma—basaltic, andesitic, and rhyolitic—are classified according to ______. texture color composition

composition

The source of rhyolitic magma is ______ and the heat source to melt it comes from ______. continental crust; other magma basaltic magma; basaltic magma ocean crust; the core

continental crust; other magma