GEO107 MIDTERM 2

The Volcanic Explosivity Index (VEI) of historical events ranges from _______________. Question 62 options: A) 1 to 10 B) 0 to 8 C) 1 to 20 D) 0 to 100

0 to 8

Over _________ of volcanism is associated with the edges of tectonic plates, and close to about _________ of Earth's magma extruded through volcanism takes place at the oceanic spreading centers. Question 10 options: 90%, 80% 80%, 90% 70%, 80% 90%, 10%

90%, 80%

Many hill-slope masses are weak due to preexisting geologic conditions such as __________. Question 38 options: ancient slide surfaces rock layering dipping less than topographic slopes structures within the rocks, such as fractures, ancient faults, and thin clay seams All of these choices are correct

All of these choices are correct

External processes that increase the probability of a slope failure include __________. Question 37 options: adding mass high on a slope, as in sediment deposition steepening the slope, as by fault movements removing support from low on a slope, as by stream or ocean-wave erosion All of these choices are correct.

All of these choices are correct.

Mt. Rainier, Washington, is number one on the danger list of many U.S. volcanologists because of its __________. Question 47 options: Great height Extensive glacial cap Frequent earthquakes Active hot-water spring systems, which have weakened the mountain internally All of these choices are correct.

All of these choices are correct.

Rock may melt by _______________. Question 45 options: lowering the pressure on it raising its temperature increasing its water content All of these choices are correct.

All of these choices are correct.

The typical trend in a rising plume of subduction-zone magma is to increase the ____________. Question 35 options: percentage of SiO2 viscosity explosive potential of the magma by holding in the gases more tightly All of these choices are correct.

All of these choices are correct.

The viscosity of magma is lowered by __________. Question 41 options: increasing temperature decreasing crystal content decreasing SiO2 content All of these choices are correct.

All of these choices are correct.

Violent causes of death from volcanic eruptions include _______________. Question 50 options: pyroclastic flows tsunami lahars poison gases All of these choices are correct.

All of these choices are correct.

Why does the magma from some volcanoes flow smoothly and relatively peacefully, while the magma from other volcanoes blasts forth violently and deals death over wide areas? Question 5 options: differences in the chemical and mineral makeup of magmas variations in the temperature, water and gas content, and viscosity of magmas different geographic positions with respect to hot spots and edges of tectonic plates All of these choices are correct.

All of these choices are correct.

The formation of a giant continental caldera includes all but which of the following? Question 19 options: Rising magma forms a low-density cap rich in SiO2 and gases, bulging the ground surface upward. Basaltic eruptions begin forming circular fractures surrounding the bulge. Magma pours out in high-volume pyroclastic flows, causing the ground surface to sink into a caldera. Removal of magma decreases the pressure on the magma below the caldera, causing new magma to bulge up the caldera floor.

Basaltic eruptions begin forming circular fractures surrounding the bulge.

__________ melting occurs when a rock melts due to a lowering of pressure. Question 24 options: Release Elevation Ascension Decompression

Decompression

At oceanic spreading centers, magmas are rhyolitic in composition. Question 31 options: True False

False

Less than 20 percent of Earth's magma extruded through volcanism occurs at oceanic spreading centers. Question 29 options: True False

False

The most peaceful eruptions are __________ eruptions. Question 11 options: Icelandic type Plinian type Strombolian type Vulcanian type

Icelandic type

Crater Lake, Oregon, fills the caldera of ____________ which collapsed about 7,600 years ago. Question 20 options: Mt. Mazama Mt. Shasta Mt. St. Helens Mt. Baker Mt. Rainier

Mt. Mazama

A genuine success story of advance warning before a large eruption occurred in the Philippines in 1991 before the climactic eruption of _________________. Question 1 options: Popocatepetyl Nevado Del Ruiz Mont Pelée Mt. Mayon Mt. Pinatubo

Mt. Pinatubo

The two most active Cascade Range volcanoes over the past 4,000 years are _______________. Question 49 options: Mt. Rainier and Mt. Adams Mt. Shasta and Mt. Jefferson Mt. Baker and Mt. Hood Mt. St. Helens and Mt. Shasta Lassen Peak and Newberry Volcano

Mt. St. Helens and Mt. Shasta

Among different types of volcanic eruptions, __________ eruptions are the most violent types of explosive eruptions. Question 16 options: Icelandic-type Vulcanian-type Plinian-type Hawaiian-type Pompeiian-type

Plinian-type

The most famous of all volcanoes probably is Vesuvius, and the most famous of its eruptions are those of 79 ce, which buried the cities of ____________. Question 3 options: Pompeii and Herculaneum Naples and Rome Naples and Milano Petra and Florence Florence and Pisa

Pompeii and Herculaneum

Spreading centers have relatively peaceful eruptions of magma because the __________. Question 23 options: SiO2-poor magma is at high temperatures. SiO2-rich magma is at a temperature just above the melting point of quartz. Olive-poor magma has a high-volatile content. Olive-rich magma has a high-viscosity.

SiO2-poor magma is at high temperatures.

Mt. Kilimanjaro in Tanzania, Mt. Shasta in California, Mt. Rainier in Washington, and Mt. Fuji in Japan, are ______________, which are steep-sided, symmetrical volcanic peaks built of alternating layers of pyroclastic debris capped by high-viscosity andesitic to rhyolitic lava flows that solidify to form protective caps. Question 2 options: Shield volcanoes Scoria cones Stratovolcanoes Calderas

Stratovolcanoes

__________ are steep-sided, symmetrical volcanic peaks built of alternating layers of pyroclastic debris capped by high-viscosity andesitic to rhyolitic lava flows that solidify to form protective caps. Question 13 options: Stratovolcanoes Scoria cones Shield volcanoes Calderas

Stratovolcanoes

Although there are 92 naturally occurring elements, a mere eight make up more than 98 percent of Earth's crust. Question 27 options: True False

True

Hot spots can be under the oceans, under the continents, in the center of plates, and at spreading centers. Question 34 options: True False

True

Oxygen and silicon are so abundant in Earth's crust that their percentages dwarf those of all other elements. Question 28 options: True False

True

Stratovolcanoes are often associated with subduction zones. Question 12 options: True False

True

The radiocarbon process of documenting major eruption dates for volcanoes in the past 50,000 years or so is the same as that used to work out dates of major prehistoric earthquakes. Question 48 options: True False

True

The three most recent catastrophic Yellowstone eruptions occurred at 2.6 million, 1.29 million, and 640,000 years ago. Question 36 options: True False

True

When it comes to volcanic hazards, the key problem is how easily the dissolved gases can escape from the magma. Question 33 options: True False

True

_________ eruptions are common first phases in the eruptions of volcanoes as they "clear their throats" before emitting larger eruptions. Question 15 options: Hawaiian-type Icelandic-type Vulcanian-type Plinian-type Surtseyan-type

Vulcanian-type

Slow flowing, more viscous basaltic lava commonly has a rough, blocky texture called ________. Question 6 options: aa bb cc pahoehoe poi

aa

Water circulating at thousands of feet below the Earth's surface needs to be heated to temperatures _________ 100°C (212°F) in order to reach its boiling point because the pressure of the overlying groundwater body is so great. Question 51 options: above below equal to

above

Which of the following is a poor choice when trying to reduce the likelihood of a slope failure? Question 43 options: reshaping the topography by reducing the slope using rock bolts to strengthen rock masses adding water to the slope during a cold snap to freeze it in place adding a gabion and/or a resisting mass at the toe of a slope

adding water to the slope during a cold snap to freeze it in place

A caldera collapse occurs ________________. Question 18 options: before the eruption starts in the middle of the eruption after the magma chamber is mostly empty millions of years after the volcano's final dying eruption at the onset of Vulcanian activity

after the magma chamber is mostly empty

Pyroclastic debris is __________. Question 25 options: chucks of magma and rocks blown into the air by gas in a volcanic eruption solid pieces of rock contained within, and transported by, lava the SiO2-poor magma that remains as gas escapes lava as it flows the SiO2-rich magma that flows quickly down the side of a volcano

chucks of magma and rocks blown into the air by gas in a volcanic eruption

The process of mineral formation in a cooling magma is usually called ______________. Question 55 options: A) production B) crystallization C) liquefaction D) synthesizing

crystallization

The primary reason magma forms at subduction zones is that the subducting plate carries a cover of sediments, water, and hydrated minerals down with it, which usually ____________ the temperature required for the adjacent overlying mantle lithospheric rock to melt. Question 56 options: A) increases B) decreases C) does not change

decreases

When it comes to volcanic hazards, the key problem is how easily the _______ can escape from the magma. Question 63 options: A) crystals B) liquid helium C) dissolved gases D) silica

dissolved gas

Several geologic phenomena are being studied as signs of an impending volcanic eruption. These include seismic waves, _____________, and the release of gases. Question 30 options: ground deformation flash floods landslides crystallization rates unusual animal behavior

ground deformation

Magma at great depths usually does not contain gas bubbles because ___________________ Question 52 options: high temperature at depth keeps magma free of gases low temperature at depth keeps magma free of gases high pressure at depth keeps gas dissolved in solution high temperature at depth leads to the escape of all gasses

high pressure at depth keeps gas dissolved in solution

Magma rising in a subduction zone tends to get more "contaminated" with _______ than does magma rising in a spreading ridge. high silica content minerals low silica content minerals lower mantle minerals

high silica content minerals

Beneath continents, rising basaltic magmas are contaminated by sediments and continental-crust rocks, altering magma compositions; the resultant andesitic-to-rhyolitic magmas have _______ contents of SiO2, relatively low temperatures, and _________ viscosity. Question 53 options: high, low high, high low , low low, high

high, high

External processes that increase the probability of a slope failure include all but which of the following ? __________. steepening the slope, as by fault movements holding soil in place by using plants or netting removing support from low on a slope, as by stream or ocean-wave erosion adding mass high on a slope, as in sediment deposition

holding soil in place by using plants or netting

As minerals continue to form in the magma kept at a constant temperature, the viscosity of that magma will ___________. Question 22 options: increase. decrease remain the same.

increase.

Below the ocean basins, the basaltic magmas have _____ contents of SiO2, high temperature, ________viscosity, and allow easy escape of gases, producing peaceful eruptions. Question 57 options: A) high, low B) low, low C) high, high D) low, high

low, low

If two magmas have the same composition but at different temperature, the hotter of the two magmas will have a ________ viscosity. Question 61 options: A) higher B) lower C) neither lower nor higher

lower

The presence of water usually ________ the melting point of rock. Question 4 options: raises lowers does not change may raise or may lower

lowers

Spreading centers are an ideal location for volcanism because all but which of the following? ____ Question 26 options: they sit above the high-temperature asthenosphere the asthenosphere rock has low percentages of SiO2 the oceanic plates pull apart causing hot asthenosphere rock to rise and undergo decompression melting to form magma that continues to rise magma formation due to the melting caused by incorporation of water in asthenosphere minerals

magma formation due to the melting caused by incorporation of water in asthenosphere minerals

Highly fluid basaltic lava may cool with a smooth, ropy surface called _______, whereas lower temperature, slower flowing, more viscous basaltic lava commonly has a rough, blocky texture called _________. Question 60 options: A) aa, powpow B) pahoehoe, aa C) bb, pahoehoe D) powpow, bb

pahoehoe, aa

If basaltic lava reaches the sea or a lake, it cools rapidly into ____________ lava. Question 7 options: bed sheet blanket pillow

pillow

When gas escapes quickly and violently from lava it may produce a frothy glass full of holes left by former gas bubbles; this porous material, known as ____________, contains so many holes it can float on water. Question 59 options: A) obsidian B) pumice C) pillow lava D) quartz

pumice

If all of the following rocks were to completely melt and reach the same final temperature, which would produce magma with highest viscosity? Question 21 options: basalt gabbro andesite diorite rhyolite

rhyolite

Of the following types of mass movements, which can move fastest? Question 42 options: creep roots rock fall mudflow earth flow

rock fall

A mantle hot spot has generated a long-lived plume beneath Yellowstone National Park, and the North American continent is moving __________ above it about 2 to 4 cm/yr. Question 17 options: southeastward northeastward southwestward northwestward in random directions

southwestward

Some of Earth's most beautiful mountains are ________, including Mt. Kilimanjaro in Tanzania, Mt. Shasta in California, Mt. Rainier in Washington, and Mt. Fuji in Japan. Question 14 options: stratovolcanoes cinder cones shield volcanoes calderas oceanic seamounts

stratovolcanoes

Magma rising in a __________ tends to get more "contaminated" with _______ than does magma rising in a spreading ridge. Question 54 options: oceanic hot-spot; high silica minerals continental hot spot, low silica minerals subduction zone; low silica content minerals subduction zone, high silica minerals

subduction zone, high silica minerals

In magma, silicon and oxygen often link up to form the silicon-oxygen ______________. Question 32 options: dihedron trihedron tetrahedron hexahedron dodecahedron

tetrahedron

Active volcanoes today in Oregon and Washington, including Mt. St. Helens, result from _________________. Question 46 options: heat generated by friction on the San Andreas Fault spreading of the Juan de Fuca Ridge the subduction of the Pacific Plate beneath North America D. the subduction of the Juan de Fuca Plate beneath North America continent-continent collision

the subduction of the Juan de Fuca Plate beneath North America

The immediate causes of slope failures, such as earthquakes or heavy rainfall, are called __________. Question 39 options: triggers roots creators sparks trips

triggers

The three 'Vs' of volcanology are __________________. Question 8 options: viscosity, volatiles, and velocity viscosity, volatiles, and volume viscosity, velocity, and volume volatiles, volume, and variability volatiles, velocity, and variability

viscosity, volatiles, and volume

If the magma reaches the surface, it forms _________, named for Vulcan, the Roman god of fire. Question 58 options: A) metamorphic rocks B) plutonic rocks C) volcanic rocks D) metal vanadium

volcanic rocks

In magma, __________ is the most abundant dissolved gas. Question 44 options: water vapor (H2O) carbon dioxide (CO2) sulfur dioxide (SO2) hydrogen sulfide (H2S) carbon monoxide (CO)

water vapor (H2O)

A shield volcano has a great ___________. Question 9 options: height compared to its width width compared to its height amount of pumice proportion of pyroclastic material, compared with lava flows

width compared to its height

The Houston-Galveston, Texas, area has been sinking due to the __________. Question 40 options: withdrawal of groundwater by pumping dissolution of limestones emptying of a magma chamber weight of all the high-rise buildings and houses dissolution of a salt layer

withdrawal of groundwater by pumping