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Exam 6: Volcanic Eruptions: Plate Tectonics and Magmas

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Question 31

True/False

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Most magma is generated by decreasing the pressure on hot rock.

A) True
B) False

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Question 32

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Over _________ of volcanism is associated with the edges of tectonic plates.

A) 90%
B) 80%
C) 70%
D) 60%
E) 50%

F) All of the above
G) C) and D)

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Question 33

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Water circulating at thousands of feet below the surface can be heated to temperatures far above 100 ^$\circ$ C (212 ^$\circ$ F)without boiling because the pressure of the overlying groundwater body is so great.

Magma compositions are independent of the amount of crustal rock melted and incorporated into the rising magma.

Oxygen and silicon are so abundant in the Earth's crust that their percentages dwarf those of all other elements.

The higher the viscosity of a magma,the more fluid is its behavior.

Although there are 92 naturally occurring elements,a mere eight make up more than 98 percent of the Earth's crust.

This volcano erupted in 1883 in the Sunda Strait between Sumatra and Java,exploding with a loudness heard 3000 miles away,then collapsing into its magma chamber,making a caldera and setting off tsunami that killed at least 36,000 people.

While there are many hundreds of different minerals,the overwhelming majority of the Earth's crust is composed of just eight common rock-forming minerals.

Hawaiian volcanoes unlikely to erupt include _________________.

In the last 2 million years,three catastrophic eruptions have occurred at Yellowstone at about 2 million,1.3 million,and 600,000 years ago.

The typical trend in a rising plume of subduction-zone magma is to increase ____________.

The number of "hot spots" worldwide is ________________.

Over 80 percent of Earth's magma extruded through volcanism occurs at oceanic spreading centers.

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.

Antarctica does not lie above any hot spots,partly explaining its massive volumes of ice.

Highly fluid basaltic lava may cool with a smooth,ropy surface called pahoehoe,whereas lower temperature,slower flowing,more viscous basaltic lava commonly has a rough,blocky texture called a.

The largest number of hot spots lie beneath the Juan de Fuca plate.

Over 90 percent of volcanism is associated with the edges of tectonic plates,and most of the rest is caused by hot spots.

Transform faults have lots of associated volcanism because the strike slip motions keep a "lid" on the hot asthenosphere below,allowing it to melt.