Question 1

Which statement about the May,1980,eruption of Mount St.Helens is false?

Accepted Answer

A)  During the eruptive period,the mountain peak was substantially built up by new lava flows and pyroclastic debris.
B)  Plumes of ash rose high into the atmosphere during the major eruptive events.
C)  Mudflows accompanied the major eruptive events.
D)  The most powerful explosive event was preceded by a massive landslide.

Question 2

small basaltic cones built during one short,eruptive episode

Accepted Answer

The answer of small basaltic cones built during one short,eruptive...

Question 3

The higher the viscosity of a magma,the lower the potential for explosive eruptions.

Accepted Answer

A) True 
 B)False

Question 4

If you are in the path of a pyroclastic flow or a lahar,you have virtually no chance to run out of its path on foot.

Accepted Answer

A) True 
 B)False

Question 5

Which of the following statements best describes the big Hawaiian volcanoes?

Accepted Answer

A)  They lie directly above a transform plate boundary that cuts deeply into the mantle.
B)  They lie directly above an active subduction zone where the Pacific plate is sinking into the mantle.
C)  They lie along the crest of the East Pacific Rise,a mid-ocean ridge or spreading center.
D)  They are situated in the interior of a large,Pacific plate above a hot spot deep in the mantle.

Question 6

Which type of basaltic lava flow has a fairly smooth,unfragmented,ropy surface?

Accepted Answer

A)  aa
B)  pegmatitic
C)  pahoehoe
D)  scoria

Question 7

Mt.Vesuvius Mt.Mazama Mount Pelée Kilauea

Accepted Answer

The answer of Mt.Vesuvius Mt.Mazama Mount Pelée Kilauea...

Question 8

________ tend to increase the explosive potential of a magma body beneath a volcano.

Accepted Answer

A)  High viscosity and dissolved gas
B)  High viscosity and low dissolved gas content
C)  Low silica content and low viscosity
D)  Low viscosity and low dissolved gas content

Question 9

A ________ is an intrusive,igneous rock body that is tabular and concordant.

Accepted Answer

A)  laccolith
B)  dike
C)  pluton
D)  sill

Question 10

Magmas are the product of melting in the deep part of the earth that forms a layer of molten material called the asthenosphere.

Accepted Answer

A) True 
 B)False

Question 11

The largest percentage of total magma production on earth occurs at what plate tectonic setting?

Accepted Answer

A)  hot spots like Hawaii
B)  convergent plate margins
C)  transform plate margins
D)  spreading ridges

Question 12

Which of the following volcano types are short lived volcanos that last a few days to months and then shut down?

Accepted Answer

A)  shield volcano
B)  cinder cone
C)  lava dome
D)  composite volcano

Question 13

Why does magma viscosity vary with silica content?

Accepted Answer

A)  Increasing silica increases a tendency for silica bonds to link up in networks,acting like a polymerization of the magma.
B)  Increasing silica content lowers the melting temperature and since increasing the temperature of a magma decreases viscosity increasing silica content increases viscosity.
C)  Increasing silica content increases the amount of water a magma can dissolve and water decreases magma viscosity,so increasing silica content decreases magma viscosity.
D)  There is no correlation between silica content and magma viscosity.

Question 14

Considering the history of Mt.St.Helens and Kilauea volcanoes and your knowledge of volcano types in different tectonic settings,if you had to live on a volcano,which of the following would you choose if safety was your only concern?

Accepted Answer

A)  Mt.Spurr in the Aleutian volcanic arc
B)  Mt Fujiyama in the Japanese island arc
C)  Mt.Rainier in the Cascades just north of Mt.St.Helens
D)  Mauna Loa in Hawaii,on the Big Island of Hawaii near Kilauea

Question 15

massive,gently sloping volcanoes built of successive,basaltic lava flows

Accepted Answer

The answer of massive,gently sloping volcanoes built of successive,basaltic lava...

Question 16

The rock pumice often floats yet the density of the rock is greater than water.Why does it float?

Accepted Answer

A)  Pumice is a pyroclastic rock derived from rhyolite glass,and rhyolite glass has a lower density than water.
B)  Pumice is a pyroclastic rock comprised largely of open voids formed by gases released when the magma solidified as froth-like material.
C)  Pumice is a rock made of rhyolite glass that erupts into water,which traps water in voids and makes the material less dense than water.
D)  Pumice is another name for dacite,a low-density rock that floats in water.

Question 17

Shield volcanos have extensive deposits of pyroclastic rocks.

Accepted Answer

A) True 
 B)False

Question 18

The steep,upper slopes of composite volcanoes are generally produced by ________.

Accepted Answer

A)  large landslides
B)  high-viscosity,low-volume silicic magmas that are erupted from the summit
C)  satellite or parasitic cones that push up the top of the volcano to steep slopes
D)  tilting of the summit by intrusion of high-viscosity magma directly below the summit

Question 19

-the big volcanoes of Hawaii

Accepted Answer

The answer of 
-the big volcanoes of Hawaii...

Question 20

A geologist working in an area finds gravels with gentle dips of about 5 degrees.She finds a large outcrop where these gravels are overlain by tephra with prominent layers that dip 35-40 degrees.What is the history of this area?

Accepted Answer

A)  Basalt flows formed after a series of gravels were deposited,covering the local terrain,and built a shield volcano.
B)  After the gravel was deposited,a large composite cone was built on the area.
C)  Before the gravel was deposited,a cinder cone formed in this area.
D)  After the gravel was deposited,a cinder cone formed in the area.

Exam 9: Volcanoes and Other Igneous Activity

Which statement about the May,1980,eruption of Mount St.Helens is false?

Correct AnswerverifiedShow Answer

Which type of basaltic lava flow has a fairly smooth,unfragmented,ropy surface?

Correct AnswerverifiedShow Answer

Which of the following volcano types are short lived volcanos that last a few days to months and then shut down?

Correct AnswerverifiedShow Answer

Considering the history of Mt.St.Helens and Kilauea volcanoes and your knowledge of volcano types in different tectonic settings,if you had to live on a volcano,which of the following would you choose if safety was your only concern?

Correct AnswerverifiedShow Answer

The rock pumice often floats yet the density of the rock is greater than water.Why does it float?

Correct AnswerverifiedShow Answer

Shield volcanos have extensive deposits of pyroclastic rocks.

Correct AnswerverifiedShow Answer

A geologist working in an area finds gravels with gentle dips of about 5 degrees.She finds a large outcrop where these gravels are overlain by tephra with prominent layers that dip 35-40 degrees.What is the history of this area?

Correct AnswerverifiedShow Answer

small basaltic cones built during one short,eruptive episode

Correct AnswerverifiedShow Answer

The higher the viscosity of a magma,the lower the potential for explosive eruptions.

Correct AnswerverifiedShow Answer

The steep,upper slopes of composite volcanoes are generally produced by ________.

Correct AnswerverifiedShow Answer

________ tend to increase the explosive potential of a magma body beneath a volcano.

Correct AnswerverifiedShow Answer

Magmas are the product of melting in the deep part of the earth that forms a layer of molten material called the asthenosphere.

Correct AnswerverifiedShow Answer

Why does magma viscosity vary with silica content?

Correct AnswerverifiedShow Answer

Which of the following statements best describes the big Hawaiian volcanoes?

Correct AnswerverifiedShow Answer

The largest percentage of total magma production on earth occurs at what plate tectonic setting?

Correct AnswerverifiedShow Answer

A ________ is an intrusive,igneous rock body that is tabular and concordant.

Correct AnswerverifiedShow Answer

massive,gently sloping volcanoes built of successive,basaltic lava flows

Correct AnswerverifiedShow Answer

If you are in the path of a pyroclastic flow or a lahar,you have virtually no chance to run out of its path on foot.

Correct AnswerverifiedShow Answer

-the big volcanoes of Hawaii

Correct AnswerverifiedShow Answer

Mt.Vesuvius Mt.Mazama Mount Pelée Kilauea

Correct AnswerverifiedShow Answer

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