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					1.

At what depth do gas bubbles have the most effect on magma?

     1.

          A. when the magma first forms, before the bubbles can dissolve into the magma

     2.

          B. at moderate depths, when the magma is moving rapidly through the conduit

     3.

          C. at very shallow levels, such as within the volcano

2.
Which of the following are ways that viscosity affects gases in magma?

     1.

          A. viscous magma prevents gas from escaping easily

     2.

          B. gas builds up in viscous magma and can cause explosive eruptions

     3.

          C. less viscous magma allows gas to escape, which can lead to very explosive
          eruptions

     4.

          D. all of the above

     5.

          E. a and b only



3. A lava solidifies into nonvesicular basalt instead of vesicular basalt because:
     1.

          A. the magma has a low content of gas

     2.

          B. the lava forms a ropy texture

     3.

          C. the lava flow breaks apart as it flows

     4.

          D. the lava flow forms lava tubes

4.
Shield volcanoes commonly involve:

     1.

          A. fluid lava flows

     2.

          B. lava fountains

     3.

          C. viscous lava flows

     4.

          D. pyroclastic flows

     5.

          E. a and b only

5.

What are some factors that could allow flood basalts to have high-volume
eruptions?
     1.

          A. a large amount of magma is generated in the mantle

     2.

          B. magma rises to the surface along thick dikes

     3.

          C. the magma is hot and has a low viscosity

     4.

          D. all of the above

6. Flood basalts influence life on Earth because:

     1.

          A. large volumes of flood basalts are erupted during a short time

     2.

          B. eruptions can release large amounts of gas that cool the atmosphere

     3.

          C. eruptions can release large amounts of gas that warm the atmosphere

     4.

          D. all of the above

7.

Which of the following are hazards associated with scoria cones?

     1.

          A. volcanic bombs and other large projectiles ejected from the volcano

     2.
        B. toxic gases

   3.

        C. fine particles of volcanic ash

   4.

        D. all of the above

8. Composite volcanoes are so called because they:

   1.

        A. are a combination of shield volcanoes, scoria cones, and other volcanoes

   2.

        B. have many different types of geologic hazards

   3.

        C. were first discovered on the island of Composita in Italy

   4.

        D. are composed of lava flows, pyroclastic material, and mudflows

9. What types of rocks would be most common in a composite volcano?

   1.

        A. scoria and other vesicular basalt

   2.

        B. basalt mostly formed in lava flows

   3.

        C. felsic and intermediate lava flows and tephra

   4.
           D. pillow basalts

10. What was the most damaging type of eruption that occurred at Vesuvius in
Italy?

      1.

           A. a huge landslide caused a lateral blast that knocked down trees and buildings

      2.

           B. a fast-moving viscous lava flow flowed through the middle of Pompeii

      3.

           C. the volcano was so heavy that it caused part of the island to collapse

      4.

           D. one or more pyroclastic flows hit the city of Pompeii

11.

The eruption that occurred on Mount St. Helens was triggered by:

      1.

           A. a huge landslide caused a lateral blast that knocked down trees and buildings

      2.

           B. a fast-moving viscous lava flow flowed through the middle of Portland

      3.

           C. a volcano that was so heavy that it caused part of the island to collapse

      4.

           D. a scoria cone that sent up a large column of pyroclastic material

12.

Volcanic domes commonly are partially destroyed when:
1.

     A. gases are trapped in the conduit and cause explosions

2.

     B. steep parts of the dome collapse and cause small pyroclastic flows

3.

     C. fast-moving, low-viscosity lava carries away part of the dome

4.

     D. the center of the dome collapses, forming a huge caldera

5.

     E. a and b only

				
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