Volcanoes and Igneous Rocks Practice Exam

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1

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

The most powerful explosive event event was preceded by a massive landslide.

2

Considering the history of Mt. 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?

Mauna Loa in Hawaii, on the Big Island of Hawaii near Kilauea

3

__________ is the major dissolved volatile constituent in both magmas and volcanic gases.

Water

4

Which of the following factors help determine whether a volcanic eruption will be violent or relatively quiescent?

All of these

5

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

High viscosity and dissolved gas

6

Which magma type would generally have the lowest viscosity?

Basalt

7

Which one of the following shows the correct order (left to right) of decreasing magma viscosity?

Rhyolite, andesite, basalt

8

What type of volcanic material is indicative of eruption under water?

Pillow lavas

9

As magma approaches the surface, water contributes to the explosive potential of eruption because_________.

Water dissolved in magma flashes to steam as pressure decreases, and the volume increase leads to an explosive potential.

10

Volcano A erupts rocks with SiO2 content ranging from 49% for 52% whereas volcano B, 100km away, erupts materials with SiO2 content of 62-68%. Which statement best characterizes these two volcanos?

Volcano A is probably a shield volcano with typically quiescent eruptions, whereas Volcano is likely a stratovolcano characterized by violent, explosive eruptions.

11

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

Pahoehoe

12

Volcanic bombs originate_________.

As erupted magma blobs that partly congeal before falling to the ground

13

_______ magma is the most abundant type of magma erupted on Earth.

Basaltic

14

_________are usually the most abundant gases emitted during basaltic volcanism.

Water and carbon dioxide

15

Which type of basaltic lava flow had its surface covered with sharp-edged, angular blocks and rubble?

AA

16

Which of the following is not considered pyroclastic debris?

Pahoehoe

17

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

Pumice is a pyroclastic rock comprised largely of open voids formed by gases released when the magma solidified as forth-life material.

18

Pillow lavas are________.

Basaltic lava tubes erupted on the seafloor in volcanic piles analogous to toothpaste extruded from a tube.

19

Which of the following volcanic types

...