Chapter 9 Test Review

Which magma type would generally have the lowest viscosity?

• basalt
• dacite
• andesite
• rhyolite

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

• rhyolite, andesite, basalt
• andesite, rhyolite, basalt
• basalt, andesite, rhyolite
• basalt, rhyolite, andesite

In the movie "Volcano" basaltic lava flows are shown running down flat streets at speeds faster than humans could run. From your knowledge of magma viscosity, is this realistic?

• No, the viscosity of basaltic magma is much higher than water, and thus, would flow much faster than water.
• Yes, the viscosity of basalt magma is similar to water so it would flow at comparable rates.
• There is no way of knowing because basaltic magmas can have viscosities similar to water or higher depending on temperature and fluids, and thus there isn't enough information.
• No, the viscosity of basaltic magma is much higher than water, and thus, would flow much slower than water.

The viscosities of magmas increase with increasing percentages of silica.

• True
• False

A basaltic volcano is likely to produce an explosive column that would endanger flying aircraft.

• True
• False

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

• pahoehoe
• scoria
• aa
• pegmatitic

Volcanic bombs originate ________.

• as erupted magma blobs that partly congeal before falling to the ground
• as laser-guided, granite blocks launched from a supersonic jet
• as ash particles that join together in the eruptive plume and fall as cobble-sized objects
• as blocks of volcanic rock ejected from an erupting volcanic crater

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

• aa
• pillow lava
• scoria
• pahoehoe

Which of the following is not considered pyroclastic debris?

• bombs
• ash
• cinders
• pahoehoe

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

• Pumice is a pyroclastic rock derived from rhyolite glass, and rhyolite glass has a lower density than water.
• Pumice is another name for dacite, a low-density rock that floats in water.
• 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.
• Pumice is a pyroclastic rock comprised largely of open voids formed by gases released when the magma solidified as froth-like material.