Quiz 6 Study Guide

Which of the numbered features is a pyroclastic flow?

4

Some scientists think that Yellowstone could cause a future disaster because...

All of these (The area is part of a caldera. Scientists think that magma is still present at depth. Past eruptions from Yellowstone carried ash over a huge area of western North America. Land near Yellowstone is uplifting in some places and subsiding in others.)

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

All of these Viscous magma prevents gas from escaping easily.Abundant silica chains in viscous magma allow gas to pass quickly through the magma.Less viscous magma allows gas to escape, which can lead to very explosive eruptions.

Examine this figure and correctly complete this sentence using the proper phrase. Changing conditions from points __ to __ would result in decompression melting.

C to B

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

One or more pyroclastic flows hit the city of Pompeii.

Which of the following is NOT true of basaltic lava flows?

They pile up in steep, cone-shaped hills

For the volcanic eruption in this photograph, complete the two missing parts of the sentence using the type of volcanic feature and type of magma

This figure shows a lava flow (type of volcanic feature) that forms from eruption of lowviscosity, mafic lava (type of magma).

Which of the following would be evidence that a volcano has NOT been active for a long period of time?

Well-developed soils on volcanic rocks

Composite volcanoes are so called because they

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

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

at very shallow levels, such as within the volcano

Shield volcanoes are composed primarily of __________

basalt lava flows.

The main cause of caldera collapse is...

collapse of the roof of a magma chamber as magma erupts.

When basaltic lava reaches the ocean they...

form pillow basalts.

Volcanic mudflows (lahars) are common on composite volcanoes because

large amounts of rain and snowmelt mix with loose ash on steep slopes.

Which of the magma systems shown is likely to contain mostly basalt?

locations A and B only (Ocean)

What type of basaltic feature is shown in this photograph?

pahoehoe lava flow

This volcano is broad and low, and is composed of basaltic lava flows. What kind of volcano is it?

shield volcanoes

The typical form for a composite volcano is a ...

steep-sided cone.

Comparing these two photographs, which eruption has lower viscosity magma?

the fluid cascade of lava

Shield volcanoes have low slopes primarily because

the low viscosity of basaltic magma allows it to flow downhill for long distances.