Chapter 6

At which points on this graph is the magma under the highest amount of pressure and highest temperature?

1

Which of the numbered features is a pyroclastic flow?

4

This figure shows a ______ (type of volcano) that forms from____________ (type of eruption).

composite volcano, eruption o viscous, felsic lava

The most dangerous type of volcano is a

composite volcano.

Which of the following plate boundaries is least likely to produce composite volcanoes?

continent-continent convergent boundary with a high mountain range (Himalayas)

Some volcanic ash rises vertically in an, cools before accumulating on the surface, and forms deposits that are

eruption column, nonwelded

This igneous rock contains flattened pieces of pumice and small crystals of quartz and feldspar. What type of eruption probably formed this rock?

eruption of a pyroclastic flow that forms a thick and hot deposit

Shield volcanoes commonly involve

fluid lava flows.

When basaltic lava reach the ocean they

form pillow basalts.

How does the addition of water cause melting?

it changes the location of the liquid-solid boundary

Steep and unstable slopes can produce

landslides and mudflows, forming volcanic breccia

Volcanic mudflows (lahars) are common on composite volcanoes because

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

What type of eruption is shown in this photograph?

lava dome

Magma erupted on the surface can form a

lava flow, volcanic glass

Volcanic eruptions can produce huge floods by

melting ice sheets.

What type of basaltic feature is shown in this photograph?

pahoehoe lava flow

When melting forms magma

partial melting produces a magma that is more felsic than the source.

Some volcanic ash forms, that accumulate while hot and can become

pyroclastic flows, welded

Mount Pelée, a composite volcano on Martinique, destroyed the town of St. Pierre in 1902, killing about 30,000 people with

pyroclastic flows.

This dark gray igneous rock is glassy and elsewhere contains small vesicles and flow bands. What type of rock is this?

rhyolite or obsidian

Which of the following materials is NOT produced by erupting volcanoes?

sandstone

This figure shows a ________ (type of volcano) that forms from a ________ (type of eruption).

scoria cone, lava fountain

Magma that cools in ___________ has a relatively short time to cool and so forms ______________, but not volcanic glass.

shallow magma chambers, fine-grained rocks

In __________________ very large crystals can grow, forming ___________

water-rich parts of the magma , pegmatite.

Columnar joints, like the ones shown in the photograph, are formed

when hot but solid igneous rock contracts.

Which of the following sites would most likely have composite volcanoes? A is on an island arc, B is in the Andes, C is near Hawaii, D is along a mid-ocean ridge.

A and B

How could a rock at point C be melted?

All of these choices are correct.

Some scientists think that Yellowstone could cause a future disaster because

All of these choices are correct.

Which of the following are true of felsic magmas?

All of these choices are correct.

Which of the following is likely to be true about the magma that formed the left volcanic feature compared to the right one in this figure?

All of these choices are correct.

Which of the following is likely to be true about the right volcanic feature compared to the left one in this figure?

All of these choices are correct.

At which of the sites shown in this figure would melting probably be caused by introduction of water into hot rocks?

C

Which of the following sites would most likely have less dangerous volcanoes? A is on an island arc, B is in the Andes, C is near Hawaii, D is along a mid-ocean ridge.

C and D

Examine this figure and correctly complete this sentence using the proper phrase.

Changing conditions from points C to B would result in decompression melting.

The largest concentration of composite volcanoes on Earth is located along the

Pacific Ring of Fire.

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

The fluid cascade of lava.

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 low-viscosity, mafic lava (type of magma).

For the volcanic eruption in this photograph, complete the three missing parts of the sentence using the viscosity, composition, and resulting rock type.

This figure shows an eruption of high-viscosity (viscosity) magma that probably has a felsic or intermediate (composition) and would form rhyolite or andesite (resulting rock type).

A hot spot is interpreted to have formed from

a rising plume of hot mantle material.

Which of the following acts to keep a rock solid (instead of melting)?

an increase in confining pressure

What type of volcanic eruption is probably shown in this photograph?

basaltic lava flow

Hot spots in continental settings typically produce

basaltic lava flows or explosive calderas.

If bubbles cannot escape easily from a magma, the resulting eruption is likely to

be explosive.

Continental mantle plumes that are composed of felsic magma tend to be explosive when the Earth's surface is reached. These explosive eruptions create

calderas.

The igneous rocks shown in this photograph are forming

columnar joints.

In ______________, magma cools at a slow rate, allowing the formation of __________________

deep magma chambers, coarse-grained rocks

The igneous feature shown in this figure is a

dike.

Cinder cones are composed primarily of

ejected fragments of vesicular lava.

Continental rifts have a diverse suite of igneous rocks associated with them because melting occurs

in the mantle and in the crust.

What tectonic setting is interpreted to be the cause of volcanism at Yellowstone?

movement of North America over a mantle plume

When a volcano erodes and the solidified conduit is exposed, it is referred to as a volcanic

neck

Magma can partially crystallize at depth and then rise to shallow depths where the remaining magma solidifies. The early-formed crystals are

phenocrysts and the texture is porphyritic

The main cause of melting along subduction zones is the

release of water from the subducting plate.

This figure shows a _________ (type of volcano) that forms from ___________ (type of eruption).

shield volcano, basaltic lava flows

The place in the crust or mantle where igneous rocks begin to form is called the

source area.

Volcanic domes commonly are partially destroyed when

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

Potentially explosive composite volcanoes are most common above

subduction zones.

Shield volcanoes have low slopes primarily because

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

What generally happens when subduction-derived magma encounters thick continental crust?

the magma interacts with the crust, forming felsic or intermediate compositions

What type of basaltic feature is shown in this photograph?

volcanic bomb

This figure shows a ___________ (type of volcano) that forms from ______________ (type of eruption).

volcanic dome, eruption of lava and ash