Chapter 6

Why is the viscosity of a magma lower at higher temperatures?

Atoms vibrate more vigorously at higher temperatures, breaking bonds and increasing fluidity.

More than 98% of the Earth's crust is made up of only __________ elements. (Enter only one word per blank.)

8

Seismic surveys at Vesuvius have shown that a magma body lies at a depth of ____ below the surface, suggesting a future eruption is probable.

8 km

Which of the following best describes a stratovolcano?

A large volcano composed of alternating layers of pyroclastic fragments and solidified lava flows

Which of the following best describes a cinder cone?

A relatively small cone constructed of pyroclastic debris piled up next to a central vent

Which of these are the three ways in which rock may melt? (Select all that apply.)

Addition of water Lowering the pressure Increasing the temperature

Which of these descriptions best characterizes a Vulcanian eruption?

Alternating flows of thick, highly viscous lava and explosive blasts of pyroclastic material

Which of these statements explain the peaceful nature of eruptions at spreading centers?

Highly fluid magma Low volatile content of the magma High temperature of the magma Low silica content of the magma

Which one of these elements is not one of the eight most abundant in the Earth's crust.

Hydrogen

As can be seen from this image, millions of people in the Bay of Naples live in close proximity to ______, a potentially dangerous volcano.

Mount Vesuvius

Which of these is not an example of a stratovolcano?

Mount Wrangell

Which of the following best describes the appearance of the surface of an aa basalt flow?

Rubbly and jagged

Which of the following best describes the appearance of the surface of a pahoehoe basalt flow?

Smooth and ropy

Which of the following statements explain why spreading centers are the ideal locations for volcanism?

Spreading centers lie above the high-temperature asthenosphere. The upward motion of the asthenosphere below spreading centers causes a decrease in pressure.

Match each of the settings in which calderas form with the correct examples.

Summits of shield volcanoes Kilauea, Hawaii Summits of stratovolcanoes Krakatau, Indonesia Continental interiors Long Valley, California

An estimated 36,000 people were killed during the 1883 eruption of Krakatau by ______.

a tsunami

The feature in the foreground of this photo is a __________.

crater

Increasing the temperature of a lava will tend to ______ its viscosity.

decrease

The word pyroclastic comes from the Greek pyro, meaning __________, and clastic, meaning __________.

fire fragments

Vast outpourings of basaltic lava from fissures that cover very large areas of the Earth's surface are called ____________.

flood basalts

The basalt flows that compose a shield volcano typically ______, which results in gentle slopes.

flow for a long distance, forming thin flows

The less viscous a fluid, the more ______ it is.

fluid

The solubility of gases in a magma _____ with increasing pressure.

increases

A volcanic mudflow, produced by the mixing of water with volcanic ash, is also known as a _____.

lahar

Herculaneum was destroyed by ______, which is a landslide of volcanic debris.

lahars

The volcanic feature shown here is a(n) __________ __________.

lava dome

When very high-viscosity lava piles up over a volcanic vent, it typically forms a ______.

lava dome

Volcanism not associated with plate boundaries typically occurs _______.

over mantle hot spots

A(n) ______ basalt lava flow, such as the one shown in this image, has a billowy or ropy surface.

pahoehoe

Fragments of magma formed by an explosive eruption are called ______.

pyroclastic debris

People near the sea during the 79 CE eruption of Vesuvius were mostly killed by _______.

pyroclastic flows

A new mass of rising magma that bows up the caldera floor following a caldera eruption is called a ________.

resurgent dome

This diagram shows a broad, gently sloping volcano made up of low viscosity lava flows, which is called a ______.

shield volcano

A high-viscosity rhyolite magma with low water content will produce a(n) _______.

slow-moving lava flow

A typical shield volcano is composed primarily of __________.

solidified basalt lava flows

The volcano shown here is an example of a _______.

stratovolcano

Mount Mazama was a ______ that collapsed down into its magma chamber following a large eruption, thus forming Crater Lake, which is a ______.

stratovolcano; caldera

Plinian eruptions are characterized by _______.

the generation of a sustained, gas-powered eruption column that carries pyroclastic material high into the atmosphere

Shield volcanoes typically have gentle slopes because _________.

they are formed from eruptions of low-viscosity basaltic lava

A huge eruption of large volumes of viscous magma that generates high ash columns and widespread sheets of outward-flowing ash and pumice is called a(n) _____ eruption.

ultra-Plinian

The "three Vs" of volcanology are

viscosity volatiles volume

The term for gases, such as water and carbon dioxide, that are dissolved in a magma is __________ .

volatiles

Typically, the most abundant dissolved gas in a magma is __________.

water

Which of the following statements explain why basalt is typically a low-viscosity magma? (Select all that apply.)

Basaltic magmas have higher temperatures. Basaltic magmas have lower SiO2 contents.

What kind of volcano is shown here?

Caldera

Which of these images shows a Vulcanian eruption?

D

True or false: All volcanism is associated with tectonic plate boundaries.

False

Which of these descriptions distinguishes a caldera from a crater? (Select all that apply.)

Formed by inward collapse Greater than 2 km in diameter

The eruption and subsequent collapse of _______ in 1883 created a 275 meter deep depression in the seafloor.

Krakatau

Crater Lake formed through the eruption and subsequent collapse of _______.

Mount Mazama

The properties of magma vary in many ways that govern whether eruptions are peaceful or explosive. Which of these is not one of those?

Plate tectonic setting

Which of these are the two primary building blocks of knowledge for understanding volcanic eruptions?

Plate tectonics Properties of magma

The eruption of Mount Pinatubo in the Philippines, shown in this image, is an example of a _______ eruption.

Plinian

Why do resurgent domes form within calderas?

The eruption of vast amounts of magma created a void that is filled by a new rising mass of magma.

The most recent example of an ultra-Plinian eruption occurred 74,000 years ago at _______.

Toba, in Sumatra

Which of the following best describes flood basalts?

Vast outpourings of basaltic lava from fissures that do not build a central volcano

______ is a measure of the internal resistance of a fluid to flow.

Viscosity

Match each of the 3 Vs of volcanology with its effect on an eruption.

Viscosity Controls whether magma flows away or piles up Volatiles Controls the explosivity of an eruption Volume Controls the intensity of an eruption

What is the most abundant volatile in magma?

Water

Which of the following factors is usually the most important in determining whether a volcanic eruption will be peaceful or explosive?

Water content of magma

In which three settings do calderas form? (Select all that apply.)

Within continental interiors The summits of stratovolcanoes The summits of shield volcanoes

Which of these is an example of a giant continental caldera?

Yellowstone

The two most important factors in the melting of mantle rock are ______ and _______.

a decrease in pressure; the addition of water

A(n) ______ basalt lava flow, such as the one shown in this image, has a rubbly and jagged surface.

aa

Volcanism associated with the Yellowstone caldera is due to its location ________.

above a hot spot

The people who remained in Pompeii during the eruption of Vesuvius in 79 CE were killed by ______.

ash and pumice that fell on the town

The magma composition with the lowest viscosity is ______ because it is both the hottest and has the lowest silicate content.

basalt

A __________ is a large volcanic depression formed by roof collapse into a partially emptied magma reservoir.

caldera

A __________ __________ is a relatively small volcano constructed of pyroclastic debris piled up around a central vent.

cinder cone

Another name for a stratovolcano is a _________.

composite volcano