geology ch 5 review

________ magma is the most abundant type of magma erupted at oceanic spreading centers.

Basaltic

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

During the eruptive period, the mountain peak was substantially built up by new lava flows and pyroclastic debris.

Which kind of eruptive activity is most likely to be highly explosive?

Eruptions of big, continental margin, composite cones or stratovolcanoes.

Aa flows are generally thinner and have smoother surfaces than pahoehoe flows.

False

Basaltic lavas are generally hotter and more viscous than andesite lavas.

False

In general, cinder cones are much larger than shield volcanoes.

False

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

High viscosity and dissolved gas

Why do magmas rise toward Earth's surface?

Magmas are mainly liquid and contain dissolved fluids such as water; most are less dense than the adjacent solid rock.

In 1980, ________ was the first Cascade Range volcano to erupt since Mt. Lassen, California, in 1915-16.

Mt. St. Helens

What is the largest, known volcano in the Solar System?

Olympus Mons, Mars

The ________ ocean basin is rimmed by the most subduction zones.

Pacific

The 1991 Pinatubo eruption in the Philippines caused brilliantly colored sunrises and sunsets to be seen for the next few years. What caused this phenomenon?

Sulfur dioxide and other erupted gases formed aerosols in the stratosphere.

The viscosities of magmas increase with increasing percentages of silica.

True

________ is a major dissolved volatile constituent in both magmas and volcanic gases.

Water

________ are usually the most abundant gases emitted during basaltic volcanism.

Water and carbon dioxide

The Columbia Plateau in Washington and Oregon is ________.

a flood basalt plateau

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

aa

Mount St. Helens is ________.

an explosive stratovolcano

The average composition of rocks comprising a large composite cone or stratovolcano is similar to a (an) ________ magma.

andesitic

Which of the following statements best describes the big Hawaiian volcanoes?

are situated in the interior of a Pacific plate above a hot spot deep in the mantle

Volcanic bombs originate ________.

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

Kilauea and Mauna Loa are ________.

basaltic shield volcanoes

Which natural phenomenon occurs for many years after major explosive volcanic eruptions such as Tambora and Pinatubo?

brilliantly colored sunrises and sunsets

Most basaltic magmas are believed to form by partial melting of granite in the lower crust and upper mantle.

false

The active Hawaiian volcanoes are situated directly above a major boundary between two of the Earth's largest tectonic plates.

false

The eruptions of the Hawaiian volcanoes may be described as explosive in comparison to the 1980 Mount St. Helens eruption.

false

Relative to water, syrup has a _____ resistance to flow and therefore a _____ viscosity.

higher; higher

Basaltic magmas have a _____ viscosity, whereas rhyolitic magmas have a _____ viscosity.

low; high

Shield volcanoes produce lava that is primarily _____ in composition.

mafic

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

pahoehoe

Which of the following best describes seamounts and islands of the deep ocean basins?

piles of basaltic lava flows built up from the ocean floor by multiple, summit and flank eruptions

The recent (geologically) volcanic activity in Yellowstone National Park is ________.

related to intraplate, hot spot volcanism

Which one of the following best describes volcanism in the Cascade Range, northwestern United States?

related to plate subduction

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

rhyolite, andesite, basalt

A ________ volcano is a very large, gently sloping mound composed mainly of basaltic lava flows.

shield

Which kind of volcanism is typical of mid-oceanic ridge systems?

submarine; basaltic lava flows

Which region has the greatest concentration of currently active volcanoes?

the circum-Pacific area

Which of the following is associated with deep mantle hot spots?

the volcanoes of Hawaii and the recent activity in Yellowstone National Park

The Icelandic volcanoes are related to plate tectonics because ________.

they lie on a spreading center where two plates are moving apart

Ash and lapilli are different sized pyroclastic particles.

true

Basalt is the most common magma erupted along oceanic rift systems.

true

Dissolved gases may comprise up to a few percent by weight of a magma.

true

Magma generation at depth almost always involves partial melting, not complete melting of the source rock.

true

Repeated eruptions of relatively fluid lava from fissures can eventually cause an area to be covered by flood basalts.

true

Small amounts of water can lower partial melting temperatures in silicate rocks.

true

Vents that emit only heated volcanic gases and water are called fumaroles.

true

The most abundant gas found in magma is ______.

water vapor