Chapter 5 Quiz

What volcanic events formed Crater Lake, Oregon? When did they take place?

Caldera collapse followed major ash and pyroclastic-flow eruptions; 6000 years ago

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

________ 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.

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.

Which was the most powerful, explosive volcanic eruption of historic time?

Tambora, Indonesia, 1815

What statement concerning cinder cones is FALSE?

The cinders and other pyroclastic particles are consolidated into welded tuff.

What statement best describes the big Hawaiian volcanoes?

They are situated in the interior of a large, Pacific plate above a hot spot deep in the mantle.

Mount St. Helens is ________.

an explosive stratovolcano

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

andesitic

Volcanic bombs originate ________.

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

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

basaltic

Kilauea and Mauna Loa are ________.

basaltic shield volcanoes

________ only emit gas.

fumaroles

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

related to intraplate, hot spot volcanism

What best describes volcanism in the Cascade Range, northwestern United States?

related to plate subduction

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

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

water