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