Answers #2
The correct answer for each question is indicated by a This is the correct answer..
1
Three settings where volcanic rocks generally form are ________________.
A)
subduction zones, continent-continent collision zones, mid-ocean rift systems
B)
subduction zones, continent-continent collision zones, hot spots
C)
subduction zones, continent-continent collision zones, continental strike-slip faults zones
D)
subduction zones, hot spots, mid-ocean rift systems
E)
subduction zones, continental strike-slip fault zones, mid-ocean rift systems
2
Over 90 percent of volcanic activity is associated with ______________.
A)
subduction zones
B)
transform boundaries
C)
hot spots
D)
continent-continent collision zones
E)
plate-tectonic boundaries
3
Why is volcanism in subduction zones more explosive than in other volcanic settings?
A)
Magmas in subduction zones are generally rich in silica.
B)
Magmas in subduction zones contain more water because of melting of hydrated rocks and minerals.
C)
Magmas in subduction zones are generally more viscous.
D)
Magmas in subduction zones tend to become solid at lower temperatures thus increasing their viscosity.
E)
all of the above
4
The occurrence of geysers in Yellowstone National Park is evidence for the presence of what material below the surface?
A)
melted rock
B)
radioactive materials
C)
diamonds
D)
the asthenosphere
E)
carbon dioxide
5
Water at depths within a geyser system exists at temperatures above the boiling point at the Earth's surface. Why does the water
become steam at more shallow depth and erupt?
A)
Increase in pressure near the surface.
B)
Increase in heat near the surface.
C)
Decrease in pressure near the surface.
D)
Decrease in heat near the surface.
E)
Increase in radioactive decay near the surface.
6
What are the most important factors controlling the creation (not composition) of magma?
A)
radiation, water content, and oxygen
B)
water content, heat, and oxygen
C)
radiation, pressure, and water content
D)
pressure, heat, and water content
E)
heat, water content, and silicon
7
Eruption of magma at mid-ocean ridge systems occurs mostly by ___________________.
A)
decompressive melting of the lithosphere
B)
decompressive melting of the asthenosphere
C)
decompressive melting of core
D)
decompressive melting of lower mantle
E)
decompressive melting of upper crust
8
Hot spots under the continental lithosphere generally create __________ while those under oceanic lithosphere commonly create
__________.
A)
calderas, shield volcanoes
B)
shield volcanoes, stratovolcanoes
C)
cinder cones, stratovolcanoes
D)
calderas, stratovolcanoes
E)
cinder cones, shield volcanoes
9
The production of magma is favored by an increase in ____________ and __________, and a decrease in __________.
A)
pressure, water content, heat
B)
pressure, heat, water content
C)
heat, water content, pressure
D)
E)
solar heat, water content, pressure
solar heat, pressure, water content
10
The main process that causes volcanoes to explode violently is _______________.
A)
hot convection currents in the asthenosphere that push magma upward
B)
density differences within the magma that force part of the magma upward
C)
a decrease in pressure triggering rapid expansion of the gases in a magma
D)
chemically volatile substances that explode within the volcano vents
E)
rapid expansion of the solid crystals in a magma with decrease in pressure
11
Which of the following factors helps determine whether a volcanic eruption will be violent or relatively peaceful?
A)
The ease with which dissolved gas escapes from the magma.
B)
Temperature of magma.
C)
Composition of the magma.
D)
all of the above
E)
Only the amount of dissolved gas in the magma and temperature of the magma.
12
Rhyolitic magmas rich in K, Al, Na, and SiO2 typically are produced by the melting of _____________ and are associated with
_____________ eruptions.
A)
continental crust, highly explosive
B)
continental crust, peaceful
C)
mantle, highly explosive
D)
oceanic crust, peaceful
E)
oceanic crust, highly explosive
13
Basaltic magmas rich in Fe, Mg, Ca and poor in SiO2 are generated mostly by the melting of the ____________ and are erupted
mostly as _____________.
A)
asthenosphere, pyroclastic debris
B)
continental crust, pyroclastic debris
C)
continental crust, lava flows
D)
asthenosphere, lava flows
E)
core, lava flows
14
In the 1997 movie Volcano there is a violent volcanic eruption in Los Angeles. This is not realistic because _________________.
A)
this area is cut by a strike-slip fault system which typically has no associated volcanic eruptions
B)
this area is an oceanic-oceanic subduction zone which typically has no associated volcanic eruptions
C)
this area is an oceanic-continental subduction zone which typically has no associated volcanic eruptions
D)
this area is a continent-continent collision zone which typically has no associated volcanic eruptions
E)
this area is hot spot zone which typically has no associated volcanic eruptions
15
An explosive and catastrophic volcanic eruption is least likely to occur ________________.
A)
at a subduction zone such as Japan
B)
at continental hot spots such as Yellowstone National Park
C)
in the Hawaiian Islands
D)
in rift zones within continental crust such as the Rio Grande Rift
E)
An explosive eruption is equally likely to occur at any of the above locations.
16
Why are rhyolitic magmas generally more explosive than basaltic magmas?
A)
The lower silica content and higher temperatures of rhyolitic magma allow the gas to escape easily.
B)
The higher silica content and higher temperatures of rhyolitic magma allow the gas to escape easily.
C)
The higher silica content and lower temperatures of rhyolitic magma allow the gas to escape easily.
D)
The higher silica content and higher temperatures of rhyolitic magma make it difficult for the gas to
escape.
E)
The higher silica content and lower temperatures of rhyolitic magma make it difficult for the gas to
escape.
17
Why do people tend to inhabit areas with high potential for volcanic eruption?
A)
These areas generally have fertile soils.
B)
These areas generally have phenomena such as hot springs that attract people.
C)
The period between major eruptions is generally so long that people become complacent about the
dangers.
D)
These areas typically are beautiful settings.
E)
all of the above
18
When a volcanic cone collapses into its magma reservoir it forms a ________________.
A)
shield volcano
B)
stratovolcano
C)
scoria cone
D)
E)
caldera
fissure eruption
19
The type of magma erupted on the Hawaiian Islands is predominantly basaltic. What type of volcanic landform do you expect to find
on the islands?
A)
stratovolcanoes
B)
scoria cones
C)
shield volcanoes
D)
lava domes
E)
answers B and C
20
In the 1997 movie Dante's Peak, the final eruption of the stratovolcano blasted a huge cloud of ash and dust high into the
atmosphere which then collapsed down the flanks of the mountain under the force of gravity. The style of the eruption portrayed
would be best interpreted as _______ which created a _______.
A)
Plinian, pyroclastic flow
B)
Strombolian, lava flow
C)
Pelean, lava flow
D)
Hawaiian, pyroclastic flow
E)
Plinian, lahar
21
Mt. Vesuvius and other volcanoes in the Mediterranean region have formed because of _____________.
A)
rifting of Africa from Europe
B)
subduction of the Mediterranean sea floor beneath Europe
C)
a hot spot
D)
continent-continent collision between Africa and Europe
E)
strike-slip fault movement
22
In places such as Mt. Pinatubo, people were evacuated from a large area before the eruption. Yet in Hawaii volcanic eruptions
occur frequently, and eruption-viewing has become a major tourist attraction. Why?
A)
Most of the magma erupted on Hawaii is in the form of lava flows.
B)
Violent gas-charged eruptions are not common on Hawaii.
C)
The viscosity of magma erupted on Hawaii is generally very low.
D)
Hawaii lies over a hot spot where magma comes from melting of the mantle.
E)
all of the above
23
The Earth's outer core is thought to be a highly viscous zone of liquid iron. However, liquid iron never rises from this zone to erupt
as molten iron on the surface of the Earth. What is a plausible explanation for this observation?
A)
The temperature of liquid iron from the core is so low that it crystallizes in the lower mantle.
B)
The density of iron liquid in the core is higher than the overlying mantle rocks.
C)
The density of iron liquid in the core is lower than the overlying mantle rocks.
D)
The density of iron liquid in the core is the same as the overlying mantle rocks.
E)
Molten iron is too viscous to flow.
24
Magma viscosity increases with _______________.
A)
Increasing temperature, increasing silica (SiO2) content, and increasing crystal content
B)
Decreasing temperature, increasing silica (SiO2) content, and increasing crystal content
C)
Decreasing temperature, decreasing silica (SiO2) content, and decreasing crystal content
D)
Increasing temperature, decreasing silica (SiO2) content, and decreasing crystal content
E)
Decreasing temperature, increasing silica (SiO2) content, and decreasing crystal content
25
In order from least explosive to most explosive, eruptions can be described as _________________.
A)
Plinean, Hawaiian, Icelandic
B)
Hawaiian, Strombolian, Plinian
C)
Vulcanian, Icelandic, Strombolian
D)
Strombolian, Plinian, Vulcanian
E)
Icelandic, Volcanian, Hawaiian
26
When magma viscosity, volatiles, and volume are all high, a common landform that can result is _______________.
A)
a shield volcano
B)
a scoria cone
C)
a lava dome
D)
a caldera
E)
a fissure
27
When magma viscosity and volatiles are low but magma volume is extremely large, a ______________ is likely to result.
A)
flood basalt eruption
B)
caldera
C)
stratovolcano
D)
E)
scoria cone
lava dome
Part 2
1 Most of the Earth's explosive volcanoes are located in a zone that encircles the Pacific Ocean called the Ring of Fire. The types of
volcanoes that commonly form in this zone are called _____________ that form by the melting of asthenosphere and lithosphere
rocks during _____________.
A)
cinder cones, subduction
B)
shield volcanoes, subduction
C)
stratovolcanoes, subduction
D)
stratovolcanoes, rifting
E)
stratovolcanoes, formation of hot spots
2 Melting of the mantle forms the most common type of magma that is extruded onto the Earth's surface because ______________.
A)
this type of magma forms at high temperatures which allow it to rise to the surface before crystallizing
completely to become solid rock
B)
this type of magma has low percentages of SiO2 so it has low viscosity which allows it to move more
easily to the surface
C)
this type of magma is generally extruded in rift zones where there are fractures that provide avenues for
flow
D)
all of the above
E)
none of the above
3 Subduction zones are characterized by _______________.
A)
andesitic to rhyolitic volcanic rocks
B)
steep-sided volcanoes composed of alternating pyroclastic debris and lava flows
C)
pyroclastic flows and calderas
D)
answers A, B, and C
E)
answers A and C
4 At which location would you expect relatively peaceful volcanic eruptions?
A)
Mt. Shasta in California
B)
Iceland
C)
Mt. Pinatubo in the Philippines
D)
Paricutin in Mexico
E)
Yellowstone in Wyoming
5 Floods associated with melting of glaciers during a volcanic eruption are referred to as ____________.
A)
jokulhlaups
B)
lahars
C)
debris flows
D)
tsunami
E)
pyroclastic flows
6 Gases that are commonly emitted during volcanic eruptions include all of the following except _______________.
A)
water vapor
B)
carbon dioxide
C)
carbon monoxide
D)
methane
E)
nitrogen
7 The violent flank eruption of Mount St. Helens in 1980 was set off by _______________.
A)
an earthquake that caused collapse of part of the mountain thus rapidly releasing pressure
B)
interaction of hot magma with cold water
C)
caldera collapse
D)
a fault that ripped the mountain apart
E)
none of the above
8 Melting of thick caps of snow on volcanoes, such as Mount St. Helens, can generate which of the following hazards?
A)
pyroclastic flows
B)
earthquakes
C)
lahars
D)
lava flows
E)
volcanic gases
9 When magma is too viscous to flow it can form a sticky blob that blocks the conduit of a volcano and forms a steep-sided feature
known as a _______________.
A)
scoria cone
B)
lava dome
C)
cone
D)
composite volcano
E)
hornito
10 If you were in an airplane flying over a subduction zone what would you expect to observe on the continent adjacent to the zone?
A)
A long, narrow sea within a rift zone.
B)
A plain of lava flows.
C)
A chain of steep-sided volcanoes subparallel to the subduction zone.
D)
A series of broad, shield-shaped volcanoes subparallel to the subduction zone.
E)
A single, large cinder cone.
11 What causes a pyroclastic flow to move at high velocities?
A)
Gravitational collapse of an eruption cloud.
B)
Energy from the eruption.
C)
Internal turbulence that keeps particles in the air.
D)
Release of gas from magma particles and heating of surrounding air creating a "popcorn" effect
E)
all of the above
12 Why are pyroclastic flows one of the most dangerous types of hazard associated with volcanic eruptions?
A)
They can form with little or no warning and move at extremely high velocities.
B)
They can cover large areas with a dense cloud of ash and dust that can asphyxiate an entire city.
C)
The temperature of the cloud can be several hundred degrees Centigrade causing fires.
D)
answers A and B only
E)
answers A, B, and C
13 Lahars created on stratovolcanoes have high destructive energy because _______________.
A)
they move at velocities of 200-300 miles per hour
B)
they flow on top of a cushion of hot gases and heated air
C)
they are dense mass of water and rock that flows down steep slopes over thousands of feet of elevation
D)
they gain energy as powerful eruptions eject material out of the vent
E)
they form when an entire volcano collapses
14 Which continental hot spot in the United States has posed the greatest threat in historic times?
A)
Valles caldera
B)
Long Valley caldera
C)
Yellowstone caldera
D)
Hawaii
E)
St. Helena
15 Lahars can form by all of the following except ________________.
A)
melting of a snow cap on a volcano
B)
flow of lava into the ocean
C)
flow of pyroclastic material into a river
D)
heavy rainfall during eruption of pyroclastic material
E)
collapse of a crater lake or dam
16 A pyroclastic flow can best be described as _________________.
A)
a flow of gas and hot ash
B)
a flow of hot gas
C)
a flow of mud and pyroclastic material
D)
a flow of hot lava
E)
a rain of volcanic fragments