Geology Chapter 5

25 July 2022
4.7 (114 reviews)
45 test answers

Unlock all answers in this set

Unlock answers (41)
question
Which type of volcanic hazard can decrease global temperatures?
answer
Volcanic ash
question
When contrasting lava from composite volcanoes to lava from shield volcanoes,
answer
composite volcanoes most often produce silica-rich lavas with high viscosities, whereas shield volcanoes produce basaltic lavas with low viscosities.
question
Which of the below choices lists three volcanic hazards other than pyroclastic flows and lahars?
answer
volcanically generated tsunamis, atmospheric cooling from ejected ash, and sulfur dioxide ruining vegetation via the groundwater
question
How is magma generated along convergent plate boundaries?
answer
The subducting slab drives water and carbon dioxide into the mantle, which reduces the temperature at which it melts, allowing mantle rock to melt and rise.
question
What is a lahar?
answer
a mudflow of volcanic debris saturated with water
question
What is the source of magma for most intraplate volcanism?
answer
mantle plumes
question
Volcanism at divergent plate boundaries is most often associated with which rock type, and what causes rocks to melt in these settings?
answer
Volcanism at divergent boundaries is most often associated with basaltic rock, which is created by decompression melting.
question
Over what time span do most typical cinder cones form?
answer
Cinder cones are generally the product of a single eruption and thus are constructed in less than a year or less than a month.
question
is/are common in the final stages of growth of a typical shield volcano.
answer
high viscosity (rhyolitic) lava
question
Contrast pahoehoe and aa lava flows.
answer
Pahoehoe flows exhibit smooth surfaces, are hotter, and are more fluid than aa flows, which exhibit jagged surfaces with sharp edges.
question
How does the viscosity of the magma fed to volcanoes affect nearby life and property?
answer
A volcano that expels highly viscous magma is a greater threat to life and property because it is more explosive and thus is more difficult or impossible to predict.
question
What region of the world has the greatest concentration of composite volcanoes?
answer
Ring of Fire
question
Define viscosity.
answer
Resistance to flow. Magma has a higher viscosity if it has a lower temperature, is rich in silica, and contains very few dissolved gases.
question
How do lava tubes form?
answer
Pahoehoe flows develop cave-like tunnels that were previously used for carrying lava from an active vent to the flow's leading edge.
question
What type of structure is Shiprock, New Mexico, and how did it form?
answer
Shiprock, New Mexico is a volcanic neck that formed when the volcano itself eroded away, leaving the crystallized igneous rock piercing through the Mancos shale.
question
Which of the following statements correctly describes a parasitic cone?
answer
A parasitic cone is a small cone on the side or base of a volcano that has formed during repeated flank eruptions.
question
How does the composition of a typical lava dome differ from that of a typical fissure eruption?
answer
a lava dome's flow is silica-rich and has a high viscosity, whereas a fissure eruption is basaltic and has a low viscosity.
question
What does a fumarole emit?
answer
gases only
question
In addition to composite volcanoes, what other type of volcanic landform can generate pyroclastic flow?
answer
a lava dome
question
What is scoria, and how does it differ from pumice?
answer
Scoria is a vesicular ejecta that is produced from mafic magma. Although pumice is also vesicular, it differs from scoria in that pumice is felsic.
question
Which of the following indicates that a volcanic eruption could be imminent?
answer
A change in the composition of gasses being released
question
Which statement describes the composition and viscosity of the lava associated with shield volcanoes?
answer
Lava from shield volcanoes is mafic and has a low viscosity.
question
How do craters differ from calderas?
answer
Calderas, which have diameters of 1 km or more, are much larger than craters.
question
Distinguish among a conduit, a vent, and a crater.
answer
A conduit is the circular path through which magma ascends to the vent, which is the surface opening of the conduit. A crater is a funnel-shaped depression around the vent.
question
What three factors do volcanologists monitor in order to determine whether magma is migrating toward the Earth's surface?
answer
-changes in the patterns of earthquakes caused by the movement of magma -inflation of the volcano -the gases released from the volcano
question
Are pyroclastic materials a significant component of shield volcanoes?
answer
Yes; pyroclastic materials are more commonly ejected during the final stage of growth of a shield volcano, when eruptions become more sporadic.
question
Scientists monitor volcanoes in an attempt to
answer
discover precursors that may warn of an impending or imminent eruption.
question
Which of the following is the location of a currently active shield volcano?
answer
Mauna Loa in Hawaii
question
How do the eruptions that created the Columbia Plateau differ from eruptions that create large composite volcanoes?
answer
Eruptions that created the Columbia Plateau ejected basaltic magma from fissures; eruptions that create large composite volcanoes eject silica-rich magma from vents.
question
Which type of plate boundary generates the greatest quantity of magma?
answer
divergent
question
Which of the following is a feature of an aa flow?
answer
Aa flows have sharp, jagged edges.
question
Which of the following statements accurately describes the composition of a cinder cone?
answer
Cinder cones are composed of generally basaltic pyroclastic material and scoria.
question
Composite volcanoes generally consist of what materials?
answer
alternating layers of cinders and ash interbedded with andesitic lava flows
question
Which of the following can be a product of a composite volcano eruption? CHOOSE ALL THAT APPLY.
answer
-volcanic bombs -andesitic lava -gases -ash -cinders
question
Most magma on Earth is produced at ___ plate boundaries.
answer
Divergent
question
How do volcanic bombs differ from blocks of pyroclastic debris?
answer
Volcanic blocks are made of hardened lava, whereas volcanic bombs are made of incandescent lava.
question
Which volcanic landform listed below is primarily composed of loose fragments of scoria?
answer
the Parícutin cinder cone
question
Where do most shield volcanoes form?
answer
on the ocean floor
question
Comparing cinder cones to shield volcanoes
answer
cinder cones have steeper flanks than shield volcanoes, and cinder cones occupy a smaller area of land than shield volcanoes.
question
All types of volcanic cones share which feature?
answer
Conduit
question
How did Crater Lake form, and how does it compare to the calderas of shield volcanoes?
answer
The summit of the composite volcano collapsed after an explosive eruption of silica-rich pumice and ash fragments; rainwater later filled this caldera. Had this volcano been a shield volcano, the collapse would have been a result of a gradual subterranean drainage of a central magma chamber.
question
The volcanoes in the Ring of Fire are generally described as
answer
having violent eruptions, as most of these volcanoes are composite cones which eject andesitic lava.
question
Which of the following would decrease the viscosity of magma?
answer
an increase in temperature
question
Which statement accurately describes a pyroclastic flow?
answer
Pyroclastic flows, which consist of basaltic lava infused with incandescent ash and lava fragments, can reach many miles away from their sources because they are nearly frictionless and are driven by gravity.
question
LaGarita, in the San Juan Mountains, is an example of a _____.
answer
Yellowstone-type caldera