Geology Chapter 5

Which of the following statements correctly describes a parasitic cone?

A parasitic cone is a small cone on the side or base of a volcano that has formed during repeated flank eruptions.

How does the viscosity of the magma fed to volcanoes affect nearby life and property?

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.

Which of the following is a feature of an aa flow?

Aa flows have sharp, jagged edges.

How do craters differ from calderas?

Calderas, which have diameters of 1 km or more, are much larger than craters.

Which of the following statements accurately describes the composition of a cinder cone?

Cinder cones are composed of generally basaltic pyroclastic material and scoria.

Over what time span do most typical cinder cones form?

Cinder cones are generally the product of a single eruption and thus are constructed in less than a year or less than a month.

All types of volcanic cones share which feature?

Conduit

Most magma on Earth is produced at ___ plate boundaries.

Divergent

How do the eruptions that created the Columbia Plateau differ from eruptions that create large composite volcanoes?

Eruptions that created the Columbia Plateau ejected basaltic magma from fissures; eruptions that create large composite volcanoes eject silica-rich magma from vents.

Which statement describes the composition and viscosity of the lava associated with shield volcanoes?

Lava from shield volcanoes is mafic and has a low viscosity.

Which of the following is the location of a currently active shield volcano?

Mauna Loa in Hawaii

How do lava tubes form?

Pahoehoe flows develop cave-like tunnels that were previously used for carrying lava from an active vent to the flow's leading edge.

Contrast pahoehoe and aa lava flows.

Pahoehoe flows exhibit smooth surfaces, are hotter, and are more fluid than aa flows, which exhibit jagged surfaces with sharp edges.

Which statement accurately describes a pyroclastic flow?

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.

Define viscosity.

Resistance to flow. Magma has a higher viscosity if it has a lower temperature, is rich in silica, and contains very few dissolved gases.

What region of the world has the greatest concentration of composite volcanoes?

Ring of Fire

What is scoria, and how does it differ from pumice?

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.

What type of structure is Shiprock, New Mexico, and how did it form?

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.

What three factors do volcanologists monitor in order to determine whether magma is migrating toward the Earth's surface?

-changes in the patterns of earthquakes caused by the movement of magma -inflation of the volcano -the gases released from the volcano

Which of the following can be a product of a composite volcano eruption? CHOOSE ALL THAT APPLY.

-volcanic bombs -andesitic lava -gases -ash -cinders

Which of the following indicates that a volcanic eruption could be imminent?

A change in the composition of gasses being released

Distinguish among a conduit, a vent, and a crater.

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.

How is magma generated along convergent plate boundaries?

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.

How did Crater Lake form, and how does it compare to the calderas of shield volcanoes?

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.

Which type of volcanic hazard can decrease global temperatures?

Volcanic ash

How do volcanic bombs differ from blocks of pyroclastic debris?

Volcanic blocks are made of hardened lava, whereas volcanic bombs are made of incandescent lava.

Volcanism at divergent plate boundaries is most often associated with which rock type, and what causes rocks to melt in these settings?

Volcanism at divergent boundaries is most often associated with basaltic rock, which is created by decompression melting.

LaGarita, in the San Juan Mountains, is an example of a _____.

Yellowstone-type caldera

Are pyroclastic materials a significant component of shield volcanoes?

Yes; pyroclastic materials are more commonly ejected during the final stage of growth of a shield volcano, when eruptions become more sporadic.

In addition to composite volcanoes, what other type of volcanic landform can generate pyroclastic flow?

a lava dome

How does the composition of a typical lava dome differ from that of a typical fissure eruption?

a lava dome's flow is silica-rich and has a high viscosity, whereas a fissure eruption is basaltic and has a low viscosity.

What is a lahar?

a mudflow of volcanic debris saturated with water

Composite volcanoes generally consist of what materials?

alternating layers of cinders and ash interbedded with andesitic lava flows

Which of the following would decrease the viscosity of magma?

an increase in temperature

Comparing cinder cones to shield volcanoes

cinder cones have steeper flanks than shield volcanoes, and cinder cones occupy a smaller area of land than shield volcanoes.

When contrasting lava from composite volcanoes to lava from shield volcanoes,

composite volcanoes most often produce silica-rich lavas with high viscosities, whereas shield volcanoes produce basaltic lavas with low viscosities.

Scientists monitor volcanoes in an attempt to

discover precursors that may warn of an impending or imminent eruption.

Which type of plate boundary generates the greatest quantity of magma?

divergent

What does a fumarole emit?

gases only

The volcanoes in the Ring of Fire are generally described as

having violent eruptions, as most of these volcanoes are composite cones which eject andesitic lava.

is/are common in the final stages of growth of a typical shield volcano.

high viscosity (rhyolitic) lava

What is the source of magma for most intraplate volcanism?

mantle plumes

Where do most shield volcanoes form?

on the ocean floor

Which volcanic landform listed below is primarily composed of loose fragments of scoria?

the Parícutin cinder cone

Which of the below choices lists three volcanic hazards other than pyroclastic flows and lahars?

volcanically generated tsunamis, atmospheric cooling from ejected ash, and sulfur dioxide ruining vegetation via the groundwater