GEOL 1001 chp 6 hw questions

Which of the following are true of felsic magmas?

-They tend to have high viscosities -They do not allow gas bubbles to escape easily -High gas pressure commonly lead to highly explosive eruptions

What are some factors that could allow flood basalts to have high-volume eruptions?

-a large amount of magma is generated in the mantle -magma rises to the surface along thick dikes -the magma is hot and has a low viscosity

Which of the following is common in most calderas?

-a large, circular depression with steep walls -thick sequences of volcanic ash -rounded mountains that are volcanic domes

Hazards associated with basaltic lava flows and eruptions are

-burial of roads and neighborhoods by lava flows -house fires -floods from catastrophic melting of ice

What types of rocks would be common in a composite volcano?

-felsic and intermediate lava flows -pyroclastic rocks from an eruption column -pyroclastic rocks from pyroclastic flows -rocks with fragments formed by landslides and mudflows

Flood basalts influence life on Earth because

-large volumes of flood basalts are erupted during a short time -eruptions can release large amounts of gas that cool the atmosphere -eruptions can release large amounts of gas that warm the atmosphere.

Which of the following activities is NOT used to monitor volcanoes?

-measuring seismic activity with seismic instruments -measuring sulfur dioxide gas emissions -measuring changes in heat flow from satellites -measuring tilting on the flanks of a volcano

Which of the following is NOT a way in which a volcano's history indicates the level of hazard it poses to nearby population centers?

Age of the oldest volcanic layer present

Magma rising through the crust fractures rocks, producing rhythmic, repeating

Seismic shaking

Which of the following are differences between an eruption column and pyroclastic flow?

a pyroclastic flow forms when the gas flux cannot supports the column

What is the interpreted origin for magma that forms flood basalts?

a rising mantle plume

Which of the following is a hazard but not a risk, according to the textbook?

a scoria cone that erupts hot molten fragments on an unpopulated Pacific island

Which of the following is the best indicator that a volcano might be very dangerous?

a volcano that contains andesite and welded tuffs

Which of the following factors indicates a high risk for volcanic mudflows or lahars?

a volcano with a thick covering of snow or ice

Which of the following is NOT a major controlling factor on volcanic eruption style?

age of volcano

At what depth do gas bubbles have the most effect on magma?

at very shallow levels, such as within the volcano

Reduced temperatures and growing seasons in Europe following the 1783 Laki eruption were primarily caused by

blocking of sunlight by volcanic ash and aerosols

The main cause of caldera collapse is:

collapse of the roof of a magma chamber as magma erupts

Which of the following plate boundaries is least likely to produce composite volcanoes?

continent-continent convergent boundary with a high mountain range (Himalaya)

Scoria cones are composed primarily of

ejected fragments of vesicular lava

Large shield volcanoes are associated with which plate tectonic setting?

hot spots

Which of the following commonly precede a volcanic eruption?

increased gas flow from a volcano -steam eruptions from the volcanic crater -increased heat flow from the volcano

Prior to an eruption, the surface of a volcano may rise centimeters to hundreds of meters as a result of

injected-magma inflating the mountain

Volcanic mudflows (lahars) are common on composite volcanoes because

large amounts of rain and snowmelt mix with loose ash on steep slopes

Flood basalt eruptions are fed by

long fissures/dikes

According to the fossil record, what events have coincided with the approximate times when flood basalts were erupting?

mass extinctions

Which of the following is NOT a reason why heat flow and gas output from a volcano tend to increase before eruptions?

melting of snow caps dissolves large amounts of water into the magma

The most dangerous type of volcano is a

scoria cone

This volcano is broad and low, and is composed of basaltic lava flows. What kind of volcano is it?

shield volcano

volcanic domes commonly are partially destroyed when

steep parts of the dome collapse and cause small pyroclastic flows

Shield volcanoes have low slopes primarily because

the low viscosity of basaltic magma allows it to flow downhill for long distances.

Which of the following is NOT true about flood basalts?

they are fed from large interconnected composite volcanoes

Geologists use tiltmeters, GPS, and satellite radar maps to analyze the changes in __________ of a volcano.

topography

Which of the following are ways that viscosity affects gases in magma?

viscous magma prevents gas from escaping easily.

Changes in topography, water chemistry, and gas output all are used to help predict

volcanic eruptions