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