Geology Chapter 5 SB

quartz; ferromagnesians

The felsic rock granite is rich in ___________________ and feldspars, whereas the mafic rock basalt is rich in ________________________ and feldspars

shield

The largest on earth_______________ volcanoes are created from hundreds to thousands of runny basalt flows

mafic

The partial melting of the ultramafic mantle creates magma that is ____________________ in composition

granite

The plutonic equivalent of rhyolite is ______.

hot spots

The volcanic activity in both Hawaii and Yellowstone is the result of ______.

fissure

The Columbia River flood basalts are the result of a _____________ eruption

Silica

Felsic magmas are rich in the compound ______________________

B

Fissure eruptions occur ______ and can result in massive outpourings of basalt. A. Only at spreading centers B. on continents or on the seafloor C. Only on continents

caldera

Formed by either the collapse of a volcano into an emptied magma chamber or the enlargement of an existing crater, a ______ represents a very large volcanic eruption.

lahar

A fast-moving volcanic mudflow created through the combination of ash and water is called a ________________

cinder cone

A relatively small and steep volcano, a _____________________ _______________ is made of pieces of basaltic magma thrown into the air near the vent due to the escape of dissolved gases

pyroclastic

A very hot, very fast-moving flow of hot gases and ash from a volcano is known as a(n) __________________flow.

Gabbro

Basalt is _____________

A, B, D

Choose all of the statements that correctly describe the relationship between plate setting, magma behavior, and hazards. A. Each plate setting creates magma of a certain composition. B. The way a magma erupts determines the type of hazards associated with it. C. Volcanic hazards are dependent only on human factors and not on plate setting or magma behavior. D. The composition of the magma controls how the magma erupts. E. It is difficult to correlate magma behavior with plate setting.

Andesite

Dominated by feldspars and ferromagnesians, with some quartz (intermediate)

Basalt

Dominated by ferromagnesians and feldspars (mafic)

diorite

Andesite is _________________

Granite

Dominated by quartz and feldspars (felsic)

felsic

Magma that is rich in silica is called ______.

volcanic

What is pyroclastic material? ____________ fragments of all sizes

upper mantle

Most magma originates in the ______.

A, B, C

Which of the following describe stratovolcanoes? (Choose all that apply.) A. They are also known as composite volcanoes B. They are made up of both pyroclastic and lava flow layers C. They are known to erupt explosively D. The composition of their magma is basaltic

B, D

Which of the following describe the volcanoes of the Cascade Range? (Choose all that apply.) A. Mount Rainier is the most recently active B. They are composite volcanoes C. They are located in a chain of islands running west of Alaska D. They are created through the process of subduction

mafic

Magmas that contain 45 to 50% silica are called

basaltic

Hot spot activity under ocean crust is associated with __________________ magma, whereas hot spot activity under continental crust can create more felsic magma

Basalt

What mafic volcanic rock is formed at seafloor spreading ridges?

fissure

Eruptions of lava from cracks in the earth's surface, as opposed to from single vents, are called ___________________eruptions

fissure

Eruptions of lava from cracks in the earth's surface, as opposed to from single vents, are called_______________________ eruptions.

radioactive materials

Explanations for hot spots include that they lie above regions in the mantle or in the outer core that are hotter due to a higher percentage of ______.

mafic; felsic

Hot spots underneath ocean crust result in ______ magma, whereas continental hot spots may produce more ______ magma.

C

How is magma behavior related to plate setting and volcanic hazards? A. Magma composition controls eruption style, but is independent of plate tectonic setting. B. Magma composition is not associated with plate tectonic setting, and all magma erupts in the same fashion. C. Each tectonic setting produces a distinct type of magma which erupts in a way directed by its composition.

A, B, C

How is volcanic activity associated with landslides? (Choose all that apply.) A. Landslides may allow volcanic gases to escape B. Steep and/or coastal volcanoes may have materials that are weakened and fail suddenly. C. Earthquakes associated with moving magma may cause landslides. D. Landslides occur only on composite volcanoes.

B

Landslides may lead to volcanic eruptions when ______. A. the moving material creates an earthquake that destabilizes the volcano B. the removal of material allows gases to escape C. material piles up and puts pressure on a volcano

thick, viscous

Lava domes are made of ____________ lava

850

Lava is typically ______ C or hotter.

rock

Magma composition is controlled by the type of________________ that is being melted and the extent to which it is melted.

mafic; felsic

Magma generated in subduction zones is initially ______ in composition but can change as it makes its way to the surface. If this magma encounters continental crust, which it is hot enough to melt, the composition will change to intermediate or ______.

Pacific

Many of the world's active volcanoes are located along the rim of the ___________________ Ocean

drop

Melting of the asthenosphere can occur due to a(n)________________ in pressure, which is how magma is formed at spreading ridges and hot spots

temperature; pressure

Most magma originates in the upper mantle because the ______ is high enough and the ______ low enough to at least partially melt the rock there.

plate

Most of the world's active volcanoes are located along __________________ boundaries

Granite

Rhyolite is _________________

lava domes

Rhyolitic and andesitic lavas can erupt rather quietly, piling up to form somewhat small and steep _________ ______________

pyroclastics

Rock fragments of any kinds ejected from a volcano are called______________

widespread

Seafloor spreading ridges are the most volcanically active areas on earth's surface because they are so_________________

pyroclastics

The Volcanic Explosivity Index is a way to categorize the size of eruptions based on three categories which include the volume of ______ produced.

mafic

The asthenosphere is described as being ultramafic, meaning that it is very rich in ferromagnesian minerals. When it melts, it usually forms ______ magma.

B, C, D

The caldera underneath Yellowstone National Park is filling with magma created at a hot spot and is responsible for the ______ in the area (Choose all that apply.) A. lava flows B. geysers C. Hot springs D. Earthquakes E. cinder cones

C

The majority of magma at subduction zones is created ______. A. by friction between the two plates causing the rocks to melt B. as the subducted plate moves downward so far that it melts due to high temperatures C. when water from the subducting plate moves upward into the overlying asthenosphere

Felsic

The viscosity of magma is its resistance to flow and is controlled by the silica content. Which is more viscous: mafic or felsic magma?

cinder cone

This symmetric volcano made of pieces of magma thrown into the air by the escape of dissolved gases is called a _____________ _____________

active; dormant

Volcanoes that are labeled _____________ have erupted within recent history, whereas _________________ volcanoes have not erupted during recent history but have the potential to do so

phreatic

Water that is heated because it is near magma may cause a volcanic eruption called __________________ explosion.

A, D

What are the two primary controls on magma composition? A. The extent of melting B. Depth C. Time D. The parent material

VEI

What is the acronym for the scale used to rank the size of volcanic eruptions based on the volume and height of pyroclastics released, as well as the length of the eruption?

lahars

What type of hazard is associated with volcanoes that are steep and snow-covered?

Mafic

What type of magma allows gas to escape more easily?

stratovolcano

What type of volcano is composed of both pyroclastic and lava flow layers?

Shield

What type of volcano is produced from fluid basalt flows that create a large, broad, gently sloping structure?

A, D

What were the two primary sets of information used to successfully implement evacuations for the impending eruptions of both Mount St. Helens in 1980 and Mount Pinatubo in 1991? A. Monitoring of changing volcano shape B. Gas emissions C. Earthquake activity D. maps of the debris from past eruptions

C

What will a decrease in pressure do to a rock that is already nearly hot enough to melt? A. It will not affect the rock in terms of melting. B. It will decrease the likelihood of the rock melting C. It will cause the rock to start melting

A, D

Which of the following describe a pyroclastic flow? (Choose all that apply.) A. It is a very dangerous volcanic hazard B. It is slow moving C. It is composed of liquid water mixed with ash D. It is also known as nuee ardente

C, D

Which of the following describe mafic magma? (Choose all that apply.) A. Contains no silica B. Has a relatively high amount of silica C. Has a relatively high amount of iron and magnesium D. Contains 45 to 50% silica