volcanoes

Lava is typically ______ or hotter.

850 degrees

The felsic rock granite is rich in ___ and feldspars, whereas the mafic rock basalt is rich in ___ and feldspars.

Blank 1: quartz Blank 2: ferromagnesians

Which of the following commonly precede a volcanic eruption? (Choose all that apply.)

Changes in gas emissions Changes in the volcano's shape Seismic activity

Earthquakes, harmonic tremors, and changes in topography and gas emissions are all precursor to volcanic

activity

Most of the world's active volcanoes are located ______.

along plate boundaries

What type of pyroclastic material causes the following problems: it can bury cities, it is slippery, it can cause roofs to collapse, it is bad for people's lungs, and it is damaging to engines and other mechanical equipment?

ash

What mafic volcanic rock is formed at seafloor spreading ridges?

basalt

Scientists are still uncertain the reason for ___ ___ , but the leading explanations suggest a locally warm area at the boundary between the outer core and the mantle.

hot spots

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

lahar

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

lahar

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

mafic

Magmas that contain 45 to 50% silica are called ___

mafic

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

mafic

The partial melting of the ultramafic mantle creates magma that is ___ in composition. (Use just one word for your answer.)

mafic

What is the composition of the magma and rocks formed at seafloor spreading ridges?

mafic

What type of magma allows gas to escape more easily?

mafic

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

mafic; felsic

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

material

Fissure eruptions occur ______ and can result in massive outpourings of basalt.

on continents or on the seafloor

Landslides may lead to volcanic eruptions when ______.

the removal of material allows gases to escape

Seafloor spreading ridges are the most volcanically active areas on earth's surface because ______.

they are so widespread

Carbon monoxide, carbon dioxide, fluorine, sulfur compounds, and water vapor are all ___ emitted by volcanoes.

gases

While lava usually is not life threatening, it is enough to burn and destroy any property it encounters.

hot

The volcanoes of the Aleutian Islands are ______ volcanoes that are ______ in composition.

strato-; andesitic

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

temperature; pressure

Which of the following describe mafic magma? (Choose all that apply.)

Contains 45 to 50% silica Has a relatively high amount of iron and magnesium

Choose all of the statements that correctly describe the relationship between plate setting, magma behavior, and hazards.

Each plate setting creates magma of a certain composition. The composition of the magma controls how the magma erupts. The way a magma erupts determines the type of hazards associated with it.

How is magma behavior related to plate setting and volcanic hazards?

Each tectonic setting produces a distinct type of magma which erupts in a way directed by its composition.

How does volcanic ash and dust cause cooling of the climate?

It blocks sunlight from reaching earth.

Which of the following describe a pyroclastic flow? (Choose all that apply.)

It is a very dangerous volcanic hazard. It is also known as a nuée ardente.

Select all that apply Choose all of the hazards associated with volcanic ash.

It is dangerous to breathe since it is composed of microscopic glass. It causes mechanical failures. It can bury entire cities.

How important is it to understand a volcano's eruptive history in order to understand its potential for eruption in the future?

It is essential knowledge.

How will a large amount of volcanic ash and dust from a single large eruption affect global climate?

It will cause regional or global cooling for months up to a few years.

What will a decrease in pressure do to a rock that is already nearly hot enough to melt?

It will cause the rock to start melting.

What is the key element in understanding the potential for a volcano to erupt in the future?

Its eruptive history

How does silica content affect the escape of gas in magma?

Magma high in silica content does not allow gas to escape easily.

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?

Monitoring of changing volcano shape Maps of the debris from past eruptions

Many of the world's active volcanoes are located along the rim of the ______.

Pacific Ocean

How do sulfur gases emitted during volcanic activity affect climate? (Choose all that apply.)

Sulfuric-acid aerosols block sunlight and lead to cooling. They are long-lasting and get moved around in the atmosphere, affecting climate in areas far removed from the source.

Where does the majority of volcanic activity occur?

Seafloor spreading ridges

How is volcanic activity associated with landslides? (Choose all that apply.)

Steep and/or coastal volcanoes may have materials that are weakened and fail suddenly. Earthquakes associated with moving magma may cause landslides. Landslides may allow volcanic gases to escape.

Which of the following volcanic emissions are associated with both global cooling and the formation of acid rain?

Sulfur gases

What are the two primary controls on magma composition?

The extent of melting The parent material

Which of the following describe stratovolcanoes? (Choose all that apply.)

They are made up of both pyroclastic and lava flow layers. They are known to erupt explosively. They are also known as composite volcanoes.

Which of the following describe lahars? (Choose all that apply.)

They move quickly. They are made of ash and water.

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?

VEI

Of all the gases listed below that are emitted by volcanoes, which is the primary?

Water vapor

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.

cinder cone

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

decrease

Mafic magmas flow much more easily, or are less viscous, than ___ magmas

felsic

Magma that is rich in silica is called ______.

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?

felsic

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

pyroclastic

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

pyroclastics

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 ______.

radioactive materials

The area around Mount St. Helens was successfully evacuated before it erupted in 1991 because scientists monitored its changing ___ , and they had previously mapped debris from prehistoric eruptions.

shape

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

shield

Felsic magmas are rich in the compound ___

silica

Mountains that are steep and ______ are particularly susceptible to the creation of lahars.

topped with snow

Most magma originates in the ______.

upper mantle

The majority of magma at subduction zones is created ______.

when water from the subducting plate moves upward into the overlying asthenosphere