GLY101 CH 6

Which prompts are ways that viscosity can be raised? Increase temperature Increase SiO2 content Increase mineral crystal content

Increase SiO2 content Increase mineral crystal content

Which prompts are ways that viscosity can be lowered? Increase temperature Increase SiO2 content Increase mineral crystal content

Increase temperature

As minerals form in magma kept at a constant temperature, what happens to the viscosity of that magma?

It increases

The most famous of all volcanoes probably is Vesuvius, and the most famous of its eruptions are those of 79 ce, which buried the cities of ____________.

Pompeii and Herculaneum

Match the following volcano dangers to the correct definition. Pyroclastic flow Lahars Lava flow rapid rush of gases and materials downslope muddy water-laden rush of material downslope molten rock moving downslope

Pyroclastic flow - rapid rush of gases and materials downslope Lahars - muddy water-laden rush of material downslope Lava flow - molten rock moving downslope

The basaltic magmas that erupt on the ocean floor have a low SiO2 content, high temperature, and allow gas to escape easily, all resulting in non-explosive eruptions.

True

The lowest temperatures and highest SiO2 contents occur in rhyolitic magma, material so viscous that it commonly does not flow.

True

The primary reason magma forms at subduction zones is that the subducting plate carries a cover of sediments, water, and hydrated minerals down with it, which lowers the temperature required for the adjacent overlying mantle lithospheric rock to melt.

True

The process of mineral formation in a cooling magma is called crystallization.

True

Slow flowing, more viscous basaltic lava commonly has a rough, blocky texture called ________.

aa

A caldera collapse occurs ________________.

after the magma chamber is mostly empty

Pyroclastic debris is __________.

chucks of magma and rocks blown into the air by gas in a volcanic eruption

If basaltic lava reaches the sea or a lake, it cools rapidly into ____________ lava.

pillow

If all of the following rocks were to completely melt and reach the same final temperature, which would produce magma with highest viscosity? basalt gabbro andesite diorite rhyolite

rhyolite

What erupts in a geyser?

superheated water and steam

What is the cause of volcanism at Italy's Vesuvius, Stromboli, Vulcano, and Etna?

the subduction of Mediterranean seafloor beneath Europe

Over _________ of volcanism is associated with the edges of tectonic plates.

90%

Which of the following can help make rocks melt beneath Earth's surface? Increasing pressure Adding volatiles Increasing temperature Decreasing pressure Increasing density

Adding volatiles Increasing temperature Decreasing pressure

__________ melting occurs when a rock melts due to a lowering of pressure.

Decompression

At oceanic spreading centers, magmas are rhyolitic in composition.

False

Most volcanism is associated with hot spots.

False

The higher the viscosity of magma, the more fluid is its behavior.

False

Some of Earth's most beautiful mountains are ________, including Mt. Kilimanjaro in Tanzania, Mt. Shasta in California, Mt. Rainier in Washington, and Mt. Fuji in Japan.

Stratovolcanoes

__________ are steep-sided, symmetrical volcanic peaks built of alternating layers of pyroclastic debris capped by high-viscosity andesitic to rhyolitic lava flows that solidify to form protective caps.

Stratovolcanoes

Rank the following plate tectonic boundaries from most explosive volcanic activity to least explosive volcanic activity. Subduction zone Spreading center Transform boundary

Subduction zone (1), Spreading center (2), Transfrom boundary (3)

Beneath continents, rising basaltic magmas are contaminated by sediments and continental-crust rocks, altering magma compositions; the resultant andesitic-to-rhyolitic magmas have high contents of SiO2, relatively low temperatures, and high viscosity.

True

Why does the magma from some volcanoes flow smoothly and relatively peacefully, while the magma from other volcanoes blasts forth violently and deals death over wide areas?

differences in the chemical and mineral makeup of magmas variations in the temperature, water and gas content, and viscosity of magmas different geographic positions with respect to hot spots and edges of tectonic plates

A well-formed conical volcano located above an active subduction zone that has not erupted in 12,000 years is __________.

dormant, but will likely erupt again at some point

The viscosity of magma is lowered by __________.

increasing temperature decreasing crystal content decreasing SiO2 content

Most rifting occurs at spreading centers __________.

located below sea level

Rock may melt by _______________.

lowering the pressure on it raising its temperature increasing its water content

The presence of water ________ the melting point of rock.

lowers

Which of following correctly lists the order in which the listed minerals form in a cooling magma from the first to the last to form? biotite mica pyroxene olivine amphibole quartz

olivine, pyroxene, amphibole, biotite mica, and quartz

Spreading centers are an ideal location for volcanism because ______________.

they sit above the high-temperature asthenosphere the asthenosphere rock has low percentages of SiO2 the oceanic plates pull apart causing hot asthenosphere rock to rise and undergo decompression melting to form magma that continues to rise

In magma, __________ is the most abundant dissolved gas.

water vapor (H2O)

A shield volcano has a great ___________.

width compared to its height