Unit 6

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

False

Transform faults have lots of associated volcanism because the strike slip motions keep a "lid" on the hot asthenosphere below, allowing it to melt.

False

The most peaceful eruptions are _____________.

Icelandic type eruptions

About 80 percent of the magma reaching the Earth's surface is basaltic, with only about 10 percent andesitic and 10 percent rhyolitic.

True

Although there are 92 naturally occurring elements, a mere eight make up more than 98 percent of the Earth's crust.

True

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

aa

The number of "hot spots" worldwide is ________________.

More than 100

On 20 February 1943, a new volcano, a scoria cone, was born when an eruption rose up through a farm field near a village in Mexico. The volcano is ________________.

Paricutin

__________ eruptions are the most violent types of explosive eruptions.

Plinian-type

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

90%

Rock may melt by _______________.

All of the choices are correct

The viscosity of magma is lowered by __________.

All of the choices are correct

Areas of geyser activity include _______.

All of these are correct

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?

All of these are correct

If the magma reaches the surface, it forms volcanic rocks, named for Vulcan, the Roman god of fire.

True

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

True

The formation of a giant continental caldera includes all but which of the following?

Basaltic eruptions begin from circular fractures surrounding the bulge.

No magmas contain dissolved gases.

False

The dominant volcanic gas (commonly 90% or more of total gas) is _____________.

Water vapor H2O

A caldera collapse occurs ________________.

after the magma chamber is mostly empty