Exam 8: Volcanoes and Plutons

About 75 percent of the Earth's volcanic activity occurs along a circle of subduction zones in the Pacific Ocean called the __________ __________ __________.

A chaotic mixture of volcanic ash and rock fragments that is left behind when most of the gas escapes into the atmosphere during an ash flow and solidifies is called a/an __________ __________ __________.

Continental crust is typically of __________ composition.

__________ is lava with a jagged, broken surface.

A granitic pluton that is exposed for less than 100 square kilometers is called a/an __________.

Pahoehoe lava cools and stiffens as it flows, forming basalt with smooth, glassy-surfaced, wrinkled, or "ropy" ridges.

Yellowstone Park is an example of three overlapping:

Typical granitic magma contains __________ silica and __________ water than typical basaltic magma.

Granitic magma contains up to __________ percent water.

The most catastrophic volcanic explosions occur when __________ reaches the Earth's surface.

Explosively erupted rock particles or magma form __________ rock.

Pyroclastic bombs, cinders, and ash:

A/an __________ __________ is a small volcano composed of pyroclastic fragments.

Magma production occurs through __________ __________ __________ in a mantle plume.

Lava and rock fragments commonly erupt from a __________ located in the crater of a volcano.

Dated rocks and zircon crystals suggest that granitic continental crust had formed by about __________ years ago.

As lava cools and solidifies from the surface down, cracks frequently grow downward through the rock. Such cracks are called:

Mount St. Helens in the state of Washington is an example of a stratovolcano.

Volcanic eruptions have no effect on global climate.

A dike is a sheet-like, intrusive rock that forms when magma oozes into a fracture.