City of Puyallup

Mt. Rainier Volcano Facts

Height:  14,410 feet

Age:  About 1 million years

Principal Hazards:  Lahars generated by melting of snow & ice; landslides

Principal Eruptions Types:  Lahars generated by melting of snow & ice; landslides

Snow & Ice Cover:  One cubic mile of permanent snow & ice

Definitions

Volcanic Ash

Volcanic ash is rock that has been pulverized into dust or sand by volcanic activity and can consist of tiny jagged pieces of rock and glass.  Ash is hard, abrasive, mildly corrosive, conducts electricity when wet, and does not dissolve in water.  Volcanic ash is hot near the volcano, but is cool when it falls at greater distances.  Ash accumulates like heavy snowfall, but doesn't melt.  Ashfall can be accompanied by lightening.  In very large eruptions, ash is accompanied by rocks having the weight and density of hailstones.  The weight of ash can cause roofs to collapse.  A one-inch layer of ash weighs 5-10 pounds per square foot when dry, but 10-15 pounds per square foot when wet.  Ash is spread over broad areas by wind. 

Lahars

Landslides transform into lahars, fast-moving slurries of rock, mud & water that look & behave like flowing concrete.  Eruptions melt snow & ice that transform into lahars.

Lava Flows

Lava is molten rock that pours or oozes onto the earth's surface.  Numerous eruptions of lava interbedded with rock rubble constructed Mt. Rainier.

Pyroclastic Flows

Pyroclastic flows are hot avalanches of lava fragments and volcanic gas formed by the collapse of lava flows and eruption clouds.

Tephra

Explosive eruptions blast fragments of rock high into the air.  Large fragments fall to the ground close to the volcano.  Small fragments from large eruptions travel thousands of miles.

What is it like during ash fall?

Falling ash can turn daylight into complete darkness.  Accompanied by rain and lightening, the gritty ash can lead to power outages, prevent communications, and disorient people.

For more information:

United States Geological Survey, Cascades Volcano Observatory  -  http://vulcan.wr.usgs.gov

US Dept. of the Interior - http://volcanoes.usgs.gov/ash