Tephra Fall

What is Tephra fall?

Tephra, a volcanology term for ash, is small rock fragments ejected from a volcano into the atmosphere, which is then deposited around and downwind of the volcano. The size and thickness of the deposits decreases with increased distance from its source.

Tephra can be a nuisance to people in many ways. Even small amounts can cause or aggravate respiratory problems in humans. It kills crops, damages machinery, and is a hazard to aviators. Tephra is heavy - a significant accumulation (4 inches) on a roof top could collapse a building (Hoblitt and other, 1995:2). In addition, it often blocks out the sun creating darkness and unnecessary panic.

Tephra fall at Mount Rainier?

The winds around Mount Rainier generally flow from southwest to northeast (U.S. Geodynamics Committee, 1994:34); therefore, the tephra deposits would probably only affect the towns around the volcano - not the Seattle-Tacoma metropolitan area unless the winds happen to be blowing in the opposite direction. (U.S. Geodynamics Committee, 1994:34). The hazard map above shows the probability for tephra fall deposits of 1/3 of an inch and 4 inches during one year.

 Click Here - Learning From Experience Tephra