Geological Survey Bulletin 1238 Volcanic Hazards at Mount Rainier, Washington

During postglacial time Mount Rainier volcano apparently was characterized by long quiet periods punctuated by brief episodes of activity; thus, its present dormant state cannot be regarded as a reliable sign that the volcano is now extinct. If the pattern of past activity continues, a substantial steam, pumice, or lava eruption might occur on an average of once each 500-1,000 years.

The direct hazard presented by future eruptions of lava, pumice, or steam is not regarded as great, but such eruptions may cause devastating floods and debris flows. Whatever their origin, debris flows are regarded as a major hazard because of their frequency and their movement along valley floors where works of man are concentrated. Their destructive effects can be minimized by careful land-use planning on valley floors.