Mt. Rainier National Park

Seismicity within Mt. Rainier's center is not well understood, but most likely of volcanic origin. Both high- and low- frequency events occur about twenty-four times each month. The low-frequency events are usually poorly recorded, and are probably generated by glacier movement. The shallow high-frequency events are usually well recorded in the magnitude range -0.5 to 3.0. Epicenters appear to align in a NE- SW trend across the summit.

Mount Rainier has other hazards besides the volcanic. Glacial floods, avalanche, and edifice failures (either spontaneous or triggered by a local earthquake), could cause significant damage which is hard to quantify. The monitoring of Mount Rainier seismic activity is part of the normal operations of the Pacific Northwest Seismograph Network. Alarm mechanisms can rapidly notify personnel of unusual or increasing activity which would likely precede a volcanic event. It also can, and has, provided information about other dangers such as rock-fall and debris flows. Unfortunately, in its present configuration it is doubtful that it could provide information needed for the timely evacuation of nearby towns potentially impacted by a large scale collapse of the edifice.

The International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) selected 14 active volcanos near highly populated areas throughout the globe for special study. Mount Rainier was selected as a "Decade Volcano" because of the hazard it poses, especially the Seattle-Tacoma metropolitan area. If melted rapidly, Mount Rainier's cover of snow and ice could produce catastrophic floods and mudflows. The volcano has an extensive but poorly studied geological record. The most recent eruption was about 2,200 years ago and covered the eastern half of the park with up to one foot of lapilli, blocks, and bombs. Although minor eruptions did occur as recent as mid 1800s, we only have about 200 years of written history of the Pacific Northwest to study, the rest must be by geophysical survey. Some lahar deposits are extend into the populated Puget Sound lowlands. Because urban development of Mount Rainier's flanks and nearby valleys is still in the early stages when compared to many volcanos, there is a chance to lessen the hazards by proper land useage.

Visitor Info
360-569-2211 x3314

Mount Rainier became a designated national park in March of 1899. Its 235,625 acres (97% was designated Wilderness in 1988) makes Rainier the highest (14,410') and third most voluminous volcano of the Cascade Range. The active volcano is encased in over 35 square miles of snow and ice.

Almost two million people come to enjoy Mount Rainier National Park each year. The park contains old growth forests, natural waterfalls, and subalpine meadows. Whether climbing to the summit, hiking the trails, or waiting for a deer to photograph against the wildflowers, Mt. Rainier holds something for all. By the way, if you don't care for "roughing it", you can ask at the ranger stations which way to the restaurant. I believe it was John Muir that settled by the hot springs, but in any case, there are restrooms and dining there now.

The subduction of the Juan de Fuca oceanic plate eastward under the North American continental plate has created the Cascade Mountain Range. Mount Rainier is at the north end of a segment of this volcanic string which contains five large strato- volcanos (including Mount St. Helens) intermixed with numerous minor basaltic centers.

After Mount St. Helens, Mount Rainier is the most seismically active volcano in the northern Cascade Range. Seismicity is concentrated in two zones: one about 10km to the west known as the western Rainier seismic zone (WRSZ), and in another cluster directly beneath the summit. It is theorized that the seismicity in the WRSZ is of tectonic origin and unrelated to the volcanic processes. While large earthquakes are not expected in this area, there is concern that a minor shake this close to the unstable volcanic slopes could trigger a major edifice collapse.