Mount Rainier is quite suseptible to rock falls at any time of year but particularly during the summer melt season. Most commonly rock falls are small and generate very weak or no seismic signals and pose no hazard to anyone other than climbers directly under them. They also can be quite large and record very well on many seismic stations and can be hazardous over a large part of the mountain. In the extreme and very rare case of very large rockfalls they can mix with enough snow and ice to generate a lahar that can be hazardous off the mountain.
In the summer of 2011 there were a series of moderately large rock falls off of Nisqually Cleaver onto the Nisqually Glacier that generated well recorded seismic signals on all station on the volcano. This page documents these seismic records and their analysis by the PNSN along with some other documentation of these events.
The following links are to samples from the next few weeks of Webicorder records for periods when PNSN staff characterized seismic signals as being typical of moderate to large rock falls. Signals are given in Universal time (UTC), which is 7 hours ahead of PDT.
Click on a station name for a date-time below to view the data from that time period.
Figure showing the number of rockfall type signals detected and characterized by the PNSN analysis staff in summer of 2011. The significantly larger rockfalls are indicated by a red dot. Each day starts at hour 0 GMT, Ie at 5pm PDT.
... PNW EARTHQUAKES
University of Washington Dept. of Earth and Space Sciences, Box 351310 Seattle, WA, 98195-1310