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.

References to interesting details
• The 6/24/2011 (UTC) RCM 12 hour Webicorder record shows an unusual, higher amplitude signal starts at June 24, 16:37 UTC (09:37 PDT) followed by a much larger and longer lasting strange signal at 16:41 UTC. While there may have been smaller, precursory rock falls (such as seen on this record at 15:43 UTC) we think that these two larger signals represent the first major rock falls during this extended sequence.
• There also is a 10 minute spectrogram arround the larger signal illustrating the timing and frequency content of this rock fall record.
• Aerial photos taken shortly after.
• Here is a YouTube video of one of the rockfalls we think was taken on June 24th or 25.
• A more detailed longer with some close up YouTube video dated on afternoon of June 25, 2011.
• Another YouTube video of end of rockfall on June 25.
• YouTube of skiers leaving rockfall runout area. Date unknown.
• YouTube video of rockfall dust cloud at Camp Muir taken afternoon of June 25, 2011.
• YouTube video of lower part of rockfall taken from west of Nisqually glacier on afternoon of June 25.
• YouTube video of July 4 rockfall.

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.

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