Huge Avalanche recorded at Mount Hood - March 29, 2010
We got reports from the snow safety person at Hood Meadows ski area about an avalanche in the spring of 2011 that looked very similar to one that took place a year before. We could dig up some of the seismic records from this period, March 29, 2010. Unfortunately some of the local stations were not functioning properly at the time of the avalanche. However, the station located near the base of the Hood Meadows ski area called “HOOD” and one located near the Timberline Lodge, “TIMB”, were working, and they recorded this event very well. Here is a 13 minute long set of seismograms from these stations. “HOOD” is a three-component station, so we show all three components even though the vertical (BHZ) shows pretty much the main characteristics of the signal. The shaking lasted for just about 10 minutes with the strongest shaking within the first three minutes of the seismogram starting at 23:38:20 GMT (3:38 pm PST). It is interesting that the event ends with a small burst of extra shaking rather than just dying away to normal background signals.
Below is a spectrogram of the exact same data. This has the same time axis, but the vertical axis shows frequency content going from 0 to 20 Hz, and the colors are signal strength going from the strongest as red to the weakest as blue. One can see that most of the energy is concentrated around 2 to 4 Hz other than at the very beginning where higher frequencies are also strong. This type of signal is typical of a source extended in time that is not too far away (within 10 km) from the seismographs.
The following two pictures were the only ones mentioning this event that I could find from publications of avalanche bulletins. The first was taken from or under the Heather Chair Lift looking down at the terminus of the avalanche, and the second is apparently taken from the skier's left side of Clark Canyon looking down valley toward the terminus. Note the two skiers in the debris field.
See the exotic events web page for a list of other interesting non-earthquake seismic events including other avalanches on Cascade volcanoes and, in particular the event that took place in this same drainage just under a year later on March 10, 2011.