Wednesday, June 16, 2010

Unusual Seismic Recordings from Mount Rainier Glaciers

This is Steve Malone with the Pacific Northwest Seismic Network located at the University of Washington in Seattle. We operate seismographs throughout the Pacific Northwest and have three located high on Mount Rainier. We often record seismic events from all of our glacier-clad volcanoes that we associate with glacier motion, i.e. "ice-quakes." However, since about May 20, 2010 we have detected a strange set of these events coming from the upper Winthrop Glacier. We are calling these small events "clones" because the seismic waveforms from one event are near-duplicates of those from other events indicating a repeating source. They also seem to occur at very regular intervals.


The interval between events is often as short as every 3 minutes but changes from time to time and has been as much as 15 minutes between events. We think that their magnitude (on the Richter scale) is about M = -1 (i.e., 8 orders of magnitude smaller than the Nisqually earthquake of 2001).




So, what are these puppies? We think they represent small periodic slips at the bed of the glacier. Perhaps there is a large rock embedded in the bottom of the glacier and as the glacier moves it scrapes this rock along the bed, only a few mm in each slip. But why are they so regular in time? Maybe water pools up-hill of the rock until it slightly lifts the glacier allowing the rock to more easily slip and this then drains that small pool of water starting the process over. We think that water has an important influence on glacier sliding but don't understand the mechanism very well.


How can you help? Anyone climbing Rainier on the east side (upper Emmons or Winthrop Glacier routes) may see or hear things that would help us pin these suckers down. Please let me know of anything you think may be out of the ordinary (sounds, sights, feelings???). Particularly those of you who have been in this area before and can compare what may be different from previous climbs. Our best guess where these originate (based on stacking 4000 individual events to get the best relative seismic wave arrival times at six seismic stations and using a 1-D seismic velocity model with station elevation corrections, blah blah blah, other scientific mumbo-jumbo) puts the location at 46.85950 north 121.7610 west (i.e., 2.5 km WSW of Camp Schurman or 3.4 km NNW of Camp Muir or about 600 meters up from the top of Russell Cliffs).

To see these suckers yourself check out our "webicorders" at:
http://www.pnsn.org/WEBICORDER/VOLC
and click on the date-time for one of the high Rainier stations (RCS, RCM, STAR). The small blips that have about the same size and shape are our "clones".

Send email to: steve@ess.washington.edu or give me a call (206-685-3811)


Steve Malone

Monday, June 07, 2010

SPECIAL AVALANCHE STATEMENT ~ June 7, 2010






View of Saturday's Avalanche Path from the Rescue Helicopter

Significant avalanche danger at higher elevations on the volcanoes, mainly above 7 to 8000 ft.

Several strong storm systems moving through the region last week produced increased accumulations of new snowfall at higher elevations on the NW volcanoes from Mt. Hood northward through Mt. Baker and in the Olympics. Water equivalents during this period ranged from an inch to over 3 inches, the storm likely produced new snow amounts of 1 to more than 3 feet above about the 7 to 8000 ft. level, greater at higher elevations and on southeast through northeast exposures where intermittently strong winds produced deep drifting. These new snow amounts taper quickly below 6000 to 7000 ft. with only minor amounts of a trace to an inch or so of snow recorded at the 5000 ft. level.

This weather has resulted in significant unstable snow accumulations at higher elevations on the volcanoes, especially on lee slopes where unstable slabs of 3 to 5 ft. or more may have developed over either previous crusts or some wet weak snow layers, depending on elevation and aspect. Most recent information from Mt. Rainier indicates that Camp Muir has received about 2 feet of snow, with 3 to 5 ft. drifts...especially on east exposures. Although only preliminary information on the recent avalanche accident on Mt. Rainier has yet been received, it appears that the avalanche was a human triggered 3 to 6 ft. deep hard slab, approximately 1 to 200 yards wide, and running about 1,200 vertical feet. Latest information indicates that the slide caught 11, fully burying or partially burying 4, one of whom remains unacccounted for at this time and is presumed dead. Mountain guides from other climbing parties in the area were able to recover three of those who were buried or partially buried, two of whom suffered injuries necessitating airlift rescue from the site with the third able to walk out with minor injuries.

This serious incident underscores the fact that the weather, not the calendar, dictates avalanche danger on higher elevations in any mountainous terrain.

Currently, a storm system moving through the Northwest should deposit an additional 4 to 6 inches or more of snow at elevations above 7 to 8000 feet along with moderate southwest wind transport helping to further load the steeper leeward side terrain. More showery weather anticipated late Sunday should be followed by decreasing showers early to mid Monday, with slowly clearing skies, decreasing clouds and brief warming likely later Monday and early Tuesday before another moderate storm system affects the area and brings another surge of precipitation and winds late Tuesday and Wednesday along with lowering freezing levels. As a result of both current and expected weather and avalanche conditions, travelers venturing into higher elevation terrain in the Cascades and Olympics should be conservative in their decision making, cautious in their route finding, and factor avalanche danger into their goals and route selection for the upcoming week...as very few goals or routes are worth injury or death.

Finally, extended range forecast models indicate that a strongly building upper ridge may begin to move over the region late next week. If models are correct, the associated sunshine and freezing levels of 10-12,000 ft. or more should make the storm snow that has accumulated in late May through early June increasingly wet and weak, with further significant avalanche activity likely. Please stay aware of expected weather over this time of transition toward a gradually more stable snowpack at higher elevations, and ratchet back both goals and expectations to help minimize potential avalanche involvement.

Please note that NWAC forecasts normally apply to elevations below 7000 feet outside of ski areas and adjacent to highways. However, owing to the recent avalanche accident on Mt Rainier, some additional snowpack information at higher elevations, combined with the unusually strong late spring storms buffeting the region, this statement has been issued to alert those venturing into higher elevations of the NW mountains that there is, in fact, an increased level of avalanche danger.

This statement will be updated as conditions warrant.

Mark Moore
NWAC Director/Avalanche Meteorologist