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 Glacier National ParkIssued:Friday, November 23, 2007 07:44Valid Until:Until Further NoticeBulletin Area:This bulletin covers the areas adjacent to the Trans Canada Highway corridor in Glacier National Park and the drainages directly accessed from this corridor.Large Areas of Glacier National Park Are
CLOSED
For Avalanche Control Using
EXPLOSIVES
For access information visit the Rogers Pass Discovery Centre
Synopsis:Snowprofiles done on a 1900m East aspect Wednesday and a 2200m North aspect confirm the existence of an upper level weakness, down 25 - 35cm depending on elevation. Stability test failures on both test pits are occurring at the interface of the most recent storm snow and the previous snow surface. Compression test scores the East aspect produced easy-moderate scores and a partial block Rutschblock score of 4. On the north aspect, the compression tests failed in the hard range however a 'sudden planer' shear quality was observed. This combined with observable wind effect on some open slopes in the alpine suggests that pockets of unstable snow are likely to exist. Areas having soft slabs sensitive to human triggering are possible, particularly adjacent to terrain features and in the lee of ridges in alpine areas.Recent observations on a southeast slope at 2190m in Ursus Trees showed a generally well settled snowpack of 150cm, with a couple of concerns in the upper 70cm. The first is a touchy new snow instability now buried approximately 35cm. Easy compression tests were recorded on this layer, and in steep areas with additional load from the winds, may be a factor for sluffing or soft slab avalanches. The second feature is a surface hoar layer down 70cm that was reacting in the hard range of compression tests and the easy range of shovel tests. In both tests the shear quality showed up as clean pops. Information is limited on the distribution and variability of this layer but it is likely most prominent in treeline areas and will bear watching as the slab above the surface hoar sets up and additional load accumulates. On south to east aspects in the alpine a thin suncrust exists providing a potential bed surface for skier-triggered avalanches (see below). Avalanche Activity:Since last Saturdays more extensive cycle, only a few loose snow avalanches have been observed in response to the cold air temperatures. Avalanches to size 2 have been observed from steep alpine areas of all aspects.A skier-triggered avalanche size 2.0 was reported Sunday from a southeast aspect at 2475m near Bruin's Pass. The avalanche was 30cm deep by 40m wide and ran 100m to the middle of the slope. The slope angle was 37 degrees and the bed surface was a thin suncrust with large stellars on top with a whumpf occurring before the failure. Investigations in a thicker snowpack area nearby gave easy compression tests down 15cm and 35cm on new snow instabilities and easy results on the crust down 49cm. The greatest likelihood of skier-triggered avalanches remains on lee and crossloaded slopes in alpine areas. Wind events from this past week had peak speeds up to 150kph from the south to southwest, so expect a high variability in where the slopes have been loaded or scoured and where windslabs have developed. Limited observations make the extent and sensitivity to skier triggering of these slabs (which may be buried) uncertain at this time. Skiers should exercise caution approaching north and east lee slopes. Outlook:The ridge of high pressure is forecast to continue today and then move east overnight bringing snow for Saturday. Confidence is low on forecast amounts however only light snow amounts over the developing weak surface layer will increase the avalanche danger by the end of the weekend. Temperatures will remain relatively cold.Travel Conditions:Travel conditions are improving however below 1800m alders, rocks and tree hazards continue to present themselves on the approaches to all areas. Glacier travel is not recommended due to thin bridges over crevasses. Trailbreaking is easy to moderate with penetrations approximately 20 - 30cm.Backcountry travelers are advised to use caution as buried obstacles exist just below the snow surface up to treeline.
FOR MORE DETAILS:Warden Office: (250) 814-5202 Emergency: 1-877-852-3100 24 Hours Recorded Message: (250) 837-6867 Related Link: http://www.avalanche.ca/ Seasonal Archives |
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