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Saturday, April 12, 2008

[MCR] Wapta Icefields April 5 to 11

We traveled in 3 different groups across the Wapta to the Little Yoho Valley.  One group went via Peyto Lake, one group via Bow Lake and the other via Sherbrooke Lake.

Weather
There was overall cool weather and significant solar radiation throughout the week.  Springtime squalls came and went leaving anywhere from 5 to 40cm of accumulation in the alpine.  Average temps ranged from -21° in the alpine overnight to -1° in the daytime. Moderate SW and NW winds have redistributed new snow at higher elevations.  Yesterday was the warmest day of the week resulting in sun crust forming on most solar aspects.

Snowpack
South and West aspects: mix of weak facets and crusts. 5-10cm of new snow lies on a melt freeze crust with facets below. 
North and East aspects: the February 26 surface hoar exists at different elevations.  This surface hoar is still hard to predict with significant whomphs with skier traffic occurring mainly from areas with shallow snow pack. Stability tests (compression tests) showed significant weakness on the surface hoar ranging in depth from 80cm to 100cm.

Avalanche Activity
Widespread sloughing out of steep unsupported features under daytime warming on S and W aspects (Occasionally stepping down into slab avalanches).  Natural cornice falls have resulted in the triggering of large slab avalanches.  We triggered a Size 3 avalanche from a distance of 20m away at the west saddle of Isolated Peak triggering the whole slope below.  This occurred on an N aspect at 8870ft, on 25°slope, and released 70cm to 1m deep. The avalanche cleaned all the winter snow away to the bare ice of the glacier.  We had widespread whumphing in flat shallow rocky areas and low angled terrain.

Confidence remains low as to the predictability of the surface hoar layer.

Travel Conditions
Travel is fast and easy. Trails down low are hard and fast in the morning, and trail breaking in the alpine varies from 5-30cm ski pen depending on aspect and elevation.  Ski crampons are starting to be needed on south aspects in earlier parts of the days.  Travel in shallow areas is more trying as the snowpack is weak and less supportive.

Ski quality
Good skiing can be found on N and E aspects for the fresh boot top powder or on South aspects where spring corn can be found if timed right.   If not timed right this can be breakable crust.

ACMG ASG Exam






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