Juneau Area Avalanche Advisory
2006-02-23
Eaglecrest & Mt. Stewart
by Bill Glude, SAAC Observer
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We did fieldwork today at Eaglecrest and on Mt. Stewart. In the ski area the new snow from two days ago, now turned into sugary faceted grains with a topping of surface hoar, showed little instability. It sluffed easily but only very small windslab areas showed any sign of slabbing. Conditions were best below 700 m, where the unusual NW winds that followed the storm had not scoured or drifted the slopes. In sheltered hollows with smooth snow under the newest layers, there was 15 - 20 cm of loose snow that provided excellent turning with only occasional scrapes on the underlying icy rime and melt-freeze crusts.

The windward slopes high on Mt. Stewart were wind-scoured right down to icy crusts, and the lee slopes had sensitive windslab. The windslab areas we found were small, isolated, and thin, but produced easy fractures on our block tests and shooting cracks and mini-slabs on test slopes. Though they were a couple days old and slightly faceted, and tested in the slightly less sensitive #2 - 3 range on the Slab Test (more than half the undermined area but a bit slow and irregular), the bond to the facets beneath them is so weak they still fractured and slid easily.

Our test site was useless for testing for deeper instability because it was on the side that is usually windward, in an area that rimes heavily. The lower layers were all hard rime globules interspersed with snow that has turned into intermediate to advanced faceted grains due to cold weather and thin snowpack. We tested there because the windward side of the mountain was so scoured that no suitable sites could be found.

But testing over the last weekend indicated little deep weakness. The main concern now is windloaded areas, especially where windloading may have been stronger. Any freshly windloaded areas should be expected to produce human-triggered slabs, and the next new snowfall could be interesting if there is much loading. The facets over crust are a setup for an avalanche cycle if loaded heavily or rapidly.
Field Notes
Photos
Slopes below 700m that were not exposed to the unusual NW wind that followed the last storm had faceted powder topped with sparkling surface hoar. Both the traveling conditions and the snow stability are better at lower elevations right now.
The NW wind wreaked havoc on the snow surface at higher elevations. Here, graupel particles that the wind could not pick up or roll show in the eroded areas on top of the icy melt-freeze crust on the lower right, while the patterns on the left indicate snow that has drifted in and then been eroded as the wind shifted.
For those who have not been getting up to Eaglecrest, conditions there are now very good. While the snowpack at the top is thinner than normal, there is plenty of snowcover and the surface layers are dry and light.
Windslab areas were generally small and isolated, but we found a thin patch on the leeward S side of Mt Stewart to do our block tests in. As we were laying out the blocks, the windslab was cracking off on the underlying sugary faceted grains. Areas with more extensive or thicker windslab are likely to release slab avalanches.
Our block tests for the day,neatly cut and ready to shear. The Rutschblock is at the far end, the Cutback AK Block is in the middle, and the AK Block is at the near end. All three produced the same sensitive results on the 37° slope, fracturing cleanly and quickly on the 89 cm facet layer as we stepped onto the block (RB2Q1, CAK2Q1, AK2Q1).
In the firm windslab, both cutback blocks broke at the back cuts, a relatively rare occurrence in our testing. This Rutschblock actually slid as the slab above it pushed the block, before we stepped onto it.
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