Juneau Area Avalanche Advisory
2005-12-18
Mt. Stewart
by Bill Glude, SAAC Observer
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Text
The thaw that began on the 15th continued through yesterday. It brought only moderate winds and not much rain, but temperatures were very warm. The snowpack settled markedly and the top 10 cm wetted out.

The surface has now refrozen and did not thaw today. Radiation cooling of the snow surface is keeping it frozen despite above freezing air temperatures. The surface is yielding enough to take a ski edge in places, but is hard and fast, and in some areas it is hard to edge or kick steps in.

We saw none of the seven signs of instability and had no results on our slope and traveling tests.

We turned back from seeking the sunshine atop Mt. Stewart due to the risk of a sliding on the hard icy surface and did our pit studies in a less than ideal spot below a cliff band in the upper N Bowl because the rest of that slope had slid out about a week ago. The snow there was much deeper there than average and the layer sequence was not very representative due to spindrifting from above, but the layers near the surface were our main concern and we could test those quite well in that location.

We did one AK Block which fractured on multiple hard jumps at average shear quality (AK6Q2) on the 40° slope, just below a thin crust above a thick soft moist thawed melt freeze layer 13 cm below the surface at 130 cm on the graph (230cm true height). It scored two out of five lemons, indicators of structural weakness. Our slab test scored a low energy #4, breaking out less than half the undermined area in an irregular fracture.

We judged the strength to be +, the stress to be +, the energy to be +, and the structure to be +, where + indicates a strong snowpack, ~ is neutral, and - is weak.

The major danger right now is losing your footing and sliding, especially with the many exposed rocks. Ice axe and crampons are advisable for any serious mountaineering.

The next snow may slide on the icy melt freeze crust as well, depending on whether the temperatures as it comes in allow it to bond or not.

Field Notes
Photos
Even the higher mountains in the Grandchild Peaks (left) and McGinnis Mountain (right) area lost snow in the last three days. Some of the ridges at the left are completely bare.
The slab that fractured in our AK Block test scored a low energy #4 on the slab test, where we dig out the weak layer and then load the slab with our hands. It took some snow beyond Anne's hands, but less than half the undermined area broke out and the break was irregular.
The thaw of the last three days did not bring much rain, but warm temperatures and light drizzle settled the snowpack enough so many rocks are now showing where they were not just three days ago.
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