AdvisorySAAC04

02-01-05 Mt Stewart

We went up on Mt Stewart today to see how much and what type of new snow there was, how the weak layers might be changing, what sort of bonding the new snow might have to the layers from the last few days' warm weather, and whether windloading was yet a factor.

We found moist new snow at the Eaglecrest parking lot, about 10 cm as we departed and 20+ cm of drier snow when we returned at the end of the day. On the climb, the snow dried out markedly at 600 m. There was only very minor SE wind loading, though a north wind was blowing at least 5 m/sec down the Channel when we returned to town. Snow accumulated at 1 to 5 cm/hr all day, totaling 25+ cm of new snow at higher elevations.

We saw no signs of instability other than abundant new snow, very localized shooting cracks in the surface layer, and a few large but slow surface sluffs on 40°+ slopes.

The principal weakness in our block tests was the old facets, now rounding but still sugary, on top of the December 23 - 24 faceted melt freeze crust. The Rutschblock released on that layer with multiple hard jumps (#6) and the AK Block released on the second jump (#5), both Quality 2 (clean and average) at nearly a meter depth on 40°. These results indicate the spatial variability of this layer, which has shown more strengthening in other locations this week.

Loading did not appear to be critical today, but the forecast heavy snow and wind may create fresh windslabs on the poorly bonded new snow layer, and slides fracturing initially on the surface windslab - light new and early rounds - melt freeze crust sandwich might generate enough force to release the deep layer in its weaker spots.

Today, we found excellent light deep snow that can still be ridden up to 45°with appropriate care. By morning, heavy snow and wind may change the snowpack to one demanding more caution. Take care out there and don't let your guard down.

Large fresh needle crystals on a rucksack. The new snow alternated between these and rimed stellar fragments. Though these crystal types often pack densely, they were accumulating rapidly and at random orientation, making for a fluffy 80 Kg/m3 surface layer.

Interestingly, we have found far more new snow in the field than the Fish Creek Research Site snow height gage has been recording over the last few days. This could be due to wind action at the site, but is most likely because settlement, or compaction of the snowpack under its own weight, has been almost as rapid in these mild temperatures as the rate of new snow accumulation.

Gerry Landry shears the Rutschblock on multiple hard jumps (#6) Quality 2 (clean and average shear) on 40°, fracturing the roughly one meter deep facet layer on top of the December 23 - 24 faceted melt freeze. The block, as is usual in our tests, did not break at the back cut.

Gerry shears the AK Block on his second, hard jump (#5). Otherwise, the AK Block results were identical to those for the Rutschblock. We usually find that test pairs either have identical scores, or the AK Block is one step lower. The lack of a cut back does not appear to give the AK Block a higher score, as might be expected. Instead, the slightly smaller block for most testers seems to bias it slightly toward a lower score.

Gerry Landry conducts a slope test. His scientific ardor was such that we could hardly get him to stop testing and go home at the end of the day.

Juneau gets only wet snow, right? So why is Gerry so deep in the fluff? Could it be that the wet maritime snowpack stereotype is not true at high latitudes? Is winter really here at last? Does anyone really know what we will get next? Stay tuned...