Feb 28, 2009, Silver Star Creek Basin
2/28/09
WA Cascades East Slopes North
1897
0
Went on a last minute trip to Winthrop for the weekend.
Saturday, we drove to the end of the plowing on SR20 at Silver Star Creek. Lots of sleds and several with skis at the trailhead. With no sled and Delancy looking really thin, we opted to head south towards Silver Star.
No tracks on the way in, cloud deck was 6000-7000' all day. We got to the end of the flats (elev 5000) and had a little snack at the heli-pickup spot. There were at least 8 heli-$$kier tracks above, but all were located near the main NE-aspect run. Due south of us on low northern aspects were numerous slab releases (SS-natural-R4-D1.5). Moving around in this area we heard many whoomps and felt numerous collapses.
We dug a pit and found easy and clean shears Q1.5 on buried surface hoar at about 8-12 inches down. The new snow on top was generally fist hard, and was more cohesive at the bottom. Compression tests showed easy failures (CT5-8), but ECT did not propogate.
The other disturbing find was that about 3-4 ft down, the entire 1F hard slab was sliding on an exceptionally high quality (Q1) shear plane. I forgot my magnifier, but the plane seemed to be ~1mm rounded facets. This could potentially produce a deep hard slab failure. This hard slab failed at CT25+, ECT 28+(no propogation), SS-med-hard.
With the poor vis and not-bomber snowpack we opted to lap some moderate E-aspect terrain from 6000 to 5000. Skiing was very nice and we did not notice any signs of the top 8-12" being cohesive. The surface hoar causing much of the concern with the top layer was located in the valley between 5-5400-ft, and seemed to be mostly on northern shaded aspects.
Saturday, we drove to the end of the plowing on SR20 at Silver Star Creek. Lots of sleds and several with skis at the trailhead. With no sled and Delancy looking really thin, we opted to head south towards Silver Star.
No tracks on the way in, cloud deck was 6000-7000' all day. We got to the end of the flats (elev 5000) and had a little snack at the heli-pickup spot. There were at least 8 heli-$$kier tracks above, but all were located near the main NE-aspect run. Due south of us on low northern aspects were numerous slab releases (SS-natural-R4-D1.5). Moving around in this area we heard many whoomps and felt numerous collapses.
We dug a pit and found easy and clean shears Q1.5 on buried surface hoar at about 8-12 inches down. The new snow on top was generally fist hard, and was more cohesive at the bottom. Compression tests showed easy failures (CT5-8), but ECT did not propogate.
The other disturbing find was that about 3-4 ft down, the entire 1F hard slab was sliding on an exceptionally high quality (Q1) shear plane. I forgot my magnifier, but the plane seemed to be ~1mm rounded facets. This could potentially produce a deep hard slab failure. This hard slab failed at CT25+, ECT 28+(no propogation), SS-med-hard.
With the poor vis and not-bomber snowpack we opted to lap some moderate E-aspect terrain from 6000 to 5000. Skiing was very nice and we did not notice any signs of the top 8-12" being cohesive. The surface hoar causing much of the concern with the top layer was located in the valley between 5-5400-ft, and seemed to be mostly on northern shaded aspects.
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