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Avalanche: Turnagain

Location: Sunburst and Road obs

Date:
Observer:
Route & General Observations

Ascended/descended Sunburst to 3100′ on W shoulder. As we were ascending we spoke to a group who experienced a very large/loud collapse at 2300′ on a SW aspect next to their pit where they had found a reactive suncrust/facet layer 60cm below the surface. We did not experience any collapsing, but did find reactive buried surface hoar in two (W and N aspects) out of three pit locations. There was a supportable melt/freeze crust all the way to 2000′, before the surface crust became thinner and covered with heavy surface snow. On steep (and direct) South aspects this m/f crust gone completely wet and saturated by 5:30pm. Just before 5:30pm we noticed a fresh crown on a SW aspect in Seattle Creek. We could only see the very top of it, but photos and web cam pics taken earlier confirmed it was new today. We found out later (second hand) it was triggered by a snowmachine, but details are still vague. We also received reports of a few more human triggered avalanches in Seattle Cr. There was also a large natural avalanche in Portage Valley today. More info/pics can be found HERE. It is also suspected thatĀ Pete’s South avalanche happened sometime just beforeĀ 6pm today. Photo below.

Avalanche Details
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Trigger NaturalAvalanche Type Unknown
Aspect UnknownElevationunknown
Slope AngleunknownCrown Depthunknown
WidthunknownVertical Rununknown
Red Flags
Red flags are simple visual clues that are a sign of potential avalanche danger. Please record any sign of red flags below.
Obvious signs of instability
Recent Avalanches?Yes
Collapsing (Whumphing)?No
Cracking (Shooting cracks)?No
Observer Comments

Several large human triggered avalanches in Seattle Creek
Large collapse (reported to have been 200' in diameter on a SW aspect of Sunburst at 2300')
Large natural avalanches in Portage Valley on South facing slopes
Natural avalanche on South face of Pete's (not sure when it released, but sometime after 1pm on Friday)
Sun triggered wet loose and roller balls on Solar aspects and temperatures in the 40F's

Weather & Snow Characteristics
Please provide details to help us determine the weather and snowpack during the time this observation took place.
Weather

Clear and sunny, daily temperatures swings from 26F to 44F near road level. Sunburst wx station recored temps above 32F from 1-5pm, with a high of 38F. Winds were calm to light from the East. No new precip.

Snow surface

-Stout and supportable m/f crust to 2000' in the morning, but on steep South aspects this crust completely melted and was wet and saturated. On shaded aspects there about 1cm of dry snow on the surface.
-At 2000' the m/f crust starts to become thinner, ~4 inches' where you can punch your boot through.
-As you gain altitude there is dense heavy snow on the surface with a 1-2" sun created melt/freeze on Solar aspect. This was wet by 1pm yesterday.

Snowpack

Below the stout crust in the lower elevations the snow is still very moist.

In the upper elevations there is a wet snow layer that was still moist under 4-6" of heavy newish snow from the end of the storm. This wet layer is from April 5th, the warmest day of the storm, where rain fell to at least 3100'. Our highest point yesterday.

*We dug three pits and found a reactive layer of buried surface hoar (buried March 27th) in two out of three pits.

*Pit 1 - NW aspect, 2400', 29*slope, HS=175cm, a thinner area where the snowpack is more scoured, this layer was only 16" below the surface. It propagated with Easy force in Extended Column tests (ECTP11 x2) and failed all the way to End in Propagation Saw test. (PST 40/100 End.) The March facets (4F hard and rounding) were also found 20" below the surface and did not fail in ECT's. The rain layer from April 5th was 5" below the surface and was 3" thick and 1F- hard and still a little moist.

*Pit2 - W aspect, 2700', 31* slope, HS=258cm. The March 27th buried surface hoar was 33" (~3') below the surface and did not fail in Extended Column tests. It did fail in CT's with moderate to strong force. Deep Tap test failed with moderate to hard force (DT20.) The April 5th wet layer was 8" below heavy dry snow and it was 2" thick and still moist.

*Pit 3- SSW aspect, 3100', 24* slope, HS=250cm. We did not find buried surface hoar, but did find the sun crust that was buried on March 27th. The new snow was well bonded to this layer and did not fail in any tests. There was still a very thin m/f crust from April 5th warm up 8" below the surface, and it was only 1cm thick and pretty light an breakable.

Photos & Video
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