Avalanche: Hatcher Pass

Location: Hatch Peak > $1000 Run

Date:
Observer:
Route & General Observations

Willow Fishhook Road to Hatch Common, triggered remote avalanche on 35 degree N slope on $1000 run, then traveled to the 12/9/2018 avalanche site, conducted crown profile and instability tests. Skied flank, and descended $1000 Run back to road.

Avalanche Details
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Trigger SkierAvalanche Type Hard Slab
Aspect NorthElevation 4200ft
Slope Angle 35degCrown Depth2ft
Width 100ftVertical Run 250ft
Observer Comments

$1000 Run, steep, 35 degree, N aspect. Intentionally triggered from safe location on 0 degree slope angle ridge, jumping to collapse weak layer. HS-ASr-D2-O/G Failed on rounding buried surface hoar 4.0mm and facets 2.0mm above MF crust and on basal facets 2.0mm below MF crust. Multiple weak layers failing. Depth of avalanche 1-3 feet.

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)?Yes
Cracking (Shooting cracks)?Yes
Observer Comments

Whumphing was present in many locations, however it did not always result in cracks or avalanches. Shooting cracks were limited. Many prime locations for triggering avalanches where jumped on, but did not result in activity even after collapsing. However, if you find the right spot, no more weight than a single skier walking over a specific trigger point, on terrain 0-15 degrees in slope angle, can result in a remotely triggered avalanche on slopes generally greater than 35 degrees.

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

Broken Skies, -7C, E 6.7 mph

Snow surface

12cm (5") Low density, new snow, precipitation particles 1.5mm in size. New snow had a density change, right side up.

Snowpack

Above 4000ยด: Boot pen 50cm (19 in)
Highly variable strength, Poor structure, variable energy to high energy.
Stability tests were highly variable, ECTX > ECTP12 > remotely triggered avalanches

Low elevation has a very thin snowpack 0-1 foot, mid elevations up to 2 feet, upper elevations up to 4 feet. Most early season snow accumulation occurred at the upper elevations. Due to a very warm early winter lower to mid elevation snow accumulation was significantly less. The result is an unusual juxtaposition of snowpack height by elevation for Hatcher Pass. This may mislead backcountry travelers as the start of their tours in the lower to mid elevations is not be representative of the hazard at the upper elevations.

A dangerous set up of weak basal facets will NOT heal quickly and may plague snow stability for the season. Expect repeat offenders, as multiple occurrences of avalanches will be possible in the same locations.

Photos & Video
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