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Recreational Observation

North approach/descent

March 19, 2017, 3:40 p.m. PST

Weather: 25F, mostly sunny, light E winds. A perfect day for the alpine!?

Snowpack: 24-hr storm snow (12"+ bone-dry pow), over supportable base, moistened by previous day's precip. Ideal skiing. Ski pen of 6"-16". Deeper snowpack not observed, except at crown face.

Area Description: A quick heads-up to a random, massive and destructive size 3.5+ natural avalanche we witnessed on the upper alpine zone of Ruby yesterday. It was triggered by a massive, natural cornice release/pull-out, which triggered a 400-yard+ wide hardslab avalanche that raked the entire upper mountain. It ran all the way down to and through the treeline, including the lower-mid elevation gully feature often ski (it stopped just above the "choke"). The slide ran over ~1400' vertically, and a far greater distance laterally. The power, scale and destruction-potential of this avalanche is hard to describe. Debris chunks the size of Sprinter vans... Hard to capture this in one photo attachment. We were at the top (on the SE sub-summit, SE of standard low point in ridge) of our second run when we observed the entire avalanche, start to finish, including the initial (natural) cornice fall that triggered the slide. This was not a skier trigger. All of our lap-#1 ski tracks and our skin track were completely obliterated. The crown fracture face was between 7'-25' tall; more where the triggering cornice failure face is included. We had a difficult time even getting over/off the crown fracture (~7' high; a necessary free-fall drop to the icy bed surface) in order to get off/down from the summit ridge. Amazingly, nobody was buried, injured or killed, all very likely/possible had the timing of our (or other's) ascent/descent been any different. There were also two other touring parties on the lower alpine zone at the time of the avalanche; two skiers were almost engulfed by the debris fan had we not yelled down to them as the avalanche started. I would say that Ruby is completely done for the season. The entire "money run" from the summit ridge is nothing but debris and/or solid-ice bed surface at this point. One would need technical ice tools to get over the crown face, and to travel across the icy bed surface. I am trying to grapple with how to report and share this observation. It is by far the biggest natural avalanche I have ever witnessed so posting seems prudents. Unless someone wants to do a proper bed surface investigation (or to snap proper photos), Ruby is a wasted trip at this point. Skiing ATL+ was good yesterday, but that's history now. This observation ties in nicely with recent blog post about cornice hazards. Yes, spring is here. PS - I would not make mention of this zone had the observation not warranted public awareness of a signifiant but random cornice concern.

Avalanches: yes. from previous 24-hr rain-on-snow event below TL. Some recent (24-hr old?) small crowns in alpine. No sign of previous cornice failures. The avalanche we observed was of the low probability, extra high consequence variety.

Latitude: 48.349404

Longitude: -119.970703

Did you see any avalanches? Yes

Did you trigger any avalanches? No

Was anyone caught in an Avalanche? No