Quick report
On Saturday around the time of the avalanche there were at least four parties navigating the ridge and west face of Marmot. One on the up-track of the Mid-Rib skin track, and at least another three parties on the ridge ascending or descending.
A solo skier was observed to be descending the Marmot ridge and approaching the SW facing slope near the avalanche starting zone. This individual alerted another party above them that they had triggered an avalanche before continuing down the slope. The party above descended to observe the slope but did not see anyone involved.
There was, however, a party on the slope below that had left the parking area below Hatcher Pass Lodge, near the gate and ascended the established skin track on the west face of the lower Marmot Ridge. Their plan was to stay out of the isolated areas that looked cross loaded. At around 3500' a not so small avalanche was observed charging down the hill directly towards the party. One individual alerted their partner and deployed their air bag. Fortunately, the slide stopped short of their location and turned down the chute. They moved to the side and switched beacons into search mode. One partner stayed to the side while another conducted a beacon search of the slide debris. No signal was detected. The party transitioned and left the area.
This party never saw or spoke with who ever triggered the avalanche. The crown appeared to be along the ridge, just below and to the lookers right of the most prominent, west facing false peak/chute as seen from the parking area. There is uncertainty about what layer failure occurred on, but it ultimately ran on the basal ice at the bottom of the snowpack.
This party was comfortable with the choices they were making but acknowledged that they failed to account for other riders poking around above them. They were inclined to give the benefit of the doubt that who ever triggered the slide didn't know they dropped their line on other people, and otherwise they would have come over and checked on them.
Another party that observed the slide and interacted with the party above was encouraged to post an observation as a "reminder to try to set skin tracks away from terrain traps and run out zones."
Forecasters would like to thank the parties that submitted observations and helped piece together the events of the day. It's a great reminder to be aware of the possibility of other riders on the slope and how you plan to navigate both up and down avalanche terrain in consideration of other parties. Stay safe out there and enjoy the season!
This avalanche likely failed on the new/old snow interface or a faceted layer within the old snow. Regardless, the bed surface was facet/ basal ice layer from a late-October snow/rain event tfrom early season.Weather
- Air Temp
- 5-10
- Cloud Cover
- clear
- Wind Loading
- none
- Recent Snowfall
- 5-8 inches
- Snow Avail For Transport
- moderate amounts
Hatcher Pass received about 5-8'' of new snow in the 48hours previous to this avalanche. The day of the slide skies were mostly clear to partly cloudy. Winds on Marmot were light from the NNW.
Snowpack
About 5-7'' of new snow had fallen on an existing snowpack of loose facets, old wind slabs, and basal ice. Based on the charactaristics observed in the start zone, it's likely this avalanche was triggered within the old snow, likely near the buried wind slab.
Avalanche
This was a size 1.5, unintentionally skier-triggered slab avalanche that ran about 1000 ft. Regardless, it quickly and easily entrained the entire snowpack (which was shallow) in its path as it moved down the hill, failing on the October snow/rain bed surface crust.