Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 1–2
There are just a few inches of new snow to blow around in Summit Lake, but the wind always finds a way to make new slabs despite a seemingly low amount of snow available. Especially in wind loaded places, a slab may be forming that is thick enough, which combined with a human-trigger, could overload the layer of buried surface hoar that may be 1' deep or more. The distribution of the buried surface hoar is spotty, which makes this problem difficult to predict. Snowpits are less reliable as a way to determine the stability of a particular slope as a result of this spotty distribution. The tricky nature of this problem is illustrated by the human-triggered avalanche that occurred Monday, March 17 on Seattle Ridge. See video below for the story. The summary is that there were 30 tracks already on the slope and 2 snowpits were dug with stable results within close proximity to a large human-triggered avalanche.
This layer isn't as big of a problem in Summit Lake yet because there is not enough snow on top of the buried surface hoar to overload the layer in many places. Sticking to safe travel protocols like choosing low angle up routes and traveling one at a time in steep terrain will reduce chances of an accident if we find the wrong spot. This layer did get overloaded by a person on March 3rd on the north side of Tenderfoot. This was in a small gully that was being actively wind loaded at the time of the avalanche. The avalanche was not likely big enough to bury a person, but it may have injured them if they had been caught.
The photo to the right illustrates some of the recent natural avalanches that have occurred on the northern border of the Summit Lake area in Lynx Creek. The buried surface hoar in this area has a bigger slab on top, which makes it easier to trigger either naturally or by a person.
Cornices: Warming temperatures over the last few days may be weakening cornices. Include cornice avoidance in the route plan, whether it's giving them space on the ridge or watching out for them from below.
Glide Avalanches: Within the last 2 days, some movement in the massive south facing Cornbiscuit glide crack (in Turnagain Pass) triggered a few storm slabs (see photo below). Avoid spending time underneath glide cracks or reduce exposure by spreading out or moving one at a time if they are unavoidable.
(3/17/2025)
Several generations of avalanches in Lynx Creek. Some of these were 500-1000' wide.
Photo: Andrew Schauer
