Deep Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Unlikely
- Size
- 2–3
Recent Avalanches: On Saturday there were four snowmachine-triggered avalanches and two cornice falls on the backside of Seattle Ridge. No one caught. These were triggered remotely and were 6 to 12" deep. More info here and here. There was also a cornice fall into PMS Bowl on Magnum Ridge (pictured below). Down south in Seward there was a skier-triggered large wind slab avalanche on Mt Alice. The skier was initially caught then able to escape unharmed. We did not hear of any slab avalanches yesterday. Big thanks to everyone for relaying their respective information.
None of these avalanches occurred in the Summit Lake area. The last avalanche that we know of here was from Thursday/Friday last week on John Mtn. We are still hoping to get more information but it was likely a large natural that broke into those weak layers at the base of snowpack. This was during the strong east winds at that time. For today, keep you eyes peeled for wind loaded slopes. There could be some stiff old wind slabs to avoid along with the big open bowls that harbor those buried weak layers. Watching for red flags like shooting cracks and whumpfing is also key.
Sun Effect: The southerly slopes got quite warm yesterday as the sun broke through the clouds. There was also some 'greenhousing' going on making it feel really warm (one of my grad school advisors does a good job at explaining this effect HERE). We can guess these aspects are crusted over this morning but should warm enough again today to soften those sun crusts to some degree. Warming can also cause cornices to start peeling off and becoming easier to trigger so heads up.
Glide Avalanches: We're continuing to see glide cracks open and release every now and then. These avalanches are large and unpredictable, so the only way to manage this problem is to avoid spending time under cracks.
(2/20/2025)
Snowpack at 2,400' on Summit Mountain. Poor structure exists with a weak layer of facets below a large 3' slab.
Photo: Mik Dalpes