Remotely Triggered Avalanche Mt Emmons

CB Avalanche Center 2019-20 Observations

Location: Kebler Pass Area
Date of Observation: 01/17/2020
Subject: Remotely Triggered Avalanche Mt Emmons

Avalanches: Remote triggered one large slab avalanche. Crown depth was around 2′ deep, but we were in lower angled terrain above and couldn’t really see anything other than the crown since the terrain rolled out of sight below. Test slopes were easy to crack. Saw a couple of natural avalanches, but we could not make out how far they propagated in steep terrain because the visibility was too poor.

Weather: S2-S5 all day, with unrelenting westerly winds. Visibility remained poor.

Snowpack: Dangerous conditions developed by the afternoon. Soft, dense drifts up to 3 feet. The most dangerous snowpack we found was where 2-3 foot deep drifts built on buried melt-freeze crusts on southeasterly terrain near and below treeline (we didn’t get above treeline). Easterly-facing slopes without crusts had more load (3+ feet deep drifts), but seemed less hair-trigger. We observed many slope-wide collapses where drifted snow overloaded thin crusts with facets below, or even just overloading weak faceted layers in the upper snowpack. We measured 2.5″ SWE above a faceted crust on a lightly drifted slope at 11,400′. This 2.5″ SWE is the 2020 snow total and the weakness below was formed in late December. This ~30 degree slope collapsed and cracked but was not quite steep enough to slide. This seemed to be theme for the afternoon as we travelled through 20-25 degree slopes with widespread and obvious signs of instability. We extrapolated that we would have been likely to trigger a large avalanches in more consequential terrain.

A natural avalanche had run a short while before we approached this steep slope. We couldn’t see how far this slide propagated into the steep terrain that lies out of site.

This slope collapsed and we watched cracks shoot out beyond how far we could see. Where the slope rolls-over below a slab avalanche broke and ran out of site. The ~2 foot deep crown is just visible in the center of the image.