Skies transitioned from clear in the morning to broken by the time we left at 3pm. Wind picked up late morning, with light-mod average and occasional strong easterly gusts.
Mar 26, 2023
|SS-Soft Slab||I-New/Old Interface||0.5ft||
The avalanche off the summit of Mt Lichtenberg occurred mid slope on a small slope at about 5800ft on a north aspect. I didn't drop down to it, as there was extensive hangfire above it. Investigating above the crown, I found soft but wind-affected snow, and a subtle layer of just-barely-detectable faceted forms above the old snow layer. Where I dug the old snow layer was only about 12cm, or 5" deep. About 20ft further down, where the crown was, the height varied from 15cm to 30cm (6" to a ft). It was a small slope, although the entry was steep, at 40-45°. The path was about 12m wide and 50m long. Debris was relatively shallow, probably only about a foot deep, aside from where it was pushed up against trees and 2-3ft deep in small areas.
We started on the SW side of Lichtenberg, working our way to the summit. Snow varied from a couple inches of low density snow over last week's crust and then the higher we went the deeper it was, about 6" of blower pow above 5000ft. Any subtlety that trended south-facing had a breakable 1cm crust with about 3cm of snow over last week's crust. We didn't make it onto direct south-facing, where I suspect the crust at the surface would have been a bit thicker at the start of the day. Surface hoar was present everywhere we traveled, but it was larger, up to about 4mm, at higher elevations.
Older wind-effect and drifts became noticeable at about 5000ft. Just below the ridgeline (5700ft) we first began encountering wind, around midday for us. We made our way to the summit, where the north-facing terrain looked extremely inviting- dry, low density snow that was minimally wind affected. We were short on time and were there to investigate an avalanche which was triggered off the summit the previous day, so were unable to search out and access a lower-angle entry to the north-facing snow.
I stomped on a few of the smaller cornices along the ridgeline, which only resulted in small sluffs. A few older and larger natural sluffs were present along the ridge.
Upon return, we mostly stuck to a slight northerly aspect, and we were in dry snow for over half of our descent. Lower down or if we shifted a little to the south, snow was moist-wet, which we hadn't detected at all on the way up. Very small slides were triggered on steep rollovers, only a few inches deep, running on the very solid crust from last week. In the trees, even at lower elevations, snow that hadn't seen the sun and/ or was on a north-facing aspect was still dry.
Comments: Suspect slabs to be most reactive on due north aspects, but could span wider and be more difficult to trigger.