Southern San Juan
SnowpackChris Bilbrey · Jan 14, 2024 · Southern San Juan
Weather
Periods of moderate to heavy snowfall. Skies broke late-morning with a few pokes of blue, but then socked in for the rest of the day. Winds were generally light up to about 11,000 feet increasing to moderate along ridges and near treeline. A few gusts sounded like a jet engine flying overhead.
Snowpack
The snowpack was talkative today. Southerly-facing slopes producing loud, rumbling collapses on one of many faceted crust below, and northerly and easterly-facing slopes produced similar moments where very weak, near-surface facets sit below snowfall since January 4. Extended Column Tests (ECTs) on a south-southwest aspect around 10,200 feet only yielded non-propagating failures in facets below crust. This was after we observed a collapse and saw surface cracks. Total snow depth here was around 60 cm and the overlying slab is still shallow and soft at lower-lower elevations. This changed quickly as we climbed above about 10,500 feet - total snow depth and slab thickness above persistent weak layers increased dramatically. We dug our next pit on a southeast aspect around 11,000 feet and observed propagating failures below a faceted crust with 18 taps. The new snow was also slightly more cohesive and we started to find reactive, shallow storm slabs. These did not propagate in ECTs, but we could easily trigger them in hand pits and on small, steeper test slopes. Walking above a heavily wind-loaded ridgeline near 11,400 feet, we observed countless rumbling collapses and cracks shooting outward around 50 feet. This particular area got scoured by strong winds around January 8, and the slab above near-surface facets that formed around the New Year was about half as deep as lower down the slope. ECTs here failed with 12 and 14 taps and highlights that finding the shallow part of the slope increases the chance to trigger a larger, more dangerous avalanche. The lack of visible natural activity suggest two things - 1) The new snow load does not appear to have pushed many slopes past their tipping point. 2) The bigger question begs to be asked...what will it take for the slopes that did not naturally avalanche to avalanche? Lots of places now harbor deep slabs resting above very weak snow layers. The final push could come from ongoing wind-drifting adding more stress to weak snow below, or a rider or machine finding the shallow trigger spot. Regardless, careful snowpack evaluation and terrain management seems prudent moving forward.