Southern San Juan
AvalancheAnonymous · Mar 1, 2015 · Southern San Juan
Weather
Overcast with moderate snow, 1/2inch per hour. Visibility to 1/2 mile. High teens to low 20's through the day. Skiing on SW to E aspects during the day from 11100 to 11400
Snowpack
SW at 11100 above flat mountain yurt. 160cm snow depth. 85 cm new snow over old snow pack. Upper 45 cm were fist to four finger density and fractured SP at CT 7. New snow old snow interface fractured RP at CT 24. ECTX for both layers. Below 90 cm was rotten ice with basal facets. These were non reactive during the tests but the collum pulled ou easily E at 11400. High ridge above wolf creek. 210cm snow depth on lee slope. 120cm new snow with 40 cm of 1 finger hardness above new old snow interface. New snow old snow boundary fractured RP at CT 21. Rotten ice and basal factets below the old snow boundary were again un reactive perhaps due to the insulating effect of the new snow. The collum did pull out very easily.
Avalanche
On the same east aspect at 11400 ft but 1/4 mile south of the pit the third skier (me) triggered a 30m wide slide with an aprox 3 ft crown on a 37 degree slope. Before skiing the run a quick pit was dug down to the new / old now interface, and a cornise block was cut on an adjacent slope, neithe produced alarming results. The slide was triggered on the bottom 1/3 of a 200 ft run while the skier was maintaining speed to get to a exit point. The slope became significantly shallower at the ridge base slowing the slide and allowing the skier to ski on top of the moving snow and then ahead of the slide.The first two skiers report feeling the snow settle substantially as the slide started at the ridge top above the third skier and went to ground exposing many rocks. Simultaneously 20 m to the skiers left a second slide about 30 meters wide released on a large wind roll leaving a 10+ ft crown. This slide also went to ground. A third slide was also simultaneously triggered to the skiers left about a 1/4 mile away along the same ridge but with a NE aspect. This slide was not observed up close but looked to be 70-80 meter fracture with a 4-5 foot crown. After the slide some probing revealed that the snow pack thinned greatly to 60cm over an uneven talus field. It is likely that the third skier hit one of these shallow trigger points, perhaps primed by the first two skiers, and was able to collapse the factets be with the new/old snow interface. This could describe both the sliding to ground of the two slides in close proximity and the distant remote triggering of the third slide. This was a humbling slide to witness and substantially changed our risk assessment after skiing what hand proved to be nicely stable snow all day. Before this slide we had not even had to deal with sluff.