Human triggered avalanche on Ralston Peak below Cup Lake

This avalanche occurred on a steep sun-exposed, SE aspect at about 8600 ft. The snowboarder who triggered it was caught and carried over the rock bands seen in the photo. The initial report that he was buried was inaccurate. He was not buried and did not sustain any serious injuries. The slide released just above a cliff band in an unsuuported area of the slope. Due to continued human-triggerable instabilities in the area, I did not get to do a crown profile on the slide. I dug a pit on a nearby lower angle but simmilar aspect slope. This snowpit indicated that this avalanche likely involved the most recent storm snow failing on top of a sun crust that formed between last week's storms. Today's rapid warming weakened the snowpack to the point that adding a person to this slope caused it to break.

While skinning up to this slide, I triggered several "whumphs" on pockets of sun-exposed terrain that faced SE-S-SW between 7000 ft and 8000 ft.

Photo 1: Snowboarder triggered avalanche described above

Photo 2: A near by avalanche. It is unknown when it occurred or what triggered it.

A third avalanche also was noted on a nearby lower elevation slope. This slide likely occurred on Friday and was a natural release.

Pit: Snowpit from a simmilar aspect to the snowboarder triggered avalanche. I dug this pit in an area where I triggered a whump. It is slightly lower elevation than the slide.

Below is a first-hand account of this incident including lessons they learn from the incident from the party involved.

We were a party of three, two boarders and myself on skis.  All of us had avy gear.  The slab ripped at about 10:30.  One boarder was already down below the slide when it occurred.  He had to remove himself from harm's way as the debris was approaching him.  He was able to do so easily.  He traversed to the east, not wanting to descend too far in case we had to start a search.  I was above the cliffs but a bit to the east, on the other side of a snow spine on a slightly more easterly aspect.  I became aware of the slide when I saw a large plume in the air and felt the air blast.  I held tight, also not knowing if I would need to search for the victim.  I was not in a particularly safe spot, being below a convex roller and having been showered with rollerballs set loose by the first descender.  I was uneasy with my location even before the slide and was getting antsy to go down, but was still deciding on a descent line and waiting for the second rider to go down.  We did not want to have two people on the same slope at one time.   Soon after the slide stopped, the victim gave verbal indications that he was okay and then was visible boarding down the slope.  His board and lower legs were entrained, but he was able to extract himself.  He luckily sustained no injuries.  He was right in the middle of the cliff band when the whole thing pulled.  As can be seen in the photos, the crown was well above him, about 100' or so.  The jump turns necessary to navigate that cliff band were likely a contributing factor, especially within rocks likely to be possible trigger points. 

We did not dig a pit the morning of the slide, though it was discussed.  We were surprised to see such rapid warming of the snowpack and rollerball activity so early in the morning.  I had climbed and ascended the slope above Aspen Creek Tract, just to the west of Ralstonia, the previous afternoon.  I dug a pit that day on an aspect and elevation very similar to the slide site. I did a shovel shear test and found that the snow first failed approximately 8" down in a layer that was not detectable by just digging or running a finger down the freshly exposed vertical pit wall.  That failure occurred with about 4 medium hits.  Approximately 4 more medium blows produced a very clean failure on the buried ice crust approximately 16" down.  After re-reading your forecast my guess is that the initial failure within the soft snow above the crust took place at the interface below the slightly denser snow sitting atop the less dense snow right above the crust.  Our party stopped and evaluated the day-old pit as we passed it; we were using that skin track to ascend the mountain.  I noticed significant whumphing when I put in the track the day before the slide.  All whumphing took place that day in relatively flat areas.  It is my estimation that we would have heard whumphing the day of the slide had I not produced it the day before.  Perhaps we would have been just a bit more cautious had we heard it the day of the slide, who knows?

We did read the forecast the morning of the slide prior to leaving our car.  It was accurate in my opinion, and addressed many of the factors that likely contributed to our predicament.

Many factors likely compounded and contributed to the slide, but here a a few prominent ones that come to mind.

• Read any available avy forecasts very carefully
• Respect rollerball activity even though they are so common
• Respect the presence of obvious prior nearby slide activity
• Be aware that exposed rocks are often trigger points
• Don't linger on precarious slopes
• The type of turn you have to take may matter
• Don't become complacent because you have ridden a line before
• Riding ability should not trump avalanche concerns