My partner and I went out this morning with the plan of skiing somewhere on the west side of Mount Nebo from Mona Pole Road. We read the avalanche forecasts for both the Provo and Skyline regions and checked the weather forecast beforehand. Our plan was to skin up Pole Canyon Road until we hit the drainage coming from Pole Canyon basin, go up the drainage to the basin, and pick a specific objective once we got to the bowl and could assess conditions. The main options we discussed were the NW Couloir, the Champagne Couloir, skiing just the bowl below the couloirs, or retreating from the base of the bowl if we did not like what we saw.

Below the base of the bowl (below 9400 ft) we observed 2-3 inches of fresh snow (mostly graupel) and little to no wind. We did note graupel pooling at the base of steeper slopes in the approach gully and discussed it as something to be aware of if a slab formed on top of it. When we got to the base of the bowl we experienced relatively poor visibility and NW winds at about 20 miles per hour. We also noted what appeared to be recent avalanche debris at the base and lower parts of the bowl. There was light to moderate snowfall, alternating between dense-moderately dense snow and graupel. Here the snow was getting blown around due to the lack of any shelter and the moderate winds. For the most part, the lower two thirds of the bowl consisted of about an inch of dense new snow on top of a firm but supportable base. Slope angles in the bowl ranged from the 20s at the bottom slowly steepening to around 30 degrees below the couloirs. We aimed to stay out of the main runout zone from the two most prominent couloirs, staying to the north and zig-zagging up the slope. As we got higher we began to come across more shallow windslabs and deep pools of graupel. We headed to the base of a rocky ridge separating two couloirs where we could discuss our options and perform more thorough snowpack stability assessments.

We dug a pit (WNW facing, 10,200 feet, 30 degree slopes angle) and conducted an ECT. We got an ECT18 on a density change 20 cm down and an ECT28 above a very firm pencil hard crust 75 cm below the surface, although neither failures propagated and the shears were not clean (of note is the very deep snowpack in the area we dug. My 300cm probe did not reach the ground. Our pit was 150cm deep and my probe still did not reach the ground starting from the base of the pit. HS is greater than 450cm in the area we dug.) We discussed our test results, our observations of windslabs and the lack of visibilty and lack of knowledge of what was going on above us in the couloirs. We decided not to ski any of the couloirs due to these factors but to venture a little bit higher and continue to assess the snowpack as we went. Here we were traveling across slopes in the low 30s in steepness with much steeper terrain in the couloirs above. We crossed slopes one at a time, keeping within view of each other and moving from safe zone to safe zone (our safe zones were the areas right below rocky ridges that separated the couloirs. We continued to note shallow windslabs, most not more than an inch or two thick.

We reached the ridge separating the Champagne Couloir and the NW couloir. I began making my way across the slope. I dug a shallow hand pit and isolated a column with my ski pole. A simple hand shear test revealed that the windslab was not well bonded to the snow below. At this point I made up my mind that I did not want to go much higher, as the terrain quickly got steeper with elevation and the windslabs seemed to be growing slightly thicker. I made up my mind to keep going to next island of safety, wait there for my partner, and discuss skiing back down the slope and not going any higher.

I crested a shallow ridge of snow and shortly afterwards was swept off my feet as the snow I was traveling over let loose. It all happened very quickly and I am unsure as to whether I triggered a windslab avalanche or if I was it by a windslab or loose snow avalanche from the couloir above. I was carried on my side with my skis facing sideways in a controlled manner. I screamed avalanche at the top of my lungs multiple times to alert my partner since visibility was not great, although he reported that he could both see and hear me. While I fought to stay in position and tried to self arrest on the bed surface the slope angle soon moderated and I began to slow down. Luckily I did not suffer any injuries and did not lose any gear. When I came to a stop I got up, traversed out of the runout path from the NW couloir and yelled to my partner that I was okay and for him to ski down to me. I would estimate that I reached a max speed between 20 and 30 mph. The avalanche was shallow and I was never pulled under the snow. The runout was also clean with no rocks or trees to hit. My partner and I estimate that I was carried between 200 and 300 vertical feet before coming to a stop.

With lots of overhead hazard we quickly skied down to the base of the bowl and then through the trees down to the road and back to the car. Below are my thoughts on the incident, as well as some relevant photos I attached.

Things we did wrong:

Terrain choice and lack of respect for overhead hazards. The relatively low winds and relatively low recent snowfall totals lured us into thinking that we could safely tour in some more committing high elevation areas on Nebo. Traversing under those couloirs was not a good idea given the past snowfall, moderate winds, and current moderate snowfall rates. It would have been much smarter to choose to ski in less high consequence terrain in areas where we could more easily assess the snowpack.

Lack of attention to aspect: Right before I either triggered or got hit by the avalanche I crested a shallow ridge of snow before entering the main runout from the NW Couloir. In retrospect I realized that the slope aspect shifted from NW to NNE. It makes sense that the slope was more wind-loaded than ones we had previously been traveling on due to the dominant westerly winds.

False assumptions/human factor: After seeing that much of the new snowfall fell as graupel and noting the deep pools below the couloirs I had mentioned to my partner that it I thought it was likely that not much of the new snow had stuck in the couloirs and may have used that assumption to justify travelling beneath them. Additionally, ski conditions were excellent and although I tried to keep it from being a major factor that may have played into my decision to push it a little bit higher and gain a bit more vertical of skiing.

Things we did right:

We took constant assessments of the snowpack and discussed them extensively. I think communication between my partner and me was good for the most part.

We did acknowledge that we were traveling across consequential terrain and thus moved one at a time across the suspect slopes. My partner had eyes on me and was ready to spring into action had he lost sight of me or if I had been buried.

I am grateful to be unharmed after this experience and hope that my report is helpful.

Photos:

1). Our pit, dug at 10200 on a WNW aspect, 30 degree slope. The two layers of note are the density change 20 cm below and the stout, thick crust 75cm below the surface. Of note is the widespread spatial variability that we experienced in this area. Just several feet to the side of this pit were large pools of graupel with <2 inch windslabs on top.

2). Photo I shot of my partner traversing to an area below the bottom of a rocky ridge from which I was watching him. Gives a good idea of terrain and visibility.

3). Shot of the debris pile from the avalanche after I traversed off it.

4). GPS track from my phone of our travels in the upper bowl. Although I would not put too much stock in the exact locations indicated you can clearly see where I was caught in the avalanche and then traversed out.

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