Reflections from an Active Snowpack
Just over ten years ago I went down to New Zealand to work what was then my second season forecasting and guiding in the country. I had taken a new job for a heli-accessed cat-skiing operation called Mt. Potts that operated on the land of an old ski area called Erehwon; a telling name as it is no-where spelled backward. It was quiet, as you would imagine and the mountains were big and steep. We just lacked one thing to get going for the season, snow.
Week after week past and it tried to snow here and there but the weather was really confused. Up high on the shady aspects the snow weakened into facets, then just as we were excited to see it snow again it decided to rain instead. When it cooled off the snow surface froze into a stout crust all the way up the mountain. A few days later another storm left a few inches of fluff on top of it all and then we were high and dry for a many days. Before it snowed again the snow on the surface (on top of the crust) became weak and sugary as well and we were left with a snowpack consisting of all weak snow aside from the our stout crust at ¾ height.
Eventually we got a bigger storm, perhaps 18” or so with a good amount of wind (as per usual in the area) and we had no trouble triggering avalanches. The first major one was triggered remotely just by driving the snowcat around a few hundred yards away. We desperately wanted to get terrain ready for the season so a day later we dropped several explosives from a helicopter trying to clean the place out. What resulted was one of wildest displays of hair triggered and sympathetic released slides I have seen. It was the sort of conditions that you anticipated triggering a slide with just the weight of the explosive landing on the slope, long before the explosive even has a chance to ignite. Many of the slides broke on the weak snow above the crust but some broke deeper.
We didn’t control everything we could have, as we still wanted some options for snow to ski on, so we left some of the lower angle avalanche terrain alone to be evaluated later. A couple days later I ran a guided cat skiing trip on low angle terrain but we didn’t have a lot of area to ski that wasn’t dangerous from an avalanche standpoint or just too rocky to ski and dangerous for those reasons. At some stage the company owner decided by his own rouge self to ski out into an area that we previously had deemed unsafe for travel and triggered a large avalanche similar to the cat triggered one a couple days earlier. He was lucky that the snow was still in a hair trigger situation because he triggered the slope remotely; out in front of him a short ways before he even had a chance to get fully onto the slope. Collected in a safe spot the slide ran past our group and piled debris a couple meters deep in a gulley to the side of us. I struggled to contain my words and used it as an example for my guests of what not to do to.
Another week or so past and with no more snow in the forecast the decision was made to pull the plug on the season altogether. Out of work before it ever really started, I did the natural thing and found somewhere I could still ski. Within a few days I learned through the grapevine that a ski area nearby, Mt. Olympus, needed a new forecaster/patroller as their #2 guy had been badly injured in an avalanche doing mitigation work. They needed someone to help run the place as only their #1 patroller remained (the ski area only had two patrol positions). Within a few hours of first talking on the phone with them I was riding up their rope tows by starlight to join their small team.
With the passage of a couple more weeks and a bit more new snow since the last acute avalanche cycle the near surface slab in the snowpack (where it still remained) had consolidated some and avalanche activity became more sporadic, though still severe. Most of the ski areas in the region continued to use explosives and had mixed results and some terrain was opened which allowed for some reasonably good skiing. A few days after control work and the opening one large piece of terrain on Mt. Hamilton, Craigieburn ski area had a very large natural avalanche there, fortunately missing any skiers. It was a puzzling event and left everyone in the area struggling for any understanding. As with this slide and several others, which ran around this time, reports were made of a large crack and boom type sound when the slopes failed at the start of the slide. Slides had started breaking below the rain crust more than not and the sound was the crust breaking and reverberating across the mountainside. The crust seemed to have made it harder for slides to be triggered but when triggered the crust help link together larger pieces of terrain than normal causing some exceptional events.
Another couple weeks past and a mild spring storm affected the area with lots of rain and mild temperatures. Avalanches became widespread with a mix of point releases and slabs breaking at the ground in a sloppy mess. At Olympus we even had one slide break into previously skier compacted (surface snow) ski terrain, effectively removing moguls and leaving only dirt and rock behind. By the time it cooled off again winter was gone and so was the season.
This year here in Utah lets hope it does pan out like NZ ‘07 but we have a similar recipe early. Currently we have a weak snowpack capped with a crust and a little snow on top. It’s too far into the season for all the snow to melt on the protected aspects to start over and the snow is too shallow to gain any strength. This isn’t the first time we have seen a set-up like this here in the Wasatch, in fact several seasons have been similar. Per-say, variable weather isn’t unusual here in the early season. It seems like even in dry years, though, we still get enough snow to work past early season troubles eventually, but who knows. Rain crusts are a trouble spot; they encourage facet/weak snow development and do so quite persistently due to their durability and resistance to metamorphose. Crusts add slab integrity, for better or worse and can also act as a profound sliding surface allowing avalanches to run quite far.
So what do we need now to fix our troubled snowpack? Lots of snow, but that’s a somewhat optimistic wish. In the short term there would be some profound instability with a few big storms but we do need to reverse the adverse temperature gradient currently at work in the snowpack and start the healing process. It’s likely that it will snow but it would be best if we get lots of snow quickly to stress test the snowpack, then have it keep snowing to bridge out the instability until eventually the weaknesses dissipates under more favorable conditions. Even under the best case scenario I think it is unlikely that we will have a deep stable snowpack before late January this season. This doesn’t necessarily mean we won’t have good surface snow quality for skiing before then though. I think it is actually fairly likely that we will still have very good skiing on lower angled slopes in the early and mid winter as long as it snows even a modest amount. Our Wasatch snowpack is setting up to be an exciting one, filled with ample opportunities for learning! Lets hope it’s a better winter this season here than it was in New Zealand in 2007. Pray for snow!
#Utah #Backcountry #Guiding #Ski #Wasatch #Snowpack #Weak #Layer #Persistent #Facets #crusts