Sunday, March 9, 2014

A Perfect Storm

Good title for a movie eh? Oh yeah, that's been done before. Although I no longer live in Canada, I still lazily follow conditions there and it's obvious that there is a perfect storm of avalanche conditions brewing. Before the slab finally settles, there could be many injuries and fatalities. Already the tally of fatalities that can be attributed to the “drought layer” is beginning to tick slowly up. 

Avalanche dog working debris from a big avalanche

I haven't followed exactly the development of the “drought layer” or all the other dodgy layers in the current snowpack very carefully, but, this is one year when you don't have to have pored over weather maps, forecasts, trends, snow-reports and real time temperatures to know that things deep in the snowpack are not healthy. A strangely warm dry winter interspersed with long periods of cold clear weather followed by a more zonal flow with increased precipitation, wind and warm temperatures has left a big thick cohesive slab sitting on various persistent weak layers which are now very deeply buried and have the potential to propagate over large distances and run very, very big. 

60 cm crown slab

The first drought related fatality was in Waterton National Park in mid-February when a snowboarder was killed. The second just a week later at Kootenay Pass, the third and fourth near Lake Agnes in the Rocky Mountains, and, from the Purcell Mountains in early March, a snowmobiler has just died in hospital after a 2.5 metre burial. 

These kind of layers trick people as they don't occur to this degree very often so many people have never seen them before. Avalanche activity after a brief spike subsides, and obvious signs of instability disappear. Even digging snowpits to assess PWL's becomes difficult as they get very deeply buried necessitating both a lot of digging and knowledge of more advanced snowpit tests (like the deep tap test). Gradually skiers and riders push out into ever more serious terrain without tickling awake the dragon. This lulls everyone into a false sense of security. In other words, everything is fine until it isn't. A skier/rider or sledder somewhere hits a shallow spot, triggers the PWL and the entire mountain falls down. 

 Not a place you want to be right now

This is the year when you cannot be too careful choosing terrain that is low angle, safe from overhead hazard, avoids terrain traps, thin spots in the snowpack, rocks, gullies, etc. It might seem boring to spend the rest of the winter and the early spring meadow skipping but it's a lot less boring than lying in casket. 
March 19 Update:  Eight avalanche fatalities have now been recorded between 8 March and 15 March.  Two snowshoers in the Rocky Mountains and a snowmobiler in the Monashees on March 8, two tourists riding toboggans who were not recovered until a few days later also in the Rockies, a snowmobiler in the Purcells on March 11, another snowmobiler on March 14 in the Northern Rockies, and a skier on March 15 in the Rocky Mountains.  

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