Foley: Avalanche danger not over yet.
May 10, 2016
With this year's snowpack, spring skiing in backcountry areas like Rollins and Bethoud will last well into summer. While avalanche fatalities are most common during the snowy winter months, a significant percentage of deaths occur in spring and summer months, many due to wet snow avalanches. Climbers ascending or descending steep snow slopes or couloirs are also in potential avalanche danger.
Wet snow avalanches are a whole different animal than the common mid-winter dry slab or loose snow avalanches. They tend to move slower, their mechanics are different and they usually occur on warm or rainy days. Wet snow avalanches can occur either as sluffs or slabs and are just as unpredictable and dangerous as their dry snow counterparts.
These spring and summer snow slides are caused by water percolating through the snow as a result of rain, warm temperatures or radiation from the sun. The water reduces the strength of the snowpack or may totally change the mechanical properties of the snow either at the surface or at depth in the snowpack. Imagine water percolating in the depths of the pack, turning the consolidated snow that is attached to the ground, trees and rocks into a slurry of slush, more liquid than solid. Wet snow avalanches are not as easily triggered by humans so natural, sudden avalanches caused by the instability of the volatile, water saturated snowpack are a disconcerting danger.
Wet snow avalanches travel at speeds of 10-20 mph on moderate terrain, but almost as fast as a dry avalanche on steep terrain. They may start on shallower slopes and can travel further than their dry snow counterparts. Because they are denser than dry snow avalanches they can be quite destructive to trees, buildings or people in the slide path.
As with all avalanches, the potential of being swept through trees, rocks or over a cliff is a consequence to consider.
There are some clues that you can use to predict the probability of a wet snow avalanche. Number one of course, is the weather. Did it freeze last night? Are temperatures well above freezing? Are you on a south facing slope or bowl or couloir on a sunny day? Can you hear water running through the snowpack? Is the snowpack collapsing around you? All of these factors are indicators that you could be in the wrong place at the wrong time.
From this week's Colorado Avalanche Information Center forecast: "Watch for signs of wet avalanche activity such as rollerballs, pinwheels, and point releases in steep terrain. If you encounter any of these conditions, it is best to find a different, cooler, place to ride or simply call it a day." When the snow turns to slop it's not very fun to ride, anyway.
Don't let your guard down during your spring excursions. On warm days its best to start early and finish your run before the snowpack "falls out." East and south facing slopes will warm up first. Continue with standard avalanche terrain precautions by avoiding avalanche prone slopes, watching out for your partner and carrying a transceiver, probe and shovel.
One more caution; cornices. Cornices are the build-up of wind transported snow, usually on a ridgetop, that overhang the slope below. It's very tempting to venture out onto a cornice. Don't do it! Stay well back from the edge, preferably where you are on visible ground surface. The same factors –rain, warm weather and sun radiation – can make cornices weak and unstable. Totally unpredictable. Sometimes falling cornices will set off an avalanche when they land on a snow slope.
Spring backcountry riding, climbing and hiking is fun and challenging. By taking some simple, common sense precautions you can keep it safe.
Greg Foley is a member of Grand County Search and Rescue and has been a mountain rescue volunteer for 36 years. He can be reached by email at firstname.lastname@example.org. The GCSAR website can be found at grandcountySAR.com or on Facebook/GCSAR.
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