By SP Parker

I live in the Sierra Nevada and own a mountain education and guiding company and am writing to warn about the conditions I’m seeing this week above my home. This is turning out to be a worrisome period. It’s a year of above-average snowfall, late snowfalls, high water runoff, delayed runoff; and right now, a significant avalanche hazard that you need to consider.

On June 4, I hosted our staff training in Rock Creek Canyon and found evidence of recent avalanche activity. The type of avalanches we saw were “wet slabs” up to a D3 plus size, on north- and east-facing aspects at 11,500 feet. The Eastern Sierra Avalanche Center has closed for the season, but you’ll see similar observations on its website. With concern for people on the PCT and in the mountains, I am offering a few warnings and pieces of advice, but first, a little more about D3 plus wet slab.

Avalanche Canada (2010) states: Wet slab avalanches are caused by a thick cohesive slab of snow losing its bond to an underlying thin weaker layer or interface after becoming damp, moist, or saturated with water. Wet slab avalanches are generally slower moving that dryer slab types, tend to flow in channels, and are easily deflected by irregularities in the terrain. Wet slabs are often highly destructive due to great mass created by the high-water content of the snow.”

The D scale rates the destructive potential of an avalanche. According to the American Avalanche Association (2016), a D3 avalanche: “Could bury and destroy a car, damage a truck, destroy a wood frame house, or break trees.” The “plus” on D3 means the upper end of the rating. For perspective, the smaller D2 rating is defined as being enough to “kill, bury or injure a backcountry traveler.”

Learning about avalanches is a life-long avocation. They are difficult to predict and evaluate.

What you’re reading here is just a quick primer and is barely scratching the surface. Just keep in mind:

Wet slab avalanches will most likely occur as temperatures increase and as solar radiation warms a slope.

Most avalanches start on 30- to 35-degree slopes with 37º being the most optimal angle. But avalanches can run out onto much lower angled slopes so one does not have to be on a steep slope to be buried. Having a steep slope above you can be as much of a danger as being on the slope. The Pacific Crest Trail crosses on and below slopes that are steep enough to avalanche.

Wet slab is not the only avalanche type to be concerned about. There are also wet loose avalanches that will happen as individual snow grains lose their cohesion and come down as a wet mass. PCT hikers have been posting photos of those this week. Then there are glide avalanches where the whole winter’s snow mass slides down on the terrain underneath. This is a particular problem where the underlying terrain is a smooth rock slab – such as High Sierra granite.

There are cornices to consider. These are overhanging pillows of snow on ridges and passes, formed and compressed by the wind. Every cornice has its day and will fall. Don’t be there when it does.

What you should do about the current avalanche conditions in the Sierra Nevada.

Be aware of the potential for avalanches even though it is no longer winter.

If you don’t like what you are seeing when approaching a snow crossing that has the potential to slide, then don’t do it. Set up camp and wait for cooler temperatures, when snowpacks are more stable. Continually reassess your trip and decide if it is worth the risk. The trail and the mountains will always be there; make sure you are around to enjoy them.­­­

Be aware of the effect of the sun and changing temperature as the day progresses. If you are feeling hot, so too is the snow.

Travel up and across steep slopes and high passes early in the day, before the snow gets wet and gloopy.

Move quickly across slopes and from underneath slopes without delays and stopping.

Look for wide cracks developing in the snow on steeper slopes. These could be indicators of a glide avalanche getting ready to happen.

A cornice can break a long way back from its lip so just stay away. Do whatever you can to avoid being underneath cornices.

Just because someone crossed a slope before you do not get lulled into a false sense of security. Maybe they just got lucky.

Be safe, have fun.

Originally from New Zealand, SP Parker has been a resident of the Eastern Sierra for nearly 40 years. He is the owner of Sierra Mountain Center, is an internationally certified IFMGA guide, teaching avalanche courses for AIARE, and guiding in the mountains nationally and worldwide. Located in Bishop, California they offer rock climbing, summer mountaineering, waterfall ice climbing, backcountry skiing, emergency training, summer and winter instruction, and custom guiding in the Eastern Sierra of California.

References

Haegeli, P., Atkins, R., and Klassen, K., 2010. Auxiliary material for Decision making in avalanche terrain: a field book for winter backcountry users. Avalanche Canada, Revelstoke, B.C. Accessed at www.avalanche.ca.

American Avalanche Association, 2016. Snow, Weather, and Avalanches: Observation guidelines for Avalanche Programs in the United States (3rd ed). Victor, ID