Avalanche Size Ratings

While waiting for the avalanche gates to open at 12-Mile yesterday, I was asked about avalanche ratings and it seems like a good topic as we wait for the clouds to clear.  In a previous forecast I had mentioned the likelihood of “D2’s during the current storm cycle.

Rating the sizes of recent avalanches takes a keen eye and knowledge of past events. It’s a simple exercise to add to you roving observations and in conversations with other practitioners of mountain travel.

Valdez has a number of indicator slopes,(paths that release first during an avalanche cycle) such as Snowslide Gulch at 16-Mile and Crooked Creek on Town Mountain. Many of us were here in January 2014 and experienced the Damalanche event. Snowslide Gulch along with dozens of other slopes in the region kicked out climax avalanches(rips out entire snowpack to the ground) and most were larger than ever witnessed or recorded for a particular path.

For instance, most avalanches in Snowslide are small relative to their paths yet would be destructive if they hit something. Most debris stays up in the “gulch” and rarely threatens the highway naturally or with bombs. Occasionally one crosses the river or dust the highway. I’ve seen a handful cross the road and climb the opposite hillside over my three decades of driving through that gauntlet. The Damalanche gouged the earth and was by far the biggest avalanche in recent memory or record. Thus it rates a D5/R5 and set the new standard for future ratings in Snowslide Gulch for those who note such things.  A lot of past slides in Snowslid rated as D5/ R5 or D5/R4 may need to be reclassified because of the Damalanche.

Today, for instance, a new avalanche came down Crooked Creek and I rated it D2R1. It was quite active in Airport Chutes also with multiple D2R1s

The overwhelming amount of avalanches we see are small relative their historic paths. They are typically wet slides or dry sluffs from recent storms. Slabs on the other hand are typically larger, more destructive and more D3R3 range  But a “harmless” D1/R1 could harm someone if it involves a terrain trap or a nearby cliff to be swept off.

I worked up this picture from the SWAG manual. Feel free to copy and use.