Avalanche Details

Type: Hard Slab

Problem/Character: Wind Slab

Crown Thickness: 2-3 feet

Width: 300 feet

Vertical Run: 200 feet

Trigger: Foot penetration most likely*

Weak Layer: Hardness change

Aspect: NW

Elevation: 2,500 feet

Debris: 3-8 feet deep

Note: Much of the avalanche site was blown in with snow due to strong winds not only at the time of the avalanche but for the following day during our investigation. We were unable to find the burial site due to the wind blown snow covering much of the debris.

This was a hard wind slab avalanche with what appeared to be portions of cornice that also fell. It was estimated at 2-3 feet thick, 300′ wide and running 200′ down slope. Size D2. The slope was very steep near the top (~50-60 degrees) and around 30 degrees just above where the victim was buried. The weak layer is unknown but all signs point to a hardness change in the snow layering due to a significant wind loading event on December 7th, the day of the avalanche.

*It is still unknown if the hiker triggered the avalanche by walking out onto the slope or if it was a natural avalanche due to active windloading or a cornice fall while the hiker was below. The most likely case is the hiker triggered the avalanche.

WEATHER and SNOWPACK:

Intermittent snow showers and light winds during the week before the avalanche added between 4-8″ of new snow to the area. On the day before the avalanche, easterly winds recorded at the Glen Alps Near Anchorage weather station (2192′) rose to 10-20 mph with gusts in the 30’s mph as a warm storm was moving in. On the day of the slide, easterly wind increased to 30-35 mph with gusts near 50 mph. Additionally, a light rain/snow mix was falling and temperatures were warming into the mid-upper 30’s F at the avalanche site. The site is suspected to have seen stronger winds than the data from the weather station that sits ~300′ lower in elevation. These winds transported the new snow along with any additional loose older snow and built large drifts, wind slabs and cornices. Furthermore, the warming temperatures are believed to have encouraged this process by allowing the snow to bond together easier. The slide was triggered at the peak of the high winds and likely when the slope was the most unstable. The following day, severe wind effect was present and total snow depth in the area varied from no snow (scoured ground) to large hard wind drifts 6 feet or more thick.

Much of the avalanche site was blown in with snow due to strong winds not only at the time of the avalanche but for the following day during our investigation. We were unable to find the burial site due to the wind blown snow covering much of the debris.

Historical Significance: This avalanche path has slid earlier this season at least once as can be seen in a photo below from two days before the slide. The path is a common repeat offender for wind slab avalanches and cornice falls. It is in a notoriously windy area and sits on the lee side of the prevailing winds. There have been many close calls with people being caught in this path and one fatality in 2006 when a snowshoer was killed.