Avalanche off NW chutes of Angora Peak (South Lake)

Location Name: 
Mini Hall Couloir
Desolation Wilderness Area (including Emerald Bay)
Date and time of avalanche (best estimate if unknown): 
Sat, 03/06/2010 - 13:30
Location Map: 
United States
38° 51' 47.4084" N, 120° 4' 32.844" W

Observation made by: Public
Avalanche Observations
Trigger type: 
Weak Layer: 
Avalanche Width: 
8 350ft.
Bed Surface: 
Other - explain below
Avalanche Length: 
1 350ft.
Number of people caught: 
Number of partial burials: 
More detailed information about the avalanche: 

Four skiers in party. With a LOW avy forecast, set an objective to ski a steep couloir - Hall of Gods off the N-NW side of Angora Peak (South Lake - Fallen Leaf Lake area). Hiking by 9:30, reached the base of Mini Hall Couloir to the skiers left of Hall of Gods by 11:00. Booted up the couloir to the ridge and skied down Hall of Gods Couloir. Had several green lights which instilled a positive affirmation in the group....both couloirs had naturally released the new snow layer from Wednesday. No whumping, cracking or slab activity noticed during the boot up the couloir. And both couloirs had been skied the day before. In addition, weather was favorable: temps were staying low throughout the day, little to now wind, no precip till later in day and after avalanche when light flurries started.

Hall of Gods had the "to be expected" sloughing when skiing down but otherwise stable...three skiers went down the central shoot and one down the far skier's right. We regrouped at the bottom, a.k.a.the bottom on the cirque's run out zone. Skinned back up and booted back up Mini Hall Couloir with intent to ski Mini Hall. Reached the ridge at 1pm. Skier #1 took a 40+ degree line of the left side of the couloir. Skier #2 started at the top of the chute proper. Skier #3 scooted out to a 50 degree slope off the left flank of the couloir. Skier #4 punched a bit further left out the ridge to ski a 55 degree flank. All flanks feed into the main chute. Skier #1 was out of the couloir and at the bottom of the apron above a rocky convexity about 800 feet when they heard "AVALANCHE!" Looking up in time to see two skiers at the exit of the couloir traversing hard skier's left with a huge powder plume rocketing down the chute. The cloud banked off a lower dog-leg and exploded out onto the apron. Skier #1 skied fast , downhill and hard right to get out of the path of the approaching avalanche. Skier #4 had triggered the event and rode the avalanche b/w 800-1000 feet to just above the rocky convexity before settling and being able to push their way out of the debris pile. They had been head down, under the snow tumbling the entire time. There was so much snow, billowing powder and debris moving past that Skiers #2 and #3 didn't even see Skier #4 rush by. When Skier #4 stopped, they were able to easily push their way to the surface clearing a heavily impacted nose and mouth reporting little to no visible injuries...no head trauma but had taken a rock to the right side and back. Skier #4 lost one ski and pole but recovered hat and goggles. No one else was injured, caught or lost gear. The avalanche ran nearly the entire length of the run out, within 200 feet (MR-BR). The avalanche would be rated a D2.

We did not hike back up to evaluate the crown or starting zone but here is our assessment...The skier reported being in knee deep powder when they saw the snow around them on the entering flank start to fracture. Observations during the boot pack around a rock outcrop, uncovered large facted crystals about 2.5 feet down probably at the Feb 19th layer. We propose that the avalanche, which started on the flank, was deeper than the new snow and most likely stepped down to a weaker, more unstable layer (Feb 19th). The flank was  a rocky covered slope and had enough room for five turns before it joined the main chute. The flanks had not naturally released like the main chute. Perhaps strong East and Northeast winds over the past couple days helped stick the snow in place to the flank but underneath, facets were forming near the rocks needing only a simple trigger like a skier to release. The dry slab hit the main chute but did not propagate across the whole couloir. it did not trigger another slab to release within the main chute. Instead, when the slab hit the main chute, it gained energy within the snow snow taking it down and out the couloir hence the big cloud of powder. The debris pile was lots of dry, loose snow and now big slabby chunks.

Lesson...even when the avy Danger is LOW, pay attention to terrain. Isolated pockets can still exist. Don't be too cavalier in your terrain choices. Remember the story of recent snow and weather and how that can translate to different aspects and terrain.

Weather Observations
Cloud Cover: 
75% of the sky covered by clouds