March 1, 2021
March 2, 2021
Zone or Region:
West slope Spiral Butte to Dog Lake
Did you observe any avalanches? Yes
Size 4: Could destroy a railway car, large truck, several buildings, or a substantial amount of forest
5500 ft initiation to runout at lake level 4200 ft
Avalanche initiated at about 3:10 - 3:20 PM estimated from approx 5575 ft elevation on Spiral Butte near top of avalanche chute where substantial snow drifts had formed adjacent on the north and fully crossing the chute. Initial observation was a very large outward poof/cloud of light snow. This ultimately extended about 250 ft down the slope and outward. Then, from beneath the aerated cloud of snow, a more dense and increasingly wet flow appeared. The flow gradually expanded laterally like an inverted V moving down the butte as adjacent avalanche chutes released and contributed their loads in a combined mass. All vegetation in the path at lower elevations was shaking violently, with some of the largest trees on the slope being snapped and transported downslope within the increasingly heavy/wet and churning flow. The flow continued like thick concrete into Dog Lake, accumulating possibly 20 to 30 feet or more into the lake from the shoreline. Depth at the shoreline and into the lake estimated at 20 feet high or more. Movement from first observation to settling may have lasted 3 to 4 minutes. The amount of material moved and accumulated was massive.
I was viewing from US Highway 12 adjacent to Dog Lake looking north-northeast.