WOW. Baldy slide investigation

Date of Observation: 03/19/2023
Name: Zach Guy and Evan Ross

Zone: Northwest Mountains
Route Description: Snowmobiled to the south bowl of Baldy to get a closer look at the snowmobile triggered persistent slab from yesterday.

Observed avalanche activity: Yes
Avalanches: Huge! This was the biggest human-triggered avalanche that I’ve ever investigated and the most destructive slide we’ve seen this season since the Red Lady ran in early January. The crown was just under 2,000′ wide and ran about 1200′ vert, wrapping from south to southeast aspects near and above treeline. It is a hard slab that averaged about 5 feet thick. Some of the well-drifted areas were over 10 feet with a max crown depth of 15 feet. We estimate the debris pile was up to 30 or 40 feet deep. The snowmobiler remotely triggered the slide while ascending along a safe ridgeline. They weren’t sure exactly where the trigger point was; we estimate it was near a shallower spot near the top of the bowl, about 30 or 40 feet from the avalanche. We classified the avalanche: HS-AMr-R3-D3.5-O
Observed a handful of other small storm slabs and wind slabs that ran or were triggered sometime in the past few days, and one large persistent slab on a south aspect ATL near Avery Peak. See photos and details below.
Weather: Partly cloudy, mild temps, light winds with no transport observed.
Snowpack: The avalanche failed just above the March 10th crust, and was made up of drifted snow from the March 10th-11th storm and March 15th-16th storm. We dug one snow profile in a shallower part of the crown. See profile below. The weak layer is difficult to discern (~.5 mm rounding facets, 1F) and did not produce results in an extended column test. Grain sizes are slightly larger than the overlying slab, and one level of hardness softer than the overlying slab and underlying crust, both of which are pencil-hard. The snow surface at this location was 1.0 to 1.5 mm near-surface facets over a thin, soft crust.