The good folks from Bridger-Teton Avalanche Center travelled out to Lava Mountain in the Togwotee Zoneto check out the aftermath of a massive human triggered avalanche that they hope was an outlier event.
This slide was triggered from the ridgeline above when a snowmobiler stepped of their sled to take a photo. The crown averaged 5 feet deep with wind-loaded sections up to 10 feet deep. The crown width was 800 feet and it ran 470 feet. This Destructive Size 3 avalanche illustrates the fact that weak layers near the base of the snowpack are still capable of producing avalanches in the area.
If you plan on heading into the backcountry in western Wyoming please stay up to date on all avalanche information at bridgertetonavalanchecenter.org. Read observation summary below.
Bridger-Teton Avalanche Center Observation Summary:
We rode up to the Lava Mountain Overlook to investigate an avalanche triggered by a rider on the ridgeline above a steep, E-facing bowl off the Lava Summit. This avalanche was triggered from a slightly shallower spot on flat ground but with a well-connected hard slab. The resulting avalanche crown ranged from ~3 feet to over 10 feet tall, primarily composed of wind-compacted snow. The west face of Lava Mountain is almost entirely clear of snow (all dirt), and it is pretty clear that that snow was transported onto the E side of the peak, forming a variable depth hard slab. Around a third of the snowpack was recent snow from 1/31 onward. The middle half of the snowpack was composed of rounding NSFs from the January dry spell and everything to the ground below that was weak, faceted snow and depth hoar. The avalanche spanned around 800 feet in width and produced hard results in an extended column test (ECTP29, PST 20/100 End) at the shallowest spot. Areas where this problem lurks in Togwotee are rocky, wind-affected, upper-elevation terrain, primarily on the north half of the compass (W-N-E).
Aspect: E
Aspect Range: SE, E, NE
Slope Angle: 38°
Elevation: 10400 ft
Vertical Fall: 470 ft
Destructive Size: D3
Relative Size: R4
Type: HS-Hard Slab
Problem Type: Persistent Slab
Bed Surface: G-Ground
Weak Layer Grain Type: FC-Faceted Crystals
Slab Thickness: 350 cm (11.5 ft)
Width: 800 ft
Trigger: AM-Snowmobile r-Remote
Terminus: BP – Bottom of Path
