Half Moon 2.5

Avalanche date/time

Wednesday, February 12, 2020 at 17:00

Estimated occurrence time of avalanche

From 24 to 48 hours ago

Number of avalanches in this report

1

The size of avalanche

2.5

Slab width

30m

Run length

750m

Avalanche Character

• Deep persistent slab

Start zone aspect

• SW

Start zone elevation band

• Alpine

Weak layer crystal type

• Depth hoar

Wind exposure

Cross-loaded slope

Vegetation cover

Open slope

Avalanche observed in Half Moon on Thursday Feb 13. Steep alpine SW aspect subject to cross loading with a highly variable snowpack.

The highest crown line looked to be 20-30cm deep and about 30m wide and about 5m away from the ridge top. There were several deeper crowns in the couloir itself which appeared to be up to 1.5m deep and connected across the feature. It appears to have run on basal weaknesses. According to Google Earth it would have ran 750m with debris averaging about 80cm deep spread out over about 350m with the deposit being about 30-40m wide. We called it a 2.5 and aren't sure if it was a Na, Sr or Sa. That South facing ridgetop was about 40-150cm of depth hoar 2 weeks ago when I was last there. There was both sun crust and variable wind slab present on exposed aspects in Half Moon with the sun crust starting to become noticeable about 200m below treeline.

Uncertain if this was natural or skier triggered. That slope is very unlikely to get skied but its high enough on slope that someone traveling to the wisdom tooth may have triggered it.