Northern Gallatin

From obs: "Skied Mount Blackmore today (3/27/21). Saw a natural avalanche on Alex Lowe peak just south of the Hellmouth...". Photo: M. Lavery

From obs: "Skied Mount Blackmore today. Saw... 4 skier triggered slides on the E face between the Blackmore and Alex Lowe Basins. Most appeared to be wind slabs... " Photo: M. Lavery

My partner and I observed a deep slab avalanche in Blackmore Basin that appeared to break on the depth hoar near the bottom of the snowpack. It was on a wind loaded NE facing slope at approx. 9,500 and looked to break on a slope in the 35-40 degree range. The crown was about 8'-10' deep and 200' wide. It broke to the ground and ripped out several small trees.
As soon as we saw it, we came over a small ridge to see another skier near the debris. According to him it was triggered remotely by one of the two skiers on the coming down on the lookers right of the slide (in the second photo). We confirmed that a beacon search was done to make sure no one was buried.
Earlier in the day we dug a pit near the summer on an east facing slope and got no results. After seeing this we avoided avalanche terrain and took a low angle route down. We were glad no one was buried and found some great snow!

We had a great tour, dug a pit on the East Side of Flanders BTL around 8700. Overall the snowpack seemed fairly stable, finding no signs of instability while skinning. But, we definitely found a concerning crust at 160 cm that was very thin on the NW slope we dug on, but noticeably stouter and shallower on a more southerly slope we skinned to. We had two failures in our ECT, both with no propagation outside of the shovel width, one ECTN16@185cm with medium-poor fracture quality. The other was ECTN23@160cm right under the small crust; it had medium fracture quality, no propagation. W had no other signs of instability, just minor sluffing in the top 10cm while skiing. We dug 120cm total of 205, all of it was dry. Great skiing today!

I and one friend observed the remains of a natural avalanche below the north facing headwall up Flanders creek. It looked as if it happened within the past few days. I didn’t get close enough to really gauge the size in width but it propagated at the ground. The crown looked to be 3’-4’ deep. We tucked tail and ran after we saw this and didn’t investigate further.

Skied Mount Blackmore today. There was a lot more new snow than expected (6-8") and ridgetop winds were strong and gusty. Snow along the ridgelines and on E-facing slopes was touchy. Lots of cracking and collapsing. Dug a quick pit on a SE face at 9600ft and had a reactive density change within the recent new snow about 20cm down from the surface.

Saw a natural avalanche on Alex Lowe peak just south of the Hellmouth, and 4 skier triggered slides on the E face between the Blackmore and Alex Lowe Basins. Most appeared to be wind slabs, but around 1 pm a skier remote triggered a deep slab from ~50 feet away (around the corner lookers right in the attached picture). Broke at the ground, 10-15feet deep, and took out a small tree.

Ian and Dave stop to do a quick stability test as they hunt for a layer of weak snow 1-2 feet under the surface. Photo: GNFAC

21 March 2021: A pair of skiers triggered this slide on the east face of Mount Blackmore. No one was caught. Photo: Anonymous