Small, deep avalanche triggered by the fifth rider on the slope (2/19/2019).
<p>Close to two feet of snow fell on high elevation slopes in the Bridger Range yesterday. During the snowfall, soft slab avalanches were easily triggered and ran long distances. Large avalanches can be triggered within the new snow today. The most sensitive conditions will be found where the new snow has been stiffened by wind. Pay close attention to the snow surface texture to identify these areas. With this much new snow, large loose snow avalanches (sluffs) are a significant hazard on slopes that haven’t been wind affected. On wind-loaded slopes, human triggered avalanches are likely and the avalanche danger is rated CONSIDERABLE. On all other slopes, the avalanche danger is MODERATE.</p>
<p>In the southern ranges, the primary concern is weak snow at the base of the snowpack. While avalanches on these weak layers are becoming less likely, they are still a very real concern. Monday’s large avalanche on Lionhead Ridge that broke 6 feet deep is a good reminder of the how big and dangerous these slides can be (<strong><a href="https://www.youtube.com/watch?v=SFA1kKs6wsw&t=0s&index=2&li…;, <strong><a href="https://www.mtavalanche.com/node/20160">details and photos</a></strong>). Assessing stability on deep weak layers is difficult. Avoidance is really the best strategy for dealing with them. If you do get into steeper terrain, stack the deck in your favor by using good travel practices to minimize the consequences of a slide: only expose one person at a time and watch your partners from a safe spot. Remember that tracks on a slope don’t mean it’s stable, particularly with these deep instabilities. The 1<sup>st</sup> rider or the 15<sup>th</sup> could trigger a slide. The avalanche danger today is MODERATE.</p>
<p>Wind-loading has created two overlapping concerns: one shallow, one deep. Recently wind-loaded slopes can avalanche 1-2 feet deep. An avalanche that caught and partially buried a skier outside Cooke City on Tuesday provides a perfect example of this concern (<strong><a href="https://www.mtavalanche.com/images/19/skier-triggered-avalanche-sheep-m…;, <strong><a href="https://www.mtavalanche.com/node/20159">details</a></strong>). A less widespread, but even more worrisome concern is avalanches breaking on slopes that have a heavy wind-load sitting above weak snow deep in the snowpack. We saw a number of these slides last weekend: on Buck Ridge, in McAtee Basin, and on Crown Butte (<strong><a href="https://www.mtavalanche.com/images/19/debris-slide-triggered-mcatee">ph…;, <strong><a href="https://www.youtube.com/watch?list=PLXu5151nmAvRNl9kuY3DxfWN1qiU7IeX9&a…;, <strong><a href="https://www.youtube.com/watch?v=GlOgKM58s-g&list=PLXu5151nmAvRNl9ku…;). Avoiding slopes with large cornices above them or thick pillows of hard drifted snow sitting next to scoured ridgelines is the best way to avoid triggered one of these large slides.</p>
<p>Whether the wind-load is recent or weeks old, wind-loaded slopes have a MODERATE avalanche danger. The avalanches danger is LOW on all other slopes.</p>
<p>If you get out and have any avalanche or snowpack observations to share, contact us via our <a href="https://www.mtavalanche.com/node/add/snow_observation">website</a>, email (<a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a>), phone (406-587-6984), or Instagram (#gnfacobs).</p>
Our education calendar is full of awareness lectures and field courses. Check it out: Events and Education Calendar.
BOZEMAN
February 22 and 23, Women’s Companion Rescue Clinic, 6-8 p.m. Friday at REI, 10-4 Saturday in the field. More Info and Register.
<p>It is snowing in the Bridger Range and 6” has already fallen with west winds blowing 20-30 mph. This will create 1-2 foot thick wind-drifts that will be easy to trigger. Newborn wind slabs are typically very sensitive and some will avalanche naturally. Loading will occur along ridgelines, or in gullies from mid-mountain winds. For today, the avalanche danger is rated CONSIDERABLE on wind-loaded slopes and MODERATE on all others.</p>
<p>Eric rode into Lionhead yesterday and saw a monster avalanche that was in full view of the highway. It was either triggered by a cornice fall or snowmobiler late Monday on weak, sugary facets at the base of the snowpack. In his video Eric explains how poor snow structure and heavy wind-loading contributed to this 6 foot deep slide (<strong><a href="https://www.youtube.com/watch?v=SFA1kKs6wsw&t=0s&index=2&li…;, <strong><a href="https://www.mtavalanche.com/node/20160">details and photos</a></strong>). With thick wind-loads it is difficult to impact the weak layer and a slope might have a dozen or more tracks before a sledder, skier or cornice fall triggers it. Thin snowpacks adjacent to these deeper slopes are potential trigger points. Although many slopes are stable, a few are not. Assessing stability on deep weak layers is difficult and the best tactic is to avoid them. They are the IEDs of the backcountry. For today, avalanches are still possible and the danger is rated MODERATE.</p>
<p>Yesterday, a skier triggered a large avalanche outside Cooke City on a northeast aspect of Sheep Mountain. It released 1-2 feet deep and propagated 400 feet wide into an adjacent path. The skier deployed his airbag and was partially buried and uninjured (<strong><a href="https://www.mtavalanche.com/images/19/skier-triggered-avalanche-sheep-m…;). He emailed us details which everyone should read <strong><a href="https://www.mtavalanche.com/node/20159">HERE</a></strong>. Yesterday, avalanches involving new and recently wind-drifted snow were triggered up Hyalite on Elephant Mountain (<strong><a href="https://www.mtavalanche.com/node/20149">photo and details</a></strong>) and a natural slide was seen on Mt. Fox near Goose Lake outside Cooke City.</p>
<p>An equally serious problem involves avalanches on heavily wind-loaded slopes releasing on weak, sugary facets in the lower part of the snowpack. Alex looked at 2 avalanches on Buck Ridge and McAtee Basin that were triggered on Sunday (<u><strong><a href="https://www.mtavalanche.com/images/19/debris-slide-triggered-mcatee">ph…;, <u><strong><a href="https://www.youtube.com/watch?list=PLXu5151nmAvRNl9kuY3DxfWN1qiU7IeX9&a…;) and Ian and I saw a similar slide on Crown Butte (<u><strong><a href="https://www.mtavalanche.com/images/19/avalanche-crown-butte-1">photo</a…;, <u><strong><a href="https://www.youtube.com/watch?v=GlOgKM58s-g&list=PLXu5151nmAvRNl9ku…; Slopes with thick hard slabs of windblown snow can be identified by cornices capping the slope or ridgelines scoured to the dirt. It is best to avoid them. Slopes with either recent wind-loading or a season’s worth have a MODERATE avalanche danger. Slopes that were not touched by the wind have a LOW danger.</p>
<p>If you get out and have any avalanche or snowpack observations to share, contact us via our <u><a href="https://www.mtavalanche.com/node/add/snow_observation">website</a></u>, email (<u><a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a></u>), phone (406-587-6984), or Instagram (#gnfacobs).</p>
Our education calendar is full of awareness lectures and field courses. Check it out: Events and Education Calendar.
BOZEMAN
February 22 and 23, Women’s Companion Rescue Clinic, 6-8 p.m. Friday at REI, 10-4 Saturday in the field. More Info and Register.
The crown on this slide ranges from 4-6' deep. It occurred on a heavily wind loaded slope and broke on facets near the ground. It's a clear reminder that large avalanches are possible in the mountains near West Yellowstone. Photo: GNFAC
This picture of the large avalanche on Lionhead Ridge was taken from Two Top Mtn to the south. Photo: P. Smith
From the email:
"At around 11 we ascended the slope north of sheep mountain and dug a pit at around 10,300’ on a NE aspect. Our pit was unresponsive. We skinned up to the summit of sheep mountain and dropped into the ENE spines directly off the summit. 3 turns into the slope, the entire 40° slope I was skiing propagated 12-18” deep and 250’ wide. I tried traversing out to skiers left to a clean slope but that slope then propagated even deeper, 18-20” and another 150’ wide. Once the larger slab started pulling my tips down I tried to point my skis downhill to gain some control and steer off the slope. Near the bottom of the face I had traversed onto there was a couple rocky outcroppings that I had to turn around, and the force of the liquid soft slab took me off my feet. I deployed my airbag pack, got hit with a couple waves of snow, and ended up on top with my skis and upper body/airbag above the snow. My partner above me had eyes on me for the entirety as well as a large group of sledders nearby, but it was still a scary experience. The bed surface was a hard crust that was not as obvious on the slightly more north aspect."
The crown on this slide ranges from 4-6' deep. It occurred on a heavily wind loaded slope and broke on facets near the ground. It's a clear reminder that large avalanches are possible in the mountains near West Yellowstone.
This slide occurred in the Lionhead area near West Yellowstone. It broke 4-6' deep, failing on facets near the ground. It's unknown if it was triggered by a natural cornice failure or by a snowmobiler. Either way, it's a clear reminder that large avalanches are possible in the mountains near West Yellowstone.
