18-19

Skier trigger Deep slab Bear Basin

Bear Basin
Northern Madison
Code
HS-ASu-R3-D2.5-O
Elevation
9600
Aspect
NE
Latitude
45.34360
Longitude
-111.37900
Notes

A four person party triggered this avalanche on Saturday night at around 5:30...One of the members wrote: “It broke on the persistent weak layer underneath a hard windslab directly at my feet, a yard or so from the diagonal rock band near the top of the ridge. The crown was roughly 3 feet at skier’s left and 12 feet at the rock outcrop on skier’s right. The avalanche stepped down to the ground on depth hoar around 250 ft from the crown due to the energy of the first slide. One skier was still on the skin track far below us before the track cut into the fall line. Everybody made it out. I’m sure it was triggered because of the shallower snowpack near the rock band. Snow pits were dug and that persistent layer the original avalanche went on was found but wouldn’t propagate”

From different group on Sunday e-mail: "... we saw  a debris pile that had come down from near the bat ears couloir in bear basin, it looked good size and some dirt and small trees so we decided to get a closer look. It appeared that a group skinned up North fork trail..., bootpacked up bat ears couloir, skied it with no problems, and then decided to  skin up a  real rocky  thinner face  slightly east of the couloir, the skin track appeared to make it to the top of the ridge however there was only 1 downhill ski track and that left from low on the skin track.... N-ne slope guessing 9500-10k ft. Crown was between 1and 10 ft deep, average looked about 2-3 deep, down pretty close to the ground in a lot of  spots.”

From separate e-mail: "D2.5 avalanche on an NE aspect in Bear Basin in the Northern Madisons, 9600ft, there were tracks in the run out (covered by the debris pile)... running on basal facets. Terrain was very rocky, steep, and visibly wind loaded."

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Hard slab avalanche
Trigger
Skier
Trigger Modifier
u-An unintentional release
R size
3
D size
2.5
Bed Surface
O - Old snow
Problem Type
Persistent Weak Layer
Slab Thickness
36.0 inches
Vertical Fall
700ft
Slab Width
200.00ft
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

This deep slab avalanche appeared to have been triggered by skiers on Saturday (3/9) or Sunday (3/10). It shows the type of terrain to avoid in order to avoid triggering a big avalanche: Variable snow depth, complex and rocky. Photo: D. Sandberg

Northern Madison, 2019-03-11

This deep slab avalanche appeared to have been triggered by skiers on Saturday (3/9) or Sunday (3/10). It shows the type of terrain to avoid in order to avoid triggering a big avalanche: Variable snow depth, complex and rocky. Photo: T. Grande

Northern Madison, 2019-03-11

This deep slab avalanche appeared to have been triggered by skiers on Saturday (3/9) or Sunday (3/10). It shows the type of terrain to avoid in order to avoid triggering a big avalanche: Variable snow depth, complex and rocky. Photo: T. Grande

Northern Madison, 2019-03-11

GNFAC Avalanche Forecast for Sun Mar 10, 2019

Snowpack and Avalanche Discussion

<p>Since Tuesday steady light snow buried a weak layer of facets 8-16” deep. This weak layer does not exist on all slopes, but recent avalanches are evidence some slopes are unstable. Yesterday on Buck Ridge snowmobilers experienced a collapse and got unstable test results below the recent snow (<strong><a href="https://www.mtavalanche.com/node/20342">details</a></strong&gt;). On Friday near Cooke City Doug saw natural and human triggered slides that broke below the recent snow (<strong><a href="https://www.mtavalanche.com/node/20333">details</a></strong&gt;). On Wednesday a skier triggered an avalanche on Mt. Blackmore (<strong><a href="https://www.mtavalanche.com/images/19/skier-triggered-mt-blackmore">pho…;), and on Friday skiers in Hyalite saw recent avalanches and had unstable test results on this weak layer (<strong><a href="https://www.mtavalanche.com/node/20340">details</a></strong&gt;). Eric and I did not find this layer in the Bridger Range or Cabin Creek in the southern Madison Range (<u><strong><a href="https://www.youtube.com/watch?v=oSgQnpBdkj0">video</a></strong></u&gt;), and yesterday we&nbsp;did not find it in all three pits we dug in Hyalite (<strong><a href="https://www.youtube.com/watch?v=7YtcaZzw5MQ&amp;list=PLXu5151nmAvRNl9ku…;). Before riding steep slopes dig a couple quick pits to test the new snow/old snow interface. If it breaks stick to lower angle terrain.</p>

<p>Moderate southwest wind formed fresh drifts that can avalanche under the weight of a skier or rider. These wind slabs are easier to trigger where they formed over weak facets. Avoid steep wind loaded slopes, especially if you see cracking of the snow surface in lower angle terrain.</p>

<p>Sunshine today will be the most intense so far this winter. Wet loose avalanches are possible on steep sunny slopes. These can be deadly if they catch you above cliffs, rocks or other terrain traps. These slides can also trigger a larger slab avalanche (<strong><a href="https://www.mtavalanche.com/images/19/loose-snow-and-slab-cedar">photo<…;). Be cautious of travel below steep, rocky slopes that receive direct sun where wet slides can release naturally.</p>

<p>Avalanches breaking on weak facets near the base of the snowpack are unlikely, but have large consequences. Skiers north of Big Sky yesterday reported crowns of old slides that broke on weak snow deep in the snowpack (<strong><a href="https://www.mtavalanche.com/node/20346">photos</a></strong&gt;). Avoid heavily wind loaded terrain, and complex rocky terrain with variable or shallow snow depth (3-5 feet) (<strong><a href="https://www.youtube.com/watch?v=T0nc39kxm0A&amp;list=PLXu5151nmAvRNl9ku…;

<p>Today avalanches are possible and avalanche danger is rated <strong>MODERATE</strong>.</p>

<p>Use the <strong>Regional Pages</strong> under the Forecast tab to get a more detailed look at activity, snowpack and weather in the area you plan to visit.</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&gt;, email (<u><a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a></u&gt;), phone (406-587-6984), or Instagram (#gnfacobs).</p>

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