Snodgrass Avalanche

CB Avalanche Center2014-15 Observations, Avi-map

Name: Brian Goldstein
Title: Snodgrass Avalanche
Location: Crested Butte Area
Date of Observation: 11/25/2014
Aspect: North East
Elevation: 11,000

Avalanches: Observed an Avalanche on the Northface of Snodgrass in between first bowl and second above the open pillow zone. Propagated 120 feet wide and was much bigger than the anticipated potential. Probably an R3D2.5. Ran approx. 500 feet into the terrain trap below snapping numerous small trees. Almost propagated an additional 40 feet, but stopped with a major crack on a knob above an adjacent gully. We were observing the terrain from sheltered trees about 5 feet from an open area on the ridge above the rock formations/pillows. Aspect was NorthEast. We stomped around above some convexities with no reaction. Deciding the terrain was unsafe we turned around, walked five feet into the trees and the slope was remotely triggered presumably from a small buried tree. Slid all the way to the ground. The storm slab, and slab from last week, slid on the weak faceted layer at the base of the snowpack, taking the entire snowpack with it. One other wumph was observed in the same area prior to the slide. The crown was approx 60 cm. Consistent crown with no obvious wind deposits, although this specific area is subject to wind loading due to its exposure and openness compared to the rest of the snodgrass trees. Slope angle averaged about 38 degrees as the starting zone.

Weather: Light to moderate winds. Moderate temps (21ish?). Snowing S1.

Snowpack: 60-100 cm

Remotely Triggered Avalanche on 11.25.2014

Catagorized : (SS-R2-D2-AS-O/G)

Observation from 11/24

CB Avalanche Center2014-15 Observations

Name: EM
Title: Ob from 11/24
Location: Kebler Pass Area
Date of Observation: 11/25/2014
Aspect: South
Elevation: 11,500

Weather: Weather – Cloudy skies with light snow falling. Air temps were 17 at trailhead and 8 at 11,500. Winds were light with moderate gusting. Observed a small bit of snow being transported by wind, but low visibility didn’t allow for good views in to the alpine. Ski tracks from Sunday were partially filled in at and near treeline.

Snowpack: Snowpack – while traveling off of skin track at treeline small amount of cracking with in the new snow was visible. Jumped on several steep roll overs with out any results. No collapsing either. Snow profile was dug at 11,500 on open, south facing, 32 degree slope. It showed 65cm snow depth. It was comprised of 30cm of 1-1.5mm facets at ground from earlier in november, a 5cm crust the formed from last weeks sunny skies, and then 30cm of new snow since saturday on top. Test results showed reasonable bonding between new snow and sun crust, no results from jumping on steep rolls or shovel shears. CT showed failures below the sun crust on taps from elbow. These were generally Q2. ECT results would not propagate across entire column only about 30cm and were irregular. It appeared as though there may have been a strong temp gradient directly below the sun crust leading to a weakening of the snow directly below it. But battery in thermometer died so no data.

11/24 Kebler Pass Observation

CBAC2014-15 Observations

Date of Observation: November 24, 2014
Location: Kebler Pass Area
Aspect (N/S/E/W, etc.): N-NE
Elevation: 9800-11400

Returned to the same zone as yesterday, see WD’s report from 11/23. An additional three inches or so and evidence of strong wind activity overnight. Observed some whoomphing and cracking at the top of the skin track on the ridge where there was lots of wind deposition. Pit at the top of the line we skied confirmed the additional three inches up high. Storm snow was still unconsolidated but ran easily on the old surface, we expected to see loose snow sluffing. Entire pack failed on the ground facets with considerable force. No signs of instability on decent of that line. On the second run wrapping around toward exit trees we observed lots of wind loading and a very defined wind slab of 6 inches or so which failed easily on rollovers.

2014-2015 Snow and Avalanche Gallery

CB Avalanche CenterGallery

Forecaster and user submitted snow and avalanche photos from across the Crested Butte Avalanche Center’s forecast area in Elk Mountains of Central Colorado.


Glide

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Glide IconRelease of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. The are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.

Predicting the release of Glide Avalanches is very challenging. Because Glide Avalanches only occur on very specific slopes, safe travel relies on identifying and avoiding those slopes. Glide cracks are a significant indicator, as are recent Glide Avalanches.

Cornice Fall

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Cornice IconCornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind lips of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

Cornices can never be trusted and avoiding them is necessary for safe backcountry travel. Stay well back from ridge line areas with cornices. They often overhang the ridge edge can be triggered remotely. Avoid areas underneath cornices. Even small Cornice Fall can trigger a larger avalanche and large Cornice Fall can easily crush a human. Periods of significant temperature warm-up are times to be particularly aware.

Wet Slab

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Wet Slab IconRelease of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very destructive.

Avoid terrain where and when you suspect Wet Slab avalanche activity. Give yourself a wide safety buffer to handle the uncertainty.

Loose Wet

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Loose Wet IconRelease of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.

Deep Persistent Slab

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Deep Persistent Slabs Icon

Release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer, deep in the snowpack or near the ground. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage. They commonly develop when Persistent Slabs become more deeply buried over time.

Deep Persistent Slabs are destructive and deadly events that can take months to stabilize. You can trigger them from well down in the avalanche path, and after dozens of tracks have crossed the slope.

Persistent Slab

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Persistent Slab Icon

Release of a cohesive layer of soft to hard snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

The best ways to manage the risk from Persistent Slabs is to make conservative terrain choices. They can be triggered by light loads and weeks after the last storm. The slabs often propagate in surprising and unpredictable ways. This makes this problem difficult to predict and manage and requires a wide safety buffer to handle the uncertainty.