Snow slab avalanche A diagram illustrating the structure of the snow ahead of the avalanche. Wind slab avalanches are caused by a cohesive slab of wind-deposited snow overloading the bond to an underlying weak layer or interface. Subject: Wind slabs. Cornices are often formed on steep ridgelines but may not be present on rounded ridge tops. We often hear people say, “I was just walking along and suddenly the snow changed. Go back the way you came or find another route that avoids wind slabs. Spatial Distribution and Variability: Wind slabs form lens shaped deposits of snow with thickness tapering off at the edges. A slab avalanche occurs when a layer somewhere beneath the surface layer fails, and the cohesive layer(s) above it fracture into a block (or blocks) and slide downhill (see Fig. Most avalanches occur spontaneously during storms under increased load due to snowfall and/or erosion. 7j.6). Wind slab avalanche. • Difficult trail breaking . This may occur at any elevation depending on winds. • Also called: “sastrugi”. Artificial triggers of avalanches include skiers, snowmobiles, and controlled explosive work. The section marked wind slab would have accumulated overnight, … Wind slab was created but is now bonded well. • What it means: Weight (snow) has been removed from snowpack and it usually means that the snow has become more stable than before. General Avalanche Advisory The mountains have received 10 to 14 inches of new snow since yesterday morning. Storm slabs are generally larger and more frequent in the alpine, where the wind can cause new snow to form into a slab, but they can also form in more sheltered areas. How to Recognize Wind Slabs: Ridgetop Loading: • Jump on a few safe, test slopes to see how the snow responds. These layers are slow to bond with surrounding snow and can linger for weeks or months. MODERATE avalanche danger exists today near and above treeline while LOW danger persists at lower elevations. Other natural causes include rain, earthquakes, rockfall and icefall. This cornice collapse and wind slab avalanche was thought to have been naturally triggered sometime during the storm in the early morning hours and was covered up by additional storm snow and wind blown snow. Wind Slab. • What you should do when you find a wind slab on a steep slope: • If the slab breaks away easily on your tests, don’t cross larger slopes. Avalanche Summary. Very reactive test results and shooting cracks on north facing slopes above 2000m. Wind slabs are often smooth and rounded and sometimes sound hollow. You can easily feel this with a ski pole or a snowmobile track punching through. • Also called: pillows, wind slabs, snow transport. Snowpack Summary. Side Loading: We avoided exposure to avalanche terrain, both overhead and on adjacent slopes. Solar warming was observed throughout the day. It is important to consider that even a small wind slab might be enough to trigger a By the time we skinned back up a larger slide D2R3 was present to the northwest along the steeper rocky entry to the playground. Often only a few inches separates safe snow from dangerous snow. Some of the content is updated by the USDA avalanche forecasters including the forecasts and some observational data. Wind: Humans who venture onto steep avalanche prone slopes at the mid and upper elevations could trigger soft slab avalanches and loose snow sluffs. • If you absolutely have to cross the slope (and I can think of damned few reasons why you HAVE to cross a dangerous slope without delving into B-movie plot devices), stay on the extreme upper edge of the wind slab, wear a belay rope tied to a solid anchor, and hope the crown fracture breaks at your feet instead of above you. Wind Slab Failure, Large Corinces, and ECTP's on a Test slope on Castle Peak - Duration: 1:01. • Feels Like: “slabby” i.e. Natural and human triggered wind slab avalanches will also be possible today near and above treeline. • Looks Like: smooth and rounded, lens shaped, pillow shaped, chalky-white color It was a small pocket, but above rocky terrain that and could have sent a skier down some steep sketchy terrain. Wind erodes from the upwind side of an obstacle such as a ridge and it deposits on the downwind side, and wind can deposit snow ten times more rapidly than snow falling from the sky. Don’t go any farther! However, winds are creating wind slab problems on steep leeward slopes. Wind slabs on specific loaded terrain features were reactive to ski cuts today. A cohesive layer of snow formed when wind deposits snow onto leeward terrain. Wind-drifted snow avalanched naturally in a few areas of the northern ranges yesterday (10/23). The delayed slab avalanche in question is a different beast. Upon beginning our tour back to the car, we noticed a natural D1 wind slab avalanche that probably occured during last night's wind loading. What direction the slope faces with respect to the wind is a HUGE factor. Persistent slab avalanches can spread out far and wide, making them very hard to escape. By the time they finally come to a rest on lee of an obstacle–where the wind slows down–they pack into a heavy, dense layer of snow that can easily overload any buried weak layer. • Falling through a harder surface layer into softer snow below. • Often notice: Significant wind transport was observed throughout the climb. (See Weather chapter on weather factors affecting wind slab development). A small (R1/D1) wind slab avalanche was snowboarder-triggered in steep rocky terrain on the east/southeast flank of Powder Bowl on Green Butte. Cornices were touchy and failed easily along the ridge causing wind slab avalanches in steeper terrain. (photo) If the weight has been added recently, and it’s on a steep slope without anchors, then it almost always means danger. Release of a cohesive layer of snow (a slab) formed by the wind. Several extended column tests around 2:45pm showed no propagation on similar wind loaded aspects and elevations. Remember that wind can blow from any direction and thus deposit snow on most any slope. Wind slabs usually do not affect the entire avalanche path, and wind slab avalanches are seldom larger than size 3. Wind slabs … Triggered a small wind slab D1R2 5-7cm crown upon entering playground (pictured). The crown was approximately 6 inches (15 cm) in height and spanned 20 ft. A slab can propagate for 10s or sometimes even 1000s of metres. Expect to see an increase in wind slab activity on Thursday. The avalanche was approximately 100' wide by up to 50' long. Storm slab problems are usually widespread, so they are best managed by staying out of avalanche terrain … Lucky for us, wind creates easy-to-read textures on the snow surface and characteristically shaped deposits. Avalanches: Spotted a few more recent persistent slab avalanches fitting the usual pattern. Wind slabs will be the primary concern on all aspects near and above treeline.These wind slabs will range in both size and sensitivity, from fresh and sensitive to older and more stubborn. • When strong wind starts to blow, within minutes, wind can turn nice fluffy powder into a dangerous wind slab. “He was taken by helicopter to Sion hospital where he succumbed to his injuries upon arrival. Looks like it was human triggered, as a track led into and out of the slide path. Avalanche Details: Avalanches and cracking in Frazier Basin. Several extended column tests around 2:45pm showed no propagation on similar wind loaded aspects and elevations. • Wind slabs can form in extremely localized areas. Dangerous avalanche conditions exist today. • Back off if you’re on a big slope and dig down to investigate how well the slab is bonded to the underlying snow (see Stability chapter) However, wind slab or storm slab avalanches may be able to trigger avalanches on these deeper layers. These exist on multiple aspects. A small wind lab avalanche was intentionally triggered on a north facing test slope at about 8000 ft with recent wind loading around 11:45am. Slab avalanches. Wind Slabs can have a longer lifespan than Storm Slabs. Written Report: Snowboarder triggered tiny R1 D1 wind slab at Tam Rim in ‘playground’ area. Winds blew from left to right. We had to manage for small windslabs that were easy to identify and avoid. Wind slabs vary in size but are generally limited to specific terrain features, such as the leeward side of ridgetops. Additionally triggering a wind slab today may cause older persistent slabs residing on weak, loose, degraded snow to step down causing larger more destructive avalanches. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind was also continuing to transport snow throughout the day, though it decreased from AM to PM. Up to 15 cm of snow falling in the south and west of the region Tuesday night came with moderate to strong southwest wind. Objectives were to assess the recent wind-loading and snowpack stability with close attention to the Dec. 9th and 22nd crusts and check on the weather station. • What it means: weight has been added to the snowpack. Wind Slabs are most reactive during a wind event and the first day or two after it has ended. Ridge top winds transport wind from the windward side of a ridge to the lee slope. Wind was also continuing to transport snow throughout the day, though it Some very weak and energetic wind slab setting up in the Les Contamines backcountry this afternoon. We call this “top loading.” But wind can also blow across a slope which we call “cross loading” and wind can even cause loading when it blows down a slope. Observation Date & Time or Estimated Date & Time of Avalanche: Description of Snow, Weather, and Avalanche Conditions: Other Signs of Instability (cracking, whumpfing, collapsing). The thicker part of the wind slab is usually deeper than the storm snow height measured in protected areas. • Feels Like: often hard snow and difficult to negotiate on skis, snowboard or snowmobile. Weather: Moderate ridgetop winds. • When strong wind starts to blow, within minutes, wind can turn nice fluffy powder into a dangerous An old avalanche hunter’s adage: If you have developed a good eye for slope steepness and the effects of wind, you can avoid about 90 percent of all avalanches. Photo: B. VandenBos. Fairy Lake. These wind-deposits, often referred to as “pillows,” are usually smooth and rounded and sometimes sound hollow. Persistent slab avalanche problems occur when a cohesive slab forms over a buried weak layer such as surface hoar or facets. Contrary to popular belief, avalanches are not triggered by loud sound; the pressure from sound is orders of magnit… No one should go into avalanche terrain without first learning how to read these obvious signs. A ‘wind slab’ avalanche took place and one of the skiers was carried away and buried by the snow. We couldn’t get any to move yesterday despite crowns from recent natural wind slab avalanches in the Rattlesnake. Solar warming was observed throughout the day. CB Avalanche Center November 21, 2014 Light Box Text. Lolo Pass had two concerning faceted layers Monday, 8” and 31” deep, that are currently being buried deeper. N aspect, ~7,100ft, 37-39 degree slope, crown was roughly 15” deep, about 20ft wide and appeared to slide on the melt freeze crust that was buried by the recent storm cycle. Look for areas where the wind recently has deposited snow, typically behind ridges, ribs and in gullies. No recent avalanche activity has been noted. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind Slab avalanche. Sierra Avalanche Center 1,951 views Found a lot of wind slab in terrain during our approach and in the butte itself. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below. Snow Conditions Avalanche Activity Travel Mode: Ski or Snowboard . • Hardness: can be very soft to so hard that you can hardly kick a boot into it. • Cracks shooting away from you–the longer the crack, the more dangerous. • Stop immediately! Our current round of snow will likely not be heavy enough to create problems today. The USDA is not responsible for any advertising, fund-raising events/information, or sponsorship information, or other content not related to the forecasts and the data pertaining to the forecasts. I also dug a pit on a more protected NE slope near tree line to take a look at the persistent slab problem. Timing. We toured into Silver Peak today on a route plan that kept us in sub 30 degree terrain and moved us through areas where we had intimate knowledge of both the current snowpack and the terrain. Bridger Range, 2020-10-24. Wind deposits snow most commonly on the leeward side of upper elevation prominent terrain features such as ridges, peaks and passes. High clouds thinned through the day. An avalanche is easier to trigger where wind slabs are thin or soft. Location. Gale force SW winds on the ridgelines were transporting intense amounts of snow onto leeward slopes. Avalanche Activity Travel Mode: Ski or Snowboard . Riding conditions changed from excellent to very poor over a period of two hours as the wind took a hammer to the powder. West-southwest winds have formed pockets of fresh wind slab on leeward aspects. Aspect: South East, South. Written Report: Toured up Tumalo from Vista, came up the ridge line around 2:00pm pst and saw the released wind slab. Some of these wind slabs were up to 2-2.5' deep in the most efficient wind loaded areas. I intentionally skier triggered a couple of SS-ASc-R1-D1-S, 6-18" deep, on some small wind loaded rolls. harder snow on top of softer snow. Remember that local wind effects will cause variation in where the wind slabs occur. The runout length was 30 ft. Windward slopes may show scoured snow and or exposed rock or grass. Wind slabs consist of snow crystals broken into small particles and packed together by the wind. Keep falling through the slab. Elevation: N/ATL. Snowpack: Rec skiing on southerly aspects to take a break from looking at persistent slabs. Higher areas will typically be scoured. • As the wind bounces the eroded snow across the snow surface, it grinds up the snow into small, dense particles. • Sound: often hollow like a drum–the more drum-like, the more dangerous It started cracking under my feet, and then the whole slope let loose.”. Low areas may look smooth. The slide was about 10-12ft wide and the crown measured 8-10 inches deep. During periods of very cold temperatures and extended wind events, Wind Slabs can persist for around a week. The bottom line: be suspicious of any steep slope with recent deposits of wind drifted snow. This website is owned and maintained by the non-profit arm of the Sierra Avalanche Center. We were able to trigger a wind slab avalanche on a small test slope, Southeast facing. Large and destructive persistent slab avalanches are our main concern and will be most likely on Northerly and Easterly terrain at all elevations. • Looks Like: has a sandblasted, scoured, scalloped, roughed-up look. Evaluate snow and terrain carefully if you head into the backcountry today and be wary … No avalanche activity observed aside from a mini wind slab (D1) ski-triggered on a test slope on a SE aspect and 5600’ elevation (Test Slope 2 - photo). When very safe conditions quickly turn into very dangerous conditions, it easily takes people by surprise. A small wind lab avalanche was intentionally triggered on a north facing test slope at about 8000 ft with recent wind loading around 11:45am. The one finger-hard slab failed on a density change above the new/old snow interface.. 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