• Maritime climates: Rare and usually in the early season. Image: Agricultural Research Service, U.S. Department of Agriculture Understand and Managing Depth Hoar: By: Eric Trenbeath When the first significant storm paints the peaks white and we’re getting stoked for winter, it’s time to start thinking about how that first layer will affect snowpack stability during the upcoming season. Common persistent layers include surface hoar, depth hoar, near-surface facets, or faceted snow. 2 Laboratoire de Glaciologie et Géophysique de l'Environnement, 54 rue Molière, 38402 - Saint Martin d'Hères cedex, France. Great to get some fresh air and excercise with @ross.hewitt and @tom_grant_ @salomonfreeski @salomon @smithopticsuk @smithoptics.snow @fatmap_official The water vapour is moving quickly , and crystal growth happens quickly . Depth hoar crystals bond poorly to each other, increasing the risk for avalanches. We therefore performed laboratory experiments with snow samples containing a weak layer consisting of either faceted crystals or depth hoar. From large temperature gradients between the warm ground and the cold snow surface. The following conditions promote faceting: Their message is one of warning, an early-season snowfall that will affect the layers of snow that will fall on top of this one for … Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Doug Chabot of the GNFAC finds the top six inches of the snowpack consists of near surface facets from the cold clear nights and warmer days. Good morning; this is Jeff Carty with the West Central Montana Avalanche Center’s avalanche advisory for January 2, 2021. At mid latitudes, mainly on shady aspects (NW-NE). These colder grains first develop sharp corners, then stepped facets. Surface hoar forms on cold clear nights - it is essentially frozen dew. Weak layer fracture: facets and depth hoar I. Reiweger and J. Schweizer I. Reiweger and J. Schweizer . The snowpack around Mt Emma is generally heavily wind affected and thinner than when I was in the area 3 weeks ago, except in the most wind loaded spots. Formed: During recent high pressure, near surface facets and surface hoar have formed throughout the advisory area. Relatively stronger in compression than in shear. Snow is a wonderful insulator and even with very cold air temperatures it’s common for the snow near the ground to remain damp for most of the season. The following conditions promote faceting: Toured up the Camas Drainage for a few days. Depth Hoar is common in Rocky Mountain climates, around large rocks and high shrubs, and where the snowpack is thin. Forecasting considerations: Depth hoar crystals bond poorly to each other, increasing the risk for avalanches. Near surface facets are smaller in size than depth hoar (1-2 mm) but they are quite pesky and can persist in the snowpack for long periods of time. The one main concern I have is we found striations and cups of depth hoar, leading me to believe the cold, clear week prior advanced the basal facet layer. The Colorado Avalanche Information Center released an early season snow update on their blog a couple of years ago, which still holds true today. Found some great facet holes, depth hoar, surface hoar, and even some sugar snow that you could pretend was powder. 2. Local collapses BTL in areas with 90cm of snow or more, five days after the storm passed. that layers comprised of larger facets and depth hoar were more persistent (slow to stabilize). Depth hoar crystals are large, sparkly grains with facets that can be cup-shaped and that are up to 10 mm in diameter. As the new snow builds depth and consolidates these layers are more likely to fail and propagate to larger areas. Depth Hoar is common in Rocky Mountain climates, around large rocks and high shrubs, and where the snowpack is thin. Loose, runs through your fingers, granular, crunchy when chewed. The process in reverse, however, occurs much slowly because it takes so much energy to create a faceted crystal that when we take the energy source away (the strong temperature gradient) it take a lot of time for the crystal to return to its equilibrium state (rounds). In my travels over the years in a depth hoar plagued mountain range, I've had to learn to scale back my expectations significantly. facets and depth hoar are more prone to failure in shear than. Contrary to popular belief, as long as the ground has an insulating blanket of snow, the ground is almost always warm–near freezing–even with very cold air temperatures. Persistence: Usually requires a thin snowpack combined with a clear sky or cold air temperature. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs. Depth hoar forms because of large temperature gradients within the snowpack. Percolating melt water in spring often re-activates large-grained depth hoar. Fascinating Facets of Eagle County Snow Country. Large gradients mean the snow will remain weak, small gradients mean the snow is gaining strength but it takes several days to several weeks depending on temperature. During these experiments the samples were loaded with different loading rates and at various tilt angles until fracture. We toured in the Southern Whitefish Range to try and get a better idea of the distribution of the recently buried surface hoar. 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