AvySim

Slope Angle:

Snowpack:

Temperature:

Windspeed:

Precipitation:

Weak Layer?:

Slab avalanches generally occur at slope angles between 30 and 45 degrees. On steeper slopes, snow doesn’t typically accumulate enough to form a slab, while shallower slopes are not steep enough for the snow to slide downhill.

Too steep for snow to accumumulate enough to form a slab!

Not enough snow!

Wind Loaded: Release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. In the demo, wind transports snow from the left side of the mountain to right side. Notice the blowing snow off the summit ridge as well, this type of behavior can lead to cornice formation. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. 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. Typical wind loaded avalanche problems include cornice and windslabs.

Wet Slab: Release 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.

Persistent Slab: 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. A weak layer is essentially a layer with a weak bond to its overlying layer, making it easy for an avalanche to occur. 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.

Storm Slab: Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days following a storm. Storm-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.

Dry Loose: Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. Dry Loose avalanches are typically small especially when compared to other avalanche problems. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose dry avalanches include point-release avalanches or sluffs.