Key takeaways
- A wind slab is a dense, cohesive layer of wind-deposited snow on sheltered (leeward) slopes.
- Wind packs the snow into a stiff slab that can sit poorly bonded over weaker snow beneath.
- Wind slabs are a common cause of dangerous slab avalanches.
- They form predictably on lee slopes and behind ridges — recognizing wind loading is key avalanche safety.
This is general educational information, not avalanche training. Take a certified course to assess avalanche hazard.
What a wind slab is
A wind slab is a dense, cohesive layer of snow formed when wind transports and deposits snow onto leeward (sheltered) slopes, packing it into a stiff slab. Because this slab can sit poorly bonded over weaker snow beneath, wind slabs are a common cause of dangerous slab avalanches.
How and where they form
Wind erodes snow from windward slopes and deposits it on leeward slopes and behind ridge crests, where it packs denser and stiffer than naturally fallen snow. So wind slabs form predictably in the lee of ridges, in gullies, and on slopes facing away from the prevailing wind — which is why wind direction is a key avalanche-forecasting factor. They can form quickly during windy periods, even without new snowfall.
After a windy night, a backcountry traveler notes the prevailing wind direction and recognizes that the lee slopes are now loaded with fresh wind slab. Feeling the snow turn stiff and hollow underfoot on one such slope, they back off and choose wind-scoured, lower-angle terrain instead.
Why they’re dangerous
A wind slab provides the cohesive upper layer needed for a slab avalanche, and it can be poorly bonded to the weaker snowpack below — so a skier can trigger and release it. Recently wind-loaded slopes are a frequent, serious avalanche hazard, and wind also builds cornices on ridge crests.
The bottom line
A wind slab is wind-packed snow deposited on sheltered slopes into a stiff, cohesive layer — and a leading cause of slab avalanches when it sits poorly bonded over weaker snow. It forms predictably in the lee of ridges and in gullies, even without new snow, so reading wind direction and spotting recently loaded slopes is core avalanche safety. When in doubt, avoid wind-loaded terrain.
Frequently asked questions
What is a wind slab?
A wind slab is a dense, cohesive layer of snow formed when wind picks up snow and deposits it onto sheltered (leeward) slopes, packing it into a stiff slab. Because this slab can sit poorly bonded over weaker snow underneath, it's a common ingredient in dangerous slab avalanches.
How do wind slabs form, and where?
Wind erodes snow from windward (exposed) slopes and deposits it on leeward (sheltered) slopes and behind ridge crests, where it packs into a denser, stiffer layer than naturally fallen snow. So wind slabs form predictably in the lee of ridges, in gullies, and on slopes facing away from the prevailing wind — which is why wind direction is a key avalanche-forecasting factor.
Why are wind slabs dangerous?
Because they create a cohesive slab — the upper ingredient needed for a slab avalanche — that can be poorly bonded to the weaker snow beneath. A skier or rider can trigger the slab, releasing it as an avalanche. Wind slabs can form quickly during and after windy periods (even without new snowfall), making recently wind-loaded slopes a frequent and serious avalanche hazard to recognize and avoid.
Sources
- Avalanche problems & snow science — Avalanche.org
- Avalanche education — American Institute for Avalanche Research and Education