| What it is | Weak, faceted 'sugary' crystals at the base |
| Forms from | Strong temp gradients in shallow snow |
| Persistence | Often most of the season |
| Danger | Deep persistent-slab avalanches |
Depth hoar is a weak layer of large, faceted, sugary snow crystals that forms near the base of the snowpack, created by strong temperature gradients in shallow, cold snow. These poorly bonded grains can persist for much of the season and act as a stubborn weak layer for deep, destructive persistent-slab avalanches, making depth hoar one of the most dangerous structures in the snowpack.
This is general educational information, not avalanche training.
The base weakness
A classic weak layer in the snowpack behind persistent slab avalanches.
Frequently asked questions
What is depth hoar?
Depth hoar is a weak layer of large, angular, faceted snow crystals — often called 'sugar snow' because it's loose and grainy — that forms near the bottom of the snowpack. It develops when strong temperature differences across a shallow snowpack drive water vapor to recrystallize into these poorly bonded grains.
Why is depth hoar dangerous?
Because it's a weak, unsupportive layer at the base that can persist for weeks or the whole season, it acts as a sliding surface for deep, large persistent-slab avalanches. These deep slab releases are hard to predict and can be triggered unexpectedly, even from thin spots, making depth hoar a serious and stubborn hazard.
How does depth hoar form?
It forms when there's a strong temperature gradient through a relatively thin, cold snowpack (warm ground below, cold air above). This gradient drives water vapor upward through the snow, recrystallizing it into large, faceted, weakly bonded grains. Shallow, cold, early-season snowpacks are especially prone to forming depth hoar.
Sources
- Snow metamorphism — American Avalanche Association
- Weak layers — Avalanche.org