Key takeaways
- Depth hoar is weak, sugary, faceted snow crystals near the base of the snowpack.
- It forms from strong temperature gradients in cold, often thin early-season snow.
- The crystals bond poorly, creating a persistent weak layer that lasts weeks or months.
- It's a leading cause of dangerous, hard-to-predict slab avalanches.
This is general educational information, not avalanche training. Take a certified avalanche course to assess the snowpack.
What depth hoar is
Depth hoar is a layer of large, weak, faceted snow crystals — often called ‘sugar snow’ because it resembles loose sugar — that forms near the base of the snowpack. These crystals bond poorly to each other, making depth hoar a fragile, unstable layer.
How it forms
Depth hoar forms from a strong temperature gradient in the snowpack — typically when the snow is shallow and the ground is relatively warm while the surface is very cold, common in early-season and cold, dry climates. This gradient drives water vapor to recrystallize into large, angular facets that lack the bonds to hold weight.
Digging a snow pit, a backcountry traveler finds a layer of loose, sugary crystals near the ground that collapse easily — depth hoar. Knowing a cohesive slab sits on top of this persistent weak layer, they avoid steep, avalanche-prone slopes entirely.
Why it’s so dangerous
Depth hoar is a persistent weak layer that can lurk in the snowpack for weeks or months. A cohesive slab over weak depth hoar is a classic recipe for a slab avalanche — and because the weak layer is deep and persistent, these avalanches can be large, hard to predict, and triggered remotely. It’s a key reason some snowpacks stay dangerous all season, underscoring why avalanche education and carrying a beacon, shovel, and probe matter.
The bottom line
Depth hoar is the snowpack's hidden saboteur — weak, sugary faceted crystals near the base that bond poorly and can persist for months. As a buried weak layer beneath a cohesive slab, it's a classic trigger for large, hard-to-predict slab avalanches, and a key reason some snowpacks stay dangerous all season. Recognizing it is core avalanche-assessment knowledge.
Frequently asked questions
What is depth hoar?
Depth hoar is a layer of large, weak, faceted snow crystals — often described as 'sugar snow' because it resembles loose sugar — that forms near the bottom of the snowpack. These crystals don't bond well to each other, so depth hoar forms a fragile, unstable layer within the snowpack.
How does depth hoar form?
It forms from a strong temperature gradient within the snowpack — typically when the snowpack is shallow and the ground is relatively warm while the surface is very cold, common in early-season and cold, dry climates. This gradient drives water vapor to recrystallize into large, angular facets that lack the bonds to be strong, creating depth hoar at the base.
Why is depth hoar dangerous for avalanches?
Because it's a persistent weak layer that can sit buried in the snowpack for weeks or even months, ready to fail. A cohesive slab of snow on top of weak depth hoar is a classic recipe for a slab avalanche — and because the weak layer is deep and persistent, these avalanches can be large, hard to predict, and triggered remotely. Depth hoar is a major reason some snowpacks remain dangerous all season.
Sources
- Snow science & weak layers — Avalanche.org
- Avalanche education — American Institute for Avalanche Research and Education