A slab avalanche of relatively dense, compacted snow.

Credit: Colorado Avalanche Information Center

These slabs are hard and dense enough (generally greater than 300 kg/m³) that it is difficult to push a single finger into them and are often characterized by hard, blocky debris. Hard slabs can be thin, formed from heavily wind compacted snow, or much thicker, formed as snow hardens under the weight of several storm events. Hard slabs are difficult to manage because stiffer slabs tend to give less feedback and are more likely to fail far above you. Hard slabs are notorious for unpredictable failures. You’re most likely to trigger one from a thinner or softer part of the slab, such as near rock outcrops or near the edge of a slope.

A thin hard slab of wind drifted snow. Credit: Crested Butte Avalanche Center

The aftermath of a thicker hard slab avalanche involving the entire season’s snowpack. Credit: Sawtooth Avalanche Center

A hard slab avalanche, with its characteristic blocky debris. Credit: Colorado Avalanche Information Center