snowpacks

Snowpack refers to the accumulation of snow that remains on the ground over a season or longer, typically in mountainous or polar regions. It consists of multiple layers created by successive snowfall, wind redistribution, and cycles of melt and refreeze, including metamorphism of ice crystals. The snowpack's properties—depth, density, temperature, and grain structure—vary with location, season, weather, and exposure.

Structure and metamorphism: Each layer has distinct grain shapes and densities. Temperature gradients within the snowpack drive metamorphism, producing small, rounded crystals in some cases and large, faceted grains in others. Weak layers, such as depth hoar or faceted crystals, can form at depth and underlie stronger overlying slabs, contributing to avalanche potential. Surface crusts from melt-freeze cycles can also separate layers and affect stability.

Formation and evolution: Fresh snow adds mass that compresses underlying layers. Wind can transport snow into cornices and drifts, creating localized thickening. Melt, refreeze, and freeze-thaw cycles alter the structure and strength of layers. Warmer episodes can reduce stability by promoting the formation or growth of weak layers, while cold, stable periods may increase bonding within the snow.

Hydrology and climate interactions: The snowpack stores water as snow water equivalent, releasing it gradually as melting occurs in spring and early summer. Snowmelt feeds rivers and groundwater but can also cause floods if rapid. Evaporation and sublimation reduce the total stored water, especially in windy or arid environments.

Measurement and hazard context: Researchers study snowpack structure with snow pits, density measurements, and SWE estimates, supplemented by remote sensing and in some cases radar. Snowpack conditions influence water supply, avalanches, and habitat for plants and animals. Global climate change is altering snowfall, temperatures, and the frequency of weak-layer formation, affecting snowpack stability and seasonal hydrology.