thawing

Thawing is the process by which a frozen substance becomes unfrozen or liquid. In common usage, it refers to the melting of ice or frozen soil, such as permafrost, due to a rise in temperature or direct heat input. For water ice, the solid-to-liquid transition begins at 0 °C (32 °F) under standard pressure, though impurities, pressure, and phase transitions can shift the melting point. In soils, thawing creates an active layer that seasonally or chronically unfreezes, enabling water movement and ecological activity.

Thawing occurs when heat is transferred to the frozen material. Mechanisms include conduction from warmer air or surfaces, convection of air or water, and solar radiation on exposed surfaces. Geothermal heat in some regions can also contribute. The rate of thaw depends on temperature, insulation, moisture content, albedo, snow cover, and the thermal properties of the material.

The process has broad implications. For ice and frozen ground, thawing alters hydrology, enabling increased runoff, groundwater flow, and sediment transport. In permafrost regions, thawing can cause ground subsidence, infrastructure damage, and changes in vegetation. It can also release methane and carbon dioxide from previously frozen organic matter, influencing climate feedbacks. Rapid thaw can trigger landslides, rockfalls, or coastal erosion where ice-rich materials are involved.