Glaciology

The difference between accumulation (snowfall, avalanching, freezing rain) and ablation (melting, sublimation, calving) over a glacier's surface during a given time period. A positive mass balance means the glacier is growing, while a negative mass balance indicates shrinkage.

The analysis of cylindrical samples drilled from ice sheets and glaciers to reconstruct past climate conditions. Trapped air bubbles, isotopic ratios of oxygen and hydrogen, dust particles, and chemical impurities in ice layers serve as proxies for past temperature, atmospheric composition, volcanic activity, and precipitation patterns.

The process by which glaciers wear away bedrock and sediment through plucking (quarrying blocks of rock), abrasion (grinding by debris embedded in the ice base), and meltwater erosion. These processes create distinctive landforms such as U-shaped valleys, cirques, aretes, and fjords.

The movement of a glacier over its bed, facilitated by a thin film of meltwater at the ice-bedrock interface that reduces friction. Basal sliding is a major component of glacier velocity, particularly in temperate glaciers where the base is at the pressure melting point.

The process by which chunks of ice break off from the terminus of a glacier, ice shelf, or iceberg where it meets a body of water. Calving is a major mechanism of mass loss for marine-terminating glaciers and ice sheets, producing icebergs that drift into the ocean.

The restraining force that floating ice shelves exert on the grounded ice streams and glaciers that feed them. Ice shelves act as a dam, slowing the flow of land-based ice into the ocean. When an ice shelf thins or collapses, the tributary glaciers accelerate, increasing the rate of ice discharge and sea-level contribution.

The gradual transformation of snow into glacier ice through compaction, recrystallization, and expulsion of air as successive layers of snow accumulate. Firn is the intermediate stage between snow and glacial ice, typically reaching full ice density at depths of 50 to 100 meters depending on temperature and accumulation rate.

The ongoing response of Earth's lithosphere and mantle to the loading and unloading of large ice masses. When ice sheets grow, the crust beneath them is depressed; when they melt, the land slowly rebounds upward. This process continues for thousands of years after deglaciation.

The opening of deep cracks in glacier ice caused by tensile stresses that exceed the strength of the ice. Crevasses typically form where a glacier accelerates, changes direction, or flows over an uneven bed. They can extend to depths of about 30 meters before the overburden pressure closes them.

A positive feedback mechanism affecting ice sheets grounded below sea level on a bed that slopes downward inland. As the grounding line retreats into deeper water, thicker ice is exposed to warm ocean currents, accelerating melting and further retreat. This process can lead to rapid, self-sustaining ice sheet collapse.