Basalgleiten

Basalgleiten, or basal sliding, is the motion at the base of a glacier where the ice moves relative to the bed. It is one of the main mechanisms by which glaciers flow, alongside internal deformation of ice, and it often dominates in temperate or warm-based glaciers.

The sliding occurs when the shear stress at the glacier base exceeds the frictional resistance of the bed. The presence of liquid water at the bed lowers the effective pressure and reduces friction, enabling the ice to glide more easily. Subglacial hydrology—the distribution and pressure of water at the bed—plays a crucial role: higher water pressure can markedly increase sliding rates, while drainage or channel formation can localize or modulate motion. Sliding is frequently described by empirical sliding laws that relate basal velocity to basal shear stress and effective pressure.

Bed conditions strongly influence basalgleiten. Deformable sediments at the bed can deform and accommodate movement, while rough bedrock can impede it. The thermal regime matters as well: warm-based glaciers, with beds near the melting point, show more extensive basal sliding than cold-based glaciers, which often skate over frozen beds.

Basal sliding affects glacier dynamics, responding to climate forcing and influencing overall ice velocity, surge behavior, erosion, and sediment transport. It is measured with techniques such as surface velocity fields from satellite or ground surveys, borehole instruments, and radar or seismic methods, and is incorporated in ice-flow models through various sliding laws to estimate glacier response to environmental change.