How meltwater and sediment turn massive, frozen glaciers into sliding, landscape-carving machines

Nature · Published 3 October 2026 Swipe more like this →

In short: Glaciers are not static blocks of ice; they are dynamic, moving entities that reshape the Earth. While we often imagine them as frozen solid, many glaciers slide across their beds on a lubricated layer of meltwater or saturated sediment, a process that can account for the vast majority of their movement.

Basal sliding occurs when a glacier moves over its bed, facilitated by meltwater that acts as a lubricant. This movement is highly sensitive to environmental conditions, including the glacier's size, the slope of the terrain, and the roughness of the underlying bed. While meltwater is the most frequently cited cause, research suggests that water-saturated sediments beneath the ice can contribute to as much as 90% of the movement observed in some glaciers. This process is most active in thin glaciers resting on steep slopes, particularly during summer months when surface runoff reaches its peak.

The mechanics of this movement are complex. In temperate glaciers, which exist at the pressure-melting point, sliding is the primary mode of travel. This is achieved through two main processes: stress concentrations around obstacles on the bed that trigger plastic flow, and regelation, where ice melts and refreezes around bumps in the bedrock. Conversely, polar glaciers are often frozen to their beds. Because polar ice is more rigid, it lacks the ability to creep effectively, and the adhesion between the ice and the frozen bed significantly inhibits sliding. These cold-based glaciers move primarily through internal deformation rather than sliding.

The impact of basal sliding extends far beyond the movement of ice itself. As glaciers slide, they act as powerful geological agents, using embedded rock debris as abrasive tools to erode the bedrock. This process is responsible for shaping entire landscapes, including the formation of the Great Lakes, which were carved by basal erosion over relatively weak bedrock. However, this movement is not always constant. Debris trapped within or beneath the ice can create traction, potentially slowing or even halting a glacier's progress, especially on lower slopes where the lubricating effect of water or sediment is less pronounced.

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