How Glaciers Move

⚙️ How Glaciers Move

Glacier ice moves in two main ways. The relative importance of each depends on whether the glacier is warm-based (temperate) or cold-based (polar).

Basal Sliding

In most alpine (mountain) glaciers, the pressure from the weight of ice above causes the ice at the base to melt slightly — even where temperatures are below 0°C, the enormous pressure lowers the melting point of ice. This produces a thin film of liquid meltwater at the glacier's base, which acts as a lubricant, allowing the entire ice mass to slide forward over the bedrock. This process is called basal sliding and is the primary movement mechanism in temperate glaciers. It is responsible for most glacial erosion because it brings the ice into direct, pressurised contact with the bedrock below.

Internal Deformation (Plastic Flow)

Even without basal sliding, glacier ice can move through internal deformation — the slow recrystallisation and movement of ice crystals within the glacier under sustained pressure. This occurs in all glaciers, including cold-based polar glaciers where the base is frozen to the bedrock and basal sliding cannot occur. However, because cold-based glaciers lack basal sliding, they erode much more slowly and produce far fewer erosional landforms.

Rotational Flow and Extending/Compressing Flow

Within cirques (hollows where glaciers originate), ice moves in a rotational path — pivoting around a point partway down the cirque floor. This rotational flow deepens the cirque floor. Further down the glacier, where the valley steepens, ice accelerates and stretches apart (extending flow), causing crevasses to open. Where the valley flattens, ice slows and compresses (compressing flow), causing the ice layers to thicken and fold.