How do glaciers create striations on valley walls?

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Snow-capped, rugged Atlas Mountains encircle a green valley with scattered trees, terraced fields, and a few small buildings in Morocco. — valley The rugged Atlas Mountains surround a valley in Morocco.

Glaciers create striations on valley walls through a process of glacial abrasion. While pure ice is too soft to significantly erode solid rock, glaciers incorporate rock debris—ranging from fine particles to large boulders—into their basal ice.1

As the glacier moves, it acts like a powerful sheet of sandpaper, dragging these embedded rock fragments across the bedrock of the valley walls. This abrasive action carves scratches and gouges into the rock surface, which are known as striations. These marks can range from microscopic scratches to deep gouges several centimetres wide and tens of metres long. Because the debris is dragged by the ice, the orientation of these striations provides a record of the direction of ice movement in that specific area.213