An arête is a distinctive geological formation, appearing as a narrow, knife-edge ridge of rock found in mountainous regions. This sharp crest separates two adjacent valleys or bowl-shaped depressions. The term “arête” originates from French, meaning “edge” or “ridge,” aptly describing its characteristic appearance. Arêtes are prominent features in alpine landscapes, showcasing the powerful forces that shape Earth’s surface.
The Formation Process
Arêtes primarily form through the erosional action of glaciers. This process begins when two glaciers flow in parallel valleys or when two cirques, which are amphitheater-shaped basins, erode headwards towards one another. As these ice flows deepen and widen their features, the landmass between them becomes progressively narrower. The glaciers carve away the surrounding rock, leaving a thin ridge.
Plucking and abrasion by the moving ice contribute to the shaping of the arête. Plucking occurs when glacial ice freezes onto rock fragments and pulls them away as the glacier moves, while abrasion involves the grinding action of rock debris embedded within the ice. These erosional forces steepen the sides of the ridge. Freeze-thaw weathering further sharpens the arête; water seeps into cracks in the rock, freezes and expands, widening the cracks, and eventually breaking off pieces of rock.
Defining Characteristics
An arête is recognized by its exceedingly narrow, sharp, and often jagged or saw-toothed profile. Its sides are typically very steep, sometimes almost vertical, meeting at a distinct crest.
The sharpness of an arête can vary, but it consistently maintains a linear, elevated form. Along the length of an arête, lower points known as “cols” may occur, representing saddle-shaped passes where the glacial erosion was particularly effective. When three or more arêtes converge at a single point, they can form a sharp, pyramidal peak known as a “horn,” with the Matterhorn in the Alps being a well-known example.
Common Locations
Arêtes are found in glaciated mountain ranges across the globe, indicating past or present glacial activity in these high-altitude environments. These features are common in regions that experienced extensive glaciation during ice ages or that currently host glaciers.
Notable examples can be found in the European Alps, such as the Cosmiques Arête in the Mont Blanc massif and the Bianco Grat on Piz Bernina. In North America, the Rocky Mountains feature prominent arêtes like Clouds Rest and Matthes Crest in California’s Sierra Nevada, and the Garden Wall in Glacier National Park, Montana. Other well-known arêtes include Crib Goch in Wales and Striding Edge in the English Lake District.