Arête

Striding Edge

Clouds Rest with Half Dome in the background

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Crib Goch, Snowdonia, Wales - August 2007

Garden Wall

Arête is a term used in geography and geology to describe a narrow ridge of rock which is formed by the erosion of two glaciers from opposite sides. The word is derived from the French word arête, which means "fishbone", and it is used to describe features in mountainous regions that resemble the sharp ridge of a fish's bone. Arêtes are commonly found in regions that have been heavily sculpted by glacial activity, such as the Alps, the Rocky Mountains, and the Himalayas.

Formation

Arêtes form when two neighboring cirque glaciers erode parallel U-shaped valleys. The glaciers erode the sides of the mountains they flow down, carving away the rock and creating steep-sided valleys. When two glaciers erode parallel valleys, the ridge between them becomes sharpened into a narrow edge, known as an arête. The process of glacial erosion involves both plucking and abrasion. Plucking occurs when meltwater penetrates cracks in the bedrock, freezes, and then pulls pieces of rock away as the glacier moves. Abrasion happens as the glacier drags rocks and debris over the bedrock, smoothing and polishing the surface.

Characteristics

Arêtes are characterized by their sharp, knife-edge crests, which can make them challenging obstacles in mountaineering. They can range in length from a few meters to several kilometers. The steepness of the sides of an arête depends on the strength of the rock and the rate of glacial erosion. In some cases, arêtes can be so narrow that they are only wide enough for a person to walk along the crest.

Examples

One of the most famous examples of an arête is the Knife-edge Ridge on Katahdin, the highest mountain in Maine, USA. Another notable example is the Striding Edge in the Lake District of England, which is a popular challenge for hikers.

Ecological and Climatic Impact

Arêtes and the glacial valleys they demarcate have significant impacts on local ecology and climate. Their steep sides can create microclimates on their leeward and windward faces, affecting the distribution of plant and animal species. Additionally, the orientation of arêtes and valleys can influence wind patterns and precipitation distribution in mountainous regions.

Cultural Significance

In many cultures, mountainous landscapes, including features like arêtes, have spiritual and cultural significance. They are often seen as sacred places or as challenges to be overcome. The dramatic appearance of arêtes and their surroundings has also inspired artists, writers, and filmmakers, contributing to their portrayal in various works of art and literature.