Arêtes and Pyramidal Peaks

🗻 Arêtes and Pyramidal Peaks

Arêtes and pyramidal peaks are both the product of multiple corries eroding simultaneously from different sides of a high mountain. They are best understood as later stages in the landscape's evolution from individual corries.

Arêtes — knife-edge ridges between two corries

An arête forms when two corries erode from opposite sides of a ridge. As each glacier plucks and abrades backwards into the mountain, the rock between the two corries is attacked from both directions at once. The ridge between them narrows progressively — from a broad rounded slope, to a sharp narrow ridge, to a jagged near-vertical edge. The process continues as long as the ice remains active. Freeze-thaw weathering on the exposed rock adds further sharpening after the ice retreats, shattering surface fragments and maintaining the jagged profile.

UK named example: Striding Edge, Helvellyn, Lake District. Striding Edge runs between the Red Tarn corrie to the north and the Nethermost Cove corrie to the south. Walking it is one of England's most famous scrambles — the narrow, rocky ridge demonstrates the typical arête profile, with steep drops on both sides.

Also: Crib Goch, Snowdonia — the dramatic arête leading to the summit of Snowdon from the east. North Wales Ridgeway traverses several arête sections.

Pyramidal Peaks — three or more corries, one pointed summit

A pyramidal peak forms when three or more corries erode simultaneously from different aspects (faces) of the same mountain. Each glacier excavates its own corrie, biting into the mountain from a different direction. The rock that remains between all three (or four, or more) corries forms the pointed, pyramidal summit. The more corries, the more dramatic and pointed the peak.

UK named example: Snowdon (Yr Wyddfa), Snowdonia, at 1,085 m. Multiple corries erode from the mountain's flanks — Glaslyn corrie (south face), Cwm Dyli, and others — leaving the distinctive pointed summit that is the highest point in Wales and England.

International example: The Matterhorn, Swiss Alps (4,478 m) — arguably the world's most famous pyramidal peak, with four near-vertical faces formed by four converging corries eroding from each compass point. Its dramatic pyramidal shape is the most photographed mountain form in the world and is the direct product of glacial erosion.