Glacial erosion is an incredible force capable of shaping landscapes. It forms landforms like kettle lakes and drumlin fields as well as aretes with pyramidal peaks.
Glaciers leave behind telltale marks known as glacial striations to indicate their path and direction of travel, as well as scars from erosion caused by their constant grinding motion, such as grooves or scratches on bedrock called glacial striations that reveal where a glacier once traveled. They wear down rocks through erosion processes including abrasion and plucking processes.
Corries (pronounced kor-ee) are deep armchair-shaped hollows typically found on mountain sides where glaciers began forming. Over time, snow accumulates here before eventually turning into ice as freeze-thaw weathering removes air through climate cycles and freeze-thaw weathering processes. Ice also causes rocks debris to be plucked off the walls by weathering processes, gradually leading to steepening backwalls of corrie valleys due to abrasion.
Corries often form bowl-shaped basins which fill with water as the soil retreats, creating small, circular lochs known as tarns or corrie lochans. If enough water leaves this tarn, a rock lip may form along its back wall to hold onto any excess.
When two or more corries erode backwards from either side of a mountain peak, they often create an arete ridge resembling a knife-edge ridge that can be seen on many famous mountains such as The Matterhorn and Helvellyn in the Lake District.
As glaciers erode their valleys, they create landscapes similar to river valleys – V-shaped canyons and U-shaped valleys in particular. Glaciers erode these valleys through mechanical weathering and sliding against rock layers; carrying both rocks of all sizes as well as debris – large rocks not characteristic of their surroundings are called glacial erratics while smaller pieces are known as moraines.
Aretes are thin spiky ridges that form when two cirques erode towards one another. When two adjacent cirques meet back-to-back, their sides will become steeper and more sheer as erosion continues; when three or more meet, pyramidal peaks may form. Glaciers rubbing against rock can produce many interesting effects like facets, striations grooves and glacial pavements that further augment these features.
High in the mountains, mechanical weathering loosens rocks from valley walls. Glaciers then collect these rocks and transport them across kilometers as they flow. When these glaciers melt away, all these large and small rocks come tumbling to one place to form moraines – these deposits being known as glacial erratics.
Melting ice also scrapes away at the rock underneath it, creating grooves known as striae that help scientists map where glaciers were moving and can provide clues as to their size and speed of travel. They may also leave behind landforms such as cirques, troughs, rock basins or kettle lakes or mountain crests that provide further insights.
Glaciers can erode and wear away at land, carving out valleys in their wake. Glaciers typically take advantage of V-shaped valleys created by rivers before glaciation to sculpt classic U-shaped valleys with steep walls and flat bottoms.
They leave behind an arete, such as California’s Clouds Rest in the Sierra Nevada Mountains, after glacial activity has gone through it, while narrow, steep-sided mountains with polished and striated surfaces created from glacier erosion are called “roche moutonees”, such as New Zealand’s Mt. Cook (e.g. sheep rock).
Glacial erosion produces various easily recognizable landforms such as eskers, tills, moraines, rock steps and fjords. To learn more about these landforms please visit the Glacial Erosion page!
Glacial erosion produces many different landforms, both large and small, including striations lines, moraines, and U-shaped valleys.
Glacial landforms that are most well-known are likely cirques, troughs, rock basins and fjords – typically decametric or hectometric in size – while larger forms like roches moutonnees, whalebacks and rock drumlins (up to kilometric in size) also exist.
Bedrock erosion is what creates these features, but only under certain conditions. Basal slip must occur for this process to happen and warm-based glaciers tend to rub against it more readily than their cold-based counterparts (cold glaciers don’t rub against bedrock due to being more “glued” to it). Yosemite National Park is famous for this form of erosion; this phenomenon attracts rock climbers as well as boasting large lakes which were once river valleys.