Glaciers are powerful forces, capable of altering landscapes through erosion. More specifically, they scrape against mountainside terrain to remove rocks and sediment before carrying it away in streams or rivers.
This process leads to specific landforms like corries, aretes and cirque stairways as well as numerous glacial deposits like striations lines and tunnel valleys.
Freeze-thaw weathering
Freeze-thaw weathering, also known as frost shattering, occurs on rock surfaces above glaciers. It happens when melting snow finds its way into cracks in rocks near glaciers before refreezeing as temperatures drop further, expanding them and eventually shattering apart the rock mass altogether. Scree slopes and blockfields in Lake District landscape features are ideal examples of such phenomena.
Glacial erosion shapes the landscape we live in today, through processes such as abrasion and plucking. Abrasion occurs when rocks at the base of a glacier scrape overlying bedrock with their weight like sandpaper, leaving scratches called striations marks. Plucking occurs when a glacier moves down a valley, melting temporarily around larger boulders it encounters and then refreezes, lifting them out from under their foundation and creating an outburst of rock debris as it moves along its course – ultimately contributing to formation of cirques and bergschrunds.
Plucking
Glaciers are powerful agents of erosion. They remove rocks from valley walls, shaping them into distinctive landforms like horns, cirques and hanging valleys before leaving behind telltale glacial deposits known as moraines.
Plucking occurs when the weight of a glacier pushes downward into bedrock, compressing and compressing sediment beneath. This results in cracks to appear which, over time, could widen as erosion progresses, ultimately breaking through and exposing exposed rock surfaces to air.
After glaciers melt, their pressure returns to pre-glacial levels resulting in postglacial rebound – the gradual movement of Earth’s crust back towards its original position – explaining why alpine landscapes often show evidence of erosion while others remain relatively undisturbed.
Abrasion
Glaciers scrape underlying rock as they move down valleys. Their rock fragments act like sandpaper to wear away bedrock, smoothing it over while sometimes leaving grooves or scratches known as glacial striations. When this process produces rock flour it often ends up far away from where the glacier picked it up initially.
Glacial erosion leaves behind telltale landforms like eskers, drumlin fields and kettle lakes to reveal where and how far glaciers were moving while also showing what rocks and sediments they eroded along their path. These geomorphic features provide us with clues as to their direction of flow, how far it advanced and which rocks or sediments it affected.
Glaciers also leave behind geologic structures like cirques and moraines as they erode mountains into depressions; U-shaped valleys formed when glaciers pass through V-shaped river valleys while scraping against their sides and bottom; moraines formed from till left behind when glaciers retreat; these geological features are known as cirques and moraines respectively.
Sliding
Sliding occurs when glacial ice and its load of rock fragments grind across bedrock like sandpaper to smooth and polish its surface, leaving long scratches behind – known as glacial striations – on its surface. This process creates terrain modifications known as glacial striations.
Climate and basal thermal regimes exert significant control on glacier sliding rates. Glacier erosion rates vary considerably and cannot be explained solely through simple relationships between erosion rates and glacier sliding velocity.
Erosion by glaciers produces an array of geomorphic features. These include eskers – winding ridges of sand and gravel that point in the direction that the glacier moved – and drumlin fields, or groups of asymmetrical hills of sediment. Erratic pieces encrusted in or deposited onto surfaces by glaciers are known as erratics; larger rocks, pebbles or boulders left behind may be called till, while any deposits of meltwater over an extensive region are known as outwash and fluvial drift.