Glacial erosion is a critical process that creates diverse landforms. At its height, glacial erosion peaks during an active phase of a glacier’s cycle with high mass balance turnover and an active regime at any given altitude.
Evidence of abrasion includes rocks that have been polished off by dragging, such as those showing striations or grooves, or rock flour.
Glaciers move very slowly.
Gliatic erosion leaves behind distinctive landforms that indicate their progress through an ecosystem, including aretes, cirques, horns, drumlins and moraines. These telltale marks provide evidence of glacier movements through landscapes.
Glaciers erode in two main ways: plucking material out and moving it around, or using their powerful water currents to erode rocks and sediments abrasionally. Furthermore, glaciers transport and deposit debris such as boulders and dirt; this phenomenon is called glacial drift while material may also be left behind or redistributed through meltwater streams (outwash).
Effective glacial erosion depends upon both rock type and climate conditions; soft rocks erode more quickly than harder ones and water helps lubricate glacial movement more effectively than ever before, thus explaining why glaciers advance only centimeters or meters daily but occasionally surge and advance up to hundreds of metres overnight due to weather, snow accumulation, or internal ice dynamics.
They move over bedrock.
One mechanism of glacier movement is deformation; another is abrasion. Here, embedded rocks and sand act like cutting tools on bedrock surface rubbing against it to form groove-like trough-like glacial grooves known as striations grooves. Abrasion can also be enhanced by hard materials that rub more effectively against its surface than soft ones; further increasing abrasion speed is a flow of basal meltwater between the base of the ice sheet and bedrock base which speeds it up further.
Glaciers tend to inherit V-shaped stream valleys, which they reshape by preferentially eroding their bases and lower sidewalls, flattening out valley bottoms, and creating jagged knife-edge ridges called aretes. Furthermore, glaciers erode sediment by downward creep into it, freezing water into it at its base, or by compressing the sediment under their weight causing microscopic scratches or centimeter-deep gouges that stretch for meters along its path. All this results in glacially abraded landforms from microscopic scratches to deep gouges spanning multiple kilometers long on either side.
They move over other landforms.
Glaciers often pick up chunks of rock during their movement over rocks and sediment, carrying it far away from where it began – these chunks are known as glacial erratics.
Abrasion creates some fascinating characteristics of rock that demonstrate glacial erosion at work. For instance, bits of rock carried by glaciers are very rough like sandpaper and as they scrape across rocks they create grooves in them–this process gives rise to what are known as “striations marks.”
Abrasion processes also allow glaciers to create smooth surfaces where they rub against rocks and bedrock, known as glacial polish. Abrasive processes also pluck rocks out from beneath their beds by glacial plucking or quarrying processes, creating landforms such as aretes and horns. Erosion creates circular basins known as cirques.
They move over sediments.
Glaciers contain large volumes of rock particles which can rub against rocks and sediments, eroding their surfaces to produce various landforms. This erosion process leaves behind numerous distinct landforms.
As glacial ice scrapes over rocks, it leaves behind long scratches known as glacial striations that indicate where its flow occurred and are proof that a glacier once traversed this area.
Glacial abrasion is intrinsically tied to basal sliding, the process by which warm-based glaciers scrape across bedrock1. Abrasives utilized by glacial abrasion include rock debris and sediments held within its base – from fine grains of sand to large boulders – leaving behind scratches ranging in size from microscopic marks up to centimetre-deep gouges tens of meters long.
Scratching marks and other surface features produced by glaciers result in iconic landforms like U-shaped valleys, cirques, aretes, pyramidal peaks, hanging valleys and ribbon lakes, knob-and-tail formations and striations formations that often appear nearly polished or smoothed over.