Glaciers erode rocks to form dramatic landscapes. Although direct observation of glacier erosion is challenging, researchers have made observations through drilling tunnels through glaciers.
Erosion leaves distinctive geomorphic features behind, such as faceted clasts, striations lines, rock flour and glacial pavements. Furthermore, glacial landforms such as U-shaped valleys, horns and ribbon lakes also form as a result.
Glaciers Move Very Slowly
Glaciers are massive sheets of solid ice and snow that cover large areas, moving slowly due to their weight – approximately 2 centimeters each day – due to their force of weight, eroding the land beneath them known as glacial erosion.
Erosion occurs largely by means of abrasion: Rock and mineral fragments in glacial streams rub against bedrock to wear it away, piecemeal. This creates rock flour – a fine material which gives glacial streams their characteristic milk-white hue.
Abrasion depends on the contact pressure between basal clasts and bedrock surfaces beneath, with higher contact pressure leading to more intense erosion. One source of such pressure may be cavity presence at glacier’s bed where their pressure can offset overburden pressure caused by weight of ice above, allowing abrasion and plucking out rock fragments from bed surface as a result of weight imbalance.
The Ice Is Thin
Glaciers use glacial erosion to erode land by scraping at it with their glaciers, scraping away bits of rock from bedrock surfaces by scraping or “plocking”, loosening them for transport by the glaciers to different places along their paths – often creating new landforms after they melt away.
Glacial erosion differs significantly from fluvial erosion that typically takes place along rivers. Glaciers erode more deeply due to constant movement and sharper ice than rivers do, creating an intense form of erosion.
That is one reason to avoid skating on an inch-and-a-half thick piece of ice alone or with someone else, or in spite of warning signs labeled as “Thin Ice.” Bending thin ice under your weight is another indication that it is weakening. Last month Henrik Trygg and Marten Ajne, two Swedish athletes, recorded themselves skating on such an inch-and-a-half thick sheet ice and made waves around the web by posting it online; their video went viral (you can watch here).
The Ice Is Cold
Glaciers erode land they cover through three primary means. Abrasion occurs when glacial ice grinds against bedrock surfaces to erode and polish them; plucking occurs when glaciers pick up large rock fragments too large to fit inside their ice sheets; finally, glacial striations lines remain from deep scratching into rocks by glaciers.
These striations provide geologists with valuable information about the glacier’s speed and direction of movement, the type of rock it scraped across, and whether or not it was soft or hard.
As glaciers move across the landscape, they create depositional landforms such as moraines, eskers, kames and rock drumlins – familiar landforms from your high school geology class but difficult to comprehend and interpret.
The Ice Is White
As glaciers move across the landscape, they scrape against rocks and erode sediments beneath them – this process is known as abrasion – leaving features like faceted clasts, striations grooves, rock flour (often described by its distinctive dilute-milk color) as they travel. Furthermore, moving glaciers can gouge basins into the earth, leaving U-shaped valleys or dramatic landforms such as horns, nunatuks or ribbon lakes behind.
Glacial erosion differs from fluvial erosion caused by river flows across a landscape, as many different forms of glacial processes such as abrasion, plucking and freeze-thaw weathering cause its destruction. Glacier processes produce many different forms of erosion such as abrasion, plucking and freeze-thaw weathering which combine to form some stunning landforms like cirques, aretes, horns ribbon lakes moraine and roche moutonees; also, freeze-thaw weathering loosens bits of rock which might otherwise remain on their beds while melting glaciers collect them into so-called glacial till.