Glacial erosion is an incredible force that creates diverse landscape features such as corries, aretes, roche moutonnee, crag and tail formations, ribbon lakes and striations lines.
Striations marks are left behind when glaciers move across and wear away at mountainside terrain, leaving behind scores on its rocks that serve as telltale indications of which direction a glacier was moving in.
Abrasion
As with sandpapering wood surfaces, abrasion wears down rock surfaces in similar fashion, leaving various landforms such as striations lines, U-shaped valleys, hanging valleys, ribbon lakes and mountain peaks as evidence of wear and tear. Different rock surfaces wear away at different rates so it is essential when considering specific landscapes to keep in mind their hardness as well as concentration, velocity and mass of glacier ice involved in any given region.
Unfortunately, striations do not provide information on the direction or speed of ice movement and must be combined with other evidence to identify glacial erosion rates. However, basal sliding in warm-based glaciers may result in quarrying and abrasion rates exceeding those associated with fluvial erosion.
Plucking
Glacial plucking occurs when glacial ice pulls rocks away from bedrock as it moves, carrying them with it as it travels and helping shape valleys and mountains in its wake.
The type of rock in a bedrock will have an impactful influence on erosion rates; more significant erosion tends to take place on beds with well-developed cracks and joints; for instance, granite resists abrasion much better than shale.
Meltwater availability and glacier movement rates also play a key role in erosion processes. Meltwater seeps into cracks in rocks, freezes and expands, cracking them open to release chunks of rock that break away and shatter under its pressure, further contributing to glacial erosion processes.
Cirques
Cirques are bowl-shaped depressions formed by glaciers flowing down mountains. They feature steep walls at their head and sides and may be bordered by sharp ridges known as aretes.
Cirques form due to glacial abrasion – an erosional process where rock fragments embedded in the ice score bedrock surfaces with scores. Glacial abrasion occurs most frequently on warm-based glaciers where melting occurs throughout their depth.
Erosion rates are enhanced in an ablation zone where seasonal surface melt forms subglacial channels which flush sediment away and promote high basal sliding rates. Cirques provide invaluable indicators of past environments and have contributed significantly to other geomorphic landforms forming over time.
U-shaped Valleys
Glaciers are vast, slow-moving rivers of ice that erode the land they travel across. Glaciers create valleys with steep sides and flat floors in the shape of U, creating valleys which may include features such as hanging valleys or ribbon lakes.
Tools (rocks and mineral particles, both large and small) packed at the base of a glacier can abrade bedrock beneath, eroding its surface while leaving behind visible marks known as striations or rock flour.
Hanging valleys can be identified by waterfalls cascading down their steep walls, created when smaller glacial streams merge with larger main valleys.
Interlocking Spurs
Glaciers use their weight of ice to erode rock by rubbing against it – known as abrasion. This causes rocks to be smoothed away into grooves and striations known as glacial pavements; additionally it ‘plucks’ rocky bits from surface bedrock surfaces with its claw-like prongs – known as plucking.
Landforms created from glacial activity include v-shaped valleys, interlocking spurs, and ribbon lakes. Tributaries that hang over steep valley sides prevent ice from flowing around them, instead cutting straight through them to form truncated spurs which form ribbon lakes in their troughs.
Ribbon Lakes
Plucked When rocks and stones become frozen to the bottom or sides of a glacier and move along its surface erodeing surrounding land as it moves, and abrasion.
As soft rocks on the valley floor are worn away more deeply by erosion than other areas, their deepest sections form rock basins which fill with melt water from melting glaciers (and later rain water from overflow) to form ribbon lakes.
Glacier erosion of V-shaped valleys creates hanging valleys by cutting off spurs descending from either side, leading to much wider and deeper valleys with features like truncated spurs, ribbon lakes and misfit streams.