Glaciers’ movements can erode land to form dramatic landscapes, leaving behind striations lines, grooves and glacial polish.
These features are created through abrasion between rock debris from moving ice and bedrock, or when certain conditions exist whereby moving ice moves at its base, and bedrock.
Why is it hard to see glacial erosion in action?
Glaciers are powerful geological agents that shape remarkable landscapes while altering Earth’s climate. Unfortunately, their long-term erosional efficacy and control remain poorly understood on both glaciological and climatological timescales across Polar continental shields1.
While glacier movement does not directly erode rocks, other processes can help facilitate its erosion and transport. One such process is plucking, where rock fragments embedded in ice scrape the bedrock beneath and carry it along, producing distinct landforms like corries (elongated depressions with notches on one side), aretes (diamond-shaped features), or pyramidal peaks.
Abrasion, in which ice grinds and polishes the rocks it moves over, leaves behind signs of wear that are easily identifiable such as parallel scratches on rocks known as glacial striations and large rocks carried along by the ice known as erratics. Furthermore, it may leave behind deposits known as moraines (linear ridges of boulders, gravel, sand and clay) and till plains (flat areas with deposits).
It takes time
Glaciers’ weight and slow movement can dramatically transform landscapes over thousands of years through erosion, transporting broken rocks and soil debris far from where they originally belonged, leaving behind distinctive glacial landforms in their wake.
One of the most iconic glacial landforms is a ribbon lake, formed when glaciers erode a rock basin and fill it with water, leaving behind an accumulation of rocks, dirt and sand known as moraine.
Gletschers further erode landscapes through a process known as plucking and abrasion. Plucking occurs when glaciers drag rock or gravel over hard and brittle bedrock surfaces, leaving crescentic marks or lunate marks. Abrasion occurs when glacier weight grinds against rock surfaces – however this only works if basal slip occurs (only possible with warm-based glaciers).
It is hard to see
Glacier movement may be difficult to observe on the ground, but several landforms serve as indicators of glacial erosion. These include periglacial trim lines which illustrate how high the ice was during erosion process; crevasses and flowstripes which demonstrate rotational movement patterns; as well as glacially abraded bedrock known as striations marks.
Glacial striations, or glacial striae, are subparallel grooves cut in rock surfaces by tools frozen into basal ice and may range in depth and width up to many meters deep, wide and hundreds of meters long.
Other evidence of glacial erosion and deposition includes drumlins (streamlined elongated features) as well as gravel and rocks bulldozed into mounds by moving ice. Glaciers leave behind striations that erode rock into glass smooth finishes, creating cirques and aretes such as those seen around Mont Blanc in the Alps.
It is hard to imagine
Glaciers are incredible bodies of ice that excel at both eroding and depositing rocks. As they move down valleys, glaciers erode rock surfaces they come into contact with – such as mountains. Their movement can leave behind U-shaped valleys, U-shaped depressions called cirques (bowl-shaped depressions), and pointed peaks as well as striking landforms such as moraines and till plains (unsorted mixtures of boulders gravel sand clay) as well as smooth surfaces known as glacial striationss – just some examples of what glaciers can do when it comes to leaving their mark behind!
Glaciers often create erosion through abrasion. This occurs when rock fragments embedded within their base rub against bedrock underlying it – much like when you rub paper against wooden surfaces – creating small fragments of garnet embedded within it, which in turn lead to much larger changes! Abrasion erosion creates distinctive landforms such as ribbon lakes, corries, aretes, and pyramidal peaks.