Glaciers shape and carve their environment as they advance. By transporting rocks and soil debris across its path, ice flows form ribbon lakes, whalebacks, moutonnees roches moutonnees (mountainous rocks) or rock drumlins (rock piles).
Abrasion is essential to glacial erosion, but certain conditions must first be fulfilled in order for this process to take place. Read on to gain more knowledge about abrasion, plucking, freeze-thaw weathering and striations.
1. The ice is too thick
Glaciers are powerful erosional forces, responsible for creating some of the planet’s most breathtaking landscapes. From carving subtle grooves into rocks to creating depressions that fill with water to form ribbon lakes, glaciers create many different landforms – even plucking chunks from mountain tops for creating knife-edged features known as aretes.
These processes don’t happen instantly, and glacier movement speed plays a key role in how much erosion they cause. Up until recently, scientists weren’t sure what controlled this velocity; now we know that temperature plays an integral part.
Glaciers act like giant bulldozers when moving across bedrock surfaces, grinding and scraping away at its surface. Although effective at clearing away soft materials such as sand and silt from surfaces such as beaches or riversbeds, bedrock’s hard surface limits their efficiency; to get around this issue glaciers use an erosion technique known as abrasion to wear away rock by rubbing against it with their surface like sandpaper rubbing against wooden surfaces – this causes the glacier ice to rub against rock surface causing wearaway of both materials from bedrock while leaving soft material behind.
2. The ice is too thin
Glacial erosion requires thick ice in order to produce landforms like striations, grooves and abrasion. Even when mapping these features over large areas, however, measuring how quickly ice was moving is still challenging; since striations only records recent erosion events; thus making its rate difficult to pinpoint; especially if different parts of a cliff had different rates of erosion at different times.
Other evidence of glacial erosion may be easier to interpret; but still requires effort: the so-called stoss-and-lee topography where rocks are removed by scraping, then pulled back under by glaciers. However, basal slip is usually more significant in creating this feature, while preexisting fractures in bedrock often play an essential role; similarly it tends to occur less in places with “glued-on” ice such as cirques; thus creating more opportunities for its formation in places with both recent and distant glacial activity.
3. The ice is too fast
Glacial erosion is a complex process that produces diverse landforms. Examples include facets, striations lines, grooves and glacial pavements formed from rocks carried by glaciers rubbing against each other; rock flour formed from bits of broken off rock fragments abraded and ground down by glacial movements;
One condition for abrasion to occur is for glacier ice to be shifting at its base – known as basal slip. This movement only happens in warm-based glaciers as cold-based ones are “glued” to bedrock and must be pulled along their surface by means of large tools (e.g. sleds).
Erosion by glaciers can easily be seen in cirque floors, trunk valleys and fjords with overdeepenings caused by an increase in depth; however, this process is difficult to predict since simple correlations between erosion rates and glacier speed do not always hold.
4. The ice is too slow
Glaciers move slowly, making their effects difficult to see, yet glacier erosion serves as a vital indicator of global temperatures trends and their retreat endangers vast quantities of usable water sources.
Glacial erosion sculpts extraordinary landscapes over geological timescales, yet its effect and control remains poorly understood, particularly across Polar continental shields.
Glaciers use various tools to etch subtle striations into rock surfaces and break off chunks from mountain sides, wearing down bedrock into features such as U-shaped valleys, horns, moraines and lakes. Furthermore, glaciers may scour depressions which become lakes while creating spikey ridges known as aretes.
Glaciers erode in two main ways: abrasion and plucking. Abrasion occurs when the glacier moves over rocks, scraping away bits from their surfaces while plucking occurs when melt water re-freezes around broken stones, carrying them downstream with it.