Glacial erosion has the power to transform landforms like cirques, rock basins and fjords into breathtaking scenes, as well as extraordinary landforms like staircase lakes (known as tarns) or mountainous terrain.
These landforms are formed by glacial erosion, caused by glaciers dragging or scraping rocks across the ground. This process leaves behind landforms such as striations grooves and glacial pavements.
Glacial erosion gives glacial landforms distinct characteristics. Two such landforms are plucking and abrasion. Plucking occurs when ice slips into fissures in bedrock like stones bouncing across water, gradually eroding away at its surface until eventually breaking off pieces of it altogether.
Abrasion is also responsible for producing distinctive glacial landforms like striations and drumlins; for instance, turning V-shaped valleys into U-shaped ones.
One of the primary factors governing how much abrasion takes place is surface tension of ice. This determines whether or not drumlins form and creates trim lines – markings along valley walls where one side contains more vegetation than another side.
Cirques are bowl-shaped depressions carved out by glaciers at high elevations in mountains and valley sidewalls by subglacial abrasion, quarrying and backward headwall erosion. Glaciers widen and deepen cirques through subglacial abrasion, quarrying and backward headwall erosion processes.
Crushed bedrock striations is the primary sign of erosion. The sharp fragments embedded within it act like tiny pieces of sandpaper on wood surfaces, wearing away at them as time goes on.
When two adjacent cirques collide, their erosion produces an arete or steep-sided ridge; when three or more collide, a pyramidal peak forms. Cirque lakes called tarns can fill these depressions when glaciers melt; such areas often boast histories of cirque glaciers.
Glaciers’ erosive power can shape valleys when they move over steep slopes, often leaving U-shaped cross-sections with steep sides and flat bottoms, littered with till and moraine from rocks being scraped up by the ice and carried downstream, leaving behind layers of debris in their wake.
U-shaped valleys may form from glacier cirques that extend downhill from river valleys or steeply-sloping spurs of rock called aretes, when multiple aretes join forces they create sharp ridges known as horns – these landforms may be stunning but may pose unique challenges when visited by visitors; sustainable tourism practices and responsible recreation activities must be implemented to minimize impactful ecosystems created by such features.
Glaciers eroding bedrock can create a series of steps resembling an amphitheater with steep sides; this formation is known as a cirque.
Glaciers erode rocks through quarrying (the process of extracting rock in cobble-sized increments), abrasion (when ice rubs against bedrock and transports sediment away), and subglacial erosion (when ice flows over bare rock). Which form of erosion takes place depends on basal contact pressure.
Glaciers often encounter rock which has fractures or fissures which become broken up when hit by glacial ice, picking up fragments which can then be carried downstream and left behind as moraines. On the other hand, harder rocks often resist being abraded by glacier forces, making for less abrading impact and faster travel time downstream.
Glacier ice contains rock fragments of all sizes, and its rough surface (known as basal ice) scrapes against bedrock surface in an act known as abrasion; this form of erosion leaves scratches called striations which resemble wood scratches caused by rubbing sandpaper against it.
Erosion creates stunning landscapes, including cirques, troughs and rock basins, staircase lakes and horns. But these landforms only form in certain conditions – the efficacy of glacial erosion being determined by climate/altitudinal factors – an aspect of study which will be essential in understanding glacial evolution.
Crag and Tails
A crag-and-tail is an elongate hill or ridge characterized by two features at either end: at its stoss (up-ice) end is a steep knob of rock or ice-smoothed resistant bedrock that blocks glacier movement; and on its lee end there is an intact and less resistant tail protected by the crag itself – also referred to as drumlins.
Horned crag-and-tails may form due to a series of changing basal conditions. A period of fully frozen bed may be followed by periods with partial frozen patches at lower points and full sheets of ice at higher elevations; this pattern generally prevents abrasion; however, tools present near the glacier base could potentially cause it.