Glaciers scrape and erode rock, transporting it away in their flow to create landscapes with features such as faceted clasts, striations grooves and glacial pavements. Furthermore, they leave behind landforms such as corries and aretes (spiky ridges), pyramidal peaks and ribbon lakes – leaving their mark upon our landscapes forevermore.
Rocks vary considerably in how they erode. Softer rocks tend to erode more quickly than harder varieties.
Glaciers leave behind evidence of where glaciers once passed, from leaving subtle grooves that later fill with water to form lakes and streams, to plucking chunks from mountains to form knife-edge features called aretes. Glacial erosion leaves behind all sorts of telltale clues for scientists that allow them to pinpoint exactly where glaciers passed over land masses.
Separating glacial, fluvial, and marine deposits that appear similar can be an immense challenge. Another issue involves determining what kind of glacier created the bedrock beneath.
Plucking is a type of glacial erosion found in valley glaciers. When these valley glaciers melt and infiltrate rock joints or cracks with basal ice, cracks widen, loosen, or even break apart over time; large pieces known as joint blocks form. Plucking also smoothes rock surfaces through polishing; an additional process.
As glaciers erode the landscape, they pluck rocks from bedrock and drag them along, producing rock flour or “glacial polish”, along with striations and grooves in bedrock. Furthermore, this abrasion loosens bits of rock that fall away from their bedrock surroundings to be carried along on melting glaciers; these are known as erratics which often differ in size, shape and origin from their bedrock surroundings; melting glaciers eventually collect these erratics to deposit in different locations – leading to landforms such as cirques and troughs.
Glacial erosion differs significantly from its more familiar fluvial counterparts such as rivers and streams in terms of both movement and intensity of rock erosion, thanks to being made of sharper ice particles. These differences give glaciated valleys and their associated depressions known as cirques their signature zigzag pattern that creates characteristic zigzag features on long profiles of glaciated valleys and their accompanying zigzag-patterned profiles that mark long profiles along their lengths.
Glaciers scrape the bedrock surface as they move across it, leaving long parallel lines known as striations which provide geologists with important information about glacier movement.
Striations on glacier surface rocks provide us with information about which direction the glacier was traveling when it cut them, while geologists can use striations patterns to reconstruct a glacier base position.
Glaciers may not be effective erosive agents on their own, but when coupled with rock fragments embedded within, their efficacy increases dramatically despite having only minimal contact force with rock surfaces. The result can be significant abrading forces that significantly outstrip those generated by regular erosion agents like soil.
Nonglaciated valleys typically take on V-shapes while glaciated ones can often take U shapes. V-shaped valleys create steep sides which make it harder for glacial ice to reach and grind away at rocks near the bottom, while U shaped ones allow more effective ice erosion processes – key indicators of how glaciers influence landscape shape.
Glaciers leave behind various erosional landforms when they scrape across bedrock surfaces, such as faceted clasts, glacial striations grooves (known as glacial striations striations ), rock flour as well as more complex features like U-shaped valleys, horns horn lakes and moraines.
Glacial erosion is more rapid and intense than river erosion due to two primary factors. First, glaciers move constantly while their ice is much sharper than river sediment.
These characteristics also mean that erosional patterns can be difficult to discern over short (10-4 year) timescales, particularly for studies of abrupt warming where increased melt runoff accesses previously buried subglacial material at rates orders of magnitude above what would normally be considered normal2. It takes patience to decipher what the erosional signatures are; even so, it is vitally important that one be aware of all processes at work in any particular instance.