Glaciers dramatically reshape landscapes through erosion and deposition over long periods.
Glaciers, massive bodies of ice, possess immense power due to their weight and slow movement. This combination leads to significant alterations of the land they traverse. The primary ways glaciers impact the landscape are through erosion, transportation, and deposition of materials.
Erosion
Glaciers erode the landscape through several processes:
- Abrasion: As a glacier moves, rocks and debris embedded in its base act like sandpaper, grinding down the bedrock below. This creates smooth, polished surfaces and striations (scratches) on the rock.
- Plucking: This occurs when meltwater seeps into cracks in the bedrock, freezes, and expands. This expansion fractures the rock, and as the glacier moves, it plucks away these fractured pieces.
- Ice Wedging (Frost Wedging): Though not directly caused by glacial ice, it's a crucial pre-glacial process. Water freezes and expands in cracks, weakening rock before the glacier arrives.
The results of glacial erosion are varied and significant, creating features such as:
- U-shaped valleys: Unlike river-carved V-shaped valleys, glaciers carve broad, U-shaped valleys.
- Cirques: Bowl-shaped depressions at the head of a glacier.
- Arêtes: Sharp, jagged ridges formed between two cirques.
- Horns: Pyramidal peaks formed by the intersection of three or more cirques.
- Roche Moutonnées: Asymmetrical rock formations with a smooth, gently sloping upstream side and a steep, jagged downstream side.
Transportation
Glaciers are incredibly effective at transporting vast amounts of sediment and rock debris. This material, known as glacial till, can range in size from fine silt to massive boulders.
- Englacial Transport: Material carried within the ice itself.
- Supraglacial Transport: Material carried on the surface of the glacier.
- Subglacial Transport: Material dragged along the base of the glacier.
Deposition
As glaciers melt and retreat, they deposit the sediment they've been carrying. This deposition creates various landforms:
- Moraines: Accumulations of glacial till deposited at the edges or base of a glacier. They can be lateral (along the sides), medial (where two glaciers merge), end (at the terminus), or ground (a blanket of till).
- Eskers: Long, sinuous ridges of sediment deposited by meltwater streams flowing beneath the glacier.
- Drumlins: Elongated hills of glacial till, shaped like inverted spoons, that indicate the direction of ice flow.
- Kettles: Depressions formed when blocks of ice become buried in glacial outwash and then melt.
- Outwash Plains: Broad, flat areas of sediment deposited by meltwater streams flowing away from the glacier.
In conclusion, glaciers are powerful agents of landscape change. Through erosion, they carve out distinctive features. Through transportation, they carry vast amounts of sediment. And through deposition, they create new landforms as they retreat.
