1. Erosion:
* Plucking: As a glacier moves, it freezes onto bedrock and pulls out pieces of rock, like a giant ice chisel. This process, known as plucking, widens and deepens the valley.
* Abrasion: The ice also carries rock fragments embedded within it, grinding and scraping against the valley floor and walls. This process, called abrasion, polishes and smooths the rock surfaces.
* Erosion of Headwalls: Glaciers erode the headwalls of valleys, creating steep, vertical cliffs. This erosion is also responsible for the formation of cirques, bowl-shaped depressions at the head of a glacier.
2. Deposition:
* Moraines: As glaciers melt, they deposit the rock debris they carry, forming moraines. Lateral moraines form along the sides of the valley, medial moraines form in the center where two glaciers merge, and terminal moraines mark the furthest extent of the glacier.
* Outwash Plains: Meltwater from glaciers carries sediment downstream, forming outwash plains, which are flat, sandy areas.
* Kettles: When blocks of ice become buried in glacial deposits, they melt and leave behind depressions called kettles, which often fill with water to form lakes.
3. Shaping the Valley:
* U-Shaped Valleys: Glaciers carve out U-shaped valleys, in contrast to the V-shaped valleys created by rivers. This characteristic U-shape is a hallmark of glacial erosion.
* Hanging Valleys: Tributary glaciers often flow into larger glaciers at a higher elevation. As the main glacier erodes, it leaves behind a hanging valley, which often ends in a waterfall.
* Fjords: In coastal areas, glaciers can carve out deep, narrow inlets called fjords.
4. Other Features:
* Striations: The scraping action of glaciers leaves behind parallel grooves and scratches on the bedrock called striations, which provide evidence of glacial movement.
* Roches Moutonnées: Glaciers smooth and polish the upstream side of rock outcrops, creating a rounded shape, while the downstream side remains steep and jagged, forming a roche moutonnée.
In summary, glaciers modify valleys through a combination of erosion, deposition, and shaping processes, leaving behind distinctive landscapes that bear the marks of their powerful influence.
