Glaciers created and continue to create a wide variety of dramatic landforms through erosion and deposition. These include sculpted mountains, carved valleys, and the movement of vast quantities of rock and sediment.
Glaciers, massive bodies of ice in motion, act as powerful agents of landscape transformation. Their impact is evident in diverse geological features around the world. The processes involved can be broadly categorized into erosion and deposition.
Erosional Landforms
Glaciers erode the landscape primarily through two processes:
- Plucking: As a glacier moves, meltwater seeps into cracks in the bedrock beneath it. This water freezes and expands, fracturing the rock. The glacier then plucks away these loosened rock fragments as it continues to advance.
- Abrasion: The ice contains rock debris of all sizes. As the glacier slides over the bedrock, this debris acts like sandpaper, grinding down the rock surface and creating polished and striated surfaces.
These erosional processes lead to the formation of:
- U-shaped valleys: Unlike river-carved valleys that are V-shaped, glaciers carve out wide, U-shaped valleys with steep sides and flat bottoms. Yosemite Valley is a classic example.
- Cirques: Bowl-shaped depressions at the head of a glacier, formed by glacial erosion.
- Arêtes: Sharp, knife-edged ridges that separate adjacent cirques.
- Horns: Pyramid-shaped peaks formed by the erosion of multiple cirques on a mountain. The Matterhorn in the Swiss Alps is a well-known example.
- Striations: Grooves and scratches on bedrock surfaces caused by rocks embedded in the ice.
- Roches moutonnées: Asymmetrical rock formations with a gently sloping, striated up-ice side and a steep, plucked down-ice side.
- Fiords: Long, narrow inlets with steep sides or cliffs, created by glacial erosion.
Depositional Landforms
Glaciers also deposit vast amounts of sediment, known as glacial till. This unsorted mixture of clay, silt, sand, gravel, and boulders is deposited directly by the ice. Meltwater from the glacier can also transport and deposit sediments, leading to stratified deposits.
Depositional landforms include:
- Moraines: Ridges of till deposited at the edges or terminus of a glacier. These can be lateral (along the sides), medial (where two glaciers merge), or terminal (at the end of the glacier).
- Eskers: Long, sinuous ridges of sand and gravel deposited by meltwater streams flowing beneath a glacier.
- Kames: Irregular mounds of stratified drift (sand and gravel) deposited by meltwater on the glacier surface.
- Kettle lakes: Depressions formed when blocks of ice left behind by a retreating glacier melt, leaving a depression that fills with water.
- Drumlins: Elongated, oval-shaped hills of till aligned parallel to the direction of ice flow.
- Outwash plains: Wide, flat areas of sand and gravel deposited by meltwater streams flowing away from the glacier terminus.
In short, glaciers sculpt and reshape the landscape through the powerful forces of erosion and deposition, leaving behind a distinctive imprint on the Earth's surface.
