Erosion
* Plucking: As a glacier moves, it freezes to the bedrock below. When the glacier moves, it pulls away chunks of rock, leaving behind a jagged, uneven surface.
* Abrasion: The embedded rock fragments within the glacier act like sandpaper, grinding and smoothing the bedrock. This process creates glacial striations, parallel scratches and grooves on the rock surface.
* Exaration: This is a combination of plucking and abrasion, where the glacier effectively "excavates" the underlying rock. This can lead to the formation of valleys, cirques (bowl-shaped depressions), and other glacial landforms.
* Freeze-thaw weathering: Water seeps into cracks in the bedrock. When it freezes, it expands, putting pressure on the rock and causing it to break apart. This process is enhanced by the repeated freezing and thawing that occurs in glacial environments.
Deposition
* Till: As glaciers melt, they deposit the sediment they've carried, creating a mixture of unsorted rock fragments called till. This till is often found in moraines, ridges of sediment deposited at the edges of glaciers.
* Outwash plains: Meltwater from glaciers can carry sediment further away from the glacier, depositing it as sorted sediment on outwash plains.
* Drumlins: These are elongated, streamlined hills of till that form when glaciers flow over previously deposited till.
* Eskers: These are long, winding ridges of sand and gravel that form when meltwater channels within a glacier deposit sediment.
* Kettles: These are depressions formed when blocks of ice become detached from the glacier and melt, leaving behind a hole in the ground.
Key Points
* Scale: Glaciers are incredibly powerful agents of erosion and deposition, capable of shaping landscapes on a massive scale.
* Unsorted vs. Sorted: Glaciers deposit unsorted till, while meltwater deposits sorted sediment.
* Landforms: The erosive and depositional processes of glaciers create a wide variety of distinctive landforms, which provide evidence of past glacial activity.
Examples
* The Great Lakes: Formed by the erosion and deposition of glaciers during the last ice age.
* The Rocky Mountains: Many of the distinctive peaks, valleys, and glacial lakes in the Rockies are a result of glacial activity.
* Fjords: These deep, narrow inlets are formed when glaciers erode valleys, which are then flooded by seawater.
By understanding how glaciers erode and deposit sediment, we can better interpret the landscapes they shape and the history of glacial activity on Earth.
