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As we know, dependant on conditions, a glacier can either accumulate more mass and advance across the land or undergo ablation and retreat.
This movement of ice over the land causes the landscape to undergo drastic changes, carving many features we can still see today. Take a look at the YouTube video, to the left, which shows how glacial landscape evolution develops different features over millions of years. Glacial Erosion When glaciers expand, accumulating increasing amounts of snow and ice, they are able erode surface rocks and bedrock as they move. There are 3 main types of glacial erosion: |
- Freeze Thaw - water in cracks in the rock freezes and expands forcing open the gap. When the ice melts more water can get into the crack and freeze again. After many cycles of freezing and thawing lumps of rock are broken off the surface.
- Plucking - at the base of glacier ice melts due to pressure and friction. This allows water to freeze into cracks in rocks, and when the glacier moves it pulls out chunks to leave a jagged surface. This provides material for abrasion.
- Abrasion - rocks stuck in the ice grind away the bedrock under the glacier
Glacial Deposition
Features formed by glacial deposition occur when a glacier is in retreat. As the glacier melts, it dumps any bedrock or material it is carrying onto the land - this material is known as glacial drift. Since a glacier has so much energy and can erode very large pieces of rock, the features it creates are usually very distinctive. The melt water may also lead to lakes forming.
This kind of erosion and deposition is responsible for carving many of the landscapes we see today. For example, those we see in the Lake District, England were formed when the ice sheets advanced over parts of the UK in the last Ice Age. See the slide show of glacial features in the Lake District below: