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Main features and landforms of glacial erosion.

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Introduction

Main features and landforms of glacial erosion. MICRO-SCALE: Striations: When a glacier moves across the underlying rock, the process of abrasion wears it away. It is the fragments of rock held in the ice that do the abrading, scraping across the rock surface like nails across a wooden desk top. Larger rock fragments leave deep scratch marks behind them. These scratch marks are straight parallel lines that reveal the direction of ice movement. Freshly exposed striations have a preferred orientation of rock grains. By lightly running a finger along the striation it is possible to discover that when moving one way along it, the rock feels smooth, but when moving the other way it feels coarser. The moving ice leaves the rock grains aligned with the direction of movement, so when the striation feels smooth, your finger is moving in the direction of ice flow. When the striation feels rough, you are moving against the ice flow. This test doesn't always work, and won't work on striations that have been exposed for a long period of time. Crag and tail: A crag and tail is a larger rock mass than a Roche moutonnee. ...read more.

Middle

Glacial Grooves: Grooves are common on recently exposed bedrock, and on stones that have been transported by glaciers. These have classically been used to infer ice flow direction over bedrock, but as some of the examples illustrate, this can be misleading Rock Basins: The floor of a glacial trough is uneven. It usually consists of a series of depressions or rock basins - with a reverse gradient at the lower end, separated from the next by a rock bar or step. The formation of such basins is not fully understood, but two theories seem likely: They correspond to areas of the valley floor where the bedrock was weak and thus more easily eroded. Or they correspond to areas where erosion by the glacier increased due to the sudden addition of ice possibly from a tributary glacier. Subglacial meltwater: When subglacial meltwater drains through tunnels, it defines stream systems similar to surface streams. Those subglacial streams may deposit sediment just as a surface stream would, but confined to the tunnel. The result is a ridge of gravel termed an esker, often sinuous (snake-like), which wanders across a formerly glaciated region. The gravel in an esker may have been transported and even eroded by the glacier, but the subglacial stream sorts the fine material out and carries it away. ...read more.

Conclusion

The tributaries are left high above the main valley, hanging on the edges, their rivers and streams entering the main valley by either a series of small waterfalls or a single impressive fall. Truncated Spurs: Spurs that projecting into the original river valley are cut short, their lower ends being destroyed by the moving ice. They may be cut back right to the edges of the new valley, or still project slightly into the valley. This shortens the spurs, or truncates them. They are then known as Truncated Spurs Areal Scour: The most extensive, but unspectacular, erosional landscape left behind by a continental ice sheet is that of "areal scour". The landscape spreads out for miles with little relief on either erosional or depositional topographic features. Local depressions may be scour features in weak or jointed rock, or small kettles. This picture from the Canadian Shield is typical of the areal scour left by large ice sheets. Crag and tail: A crag and tail is a larger rock mass than a Roche moutonnee. Like a Roche moutonnee, it is formed from a section of rock that was more resistant than its surroundings. On the lee side of the resistant rock, the bed rock was protected from the erosional power of the glacier. Kreeshan Annauth Geography 1 ...read more.

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