Glacial Landforms – Upland Features
Upland areas are home to some unique landscapes and glacial landforms. Processes of erosion carve the landscape creating environments that attract many tourists. In the UK the end of the last ice age revealed many special features. The image below illustrates some of these features.
A corrie or cwm is an example of a landform of upland glacial erosion. It is a deep, armchair shaped hollow found in the side of a mountain where a glacier first formed. Corries are formed when snow accumulates in a hollow in the side of a mountain. If the snow does not melt during the summer further snowfall leads to the accumulation of snow, which, over time, becomes compressed forming ice. Freeze-thaw weathering supports the formation of ice by removing air. The accumulated ice begins to flow from the hollow. As this happens plucking removes rocks and debris which freezes to the base of the glacier. As the glacier moves this material abrades the hollow causing it to get wider, deeper and steeper. On the back wall of the corries, above the ice, freeze-thaw weathering causes the top of the ice to be covered in rock debris. Over time, the back wall retreats backwards, cutting deep into the side of the mountain.
The image below shows Cwm Idwal, Snowdonia.
When the ice has melted a cirque, also known as a tarn or corrie lake, is formed. An example is Red Tarn, The Lake District.
The video of Helvellyn below features a corrie containing a lake known as Red Tarn.
When two corries develop side by side or back to back, an arête, a narrow knife-edge ridge forms separating the two glaciers. An example of this is Striding Edge, Helvellyn in the Lake District. The image below shows Striding Edge.
The video below shows an arete in the Swiss Alps.
When three or more corries grow in hollows on all sides of a mountain, a pyramidal peak is produced. As the corries erode the mountain behind them, the remaining rock is weathered into a sharp point. Examples include The Matterhorn, Switzerland or Mount Snowdon, Snowdonia National Park, Wales.
As corrie glaciers formed in upland areas during the last ice age they soon began to flow into upland river valleys. Over time these v-shaped valleys were made deeper and wider by the erosive power of these valley glaciers. Plucking and abrasion transformed them into u-shaped valleys or glacial troughs. The sides of these valleys are very steep and the floors are flat.
The tributaries that once flowed down the valley sides now exit abruptly into the valley as waterfalls. What remains of the former river valley is known as a hanging valley.
The spurs, or areas of land that rivers once meandered around were often removed by the ice, forming truncated spurs.
Parts of the valley floor that were over-deepened by plucking have filled with water to create a ribbon lake.
These landforms are best seen in areas that have recently become de-glaciated. Many of these landforms can be seen in the Lake District and Snowdonia in the UK.
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