Glaciation Flashcards
Formation of an Arête
Snow collects in hollows then turns to ice(1). Ice erodes the mountains on all sides creating corries(1). The backwalls of the corries are eroded back towards each other(1) by the processes of plucking and abrasion(1) until a narrow knife-like ridge is formed. An arête is formed when two corries erode back to back
Formation of a Corrie
Snow gathers in north facing hollows of a hill or mountain and compacts to form a glacier(1). The action of gravity allows the glacier to move downhill(1).
Ice freezes onto rock on the back wall of the hollow and as it moves it plucks rocks from the landscape(1). This helps to create a steep back wall(1). Rocks on the back wall are also removed by freeze-thaw weathering(1). Rocks frozen in the base of the ice act like sandpaper and deepen the hollow by abrasion(1). The rotational movement of the ice helps to create a deep hollow and a rock lip is formed by over deepening(1).
When the glacier melts, a pool of water is left called a tarn(1). The glacier deposits material it has gathered as a pile of moraine forming a lip.(1). Scree continues to form at the steep backwall due to freeze-thaw weathering
Formation of a Pyramidal Peak
When 3 or 4 corries erode back to back around a mountain the arêtes between the corries rise to a central peak, called a pyramidal peak. Plucking of the back wall makes the corries larger until the top of the mountain is eroded and only a sharp pointed peak remains. The exposed rock is also eroded by freeze-thaw weathering.
Formation of a U-Shaped Valley
A glacier moves down the main V shaped valley which it erodes(1) by plucking, where the ice freezes on to fragments of the rock and pulls them away(1) and abrasion where rock fragments embedded in the ice scrape the land surface like sandpaper(1). As a result the valley becomes deeper, straighter and wider(1). When the ice melts the valley becomes U shaped. It has very steep sides and a fairly flat floor, any rivers running through the valley are called misfit streams because they are too small to have cut and shaped the valley.
Formation of a Hanging Valley
A hanging valley is formed when a large glacier is joined by a small tributary glacier(1). The large glacier moves down a V-Shaped valley and through the processes of plucking and abrasion deepens the valley floor and straightens the valley sides, leaving a large U-Shaped valley(1). The interlocking spurs become truncated spurs. The same processes of plucking and abrasion take place in the tributary glacier, but at a much slower rate(1). This is because the large glacier is far heavier and more powerful and therefore can erode the land more quickly(1). The small tributary glacier does not vertically erode as much as the large glacier. When the ice melts a large U-Shaped valley is left where the large glacier had been. The small glacier leaves a small valley leading into the main U-Shaped valley and is left ‘‘hanging’’ from the truncated spurs(1). Often a waterfall is left coming from the hanging valley flowing down into the main U-Shaped valley(1)
Formation of a Ribbon Lake
A ribbon lake is formed in the floor of a U-Shaped valley when a large glacier moves down a valley eroding everything in it’s ways. Through the processes of plucking and abrasion the valley is made deeper and wider. The ribbon lake was formed when the glacier moved over a section of softer bedrock that was more easily and quickly plucked and abraded than the surrounding harder bedrock. When this happened an over deepened hollow or depression was made in the softer bedrock. After the Ice Age the hollow then fills with glacial meltwater and becomes a ribbon lake. They also formed when melt water was trapped behind moraine which had been deposited across the valley as the ice melted
