gorge
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When water flows over hard rock and soft rock, the soft rocks erode creating waterfalls. As the erosion processes continue, the falls move backwards, in the opposite direction of the water
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Cross section of a canyon. Canyons are formed in dry regions where rivers maintain a constant flow of water over long periods of time. The Grand Canyon, for example, was first cut around 26 million years ago, in Miocene times.
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Cheddar Gorge is a steep, narrow limestone gorge. Gorges are formed in many ways: by caves collapsing, by waterfalls retreating, and by rapid river erosion. Cheddar Gorge was formed by rapid river erosion about 18,000 years ago. As glaciers over Britain melted, huge volumes of melt water were able to erode resistant rocks, such as limestone. The winding road that now runs through the gorge marks the position of the melt water river.
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The Gap of Dunloe, Killarney, Ireland, situated in the mountain range called Macgillycuddy's Reeks. Many upland areas were affected by glaciers during the last glacial phase. Upland areas favoured the accumulation of snow and ice owing to their lower temperatures. Small cirque glaciers and larger valley glaciers flowed along pre-existing river valleys, widening and deepening them. In some cases the glacier cut through a mountain range, forming a col or gap such as this.
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The Gap of Dunloe, Killarney, County Kerry, Ireland, shows signs of the passage of a glacier during the last glacial phase. Upland areas favour the accumulation of snow and ice owing to their lower temperatures. Small cirque glaciers and larger valley glaciers flow along pre-existing river valleys, widening and deepening the valley. In some cases the glacier cuts through a mountain range, forming a col or gap. These are now often used as transport routes.
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Cheddar Gorge, in the Mendip Hills, is a steep, narrow gorge formed in limestone. It was formed about 18,000 years ago by rapid river erosion, caused by the melting of glaciers. The winding road that now runs through the gorge marks the position of the melt water river.
Narrow steep-sided valley or canyon that may or may not have a river at the bottom. A gorge may be formed as a waterfall retreats upstream, eroding away the rock at the base of a river valley; or it may be caused by rejuvenation, when a river begins to cut downwards into its channel for some reason – for example, in response to a fall in sea level. Gorges are common in limestone country (see karst), where they may be formed by the collapse of the roofs of underground caverns.
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