The valleys formed by external erosion forces are classified into the following parts:
1. River Valley
2. Glacial Valley
3. Blind Valley
1. River Valley: River Valley is formed by the vertical and horizontal erosion caused by the flow of rainwater on the earth’s surface. The development of river valley lies on its depth and breadth. The depth and breadth of the valley depend on the surface structure, slope position arid water velocity. The V-shaped valley is formed in the initial stage by river water.
2. Glacial Valley: U – shaped valleys are formed by the process of glaciations. They have a characteristic U shape, with steep, straight sides and a flat or rounded bottom. Glacial valleys are formed when a glacier travels across and down a slope, carving the valley by the action of scouring.
3. Blind Valley: A river flows over a limestone basin until the joints have opened up sufficiently and the stream disappears down a shallow hole. The valley downstream is dry and erosion stops here.
