U-shaped valleys provide evidence of which process?
A: glacial erosion
B: wind erosion
C: coastal erosion
D: deposition
A: glacial erosion
U-shaped valleys provide evidence of glacial erosion (A).
The correct answer is A: glacial erosion.
To understand why U-shaped valleys provide evidence of glacial erosion, it's helpful to first understand what a U-shaped valley is. A U-shaped valley is a type of valley that has a distinct U-shaped cross-section, with steep sides and a flat or gently sloping floor.
Glacial erosion occurs when a glacier, a large mass of ice, moves downhill due to gravity. As the glacier moves, it flows over the land and scours the underlying rock, picking up and carrying with it rock fragments and debris. This process of scraping and carrying away material is called abrasion.
One of the notable features of glacial erosion is the distinctive shape it leaves on the landscape. As a glacier moves over the land, it carves and deepens existing V-shaped river valleys into U-shaped valleys through the process of abrasion and plucking.
The process of abrasion involves the grinding and scraping of rock fragments carried within the glacier against the rock surfaces. This wearing away of the valley sides and floor by the glacier results in the characteristic steep, straight or gently curving sides of the U-shaped valley.
Additionally, as the glacier moves over the land, it can also pluck or pull out larger pieces of rock from the valley sides and floor, further contributing to the valley's U-shape.
Therefore, the presence of U-shaped valleys is a clear indication of past glacial activity, providing solid evidence of glacial erosion. This evidence can be found in areas that have experienced glaciation in the past, such as mountainous regions or areas near the poles.