Q. The sideways erosion which widens the river valley called?
Answer: Lateral Corrosion
Notes: Sideways form of erosion is called lateral erosion. In lateral erosion, the river erodes away at its banks and widens the river channel. Together, vertical and lateral erosion create the distinctive V-shaped valley that is found in rivers in their upper course. As the river gets closer to the sea, there is more lateral erosion than vertical erosion and the V flattens out into a much wider shape.