The correct answer is Lateral erosion in plains.. Explanation & Key Takeaways: • Meanders are curves or bends in a river that form primarily due to lateral erosion, which is the sideways erosion of the riverbanks. • This process occurs when a river flows through the plains, as it has lower energy compared to its flow in mountainous regions, leading to the deposition of sediments and formation of winding curves. Hence, lateral erosion in plains is the correct answer. • Vertical erosion, which involves downward cutting into the riverbed, is dominant in the upper course of a river where the gradient is steep. It does not contribute significantly to the formation of meanders. Hence, this option is incorrect. • Mountainous origin refers to the starting point of rivers, usually in high-altitude areas. While rivers originating in mountains exhibit high energy and rapid flow, meanders are not formed in this stage of the river. Hence, this option is incorrect. • Ocean tides primarily affect coastal areas and estuaries, but they do not lead to the formation of meanders in rivers. Hence, this option is incorrect. • Hence, the correct answer is Lateral erosion in plains. Related Concepts: • Meander Formation Process: • Meanders are formed due to the combination of erosion and deposition in a river’s middle and lower course. • As water flows faster on the outer bends of a river, it causes lateral erosion, wearing away the riverbank and creating a concave shape. • On the inner bend, water flows slower, leading to sediment deposition that forms a convex shape. This creates the characteristic winding curves of meanders. • Factors Influencing Meander Formation: • Gradient: Rivers in their lower courses have a gentle gradient, which favors lateral erosion over vertical erosion. • Water flow: The flow of water varies across a river channel, with faster flow near the outer bends and slower flow near the inner bends. • Sediment load: Rivers with a significant sediment load can deposit materials on the inner bends, aiding meander formation. • Examples of Meandering Rivers: • The Ganga River in India exhibits pronounced meanders in its lower course. • The Mississippi River in the United States is another example of a river with extensive meandering patterns. Important Notes: • Stages of River Erosion: • Upper Course: Characterized by vertical erosion, steep gradients, and the formation of features like waterfalls and rapids. • Middle Course: Dominated by lateral erosion and the development of meanders, floodplains, and oxbow lakes. • Lower Course: Features include deposition, deltas, and estuaries as the river approaches the sea. • Oxbow Lakes: • Oxbow lakes are formed when a meander is cut off from the main river due to erosion and deposition processes. • These lakes are common in the lower course of rivers like the Brahmaputra in India.