The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. Describe how meanders form, develop, are cut off, and then are abandoned. (D)

Meanders form as a result of the erosion and deposition of sediments that occur on the riverbanks due to the uneven flow of water in a river channel. When water flows rapidly at the outer bank, it erodes the bank and transports sediments. On the inner bank, where the flow of water is slower, sediments are deposited. This process causes the flow of the river to become increasingly sinuous, creating a series of curves or meanders.

As the meandering pattern of the river becomes more pronounced, the outer banks of the meanders are subject to more intense erosion, widening the meander loops over time. At the same time, the inner banks of each meander continue to accumulate sediments, causing the meanders to grow and develop with every successive erosion and deposition event.

Over time, adjacent meanders can grow closer to each other as their loops widen, eventually causing their outer banks to merge. When water from the river finds a more direct route between these two meanders, it begins to flow through the newly formed channel, bypassing the original meander loop. This process is called a meander cutoff.

After a meander cutoff has taken place, water continues to flow through the short, direct route between the two previously adjacent meanders, effectively forming a straightened river channel. As a result, the velocity of the water in the abandoned meander loop decreases significantly, leading to the deposition of sediments that eventually fill up the loop. Over time, the loop becomes completely cut off from the main river channel, forming what is known as an oxbow lake – a stagnant body of water that is separated from the river channel it once formed a part of. In conclusion, meanders form, develop, are cut off, and then are abandoned through a series of processes that involve the erosion and deposition of sediments on the riverbanks as water flows unevenly within the river channel. This eventually leads to the formation of a more direct route for the river flow and the abandonment of the original meander, which can result in an oxbow lake.