The Oxbow Lake: Geography Lessons from the Air

Between December 2022 and June 2023, I flew three times from Kolkata to Bagdogra and back. And on every flight, my geography lessons came alive below me.

The first surprise was a perfectly formed ox-bow loop in the river. Picture perfect, sharply defined, on the verge of breaking away from the river to form a textbook oxbow lake. I don’t know which river I was looking at flying north to south, but the meander was perfect. And huge. I would like to fool myself into believing I could pinpoint it on the map. On other flights, I have seen meanders. A river curving and looping upon itself, in squiggly patterns along the ground.

Meanders are usually seen in the middle course of a river, once it has descended from the mountains to the plains via the valleys. In this phase lateral erosion tends to replace vertical erosion, widening the valleys. Tributaries swell the volume of water in the river, resulting in a steady placid flow. Any water on the earth’s surface flows under the effects of gravity and cannot flow straight for any long distance. The irregularities in the ground cause the river to wind and swing in loops called meanders. The term ‘meander’ has its source in the name Meanderez, a river in Asia Minor of geographical and historical

importance. (https://en.wikipedia.org/wiki/B%C3%BCy%C3%BCk_Menderes_River)

As the river flows further down, the meanders become pronounced. This is the lower course of a river when the river is moving across a broad, level plain, heavy with debris. Lateral corrosion continues causing increasing erosion of the river banks and meanders become pronounced with the outside bend or concave bank being so rapidly eroded that the river becomes almost a complete circle. At one point, the river will abandon this lake to flow straight, leaving behind a U-shaped body of water, called an ‘ox-bow lake’ or a ‘mort lake’, the latter term meaning a dead lake. The dead lake degenerates into a swamp through subsequent floods, becomes marshy and eventually dries up.

https://education.nationalgeographic.org/resource/oxbow-lake/

About 120 km from Kolkata is Purbasthali, a settlement which has grown up around an ox bow lake of the Ganga and is now a famous birding spot. (https://en.wikipedia.org/wiki/Purbasthali)

Diagrams taken from a favourite school reference book: Certificate Physical and Human Geography (Indian Edition), Goh Cheng Leong, OUP, 1991