Assertion(A): In the process of river capture, the head streams of the weaker river are diverted into the powerful river. Reason (R): The powerful river erodes its valley steadily.

Assertion (A) is true as river capture, or stream piracy, occurs when a more powerful river diverts the headwaters of a weaker neighboring stream into its own channel [t4][t5]. This process is primarily driven by headward erosion, where the more energetic 'captor' stream erodes its valley more deeply and aggressively than the 'captured' stream [t2][t3]. Reason (R) is also true and provides the correct explanation for (A). A powerful river erodes its valley steadily and more rapidly due to factors like steeper gradients or higher discharge [t1][t9]. This superior erosive capacity allows the captor stream to cut back through a drainage divide (watershed) and eventually intersect the channel of the weaker stream at a higher elevation, thereby rerouting its flow [t4][t6]. The resulting geomorphic features often include an 'elbow of capture' and a 'wind gap' [t4][t5].

Sources

1. [1] https://gisdata.nd.gov/Regional/AbandonedMines/1912%20BIEN_RPT.pdf
2. [2] https://www.sciencedirect.com/science/article/abs/pii/S0169555X09003778