What is stream piracy? What causes a drainage reversal?

Stream piracy, also known as river capture or stream capture, is a geomorphological process where a river or stream erodes and captures the flow of a neighboring river or stream. This phenomenon results in a change in the drainage patterns, with the losing river's drainage area shrinking and the capturing river's drainage area expanding.

Stream piracy typically occurs due to one or more of the following factors: 1. Differential erosion: More resistant rock types slow down the eroding river, whereas the capturing river erodes the softer rocks faster and eventually intercepts the other river's course. 2. River gradient: A steeper river gradient produces more erosive power, capturing a neighboring river with a weaker gradient. 3. Tectonic activity: Earthquakes, uplift, or subsidence can change the landscape and river courses, leading to stream piracy. 4. Glacial activity: Glaciers can block or divert river channels, resulting in the capture of stream flow from another river.

Drainage reversal, also known as river reversal, is a phenomenon where the flow direction of a river or stream changes its course. It occurs as a result of changes to the Earth's topography, which alters the movement of water through drainage networks.

Drainage reversal can be caused by various geological processes, including: 1. Tectonic activity: Uplift or subsidence related to tectonic events can change the slope of the land, forcing a river to alter its course and flow in the opposite direction. 2. Glacial activity: Glaciation can modify the Earth's surface and create new drainage pathways, resulting in a reversal of the flow direction. 3. Deposition or erosion: Over long periods, the deposition of sediments or erosion by rivers can alter the landscape enough to cause a reversal of the drainage system. 4. Human influence: Dam construction, river engineering, or land use changes can lead to alterations in river systems and possibly initiate a drainage reversal.