PIRACY
Drainage piracy requires extensive base level lowering, which induces a drainage network to erode aggressively into one side of a bedrock high. Then, a drainage on the opposite side of the bedrock high eventually cuts laterally or aggrades and spills over the much reduced intervening drainage divide, eventually incising a canyon through the bedrock high. Drainage piracy is made easier if headward-cutting streams utilize less resistant rock related to faulting or jointing. The sapping process, where groundwater from the captured drainage is added to the overall discharge of the capturing drainage, can also accelerate rates of headward incision.
