Catastrophic erosion of bedrock canyons by megafloods

In rare examples, bedrock canyons can be cut in a matter of days rather than over thousands or millions of years.  In 2002, catastrophic release of water from Canyon Lake, Texas, transported meter-sized boulders, excavated ~7 m of rock, and transformed a soil-mantled valley into a bedrock canyon in ~ 3 days.  We find that canyon morphology is strongly dependent on rock type where plucking of limestone blocks produced knickpoints, inner channels, and strath terraces, and abrasion of cemented alluvium sculpted walls, plunge pools, and streamlined islands.  Otherwork includes analysis of a flood-carved canyon in Idaho with an amphitheaer head that is often used as a Mars analog.  Sediment transport constraints and exposure age dating indicate the canyon was cut ~ 48 ka.  Flume experiments suggest that such rapid canyon cutting may be accomplished by plucking and toppling of jointed rock.