HR: 0830h
AN: H31C-0484    [PDF]
TI: The Role of Extreme Flooding in the Inception of the Lower Colorado River and the Excavation of the Grand Canyon-Stratigraphic Insights from the Southern Tip of Nevada
AU: * House, P K
EM: khouse@unr.edu
AF: Nevada Bureau of Mines and Geology, Mail Stop 178 University of Nevada, Reno, NV 89557-0001 United States
AB: The origin of the course of the lower Colorado River in Mohave Valley at the conjunction of Nevada, Arizona, and California, can be traced to a catastrophic flood in the late Miocene (approx. 5.6 Ma). The occurrence of this ancient and essentially instantaneous extreme event is solidly linked to the primary integration of the lower Colorado River system and the ultimate excavation of much of the Grand Canyon--which arguably constitutes one of the most extreme geomorphic events in the late Cenozoic history of the western US. Exceptionally clear, well-preserved, and previously undocumented stratigraphic and sedimentologic evidence near Laughlin, Nevada supports a model of river integration in Mohave Valley through catastrophic divide-breaching by a large lake in an adjacent valley upstream (Cottonwood Valley). This event was followed by the formation of a deep lake in both valleys. The maximum age of the lake is constrained to 5.6 Ma by a bed of volcanic ash near the base of the lacustrine section. This lake ultimately breached a bedrock divide at the southern end of Mohave Valley and it is likely that subsequent lakes formed and failed in a similar manner in Chemehuevi and Parker valleys downstream. Following this calamitous series of events, the newly integrated course of the lower Colorado River was subject to a tremendous aggradation event forced by deep incision in the Grand Canyon. In Mohave Valley, the aggradation event culminated in the Pliocene (approx. 3.6 Ma) as indicated by a key bed of volcanic ash very near the top of the section. This major aggradation event was followed by deep incision to the pre-integration valley bottom that may have persisted into the early Quaternary. The downstream-directed, cascading lake-failure model of river integration supported by stratigraphic and geochronologic data in Mohave Valley presents a serious challenge to previous models of Lower Colorado River integration that involve marine incursion, rapid uplift, and spectacularly effective headward erosion.
DE: 1625 Geomorphology and weathering (1824, 1886)
DE: 1815 Erosion and sedimentation
DE: 1821 Floods
SC: Hydrology [H]
MN: 2003 Fall Meeting