Transient channel incision in response to the Mendocino triple junction migration, northern California

Open Access
Author:
Shi, Xuhua
Graduate Program:
Geosciences
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
January 17, 2011
Committee Members:
  • Eric Kirby, Thesis Advisor
  • Kevin Patrick Furlong, Thesis Advisor
Keywords:
  • northern California
  • Mendocino Triple Junction
  • Transient channel incision
  • Coast Ranges
Abstract:
Topography in northern California Coast Ranges is thought to reflect a complicated interplay between fluvial incision and transitory crustal thickening associated with passage of the Mendocino Triple Junction (MTJ) (Furlong and Govers, 1999) since 28 Ma (Atwater and Stock, 1998). Although the structure and geodynamics of the region are well studied (e.g., Hayes and Furlong, 2007), how the landscape responds to rapidly evolving patterns of differential rock uplift remains uncertain. It has been suggested that drainage reorganization results from capture of the Russian by the Eel River during northward migration of a wave of rock uplift at ~ 2 Ma (Lock et al., 2006). Whether the drainage reorganization is linked to the pattern of differential rock uplift and subsidence due to the MTJ migration, however, can be tested with analysis of stream profiles throughout the modern Russian and Eel watersheds, as transient fluvial incision associated with drainage reorganization should be encoded in channel profiles. Analysis of three hundred and fifty channel profiles in the Russian and Eel River watersheds reveals evidence for a recent increase in incision rate, in the form of knickpoints along main stem and tributary channels that separate headwater reaches of low gradient from downstream segments with steeper profiles. The presence of knickpoints, and associated differences in channel profile steepness appear to reflect a transient, and incomplete, adjustment of channels in this landscape to a relatively recent increase in rock uplift rate. Moreover, spatial variations in knickpoint elevation and channel steepness downstream of knickpoints suggest the presence of spatial variations in rock uplift that appear to be consistent with the wavelength and direction of rock uplift predicted by the Mendocino Crustal Conveyor (MCC) model.