Geologists have long recognized the importance of both river deltas and deep-ocean sedimentary systems as major sinks for large quantities of land-derived sediment, and as important components in the integrated source-to-sink transit of terrestrial sediments. Relatively few studies, however, have directed their attention at the linkage between the two, despite the fact that deltaic dynamics are almost always intimately related to deep marine sediment transport systems. This project examines the relationship between deltaic and deep- water sedimentation in Lake Chelan, WA, where the external forces acting on the system are relatively well constrained, and the river is directly linked to deeper water.

Lake Chelan sits in a fjord-like basin most recently scoured by a combination of the Chelan Glacier and Okanagan Lobe of the Cordilleran ice sheet during the Last Glacial Maximum. Lake Chelan sits 335 meters above sea level and reaches a depth of nearly 450 meters. The northern end of the lake is fed by the Stehekin River, which has produced a delta that has prograded some four kilometers in the last 9000 years.

In summer 2010 we completed bathymetric and sub-bottom surveys of the northern five kilometers of the lake. We also collected lake bed grab samples and gravity cores for grain size and geochemical analysis in order to characterize the transport and fate of sediment near the Stehekin Delta. The bathymetric and sub-bottom surveys reveal large-scale bedforms on the lake floor, likely the product of density currents produced during high river flows or as a consequence of failure on the delta front.

Funding source: University of Washington Royalty Research Fund

People: Chuck Nittrouer, Aaron Fricke

Project publications:

Fricke, A.T., Sheets, B.A., Nittrouer, C.A., Allison, M.A., Ogston, A.S., 2015. An Examination of Froude-Supercritical Flows and Cyclic Steps On A Subaqueous Lacustrine Delta, Lake Chelan, Washington, U.S.A. Journal of Sedimentary Research, 85(7), 754-767.