A goal of paleotsunami research is to quantitatively reconstruct wave hydraulics from sediment deposits in order to better understand coastal hazards. Simple models have been proposed to predict wave heights and velocities, based largely on deposit grain size distributions (GSDs). Although seemingly consistent with some recent tsunamis, little independent data exist to test these equations. We conducted laboratory experiments to evaluate inversion assumptions and uncertainties. A computer-controlled lift gate instantaneously released ~6.5m3 of water into a 32m flume with shallow ponded water, creating a hydraulic bore that transported sand from an upstream source dune. Differences in initial GSDs and ponded water depths influenced entrainment, transport, and deposition. While the source dune sand was fully suspendable based on size alone, experimental tsunamis produced deposits dominated by bed load sand transport in the upstream ~1/3 of the flume and suspension-dominated transport downstream. The suspension deposits exhibited downstream fining and thinning. At 95% confidence, a published advection-settling model predicts time-averaged flow depths to approximately a factor of two, and time-averaged downstream flow velocities to within a factor of 1.5. Finally, reasonable scaling is found between flume and field cases by comparing flow depths, inundation distances, Froude numbers, Rouse numbers and grain size trends in suspension-dominated tsunami deposits, justifying laboratory study of sediment transport and deposition by tsunamis.
Bibliographical noteFunding Information:
We thank the Donors of the American Chemical Society Petroleum Research Fund ( 50789-DNI8 ) for support of this research (to JJ), and the NSF REU grant EAR-1157031 . Shannon Boesch assisted in conducting experiments through the REU Program, with help from Dr. Jim Buttles, Peter Polito, Austin Morrell, and Alexander Aronovitz. Dr. Andrew Moore provided grain size data on the 2004 Aceh and 2006 Java tsunami deposits. JJ developed the flume. All authors contributed to the experimental design. KD conducted the experiments and wrote an initial manuscript draft. JJ performed additional data analysis and revised the manuscript, with input from all authors. Finally, we thank Jon Woodruff and three anonymous reviewers of this and an earlier version of the manuscript.
© 2015 Elsevier B.V.
All Science Journal Classification (ASJC) codes
- Earth-Surface Processes