Reconstructing past tropical cyclones and tsunamis in NW Western Australia: insights from detailed geomorphological, stratigraphical, and chronological investigations of different coastal sediment archives.
Past coastal flooding events related to tropical cyclones (TCs) and tsunamis may be inferred from geomorphic and sedimentary archives, i.e. in the form of particular landforms (beach ridges, washover fans) and deposits (overwash-related sand sheets in lagoons and back-barrier mudflats). Their chronostratigraphy can be used to reconstruct event chronologies on centennial to millennial time scales. In addition, modern analogues are crucial for interpretations of related depositional processes and for reducing uncertainty in evaluating the typically complex chronostratigraphic architecture of these records. Although the north-western part of Western Australia (WA) is one of the most tropical cyclone-affected areas worldwide, and ten historical tsunamis are recorded since 1858, little is known about the geological imprint of both (pre)historical TCs and tsunamis in this area. This talk will provide new data on the sedimentology and chronostratigraphy of such extreme wave deposits, which were found in different geological archives and environments along the coasts of the NE Cape and the Gulf of Exmouth (WA) within the framework of a DFG-funded research project. Specific focus of the talk will be on the southern part of the Exmouth Gulf, where (i) supratidal, chenier-type sand ridges form the landward margin of extensive mudflats in Giralia Bay, and (ii) large washover fans in supratidal mudflats are prominent landforms on Point Lefroy headland. Both the formation of the supratidal sand ridges and the washover fans is assumed to be mainly driven by TCs, although their chronology and their relation to depositional processes and inundation levels during spring tide conditions, exceptional precipitation and discharge events, and storm surges needs to be clarified. The talk will summarize the most important findings from these study areas, which are based on simple process monitoring, geomorphological mapping by means of unmanned aerial vehicle survey and structure-from-motion techniques, as well as sedimentological and geochronological investigations. In addition, a modern analogue was provided by category 3 tropical cyclone (TC) Olwyn in that area in March 2015. The modern analogue deposits provided an excellent opportunity to evaluate the use of luminescence-based proxies (luminescence inventories) including quartz single-grain age distributions and associated remnant ages, as well as quartz and feldspar luminescence signal comparisons for tracing storm surge-related sediment source environments and better understanding transport processes.
May, S. M., Brill, D., Leopold, M., Callow, J. N., Engel, M., Scheffers, A., Opitz, S., Norpoth, M., Brückner, H. (2017). Chronostratigraphy and geomorphology of washover fans in the Exmouth gulf (NW Australia)—A record of tropical cyclone activity during the late Holocene. Quaternary Science Reviews, 169, 65–84. http://dx.doi.org/10.1016/j.quascirev.2017.05.023
May, S. M., Gelhausen, H., Brill, D., Callow, J. N., Engel, M., Scheffers, A., Joannes-Boyau, R., Leopold, M., Brückner, H. (2018). Chenier-type ridges in Giralia Bay (Exmouth Gulf, Western Australia)—Processes, chronostratigraphy, and significance for recording past tropical cyclones. Marine Geology, 396, 186–204. http://dx.doi.org/10.1016/j.margeo.2017.03.005
May, S. M., Callow, J. N., Brill, D., Hoffmeister, D., & May, J.-H. (2020). Revealing sediment transport pathways and geomorphic change in washover fans by combining drone-derived digital elevation models and single grain luminescence data. Journal of Geophysical Research: Earth Surface, 125, e2020JF005792. https://doi.org/10.1029/2020JF005792