EP011-12
Evaluation of megaflood deposits with photogrammetry and photogranulometry
Tuesday, 8 December 2020: 04:33
Virtual
Silvio Aldebot, CUNY Queens College, Flushing, NY, United States, Kennly Weerasinghe, CUNY Queens College, Flushing, United States, Susannah Morey, University of Washington Seattle Campus, Earth and Space Sciences, Seattle, WA, United States, Monica Hill, University of Washington Seattle Campus, Seattle, United States, Katharine W Huntington, University of Washington Seattle Campus, Seattle, WA, United States and Karl A Lang, CUNY Queens College, School of Earth and Environmental Sciences, Flushing, NY, United States; Georgia Institute of Technology Main Campus, Atlanta, GA, United States
Abstract:
The development of efficient, low-cost and open-source software for photogrammetric and photogranulometric (e.g. grain size) analysis of digital photographs allows the modern geoscientist to “take the outcrop home” for quantitative analysis, crowd-sourced interpretation and digital preservation. We demonstrate the efficacy of two new tools: structure-from-motion photogrammetry and wavelet-based photogranulometry for interpretation of the paleohydraulic conditions of confirmed and speculative megaflood deposits along the Siang River in the eastern Himalaya. Using digital analysis of high-resolution photographs, we compare the grain size, bedforms, and stratigraphic architecture of deposits from a landslide dam-burst flood event in the year 2000 with Holocene-Pleistocene megaflood deposits with and without a Tibetan source area confirmed by detrital zircon U-Pb geochronology.
Deposits from the 2000 flood and confirmed megaflood deposits have a similar medium sand grain size. Both deposits have similar bedforms, including rhythmic parallel lamination and fine scale bedding, granule to fine sand fining-upward sequences from cm-m scales, as well as massive beds. Flood deposits are observed in both lensoid and tabular bodies that drape preexisting topography with flat intra-deposit bed contacts. We interpret the megaflood sedimentology to reflect slackwater deposition in hydraulically sheltered areas and/or during waning phases of a flood. Speculative megaflood deposits also include cm-dm cross-bedded coarse sand, gravel and cobble lenses, and cm-dm tabular clay beds, which may alternatively reflect fluvial reworking of megaflood deposits or localized damming during tributary backflooding.
Our preliminary results suggest that digital photogrammetry and photogranulometry are effective modern tools for quantitative outcrop analysis – and may be particularly useful for capturing and preserving the details of inaccessible and eroding sedimentary deposits. To take advantage of the virtual nature of this conference, we also feature annotated three-dimensional models of selected outcrops for audience members to review and make their own interpretations.
