227-6 Revisiting Megaflood Landforms of Camas Prairie and the Drainage of Glacial Lake Missoula, Montana, USA.

Session: Recent Advances in Glacial Geology, Geomorphology, and Chronology (Posters)

Poster Booth No.: 234

Presenting Author:

Jayda Rowen

Authors:

Rowen, Jayda¹, Larson, Phillip Herman², Olson, Leah³, Hurner, Neil⁴, Seong, Yeong Bae⁵, Laaksonen, Madeline⁶, England, Hendrick⁷, Breckenridge, Andy⁸, Hilgendorf, Zach⁹

Abstract:

The floods of Glacial Lake Missoula (GLM), USA, are thought to be among the largest glacial lake outburst floods (GLOFs) in the geologic record. GLM drained up to ~100 times between ~18.7ka and ~13ka due to periodic dam failure. Despite the longevity of recognition of GLM’s floods, much of the work has focused on the landscapes (e.g. Channeled Scablands) beyond the former ice dam. However, abundant evidence exists within the GLM basin of both the lake’s existence and its catastrophic drainage. These landforms and sedimentary deposits can help constrain the timing and magnitude of GLM’s floods. In addition, the genesis of the landforms produced during these events have been inadequately studied with modern methods and remain poorly understood, especially in the context of rapidly draining lake basins. The Camas Prairie of northwestern Montana is an ideal case study that preserves abundant geomorphic and sedimentologic evidence of the drainage of GLM. These landforms (e.g. giant current ripples (GCRs), expansion bars, and erosional scablands) lack high-resolution data regarding the age, internal structure, and spatial variability, thereby inhibiting understanding of landform genesis. Understanding these landforms more comprehensively could provide implications for similar landforms found where GLOFs have occurred (e.g. Lake Superior basin and Altai Mountains). 

We revisit the Camas Prairie landforms by utilizing: 1) new LiDAR-derived DEMs to remap landforms, 2) ground penetrating radar (GPR) surveys to investigate internal sedimentary structures, flow regime, and sediment transport, and 3) cosmogenic nuclide ¹⁰Be exposure ages from quartz-rich metasedimentary boulders for depositional chronology. Mapping shows detailed morphology of landforms including ripple crest continuity, spatial variability, and bar margins, providing context for flood dynamics. GPR data indicates previous classification of some landforms as antidunes is incorrect, and these forms are akin to other GCRs in the basin that contain downflow dipping reflections and form under subcritical flow regimes. GPR suggests expansion bars are sediment-laden with gravels and contain downflow dipping reflections. ¹⁰Be exposure ages range from ~14ka to ~70ka, but exhibits distinct spatial distribution. We hypothesize this spatial distribution reflects prior exposure of Belt Supergroup rocks at the surface that were subsequently eroded and transported into the basin first, while those on top the expansion bars were not eroded and transported until flows had incised deeply into the Markle and Wilks Creek passes.  

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9579

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