41-5 Eroded basins in the Channeled Scablands: Evidence for extensive food erosion

Session: Philosophy of Extreme Events and Landscape Evolution on Earth and Other Planets: Thinking Geologically in the Spirit of Victor Baker

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The Channeled Scablands is a region in the state of Washington, USA, affected by extensive catastrophic flooding. Evidence for widespread megaflooding originating from the outburst of Pleistocene glacial lakes includes carved cataracts and coulees, deposits of boulders and gravel, and rock basins (e.g., Bretz 1923, Baker 2009). This study focuses on rock basins, erosional, pit-like landforms. We used high-resolution Light Detection and Ranging (LiDAR) Digital Elevation Models (DEMs), supported by field investigations, to map the morphology and spatial relationships of rock basins in Moses Coulee and infer their implications for megaflood hydrodynamics.

Rock basins are ~10s of meters in diameter and are concentrated on flat, inner-channel basalt plateaus of the Columbia River Basalt. Field investigations revealed that they incise through a platy, hummocky basalt entablature into basalt colonnades. We measured basin depth, circularity, and eccentricity to compare with other rock basins identified in the Channeled Scablands. Rock basins in Moses Coulee show similar circularity (~1.05-1.3), spatial density (8.3 and 8.8 pits/km²), diameter (25­-100 meters), and depth distribution (unimodal peaking at ~6 meters deep) to those at Lake Lenore, which may imply that flood hydrology was similar in both locations. In contrast, basins near Deep Lake are smaller overall, depth measurements show a bimodal distribution, and there is a higher pit density (29.8 pits/km²). At Deep Lake, basalt plateaus are less broad and joints between basalt columns are better developed. We infer erosion by basalt plucking occurred differently than in Moses Coulee, or that flood dynamics were affected by topography.

Such rock basins may evolve during flooding into cataracts and coulees. We find that pits are elongated in the expected direction of flow, and pits at lower elevations (e.g., deeper in the coulee) are more eccentric. There are also collections of pits that are linked like “beads on a string.”

Landforms found in the Channeled Scablands, such as streamlined islands and longitudinal grooves, are also present in Martian outflow channels. Alongside other erosional features, the rock basins presented in this study have implications for estimating flood discharge and velocity. Similar basins may be present in Martian outflow channels, making the Channeled Scablands rock basins useful analogs for constraining magnitude and erosive power of megafloods on Mars. 

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

doi: 10.1130/abs/2025AM-9290

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