THE MOST EXTREME ANTHROPOGENIC LANDSCAPE ON EARTH: INSIGHTS ON THE GEOMORPHOLOGY OF MOUNTAINTOP REMOVAL COAL MINING IN CENTRAL APPALACHIA

Around 7000 anthropogenic valley fills (large prisms of mine spoil with volumes up to 10⁸ m³) generated by mountaintop removal/valley fill coal mining (MTR/VF) have buried over 1000 km of headwater streams in the rugged topography of West Virginia, Kentucky, Virginia, and Tennessee. This practice potentially enhances sediment connectivity to already degraded downstream reaches. We sought to determine what erosional processes occur on reclaimed valley fills and adjacent MTR/VF landscapes to form some initial, field-testable hypotheses for future researchers. Although previous studies have shown widespread detrimental effects to aquatic ecosystems and quantified changes to post-mining topography (e.g., slope distributions) arising from MTR/VF, no published study has attempted to explain how these synthetic landscapes might evolve. We believe that gully erosion will be an important process operating on valley fills and the MTR/VF landscape, as gully erosion has been observed on reclaimed mining landforms worldwide.

We used field work, analysis of LiDAR imagery (~372 km² of MTR/VF), and landscape evolution modeling with CAESAR-Lisflood to explore current and potential geomorphic responses. From the LiDAR imagery, we observed extensive gully erosion associated with perimeter drainage systems. We also observed gullies on anthropogenic valley fills in the field and in the LiDAR. Large landslides were present in some fully reclaimed valley fills in Kentucky. Landscape evolution modeling produced gullies as well. Field work and modeling results also suggested that autogenic processes operating in valley-filled catchments (overtopping of stormflow retention ponds and alluvial fan formation) could be highly influential on geomorphic responses. Valley-filled catchments could be eroding more quickly than the surrounding natural topography based on our collected observations, but sediment monitoring and/or repeat LiDAR acquisition would be needed to test this hypothesis. Long-term increases in sediment supply could further degrade downstream ecosystems on a regional scale.