PRELIMINARY MAPPING AND ASSESSMENT OF LANDSLIDE ASSEMBLAGE, MINKERS RUN AREA, ATHENS COUNTY, SOUTHEASTERN OHIO

Landslides are common hillslope features of the Allegheny Plateau in southeastern Ohio where most landslide investigations have been transportation related. Old inactive slides far from transportation routes have received little attention. Preliminary mapping of the Minkers Run area identified an assemblage of 50+, inactive, laterally contiguous slides. The area has a long history of mining and timbering, but slide initiation appears to predate anthropogenic activity. Individual slides 500-800 ft wide with runouts of 250-500 ft are defined by head scarps formed in shoulder and upper hillslope positions. Where head scarps on opposite hillslopes nearly converge, interfluves are very narrow (10-15 ft) and steep-sided. Head scarps are up to 1000 ft long, 20-35 ft high, and formed in thin-bedded siltstone and silty sandstone. Proximal areas contain one or two internal scarps 3-8 ft high with treads 8-15 feet wide, some counterrotated. The slides are deep-seated and rotational with failure surfaces likely in the Mahoning “redbeds” of the Glenshaw Formation. In this region, “redbeds” such as these are weak, slickensided, paleovertisols known for their instability. Field observations and lidar images reveal the slides comprise two broad categories of surface roughness, those with; 1) subtle features -- scarps with diminished slopes (21-28^o) and covered faces, internal blocks eroded with internal drainage lines, and little distal reactivation, and 2) moderately defined features -- scarps steep (34-44^o) with some exposed bedrock and colluvium, modest erosion, no internal drainage lines, and distal reactivation. Variations are likely due to differences in timing of initial sliding events and/or subsequent reactivation. The reactivated toe of a category 2 slide yielded buried wood radiocarbon dated to 170 + 20 years. The charred exterior of the sample is consistent with distal reactivation possibly due to slope denudation by early logging or forest fire. Hand auguring of the uppermost blocks of two slides provided evidence of different head-scarp movement histories. One slide contained three buried A soil horizons consistent with sporadic movement, whereas the other preserved one possible buried A horizon. Archival air photos support initial triggering of slides before the advent of timbering and mining.