New Mexico Geological Society Annual Spring Meeting — Abstracts

The geomorphology of the southernmost West Mesa escarpment (SWME), which is aligned with a known down-to-the-east middle to late Quaternary normal fault inferred from borehole and aeromagnetic information, is significantly different than that of the rest of the 25-km long escarpment. In addition to having an unusually straight and nearly north-south trace, the SWME includes a 1-km long zone of previously undocumented basalt capped Toreva-block-like rotational landslides characterized by arcuate scarps and concave headwalls, tilted strata, bulked convex toes, and slope profiles suggesting at least one and perhaps two episodes of retrogressive movement. The SWME is the only portion of the escarpment with significant landslides. Geomorphometric maps derived from publicly available airborne lidar digital elevation models additionally show the SWME is rougher and has more highly disrupted drainage than portions of the escarpment that are not coincident with the fault. The absolute ages of the landslides are unknown; however, the relative ages of the Albuquerque volcanoes basalt flows and the fault preclude the possibility that the SWME is a simple down-to-the-east normal fault scarp degraded by landslides. A more plausible explanation is that flowing basalt was blocked by a north-south obsequent fault-line scarp with landslides occurring after topographic inversion in which footwall sediments of the Pliocene Ceja Formation were removed by erosion along an ancestral Mirehaven Arroyo, creating the relief necessary for the landslides to occur, perhaps in response to Pleistocene downcutting along the Rio Grande. Once the relief was developed, seismic acceleration and/or water delivered from a large footwall catchment during wet periods may have contributed to slope instability. The landslides do not appear to be currently active.