New Mexico Geological Society Annual Spring Meeting — Abstracts

The Jemez River system drains the geologically active Valles Caldera; understanding its incision history may provide insight into tectonic forces within the Jemez Mountains and along the Jemez lineament. The modern river profile is complex and shows two major knickpoints. The first is located just downstream from the downstream from San Antonio hot springs and the second in the vicinity of Spence hot Springs. These knickpoints reflect bedrock lithology in part (Abo sandstones and Banco Bonito flows, respectively), but may also be providing information on drainage reorganization following young (~50 ka) volcanism. Gravels beneath the Bandelier ash flows give an idea of the profile of the ancestral Jemez. The shape of these profiles is very similar to the current river profile. The ash flows filled a valley offset to the west of the modern valley.

Geological information was superimposed on the river profile to calculate average incision rates for various time intervals during the past 1.8 Ma. In the vicinity of the Guadalupe River confluence, bedrock incision rate averaged 145 m/my from 1.6 Ma to present; 90 bedrock m/my from 1.6 to 0.6 Ma, and 230 m/my from 0.6 Ma to present, indication increased bedrock incision in the Late Quaternary. Compared to the Rio Ojo Caliente north of the Jemez Mountains, late Quaternary rates are similar, but early Quaternary rates are higher in the Jemez Mountains.