NEOTECTONIC EFFECTS OF GLACIAL EROSION AND MELT ON UNLOADING IN THE SANGRE DE CRISTO RANGE, SOUTHERN COLORADO

Understanding interactions between climate and tectonics is fundamental to tectonic geomorphology studies. While numerous studies have linked tectonic events to climate change, it has been more challenging to assess the impact of climate on tectonics in natural settings. The northern Sangre de Cristo mountains provide a unique natural example to investigate the effects of climate on tectonics as they are bounded by an active normal fault to the west and alpine valley glaciers that were likely established during the Quaternary and occupied the uplift footwall during the Last Glacial Maximum (LGM). We hypothesize that climate has affected activity of the Sangre de Cristo range front fault by altering surface loads on two different timescales: (1) through the modification of previously fluvially-sculpted footwall topography by Quaternary glacial erosion and associated hanging wall sedimentation, and (2) by melting of alpine glaciers in the footwall since the LGM. This study quantifies the magnitude and extent of these changing surface loads to constrain their potential impact on fault slip rates due to corresponding stress changes across the fault. We use remnant fluvial topography preserved in the footwall to reconstruct paleo-fluvial topography and difference this from the modern topography to quantify the magnitude of differential glacial erosion and infer the amount of sedimentation in the hanging wall from existing core and geophysical data. We reconstruct ice volumes based on LGM moraines to determine changes in ice loads. We calculate the isostatic response and stress changes on the range bounding fault, and compare the results to cumulative post-glacial fault slip pattern quantified by lidar analysis of Holocene fault scarps. This study suggests that normal faults where the footwalls were recently glaciated due to Cenozoic cooling can experience changes in surface loads that transiently elevate fault activity due to erosion, sedimentation, and ice melt. These results suggest that climate can modulate the pace and growth of recently-glaciated normal faults. These findings also suggest that seismic activity might be temporarily elevated during the post-glacial period, emphasizing a potential link between human-induced climate warming, glacial melt, and seismic hazard.