INFLUENCE OF GLACIAL EROSION AND MELT ON THE SANGRE DE CRISTO NORMAL FAULT SYSTEM, SOUTHERN COLORADO

Climate-tectonic interactions are thought to affect the development of active orogenic systems, yet few natural examples demonstrate climate's role in affecting tectonic activity. Here, we explore the role of Quaternary alpine glaciation on the development and activity of the Sangre de Cristo normal fault system in southern CO. We study the influence of changing surface loads associated with (1) longer-term glacial erosion and sedimentation, and (2) shorter-term deglaciation since the last glacial maximum. We explore how load changes affected the flexural-isostatic response of the range and fault clamping stress, which might have enhanced slip on the range bounding fault. We quantify the mass of glacially eroded material in the footwall using residual fluvial reaches downstream of glaciated drainage basins to reconstruct the paleo-fluvial topography and difference it from the modern topography. We estimate the Quaternary sedimentation in the hanging wall from existing drill cores, geophysical data, and geologic maps. We calculated ice loads by reconstructing glacial extents from preserved moraines and trimlines. We use a flexure model to determine the isostatic response to the changing loads and commensurate stress changes. Our results suggest ~45 meters of footwall uplift and ~35 meters of hanging wall subsidence due to glacial erosion and sedimentation. Glacial melt in the footwall has a smaller isostatic response, a maximum of ~3.5 meters of uplift, but given average scarp heights of 6.6 m, this contribution is significant. We map the fault trace and quantify cumulative vertical offset magnitudes on Quaternary alluvial fans to examine the relative patterns of flexure from changing erosion, sediment, and ice loads. We compare scarp displacement along-strike with the location of the three prominent glacially-eroded domains within the range to show positive correlations between the geographic pattern of glacial unloading and greater offset magnitudes along-strike of the fault. These findings suggest that along normal faults, seismic activity could be enhanced by climate-modulated erosion, sedimentation, and deglaciation processes in previously glaciated areas. Further, this work underscores a potential connection between anthropogenic warming, deglaciation, and elevated fault activity.