GSA QUATERNARY GEOLOGY AND GEOMORPHOLOGY DIVISION DISTINGUISHED CAREER AWARD: ERODING THE SOUTHERN ROCKY MOUNTAINS—WEATHERING AND FLUID FLOW IN SLOW MOTION IN THE CRITICAL ZONE

Diverse lines of evidence demonstrate slow denudation rates in the cool, dry landscape of the southern Rocky Mountains despite pervasive fracturing that dates from Laramide time and local hydrothermal alteration of mainly granitic materials. Denudation rates near 2 cm kyr^-1 result from the long-term balance between slow rock uplift and chemical weathering of silicates at cool temperatures in environments where fluid contact times are relatively short. Moisture from snowmelt dominates upland to alpine hydrology and fluid transit is rapid through sandy soils and regolith, and in channels. Soil infiltration rates are relatively high and ephemeral streams lose substantial volumes to the shallow subsurface. Groundwater velocities are slow from meters to tens of meters beneath the rocky regolith, but reactive surface area is limited and solution chemistry is relatively dilute. In the past ~two decades, new dating tools based on cosmogenic nuclides, new measurement tools, particularly those involving lidar, and integrative approaches such as critical-zone research and hydrologic connectivity offer new ways of quantifying geomorphic processes. Undergraduate field-based studies, particularly where they build upon ongoing research, offer substantial scientific and educational opportunities for studying geomorphic and hydrochemical processes in the critical zone. Research examples include analysis of: fracture spacing, rock strength and regolith thickness within and beyond the glacial limit; solution chemistry and inferred weathering pathways; chemistry of weathering profiles; long-term erosion rates inferred from ¹⁰Be in alluvium, and short-term erosion rates after fire and flooding events. Intense rainfall from infrequent to millennial events drives erosion rates that exceed long-term values by at least 10-100 X. Despite active freeze-thaw regimes at higher elevations, erosion rates are lowest above the late Pleistocene glacial limit. Landscape relief is increasing from episodic glacial stripping of alpine valleys and from canyon-downcutting into the slowly weathering, rolling upland beyond the glacial limit.