Expertise Environmental isotopes as tracers of hydrologic and surficial geologic processes and as dating tools; development of the surface exposure dating method based on cosmogenic 36CL accumulation in materials exposed to cosmic radiation at the Earth's surface; solute transport in porous media using tracers to characterize transport properties of geological formations; groundwater dating; past global climate change and its record in the lithosphere and hydrosphere. Study areas include the high Arctic, the Great Basin, the Wind River, Range and Hawaii; Eastern and Northwestern Africa