Professor in the Department of Geology, University of Maryland I study tectonic and volcanic processes on the Earth and other planets, most typically using theoretical modeling. Recent focus areas include the localization of ductile shear zone; the strength of continental and oceanic lithosphere; melt migration at subduction zones, Mars, and Io; formation of coronae on Venus; elastic flexure on Pluto; and the structure and evolution of the ice shells of Europa and Enceladus.