1. INSTAAR, University of Colorado, 450 UCB, Boulder, Colorado 80309, School of Earth and Environmental Sciences, Queens College, Flushing, New York 11367, Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York 10964, Department of Geology, Dhaka University, Dhaka 1000, Bangladesh, and Environmental Studies Program, University of Colorado, Boulder, Colorado 80309