1. Institute of Geophysics and Planetary Physics; University of California; San Diego, La Jolla; California; USA
2. U.S. Geological Survey; Anchorage; Alaska; USA
3. U.S. Geological Survey; Golden; Colorado; USA
4. Institute of Arctic and Alpine Research; University of Colorado at Boulder; Boulder; Colorado; USA
5. Department of Geological Sciences; University of Michigan; Ann Arbor; Michigan; USA