[1
]U.S. Geological Survey; 3162 Bozeman Avenue Helena MT 59601 USA
[2
]U.S. Geological Survey, Anchorage, AK, USA; and Geosciences Department, Colorado State
University; Fort Collins CO USA
[3
]U.S. Geological Survey; Lakewood CO USA
[4
]Patagonia Adventure Expeditions; Cochrane XI Region Chile