1. Department of Geoscience, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada.
2. U.S. Geological Survey, Cascades Volcano Observatory, Vancouver, WA 98683, USA.
3. Centre for Northern Innovation in Mining, Yukon College, 500 College Drive, Whitehorse, YT Y1A 5K4, Canada.
4. Department of Geology, Western Washington University, 516 High Street, Bellingham, WA 98225, USA.