The 1980 eruption of Mount St. Helens removed an estimated 4.6 billion ft3 of ice and snow from the mountain, aiding the formation of lahars and floods (Brugman and Post, 1981, p. D1). There is evidence of similar glaciovolcanic interactions on other Cascade volcanoes, and man can anticipate such threats during future eruptions. Therefore, determining the volumes of the ice and snow should be useful in assessing the potential hazard from eruptions of individual volcanoes.
Between April and September 1981 an ice-radar system developed by the U.S. Geological Survey was used to determine ice thickness at 177 measurement points on 25 glaciers of Mounts Rainier, Hood, and Shasta and the North, Middle, and South Sisters (collectively referred to here as the Three Sisters, fig. 1). Access to these measurement points was by foot, ski, and helicopter and involved personnel from the Project OfficeGlaciology, Tacoma, Wash. The measurements allowed the preparation of subglacial contour and isopach maps included in this paper, along with the resulting volume calculations. The descriptions of ice-radar operation and methods for data reduction, calculation of glacier volume, and error totals in calculating glacier volume are condensed from a study by Kennard (1983).
Suzanne Brown, Lee Benda, David Peckham, Melinda Brugman, and others from the U.S. Geological Survey Project OfficeGlaciology and from the Cold Regions Hydrology Project provided invaluable help during this study. During the 6 months of fieldwork, they aided with radar measurements and surveying and also helped by giving their constant energy and enthusiasm. Success in making measurements in nearly inaccessible places was often due to support by Sue and Anthony Reece of HiLine Helicopters.
Personnel of Mount Rainier National Park and of the Mount Hood, Deschutes, Willamette, and Shasta National Forests cooperated by providing information on mountain conditions and by allowing us to carry out the logistics within these regions.
Dr. Charles Raymond offered valuable insight and support for developing the volume estimation methods.
Paul Kennard organized and coordinated fieldwork for the study. He determined the basal contours for the Mount Rainier and Mount Hood glaciers, developed the volume estimation methods and error analysis discussed here, and prepared the appendix. Carolyn Driedger and Bruce Vaughn determined the basal contours at the Three Sisters and Mount Shasta. They applied the estimation methods to all unmeasured glaciers noted in the study.
Beneficial reviews of the manuscript were made by Dee Molenaar, Bernard Hallet, and Robert Jacobel. William Scott, C. Dan Miller, and Dwight Crandell provided information and sectional reviews in reference to geologic histories and glaciovolcanic relations.
Last Updated: 28-Mar-2006