Snow and Ice Volume on Mount Spurr Volcano, Alaska, 1981
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Snow and Ice Volume on Mount Spurr Volcano, Alaska, 1981 By Rod S. March, Lawrence R. Mayo, and Dennis C. Trabant U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 97-4142 Fairbanks, Alaska 1997 U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY GORDON P. EATON, Director For additional information write to: Copies of this report can be purchased from: District Chief U.S. Geological Survey U.S. Geological Survey Branch of Information Services 4230 University Drive, Suite 201 Box 25286 Anchorage, AK 99508-4664 Denver, CO 80225-0286 http://www-water-ak.usgs.gov CONTENTS Abstract ................................................................. 1 Introduction ............................................................... 1 Acknowledgments...................................................... 5 Surveying................................................................. 5 Determination of ice thickness and depth ........................................ 6 Measurements ......................................................... 6 Ice-radar migration ..................................................... 11 Contouring ice thickness and bed topography. ................................ 12 Seasonal snow......................................................... 18 Snow and ice areas and volumes ............................................... 18 Discussion ................................................................ 24 Selected subglacial features............................................... 24 Use of glacier volumes at Mount Spurr to improve volume-estimation methods. ..... 28 Glaciovolcanic hazards and comparison with other volcanoes.................... 29 Summary and conclusions .................................................... 31 References cited............................................................ 32 Appendix: Coordinate systems ................................................ 35 PLATES [Plates in pocket] 1. Altitude of base and surface of glaciers on Mount Spurr, Alaska 2. Ice thickness and surface contours of glaciers on Mount Spurr, Alaska FIGURES 1. Map showing location of Mount Spurr, Alaska ............................. 2 2. Photograph of Mount Spurr Volcano viewed from the south-southwest.......... 4 3. Diagram showing the exact ellipsoidal solution and the more commonly used approximate spherical solution for the location of all possible reflecting surfaces.................................................... 10 4. Photograph of Mount Spurr Volcano seen from the southwest showing Barrier Glacier ...................................................... 13 5. Photograph of Mount Spurr Volcano seen from the southeast showing Painted glacier ...................................................... 14 6. Scatter plot of measured ice thickness versus glacier surface slope.............. 15 7. Scatter plot of basal shear stress versus glacier surface slope or sine of the glacier surface slope ............................................... 16 8. Map showing horizontal surface ice velocities derived from ogive spacings ...... 17 9. Longitudinal profiles of Barrier Glacier's surface and bed .................... 24 Contents III 10. Photograph of Mount Spurr Volcano seen from the east with Capps Glacier in the foreground .............................................. 26 11. Contour map of glacier surface and bed topography of the summit region of Mount Spurr ...................................................... 27 12. Longitudinal profiles of upper South branch of Capps Glacier's surface and bed ............................................................ 28 13. Log-log scatter plot of glacier volume versus glacier area for Mount Spurr glaciers and Cascade Range glaciers on volcanoes ..................... 29 TABLES 1. Coordinates of survey control stations in the Mount Spurr area ................ 6 2. Ice-thickness measurements ............................................ 7 3. Seasonal snow data from U.S. Soil Conservation Service sites near Mount Spurr ........................................................ 18 4-11. Areas and volumes of snow and ice in: 4. Barrier Glacier sub-basin ........................................... 19 5. Painted glacier sub-basin ........................................... 19 6. West Kidazqeni Glacier sub-basin .................................... 20 7. East Kidazqeni Glacier sub-basin. .................................... 20 8. Crater glacier sub-basin ............................................ 21 9. South branch, Capps Glacier sub-basin ................................ 21 10. Main branch, Capps Glacier sub-basin. ................................ 22 11. Chichantna River drainage .......................................... 22 12. Summary of areas and volumes of snow and ice on Mount Spurr and their seasonal minimums and maximums. ................................. 23 13. Summary of snow and ice minimum seasonal area (September), maximum seasonal area (May), and volume above altitude of glacier termini.............. 30 IV Contents CONVERSION FACTORS, VERTICAL AND HORIZONTAL DATUMS, AND SYMBOLS USED IN THIS REPORT Multiply by To obtain meter (m) 3.281 foot kilometer (km) 0.6214 mile square kilometer (km2) 0.3861 square mile cubic kilometer (km3) 0.2399 cubic mile cubic meter per second (m /s) 35.31 cubic foot per second kilopascal (kPa) 0.1450 pound per square inch grad 0.9 degree degree Celsius (°C) 1 .8, then add 32 degree Fahrenheit VERTICAL DATUM Altitudes are measured relative to the National Geodetic Vertical Datum of 1929 (NGVD of 1929) which is defined as follows: A geodetic datum derived from a general adjustment of the first-order level nets of both the United States and Canada, formerly called "Mean Sea Level." The year indicates the time of the last general adjustment. HORIZONTAL DATUM The horizontal datum for all locations in this report is the North American Datum of 1927 (NAD of 1927). SYMBOLS AND ABBREVIATIONS A glacier surface area, in square kilometers deg degree E UTM Easting F shape factor h glacier thickness, measured perpendicular to glacier bed, in meters h* glacier thickness, measured vertically between glacier surface and glacier bed, in meters k scale factor £ mean scale factor m/jas meter per microsecond MHz megahertz min minutes r2 coefficient of determination S transmitter-receiver separation, in meters Contents V id time delay, in microseconds UTM Universal Transverse Mercator y estimated glacier volume, in cubic kilometers va velocity of light in air, in meters per microsecond v, velocity of light in ice, in meters per microsecond X,, local sea-level coordinate, increasing eastward Y(> local sea-level coordinate, increasing northward Z altitude above sea level, in meters ct glacier surface slope (3 average glacier bed slope (3# bed slope at the basal reflection point H micro T,, yield stress of ice, in kilopascals 1h basal shear stress, in kilopascals VI Contents Snow and Ice Volume on Mount Spurr Volcano, Alaska, 1981 By Rod S. March, Lawrence R. Mayo and Dennis C. Trabant Abstract Mount Spurr (3,374 meters altitude) is an active volcano 130 kilometers west of Anchorage, Alaska, with an extensive covering of seasonal and perennial snow, and glaciers. Knowledge of the volume and distribution of snow and ice on a volcano aids in assessing hydrologic hazards such as floods, mudflows, and debris flows. In July 1981, ice thickness was measured at 68 locations on the five main glaciers of Mount Spurr: 64 of these measurements were made using a portable 1.7 megahertz monopulse ice-radar system, and 4 measurements were made using the helicopter altimeter where the glacier bed was exposed by ice avalanching. The distribution of snow and ice derived from these measurements is depicted on contour maps and in tables compiled by altitude and by drainage basins. Basal shear stresses at 20 percent of the measured locations ranged from 200 to 350 kilopas- cals, which is significantly higher than the 50 to 150 kilopascals commonly referred to in the liter ature as the "normal" range for glaciers. Basal shear stresses higher than "normal" have also been found on steep glaciers on volcanoes in the Cascade Range in the western United States. The area of perennial snow and ice coverage on Mount Spurr was 360 square kilometers in 1981, with an average thickness of 190±50 meters. Seasonal snow increases the volume about 1 percent and increases the area about 30 percent with a maximum in May or June. Runoff from Mount Spurr feeds the Chakachatna River and the Chichantna River (a tributary of the Beluga River). The Chakachatna River drainage contains 14 cubic kilometers of snow and ice and the Chichantna River drainage contains 53 cubic kilometers. The snow and ice volume on the mountain was 67±17 cubic kilometers, approximately 350 times more snow and ice than was on Mount St. Helens before its May 18, 1980, eruption, and 15 times more snow and ice than on Mount Rainier, the most glacierized of the measured volcanoes in the Cascade Range. On the basis of these relative quantities, hazard-producing glaciovolcanic phenomena at Mount Spurr could be significantly greater than similar phenomena at Cascade Vol canoes. INTRODUCTION Following the eruption of Mount St. Helens in May 1980, the U.S. Geological Survey accel erated the assessment of hazards at other volcanoes. On the basis of their historical eruptive pat terns, Mount Spurr (fig. 1) and several other volcanoes in Alaska, including Mount Redoubt, were identified as being among those volcanoes