Glacier Change in the North Cascades National Park Complex, Washington State USA, 1958-1998 Frank D. Granshaw Portland State University Geology Department THESIS APPROVAL The abstract and thesis of Frank D. Granshaw for the Master of Science in Geology were presented December 7, 2001, and accepted by the thesis committee and the department. COMMITTEE APPROVALS: Andrew G. Fountain, Chair Scott F. Burns Martin J. Streck Daniel M. Johnson Representative of the Office of Graduate Studies DEPARTMENT APPROVAL: Michael L. Cummings, Chair Department of Geology ABSTRACT An abstract of the thesis of Frank D. Granshaw for the Master of Science in Geology presented December 7, 2001. Title: Glacier Change in the North Cascades National Park Complex, Washington State USA, 1958 to 1998 The North Cascades National Park Complex contains 25% of the glaciers of the contiguous United States. In addition to their ecological and scenic value, these glaciers are a major water resource for northwestern Washington. Despite their importance, little information about glacier change in the complex exists. To address this problem an inventory of all glaciers in the complex was constructed for 1958 and for 1998. Data from this inventory, regional climate data, and streamflows for selected watersheds were used to determine the extent of glacier change, the causes of that change, and the impact of glacier change on regional water resources. From 1958 to 1998 the glacier population of the complex dropped from 321 to 316 and combined glacier area decreased by 7.0%. Total glacier volume loss is estimated at -0.8±0.1 km3. This reduction resulted from the disappearance of five small glaciers and mass loss from 80% of the remaining glaciers. This change was due to a warming, drying trend in regional climate, particularly during the period 1977-1997. Rates of change for individual glaciers were primarily influenced by area, but unaffected by other topographic characteristics. During the period 1958-1998, glacier mass loss contributed less than 1.0 km3 to the total stream flow of the Skagit, Nooksak, and Stehekin Rivers. Though this contribution may seem insignificant, average annual glacier mass loss accounts for 0.1 to 6.0% of the runoff during the two driest months of the year, August and September. Alternately, average mass loss augments precipitation by as much as 16%. A comparison of the topographic characteristics of five regularly monitored or “index” glaciers to the regional database revealed that only one of these glaciers, Sandalee Glacier, is representative of the typical glacier in the complex. The changes in the index glaciers to area / volume changes in the bulk of the glaciers show that index glaciers can not be used to accurately infer the magnitude of the regional change in glacier cover. However, the index glaciers can be used to infer the rate of change over time. GLACIER CHANGE IN THE NORTH CASCADES NATIONAL PARK COMPLEX, WASHINGTON STATE USA, 1958 TO 1998 by FRANK D. GRANSHAW A thesis submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE in GEOLOGY Portland State University 2002 Acknowledgments This project was supported by research grants from the US National Park Service (North Cascades National Park) and the Oregon Space Grant Project (Oregon State University). Special thanks go to my thesis advisor Andrew G. Fountain and the other members of the thesis committee Scott Burns, Martin Streck, and Dan Johnson for their guidance, patience, friendship, and humor. Additional thanks go to Jon Riedel, Robert Burrows, and Anne Bratten of the US National Park Service, Bob Krimmel, Austin Post (retired) of the US Geological Survey, Mauri Pelto of Nicholls College, and Wendell Tangborn of Hymet Corporation for the data, support, and technical assistance they provided. Lastly, I thank my wife Annette who has been incredibly supportive during this research and also gave me quite a bit of good advice. page i Table of Contents Acknowledgments ......................................................................................................i List of Figures...........................................................................................................iv List of Tables.............................................................................................................vi Chapter 1 - Introduction ............................................................................................1 Project Description ..........................................................................................2 Previous work .............................................................................................. 2 Setting ............................................................................................................8 Chapter 2 - Spatial characteristics of national park complex glaciers.........................15 Regional glacier characteristics........................................................................ 15 Estimating glacier volume................................................................................ 26 Regional glacier change .................................................................................. 32 Summary ........................................................................................................35 Chapter 3 - Index glaciers: Do they represent glaciers of the region?........................37 Spatial characteristics ......................................................................................37 Glacier change................................................................................................. 42 Index glaciers as representative of regional characteristics and change ........... 44 Mass balance and index glaciers......................................................................45 Summary ........................................................................................................52 Chapter 4 - Spatial and temporal climate....................................................................54 Background ....................................................................................................54 Climatic trends based on climate station data .................................................. 57 Climatic trends based on divisional data .........................................................59 Climatic trends based on SOI and PDO ......................................................... 61 Summary ........................................................................................................63 Chapter 5 - Response of streamflow to climatic variations .......................................65 Hydrology and stream monitoring of the Park Complex ................................65 Hydroclimatology of watersheds with glaciers................................................68 Page ii Trends in streamflow ......................................................................................69 Timing and annual variability of stream flow...................................................71 Comparison of streamflow to climate..............................................................74 Summary ........................................................................................................76 Chapter 6 - Impact of glacier volume change on water flow .....................................78 Glacier melt, precipitation, and runoff in selected basins ................................ 79 Projected changes in glacier cover and runoff for selected watersheds ...........83 Summary ........................................................................................................86 Chapter 7 - Discussion and Conclusions .................................................................88 Chapter 8 - Recommendations for future work ........................................................91 References Cited...................................................................................................... 95 Appendix A - Glacier Inventory ........................................................................... 105 Appendix B - Climate data ..................................................................................... 123 Appendix C - Hydrologic data ............................................................................... 129 Appendix D - Data directory and sources ............................................................. 132 Appendix E - Contents of companion CD .............................................................134 Page iii List of Figures Figure 1.1 - Location of study site............................................................................10 Figure 1.2 - Generalized seasonal air flow over the Pacific Northwest .....................12 Figure 1.3 - Generalized air flow over northwestern Washington ............................13 Figure 1.4 - Average daily discharge for Skagit River ..............................................14 Figure 2.1 - Distribution of glaciers within the National Park Complex................... 17 Figure 2.2 - Fraction of glacier population versus area for 1958...............................23 Figure 2.3 - Number of glaciers versus area for 1958...............................................24 Figure 2.4 - Glacier population and area versus average elevation for 1958..............24 Figure 2.5 - Glacier elevation by north / south and east / west position for 1958.....25 Figure 2.6 - Glacier population and area versus average slope for 1958..................