THESIS APPROVAL The abstract and thesis of Julia Pamela Griswold for the Master of Science in Geology were presented June 11, 2004, and accepted by the thesis committee and the department. COMMITTEE APPROVALS: _______________________________________ Andrew G. Fountain, Chair _______________________________________ Richard M. Iverson _______________________________________ Scott F. Burns _______________________________________ J. Alan Yeakley Representative of the Office of Graduate Studies DEPARTMENT APPROVAL: _______________________________________ Michael L. Cummings, Chair Department of Geology ABSTRACT An abstract of the thesis of Julia Pamela Griswold for the Master of Science in Geology presented June 11, 2004. Title: Mobility Statistics and Hazard Mapping for Non-volcanic Debris Flows and Rock Avalanches. Power-law equations that are physically motivated and statistically tested and calibrated provide a basis for forecasting areas likely to be inundated by debris flows, 2/3 rock avalanches, and lahars with diverse volumes (V). The equations A=α1V and 2/3 B=α2V indicate that the maximum valley cross-sectional area (A) and total valley planimetric area (B) likely to be inundated by a flow depend only on the flow volume and topography of the flow path. Testing of these equations involves determining whether they satisfactorily fit data for documented flows, and calibration entails determining best-fit values of the coefficients α1 and α2. This thesis describes statistical testing and calibration of the equations using field data compiled from many sources, and it describes application of the equations to delineation of debris-flow hazard zones in the Coast Range of southern Oregon. Separate inundation-area equations are appropriate for debris flows, rock avalanches, and lahars, because statistical tests demonstrate that data describing A, B, and V for these types of flows are derived from distinct parent populations. For all flow types, the dependence of A and B on V is described better by power-law equations than by linear, quadratic, or exponential equations. Moreover, F-tests show that power laws with exponents equal to 2/3 produce fits that are effectively indistinguishable from the best fits obtained using adjustable power-law exponents. Calibrated values of the coefficients α1 and α2 provide a scale-invariant index of the relative mobility of rock avalanches (α1 = 0.2, α2 = 20), non-volcanic debris flows (α1 = 0.1, α2 = 20), and lahars (α1 = 0.05, α2 = 200). These values show, for example, that a lahar of specified volume can be expected to inundate a planimetric area ten times larger than that inundated by a rock avalanche or non-volcanic debris flow of the same volume. The utility of the calibrated debris-flow inundation equations A=0.1V2/3 and B=20V2/3 was demonstrated by using them within the GIS program LAHARZ to delineate nested hazard zones for future debris flows in an area bordering the Umpqua River in southern Oregon. This application required knowledge of local geology to specify a suitable range of prospective debris-flow volumes and required development and use of a new algorithm for identification of prospective debris-flow source areas in finely dissected terrain. 2 MOBILITY STATISTICS AND HAZARD MAPPING FOR NON-VOLCANIC DEBRIS FLOWS AND ROCK AVALANCHES by JULIA PAMELA GRISWOLD A thesis submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE in GEOLOGY Portland State University 2004 ACKNOWLEDGEMENTS I have many to thank but there are two to whom I am especially grateful. Dick Iverson was the lead advisor for this thesis directing the scope of the thesis, providing generous guidance, and spending many hours bringing order and sense to my writing. Steve Schilling provided the technical training and support, supplied the review for the GIS-related portions of the thesis, and bore the brunt of my daily GIS questions. I was very fortunate to be made apart of their research efforts and to work alongside such first rate scientists. Good humor, creative solutions, fieldwork projects (especially helping at the USGS flume experiments), and boxes of donuts made for a productive and thought-provoking couple of years. It has been an undeserved privilege working with Dick and Steve, and I thank them whole-heartedly for the experience and for opening many doors for me. Both Dick and Steve arranged USGS student contract positions that supported and trained me through my thesis. I also would like to acknowledge Jason Hinkle (Oregon Dept. of Forestry) and Jon Hofmeister (Oregon Dept. of Geology and Mineral Industries) who helped early on sharing their ideas and experience. Visiting the lower Umpqua River valley together stressed the consequences of debris flow-related fatalities, structural damage, and channel impacts. Their professionalism, enthusiasm, and friendship are greatly appreciated. Jason also provided the Scottsburg LIDAR. I’m indebted to Scott Burns for drawing me out to Portland and for his kind support throughout my coursework, my participation with AEG, and in reviewing my thesis. Scott’s untiring commitment to his students and his professional participation in AEG are greatly appreciated. I am especially grateful to him for slipping me extra tickets to AEG functions! Big thanks also go to Andrew Fountain and Alan Yeakley for serving on my thesis committee. Andrew provided the valuable link between the USGS and PSU. A cheer goes out to Martin Streck and Nancy Eriksson for their help, interest, and kindness during my four years at PSU. Among the many PSU students, there are a special few who enjoyed arguing the finer points of geology over a pint: Michelle i Cunico, Aaron Fox, Brent Gaston, Hiram Henry, Kenny Janssen, Robin Johnston, Meg Lunney, Jason Taylor and Susan Wacaster. Thanks to all the colorful characters at CVO who create a work place of ideas and who supplied empty threats and horror stories of what might happen if I never finished. The good wishes and coffee pot runneth over. Lastly and ultimately, hugs and kisses to my entire Woodbury family. Without my family’s help, this masters endeavor would have been more difficult, if not impossible. And I can’t forget my constant desktop companion, Pinatubo the cat. ii TABLE OF CONTENTS Acknowledgements .........................................................................................................i List of Tables.................................................................................................................iv List of Figures ................................................................................................................ v Chapter 1: Introduction .................................................................................................. 1 Description of the Physical/ Geological Phenomena .................................................2 Specific Objectives.....................................................................................................5 Chapter 2: Runout Prediction Methods .......................................................................... 7 Historic and Geologic Evidence.................................................................................7 Physically Based Models............................................................................................8 Empirical Models .......................................................................................................9 Statistical Models Constrained by Physical Scaling Arguments..............................11 Chapter 3: The Database ............................................................................................. 14 Data Quality .............................................................................................................16 Chapter 4: Discrimination between Datasets .............................................................. 19 Chapter 5: Regression Analysis .................................................................................. 25 Comparison of Various Regression Models.............................................................25 Analysis of Variance ................................................................................................27 Results of the F-test..................................................................................................30 Summary and Interpretation of Statistical Results...................................................43 Chapter 6: Debris-Flow Application using DEMs and GIS........................................ 45 Data Input.................................................................................................................46 Debris-Flow Test Area – Scottsburg, Oregon ..........................................................49 History of the Scottsburg area ..............................................................................49 Topography and geology......................................................................................50 Topographic dataset: acquisition and description ................................................51 Flow volume assessment for Scottsburg ..............................................................52 LAHARZ application ...........................................................................................54 Hazard Map Evaluation............................................................................................59 Chapter 7: Conclusions ..............................................................................................