THE ROLE OF LITHOSPHERIC DELAMINATION AND ICE-DRIVEN ROCKFALL EROSION IN THE EVOLUTION OF MOUNTAINOUS LANDSCAPES by TRISTRAM CHARLES HALES A DISSERTATION Presented to the Department of Geological Sciences and the Graduate School of the University of Oregon in partial fulfillment of the requirements for the degree of Doctor of Philosophy December 2006 ii “The Role of Lithospheric Delamination and Ice-Driven Rockfall Erosion in the Evolution of Mountainous Landscapes,” a dissertation prepared by Tristram Charles Hales in partial fulfillment of the requirements for the Doctor of Philosophy degree in the Department of Geological Sciences. This dissertation has been approved and accepted by: ____________________________________________________________ Joshua J. Roering, Chair of the Examining Committee ________________________________________ Date Committee in Charge: Joshua J. Roering, Chair Eugene D. Humpherys Ray J. Weldon II W. Andrew Marcus Accepted by: ____________________________________________________________ Dean of the Graduate School iii © 2006 Tristram Charles Hales iv An Abstract of the Dissertation of Tristram Charles Hales for the degree of Doctor of Philosophy in the Department of Geological Sciences to be taken December 2006 Title: THE ROLE OF LITHOSPHERIC DELAMINATION AND ICE-DRIVEN ROCKFALL EROSION IN THE EVOLUTION OF MOUNTAINOUS LANDSCAPES Approved: _______________________________________________ Joshua J. Roering This dissertation discusses the evolution of mountains, particularly the interaction between uplift, which is controlled by horizontally-directed plate tectonic and vertically- directed isostatic forces, and erosion, which encompasses glacial, periglacial, fluvial and hillslope processes. Eruption of the Columbia River Basalts (CRB) in northeastern Oregon is coincident with rapid uplift of the Wallowa Mountains. I mapped the modern distribution of CRB flows to quantify the amount of post-eruptive uplift in northeastern Oregon, which creates a broad “bull’s eye” pattern centered on a large granitic pluton. Rapid Wallowa Mountain uplift appears to be related to delamination of dense lower crust beneath the Wallowa batholith and is the likely cause of flood basalt volcanism at ~17 Ma B.P. v Rapid rockfall erosion rates in high mountains create extensive talus slopes. Parts of the Southern Alps, New Zealand, are dominated by kilometer-scale scree-mantled slopes which reduce hillslope gradients and decrease drainage densities. Field and aerial photograph-based analysis of scree slopes (i.e. rockfall deposits) reveal a peak in the areal extent and rate of scree slope formation in the eastern Southern Alps. This spatial distribution precludes earthquakes, post-glacial stress release, and rock type as primary rockfall triggering mechanisms. Instead, scree slopes occupy a narrow elevation range across the New Zealand Alps and the mean elevation of scree slopes is consistent with a theory for rockfall initiation by frost cracking and segregation ice growth, a process that breaks rocks through surface interactions at the ice/rock interface. Supported by data from the Southern Alps and other mountainous areas, I propose a simple numerical heat flow model to predict the climatic conditions and rock fracture spacing required for frost cracking. This model suggests that in highly fractured rocks the ultimate elevation of mountain peaks may be governed by the efficacy of frost action. This dissertation includes both my previously published and co-authored material. vi CURRICULUM VITAE NAME OF AUTHOR: Tristram Hales PLACE OF BIRTH: Christchurch, New Zealand DATE OF BIRTH: 21 May 1979 GRADUATE AND UNDERGRADUATE SCHOOLS ATTENDED: University of Oregon University of Canterbury DEGREES AWARDED: Doctor of Philosophy, 2006, University of Oregon Bachelor of Science with Honours (Geological Science), 2000, University of Canterbury AREAS OF SPECIAL INTEREST: Tectonic Geomorphology Landscape Evolution PROFESSIONAL EXPERIENCE: Graduate Teaching Fellow, University of Oregon, 2001-2006 Glacier Guide, Franz Josef Glacier Guides, 1999 vii GRANTS, AWARDS AND HONORS: PRIME Lab Seed Analysis Grant, Cosmogenic Isotope Sampling of Headwall Erosion, Purdue University, 2004 Graduate Student Research Award, Scree Production and Landscape Evolution, Geological Society of America, 2004 Outstanding Student Paper Award, Estimates of Erosion Rates for the Central Southern Alps, New Zealand, American Geophysical Union, 2002 PUBLICATIONS: Hales, T.C., D.L. Abt, E.D. Humphreys, and J.J. Roering, (2005) Convective Instability as an origin for the Columbia River Basalts and Wallowa Mountain uplift in NE Oregon, USA. Nature, 438, 842-845. Hales, T.C., and J.J. Roering (2005). Climate controlled variations in scree production, Southern Alps, New Zealand. Geology, 33, 701-704. Hales, T.C., and J.J. Roering, (2006), Climatic controls on frost cracking and the evolution of bedrock landscapes. Journal of Geophysical Research. In press. viii ACKNOWLEDGMENTS With the acceptance of this dissertation I will become the first person in my family to be awarded a Ph.D. The award is not the achievement of an individual, but instead is a testimonial to the love and support of my whanau, who are dearest to me. It has been my whanau that has taught me to love, appreciate and learn from nature, to work and play hard, and to enjoy life, and it gives me pleasure to dedicate this thesis to them. I would like to say many thanks to Josh Roering, my advisor who has provided me with much financial, academic, and emotional support over the last five years. Not only is he an example of a great scientist, but an example of a balanced human being. He is not only a great advisor and a great example of how to take the most from life. I really appreciate his friendship and collaboration and hope that it continues into the future. I am also grateful for the support of Gene Humphreys, who opened my horizons beyond process geomorphology to thinking about the dynamics of the earth at a large scale. His approach to science, particularly his focus on understanding, using simple physics, the processes that govern the evolution of Earth’s surface have been an inspiration. To the rest of the faculty at the University of Oregon who have provided me with help, support and friendship over the past five years. In particular thanks to Andrew Marcus, Ray Weldon, Becky Dorsey, and Alan Rempel, who have provided great ix scientific support throughout my dissertation. I would also especially like to thank Kathy Cashman and Marli Miller for exemplary teachers. I would also like to recognize the support of the many friends that I have made during my time in Oregon, in particular, Kate Scharer, Todd Lamaskin, Heather Wright, Reed Burgette, Noah Fay, and Darwin Villagomez for making the Geology department such a great place to work. Also many thanks to the people who kept my life balanced by taking me into the outdoors, watching world rally, teaching me about American sports, and eating Sunday brunch, particularly Pete and Sarah Erslev, Heather and Brian Ulrich, Jake Casper, Garner Britt, Jacob Selander, and George (Mac) Jenkins. Finally to the many people that made my day to day life happy in the Roering lab, many thanks to Alison Rust, Mackenzie Johnson, Molly Gerber, Suzanne Walther, Amanda Macleod, Ben Mackey, and Lisa Emerson. Last but by no means least this dissertation would not have happened without the love and support of my wife, field assistant and the best field camp student that I have ever had, Jenny Riker. x For Ralph Edward Thomas Hales and Joie Louisa Lyttle xi TABLE OF CONTENTS Chapter Page I. INTRODUCTION ...............................................................................................1 II. A LITHOSPHERIC INSTABILITY ORIGIN FOR COLUMBIA RIVER FLOOD BASALTS AND WALLOWA MOUNTAINS UPLIFT IN NORTHEAST OREGON ....................................................................................5 III. CLIMATE-CONTROLLED VARIATIONS IN SCREE PRODUCTION, SOUTHERN ALPS, NEW ZEALAND ............................................................17 3.1. Introduction ....................................................................................................17 3.2. Study Area .....................................................................................................19 3.3. Methods ..........................................................................................................21 3.4. Results ............................................................................................................23 3.5. Discussion and Conclusions .........................................................................25 IV. ROCKFALL EROSION AND POSTGLACIAL EVOLUTION OF THE SOUTHERN ALPS, NEW ZEALAND ............................................................33 4.1. Introduction ....................................................................................................33 4.2. Study Area .....................................................................................................38 4.2.1. Western Southern Alps ..........................................................................42 4.2.2. Axial Southern Alps ...............................................................................44 4.2.3. Eastern Southern Alps ............................................................................45 4.2.4. Topographic Characteristics...................................................................50 4.3. Field and Topographic Analysis of the Eastern Southern