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Thesis Approval THESIS APPROVAL The abstract and thesis of Robin Rachelle Johnston for the Master of Science in Geology presented February 12, 2004, and accepted by the thesis committee and the department. COMMITTEE APPROVALS: ________________________________________ Andrew G. Fountain, Chair ________________________________________ Christina L. Hulbe ________________________________________ Martin J. Streck ________________________________________ Aslam Khalil Representative of the Office of Graduate Studies DEPARTMENTAL APPROVAL: ________________________________________ Michael L. Cummings, Chair Department of Geology ABSTRACT An abstract of the thesis of Robin Rachelle Johnston for the Master of Science in Geology presented February 12, 2004 Title: Channel Morphology and Surface Energy Balance on Taylor Glacier, Taylor Valley, Antarctica Deeply-incised channels on Taylor Glacier in Taylor Valley, Antarctica initiate as medial moraines traced tens of kilometers up-glacier, are aligned with the direction of flow, and at their most developed occupy about 40% of the ablation zone in the lower reaches of the glacier. Development of the South Channel occurs in three stages. The first stage, the 1st Steady State, is characterized by rather uniform development, where the channel widens at much less than 0.1 m yr-1 and deepens at much less than 0.01 m yr-1, maintaining a width to depth ratio of about 8. The second stage, the Transition Phase, is characterized by dramatic widening channel (from 10 to 110 m) and deepening (from 2 to 24 m). During this stage, the peak rate of widening is about 1.5 m yr-1 and the channel is about 25 times as wide as it is deep. The third stage of channel development, the 2nd Steady State, is characterized by a steady decrease in the rate of channel deepening and a leveling off of the width to depth ratio as the channel ceases to widen. Eventually, the channel reaches a new near equilibrium state of continued uniform development where the width to depth ratio is about 4. The microclimate within the channels differs significantly from conditions on the adjacent glacier surface. The channels are warmer by 1.7°C, have wind speeds reduced by 2.4 m s-1, and the net shortwave radiation is greater by about 14 W m-2 compared to the glacier surface. As a result, melt makes up a much higher percentage of the total ablation within the channels than it does on the glacier surface – as much as 75% and perhaps up to 99% under extremely low wind regimes, compared to about 45%. While the altered microclimate within the channels drives their rapid development during the Transition Phase, the relationship between average wall slopes and solar angles may represent the channels coming into equilibrium with the solar regime in the valley. CHANNEL MORPHOLOGY AND SURFACE ENERGY BALANCE ON TAYLOR GLACIER, TAYLOR VALLEY, ANTARCTICA by ROBIN RACHELLE JOHNSTON A thesis submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE in GEOLOGY Portland State University 2004 DEDICATION Dedicated with enormous gratitude to my dear sister and friend, Kim Kathline Johnston - who teaches much to many - for her extraordinary love and untiring support throughout time. Sis, thank you for taking this journey with me. A grand journey it has been, shaped and colored by a multitude of nobulets and rainwedges. May we forever be able to recognize them in our world, and may they be abundant. I love you so much. i ACKNOWLEDGEMENTS I owe much thanks to many people: my advisor, Andrew Fountain, for making my graduate studies so interesting; my committee members, Christina Hulbe, Martin Streck, and Aslam Khalil, for their insight; Thomas Nylen, for being a great field partner and office mate; and the entire staff of the Geology Department, all of whom strive for excellence. There are others to thank as well: Karen Lewis, for sharing her knowledge; Jennifer Horsman and Chris Jaros, for their efforts to provide me with aerial photographs of Taylor Valley; Rae Spain for her superb operations of Lake Hoare Camp and her friendship; Kathy Welsh, for making being at McMurdo all the more interesting; the operation controllers and pilots at McMurdo HeloOps; and Jeff Scanniello, Chuck Kurnik, Dennis Kenley, Forrest McCarthy, Bill McCormick, and many others who helped with field support in Taylor Valley. There isn’t enough thanks in the world for the friendship and support of William Schryver, the man of a thousand pertinent questions. To my good friends Michelle Cunico-Johnson, Julie Griswold, Meg Lunney, Christina Hulbe, and Nancy Erikkson – I do, and shall, miss sharing time with you daily. I’ve made many other friends along the way for whom I’m grateful. I send special thanks to Murphy Johnston for his fuzzy, warm companionship. And thank you Kim, for everything. The National Science Foundation (NSF) provided funding for this work as part of the NSF Long-Term Ecological Research (LTER) program through grant number OPP-9810219. It was my good fortunate to be involved in this incredible project. ii Table of Contents Acknowledgements ............................................................................................................ii List of Figures.................................................................................................................... v List of Tables...................................................................................................................xiii 1 Introduction...................................................................................................................1 1.1 Geographic Setting.........................................................................................4 1.2 Glacial Characteristics....................................................................................6 1.3 Glacial History................................................................................................8 2 Surface Features and Debris Distribution on Glaciers in Taylor Valley....................10 2.1 Surface Features ...........................................................................................10 2.2 Aligned and Transverse Features .................................................................20 2.3 Sediment Distribution...................................................................................23 3 Channel Morphology and Meteorological Measurements .........................................28 3.1 Channel Geometry........................................................................................29 3.1.1 Observations .....................................................................................30 3.2 Albedo ..........................................................................................................38 3.2.1 Observations .....................................................................................38 3.3 Cryoconite Holes ..........................................................................................41 3.3.1 Observations .....................................................................................44 3.4 Surface and Channel Meteorological Data...................................................47 3.4.1 Observations .....................................................................................49 3.5 Channel Morphology – A Working Hypothesis...........................................58 iii 4 Energy Balance...........................................................................................................66 4.1 Energy Balance Model.................................................................................67 4.1.1 Radiative Heat Flux..........................................................................69 4.1.2 Turbulent Heat Fluxes ......................................................................71 4.1.3 Ice Heat Flux ....................................................................................73 4.2 Energy Balance Model Results ....................................................................74 4.2.1 Established Met Station: 1994-1995 ................................................78 4.2.2 Channel Energy Balance ..................................................................80 4.2.3 Error and Sensitivity Analysis ..........................................................84 4.2.4 Meltwater Contribution to Lake Bonney..........................................88 4.3 Energy Balance Discussion..........................................................................90 5 Conclusions.................................................................................................................92 6 References...................................................................................................................96 Appendix A – Survey Data Sample...............................................................................100 Appendix B - South Channel Cross-Sections................................................................101 Appendix C - North Channel Cross-Sections................................................................106 Appendix D - Ice Speed and Radar Data.......................................................................112 Appendix E - Rate of Change in Width, Depth, and Width to Depth Ratio .................113 Appendix F – Geographic Location of Stakes, Cross-Sections, and Met Station.........116 iv List of Figures Figure 1.1 – Satellite image of the McMurdo Dry Valleys (NSF, 1999). Upper inset shows location of larger image...............................................................................2
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