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Megaripple Stripes University of Calgary PRISM: University of Calgary's Digital Repository Graduate Studies The Vault: Electronic Theses and Dissertations 2019-04-25 Megaripple Stripes Gough, Tyler Robert Gough, T. R. (2019). Megaripple Stripes (Unpublished master's thesis). University of Calgary, Calgary, AB. http://hdl.handle.net/1880/110217 master thesis University of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission. Downloaded from PRISM: https://prism.ucalgary.ca UNIVERSITY OF CALGARY Megaripple Stripes by Tyler Robert Gough A THESIS SUBMITTED TO THE FACULTY OF GRADUATE STUDIES IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE GRADUATE PROGRAM IN GEOGRAPHY CALGARY, ALBERTA APRIL, 2019 © Tyler Robert Gough 2019 ii Abstract This thesis incorporates field measurements, satellite imagery, and numerical modeling to explain the formation and evolution of a poorly understood and relatively undocumented longitudinal aeolian bedform pattern. The pattern consists of alternating streamwise corridors of megaripples separated by corridors containing smaller bedforms. This pattern, referred to herein as megaripple stripes, is observed at sites on Earth and Mars. Measurements from satellite imagery indicate a strong positive relation between the crosswind and downwind wavelengths of megaripple corridors. Field measurements of stripe morphology and grain size indicate a consistent pattern whereby the surface texture of the megaripple corridors is coarser than the intervening corridors of smaller bedforms. The amplitude and wavelength of features in the megaripple corridors are larger than the features in the smaller bedform corridors. The three-dimensional morphology and sediment sorting pattern of megaripple stripes was reproduced in a numerical model that incorporated two aeolian transport species: saltons and reptons. Simulations suggest striped pattern development is a self-organizing process resulting from grain size and topographic feedbacks that are sensitive to the bulk concentration and erosion probability of reptons. In the simulations, regular megaripples emerge from a high bulk concentration of reptons and impact ripples develop from a very low bulk concentration of reptons. Megaripple stripes emerge when the bulk concentration is intermediate between megaripple and impact ripple formation. Therefore, it is hypothesized that megaripple stripes develop in unimodal transport environments with supply-limited reptons. The nature and dynamics of reptons are largely determined by the wind regime, the grain size distribution, and by the grain density distribution in some environments. Repton behaviour, spanwise transport, and other relevant aeolian processes are discussed in relation to megaripple stripes. iii Preface This thesis is original, unpublished, independent work by the author, Tyler Gough. iv Acknowledgements Thank you to all who have helped me along the winding path of completing a thesis. First, thanks to Dr. Chris Hugenholtz for his encouragement and guidance. Chris, your enthusiasm for research and suggestions have made this process a valuable learning experience and a good deal of fun (most days). Second, thanks to Thomas Barchyn and Elena Favaro for providing ideas and tools which have been essential to this thesis. This thesis would not be complete without MGD, and I am grateful to Tom for developing the program and for his suggestions related to this research. Elena, your encyclopedic knowledge of department and University policies, as well as your willingness to take hours to talk out ideas with me have been invaluable. Third, many thanks to Paul Nesbit for his serving as tour guide, photogrammetry expert, and American English translator (“where is the washroom?”) during field work in California. Fourth, thanks to all others in the 922 research group for being outstanding colleagues and friends: Thomas, Maja, Andrew, Mo, Clay, Brynn, Adam, Eleanor, and Sarah. Fifth, thanks to my friends and family for being so understanding and supportive despite having only the roughest idea of what exactly it is I have been doing for the past two years. Finally, thanks to my partner, Hannah, whose patience and kindness I am eternally in awe of and grateful for. v Table of Contents Abstract ......................................................................................................................................................... ii Preface ......................................................................................................................................................... iii Acknowledgements ...................................................................................................................................... iv Table of Contents .......................................................................................................................................... v List of Tables ............................................................................................................................................. viii List of Figures .............................................................................................................................................. ix List of Abbreviations, Symbols, and Nomenclature .................................................................................. xiv Chapter 1: Introduction ................................................................................................................................. 1 1.1. Motivation and Objectives ................................................................................................................. 1 1.2. Literature Review ............................................................................................................................... 1 1.2.1. Aeolian Research ........................................................................................................................ 1 1.2.2. Impact Ripples ............................................................................................................................ 3 1.2.3. Megaripples ................................................................................................................................. 5 1.2.4. Aeolian Sediment Transport Fundamentals ................................................................................ 7 1.2.5. Aeolian Sediment Transport Thresholds ..................................................................................... 8 1.2.6. Spanwise Transport ................................................................................................................... 11 1.3. Megaripple Stripes ........................................................................................................................... 12 1.3.1. Oceano Dunes and Dillon Beach, California, USA .................................................................. 13 1.3.2. Abra Pomez, Argentina ............................................................................................................. 15 1.3.3. Paracas Peninsula and Ica Desert, Peru..................................................................................... 15 1.3.4. Lut Desert, Iran ......................................................................................................................... 18 1.3.5. Longyanxia Reservoir, China ................................................................................................... 18 1.3.6. Walvis Bay, Namibia ................................................................................................................ 18 1.3.7. Rabe Crater Dunes, Mars .......................................................................................................... 23 1.4. Research Approach and Working Hypotheses ................................................................................. 23 Chapter 2: Methodology ............................................................................................................................. 27 2.1. Overview .......................................................................................................................................... 27 2.2. Morphometrics ................................................................................................................................. 28 2.2.1. Wavelength Measurements ....................................................................................................... 28 2.2.2. 3D Reconstructions ................................................................................................................... 29 2.3. Grain Size Measurements and Analyses .......................................................................................... 30 2.3.1. Oceano Dunes, California ......................................................................................................... 31 2.3.2. Abra Pomez, Argentina ............................................................................................................. 33 vi 2.3.3. Grain Size Analyses .................................................................................................................. 34 2.4. Numerical Modeling .......................................................................................................................
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