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AN ABSTRACT OF THE THESIS OF Shyam Das-Toke for the degree of Master of Science in Geology presented on April 29, 2019 Title: Creating a Predictive Model of Cinder Cone Ages in Central Oregon Abstract approved: ___________________________________________________ Adam J.R. Kent Cinder cones are useful geomorphic features for geological analysis because they generally have known initial states and follow a similar pattern of degradation as they are exposed to erosive processes. Characterizing large cinder cone fields in terms of age and composition requires significant resources, so this study aims to understand the parameters that influence cinder cone evolution in order to create a predictive age model of cones in Central Oregon. We utilize newly available high- resolution topography and new estimates of cinder cone age to evaluate a quantitative model of cone ages. The field site allows assessment of the effects of cone composition and precipitation in governing the morphology of Central Oregon cinder cones through time. We anticipate that these results will allow estimation of the age of individual cones which have not yet been dated directly. Statistical analyses show that younger cones have both significantly steeper slopes and more defined cone craters than older ones. Results also show that increased local precipitation does not appear to significantly influence cone morphology. However, composition as determined by silica content does influence initial morphology, as weight percentages vary by 15% and lead to differences of 8° in cone slope. After cone formation though, erosive processes such as mass wasting are more influential in influencing cones than chemical content. The statistical model of cone age that we create can be used to estimate cinder cone ages throughout the Central Oregon region and can be used in time-volume studies of monogenetic volcanism. The model and procedure should also be applicable in other portions of the Cascades and potentially to other volcanic fields. ©Copyright by Shyam Das-Toke April 29, 2019 All Rights Reserved Creating a Predictive Model of Cinder Cone Ages in Central Oregon by Shyam Das-Toke A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Presented April 29, 2019 Commencement June 2019 Master of Science thesis of Shyam Das-Toke presented on April 29, 2019 APPROVED: Major Professor, representing Geology Dean of the College of Earth, Ocean, and Atmospheric Sciences Dean of the Graduate School I understand that my thesis will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my thesis to any reader upon request. Shyam Das-Toke, Author ACKNOWLEDGEMENTS This work would not have been possible without the incredible support of my advisor, Dr. Adam Kent, and my committee members, Dr. Andrew Meigs, Dr. Eric Kirby, and Dr. David Cann, who provided input on my thesis and reviewed drafts several times. Thanks also to the United States Geological Survey and Julie Donnelly-Nolan, who provided age and silica content information for many of the cones in this study. Additional thanks to the Oregon Department of Geology and Mineral Industries, which provided the LiDAR imagery for the morphometric analyses. Without this data, we could not have obtained the detailed measurements of slope and crater transition that we use. TABLE OF CONTENTS Page Background ................................................................................................................. ..1 Motivation ................................................................................................................... 8 Methodology ................................................................................................................. 9 Evaluating Morphology ................................................................................................ 9 Cone Parameter Data ................................................................................................. 11 Statistical Treatments ................................................................................................. 13 Results and Discussion ............................................................................................... 15 Differences in Aspect .................................................................................................. 16 Overview of Potential Regression Models ................................................................. 22 Linear Models ............................................................................................................. 26 Effect of Precipitation, Outer Slope, and Silica Content on Age .................................... 27 Crater Slope .............................................................................................................. 30 Combined Regression ................................................................................................ 33 Uncertainties ............................................................................................................... 38 Conclusion .................................................................................................................. 43 Appendix A: Script in R ............................................................................................. 45 Appendix B: Cutoffs for Confidence Levels .............................................................. 46 Appendix C: USGS Silica Weight Percentage Database ............................................ 47 Appendix D: List of Cones ......................................................................................... 54 Appendix E: Precipitation and Angle..………………………………………………55 References ................................................................................................................... 59 LIST OF FIGURES Figure 1 Schematic of Cones. ..................................................................................... 11 Figure 2 Measured Parameters.................................................................................... 13 Figure 3 Cross Section of Cone:. ................................................................................ 13 Figure 4 Comparison of Slopes................................................................................... 18 Figure 5 Map of Cone Locations ................................................................................ 21 Figure 6 Plot of Assymetry in NVZ.. .......................................................................... 24 Figure 7 Plot of Assymetry in all Cones ..................................................................... 25 Figure 8 Plot of Crater Assymetry .............................................................................. 26 Figure 9 QQ Plots of Regressions ............................................................................... 34 Figure 10 Cone Age vs. Crater Slope. ........................................................................ 41 Figure 11 Outer Slope vs Cone Age .......................................................................... 41 Figure 12 Predicted Cone Ages. ................................................................................. 44 Figure 13 Measured vs. Predicted Ages….………………………………...………..46 Figure 14 Crater Angle vs. Cone Age………………………………………..……....46 Figure 15 Comparison of Eruptive Style..……………………………………....…...49 LIST OF TABLES Table Page Table 1:. .......................................................................................................................25 Table 2:. .......................................................................................................................25 Table 3:…………………………………………………………………………...… 27 Table 4 …………………..……………………………………………………….….27 Table 5: ........................................................................................................................43 Table 6: ........................................................................................................................50 1 Background Cinder cones are often understudied volcanic landforms, because larger stratovolcanoes often take up more attention and research. However, recent developments in technology, landscape imagery, and dating methodologies provide new techniques for detailed and accurate cone measurements and age determinations, which can save time and resources in characterizing these landforms. Cinder cones are formed when a volcanic vent erupts and volcanic debris such as tephra and scoria or spatter are deposited around it (Fig 1). The initial slopes of the cone are dictated by the critical angle of repose (Porter et al. 1972, Wood 1980). Because diffusion processes follow similar patterns in these areas, we can create predictive models of cone age based on measurable parameters such as morphology, silica, and precipitation exposure. Doing this allows us to estimate the age of cones without conducting time-consuming and resource intensive dating methodologies. While numerous potential factors can help determine how old a cone is, this study focuses on morphology, precipitation, composition, and initial eruption style. Previous studies show that age, precipitation, and chemical composition have statistically significant relationships with cinder cone morphology (Porter et al. 1972, Taylor et al. 2003, McGuire et al. 2014). However, no study has compiled a comprehensive relationship among all of these