THE VISCOSITY OF DACITIC LIQUIDS MEASURED AT CONDITIONS RELEVANT TO EXPLOSIVE ARC VOLCANISM: DETERMINING THE INFLUENCE OF TEMPERATURE, SILICATE COMPOSITION, AND DISSOLVED VOLATILE CONTENT A Thesis presented to the Faculty of the Graduate School University of Missouri-Columbia In Partial Fulfillment of the Requirements for the Degree Masters of Science by BRIDGET M. HELLWIG Dr. Alan G. Whittington, Thesis Supervisor May 2006 The undersigned, appointed by the Dean of the Graduate School, have examined the thesis entitled: THE VISCOSITY OF DACITIC LIQUIDS MEASURED AT CONDITIONS RELEVANT TO EXPLOSIVE ARC VOLCANISM: DETERMINING THE INFLUENCE OF TEMPERATURE, SILICATE COMPOSITION, AND DISSOLVED VOLATILE CONTENT Presented by Bridget M. Hellwig a candidate for the degree of Master of Science And hereby certify that in their opinion it is worthy of acceptance. _________________________ Alan G. Whittington _________________________ Peter I. Nabelek _________________________ Wouter Montfrooij ACKNOWLEDGMENTS I would like to thank Alan Whittington for his support, guidance, and patience throughout this project (and for being understanding when something broke). Thank you for giving me such a great opportunity. Next, I would like to thank Peter Nabelek and Wouter Montfrooij for being on my thesis committee. Thank you to Harald Behrens, Bastian Joachim and André Stechern at the Institut fur Mineralogie in Hannover, Germany for preparing my hydrous samples and to Bastian and Andre who also ran several of my hydrous samples on the parallel plate. I would also like to thank Oto Matias and Julio Cornejo for guiding us around Santiaguito and making the trip so enjoyable and memorable. ¡Usted es maravilloso! Thank you to Eddy Sanchez at INSIVUMEH for helping to make this trip possible. To the helicopter pilots who flew us around Santiaguito Dome Complex, thank you for showing us such a spectacular view of Santiaguito. I acknowledge the National Science Foundation for providing the funding for this project. I would like to thank Jackie Getson for spending so much quality time in the lab with me. It would have been dull without you. Finally, thank you to my parents and family, for always supporting and encouraging me to follow my dreams wherever they take me (even active volcanoes). And to Jason, thanks for your encouragement and for putting up with me through this whole project. I couldn’t have done it without you! ii TABLE OF CONTENTS ACKNOWLEDGMENTS.................................................................................................ii LIST OF FIGURES..........................................................................................................vi LIST OF TABLES.............................................................................................................x ABSTRACT.......................................................................................................................xi CHAPTER 1 – INTRODUCTION 1.1 Overview.......................................................................................................................1 1.2 Introduction..................................................................................................................1 1.3 Theoretical Background..............................................................................................4 1.3.1 Viscosity..........................................................................................................4 1.3.2 Effect of Water................................................................................................7 1.3.3 Effect of Fluorine..........................................................................................16 1.4 Geologic Setting.........................................................................................................19 1.5 Summary.....................................................................................................................25 CHAPTER 2 – METHODS 2.1 Overview.....................................................................................................................27 2.2 Sample Preparation...................................................................................................27 2.2.1 Compositions................................................................................................27 2.2.2 Glass Synthesis.............................................................................................28 2.2.3 Hydrous Sample Synthesis............................................................................30 2.2.4 Fluorine Sample Synthesis............................................................................34 2.2.5 Density Measurements..................................................................................35 iii 2.3 Parallel Plate Viscometry..........................................................................................36 2.3.1 Description of Viscometer............................................................................36 2.3.2 Sample Preparation......................................................................................42 2.3.3 Experimental Procedure...............................................................................43 2.3.4 Theory and Calculations...............................................................................44 2.3.5 Accuracy and Precision................................................................................47 2.4 Concentric Cylinder Viscometry..............................................................................49 2.4.1 Description of viscometer.............................................................................49 2.4.2 Sample Preparation......................................................................................54 2.4.3 Experimental Procedure...............................................................................54 2.4.4 Theory and Calculations..............................................................................57 2.4.5 Accuracy and Precision................................................................................59 2.5 Summary.....................................................................................................................61 CHAPTER 3 – RESULTS 3.1 Overview.....................................................................................................................62 3.2 Results.........................................................................................................................62 3.2.1 Anhydrous Samples.......................................................................................62 3.2.2 Hydrous Samples..........................................................................................68 3.2.3 Fluorine-bearing Samples............................................................................79 3.2.4 Variable compositions..................................................................................87 3.3 Summary.....................................................................................................................96 iv CHAPTER 4 – DISCUSSION 4.1 Overview.....................................................................................................................98 4.2 Viscosity Parameterization.......................................................................................98 4.3 Water Solubility and Speciation.............................................................................103 4.4 Water and the viscosity of silicate melts................................................................106 4.5 Petrological applications 1: Liquid viscosity during degassing..........................110 4.6 Petrological applications 2: Rates of igneous processes......................................116 4.6.1 Stokes Law..................................................................................................117 4.6.2 Critical Dike Width.....................................................................................118 4.6.3 Ascent rate in dikes.....................................................................................119 4.6.4 Reynolds Number........................................................................................120 4.6.5 Lava Flows..................................................................................................121 4.7 Summary...................................................................................................................123 CHAPTER 5 – CONCLUSIONS 5.1 Conclusions..............................................................................................................125 REFERENCES..............................................................................................................128 APPENDIX A – NIST STANDARD DATA................................................................139 v LIST OF FIGURES Figure Description Page Number 1.1 Map of the “Ring of Fire” 3 1.2 Effect of water on viscosity of trachytes 12 1.3 Viscosity of hydrous trachytes at constant temperature 13 1.4 Tg as a function of water content for various silicate 14 compositions 1.5 Tg of intermediate magmas with different alkali/alkaline 15 earth ratios as function of water content 1.6 Santiaguito Dome Complex and Santa Maria Volcano 20 1.7 Location Map of Santa Maria Volcano 21 1.8 The four domes of Santiaguito Dome Complex 22 1.9 Aerial photo of Caliente Dome 23 2.1 Ternary diagram showing various silicate melt compositions 29 2.2 The internally