ANALYSIS AND INTERPRETATION OF VOLCANO DEFORMATION IN ALASKA: STUDIES FROM OKMOK AND MT. VENIAMINOF VOLCANOES By Thomas J. Fournier RECOMMENDED: ________________________________________ Dr. Jessica Larsen ________________________________________ Dr. Peter Cervelli ________________________________________ Dr. Douglas Christensen ________________________________________ Dr. Stephen McNutt ________________________________________ Dr. Jeffrey Freymueller, Advisory Committee Chair ________________________________________ Dr. Michael Whalen, Chair, Department of Geology and Geophysics APPROVED: _______________________________________________ Dr. Joan Braddock, Dean, College of Natural Science and Mathematics _______________________________________________ Dr. Lawrence K. Duffy, Dean of the Graduate School _______________________________________________ Date ANALYSIS AND INTERPRETATION OF VOLCANO DEFORMATION IN ALASKA: STUDIES FROM OKMOK AND MT. VENIAMINOF VOLCANOES A THESIS Presented to the Faculty of the University of Alaska Fairbanks in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY By Thomas J. Fournier, B.A. Fairbanks, Alaska December 2008 iii Abstract Four studies focus on the deformation at Okmok Volcano, the Alaska Peninsula and Mt. Veniaminof. The main focus of the thesis is the volcano deformation at Okmok Volcano and Mt. Veniaminof, but also includes an investigation of the tectonic related compression of the Alaska Peninsula. The complete data set of GPS observations at Okmok Volcano are investigated with the Unscented Kalman Filter time series analysis method. The technique is shown to be useful for inverting geodetic data for time dependent non-linear model parameters. The GPS record at Okmok from 2000 to mid 2007 shows distinct inflation pulses which have several months duration. The inflation is interpreted as magma accumulation in a shallow reservoir under the caldera center and approximately 2.5km below sea level. The location determined for the magma reservoir agrees with estimates determined by other geodetic techniques. Smaller deflation signals in the Okmok record appear following the inflation pulses. A degassing model is proposed to explain the deflation. Petrologic observations from lava erupted in 1997 provide an estimate for the volatile content of the magma. The solution model VolatileCalc is used to determine the amount of volatiles in the gas phase. Degassing can explain the deflation, but only under certain circumstances. The magma chamber must have a radius between ~1and 2km and the intruding magma must have less than approximately 500ppm CO2. At Mt. Veniaminof the deformation signal is dominated by compression caused by the convergence of the Pacific and North American Plates. A subduction model is created to account for the site velocities. A network of GPS benchmarks along the Alaska Peninsula is used to infer the amount of coupling along the mega-thrust. A transition from high to low coupling near the Shumagin Islands has important implications for the seismogenic potential of this section of the fault. The Shumagin segment likely ruptures in more frequent smaller magnitude quakes. The tectonic study provides a useful backdrop to examine the volcano deformation at Mt. Veniaminof. After being corrected for tectonic motion the sites velocities indicate inflation at the volcano. The deformation is interpreted as pressurization occurring beneath the volcano associated with eruptive activity in 2005. iv Table of Contents Page Signature Page......................................................................................................................i Title Page.............................................................................................................................ii Abstract..............................................................................................................................iii Table of Contents................................................................................................................iv List of Figures...................................................................................................................vii List of Tables....................................................................................................................viii Acknowledgments..............................................................................................................ix Chapter 1: Interpreting Volcano Deformation in Alaska..................................................1 1.1 Introduction.............................................................................................................1 1.2 Chapter Overviews..................................................................................................1 1.2.1 Chapter 2...................................................................................................1 1.2.2 Chapter 3...................................................................................................2 1.2.3 Chapter 4...................................................................................................2 1.2.4 Chapter 5...................................................................................................2 1.2.5 Chapter 6...................................................................................................2 Chapter 2: Tracking Magma Volume Recovery at Okmok Volcano Using an Unscented Kalman Filter.......................................................................................................................3 2.1 Abstract..................................................................................................................3 2.2 Introduction............................................................................................................3 2.3 Methods..................................................................................................................9 2.3.1 Unscented transformation.........................................................................9 2.3.2 Kalman Filtering.....................................................................................15 2.3.3 Modeling GPS data.................................................................................20 2.4 Data Simulations..................................................................................................23 2.5 Data......................................................................................................................29 2.6 Results..................................................................................................................33 v 2.7 Discussion.............................................................................................................44 2.8 Conclusions..........................................................................................................49 2.9 References............................................................................................................51 Chapter 3: Deflation at Okmok Volcano and the role of volatiles in deformation.........56 3.1 Abstract................................................................................................................56 3.2 Introduction..........................................................................................................56 3.3 Geologic Setting...................................................................................................57 3.4 Data......................................................................................................................58 3.5 Mechanisms for Deflation....................................................................................62 3.6 Degassing Hypothesis..........................................................................................64 3.7 Model Constraints................................................................................................71 3.7.1 Magma Constraints..................................................................................71 3.7.2 Degassing Constraints..............................................................................72 3.8 Evaluating Model Results....................................................................................74 3.9 Results..................................................................................................................75 3.10 Discussion..........................................................................................................81 3.11 Conclusions........................................................................................................85 3.12 References..........................................................................................................87 Chapter 4: Transition from locked to creeping subduction in the Shumagin Region, Alaska 92 4.1 Abstract.................................................................................................................92 4.2 Introduction...........................................................................................................92 4.3 Data.......................................................................................................................94 4.4 Methods.................................................................................................................98 4.5 Results.................................................................................................................100 4.6 Discussion