Citation for Kathryn M. Kumamoto
Kathryn Kumamoto will receive the 2019 Mineral and Rock Physics (MRP) Graduate Research Award for her outstanding doctoral work investigating plasticity and the role of water in the dynamics of upper mantle rocks.
Katie’s work on the plasticity of olivine used instrumented nanoindentation to resolve over 40 years of debate on the plastic strength of the lithosphere. She determined that the strength of olivine depends on a characteristic length scale (e.g., grain size). Katie recognized that this size effect explains the previous inconsistency among laboratory investigations while also demonstrating that most previous studies overestimate the strength of the lithosphere.
Katie also challenged two long-standing hypotheses regarding the role of water in upper mantle deformation. As an initial step, she characterized a set of new standards for secondary ion mass spectrometry that are now available for public use and represent a valuable resource for the community. Using these new standards, Katie unpicked the role of water in localizing deformation in upper mantle shear zones in the Josephine peridotite. Previous work asserted that water is central to the process of localization, but Katie demonstrated that although water does appear important, localization in these shear zones critically depends on a complex interplay between transport of a silicate melt and local equilibration between the melt and solid phases. She also challenged previous interpretations regarding the link between water content and the development of crystallographic preferred orientations (CPOs). Katie demonstrated that CPO type can be modified without significant changes in water content. She alternatively proposed that CPO type can be modified by changes in deformation kinematics, which she validated through numerical simulation.
Since completion of her Ph.D. at Stanford University, Katie has become a National Science Foundation Division of Earth Sciences postdoctoral fellow hosted at the University of Oxford and now uses synchrotron-based deformation-DIA experiments to further elucidate the physics of plastic deformation in upper mantle rocks.
—Lars Hansen, University of Minnesota, Minneapolis
I am honored and humbled to receive the MRP Graduate Research Award. I am fortunate to have worked with many outstanding individuals who have supported me in my scientific career. My Ph.D. advisor, Jessica Warren (University of Delaware), was an incredible role model and mentor throughout my graduate school experience and strongly encouraged me to examine my research questions from multiple perspectives, ranging from fieldwork to detailed geochemical analyses to experimental rock deformation. Lars Hansen (University of Minnesota) has been an invaluable colleague since my first year in graduate school, and we have collaborated on a wealth of activities that have spanned from small group presentations all the way to multiuniversity collaborative proposals and experimental work at large synchrotron facilities. During graduate school, I also had the distinct honor to work closely with Erik Hauri (Carnegie Institution of Washington) to develop and document standards and protocols for measuring water in mantle minerals with secondary ion mass spectrometry.
It is also important to acknowledge those scientists in my undergraduate career who helped me to develop a deep and passionate interest in pursuing research in the field of geology. Bud Wobus (Williams College), Mea Cook (Williams College), and Bjorn Mysen (Carnegie Institution of Washington) all played substantial roles in providing me with research opportunities, guidance, and encouragement, along with a healthy dose of good humor when anticipated research results were less than forthcoming. My hope is that I also can provide similar inspiration and support to others who wish to understand the inner workings of our planet.
Thank you to AGU and the Mineral and Rock Physics section for this award and for supporting graduate research.
—Kathryn M. Kumamoto, University of Oxford, Oxford, U.K.
Citation for Christopher A. Thom
For his Ph.D. thesis, Christopher Thom conducted groundbreaking research at the intersection of geophysics and materials science. Through application of methods not usually associated with rock mechanics, such as atomic force microscopy (AFM) and nanoindentation, Chris made fundamental contributions to our understanding of the roughness of natural faults and the frictional and rheological behavior of rocks. He extended measurements of fault roughness to the nanoscale using AFM, demonstrating self-affine roughness over at least 11 orders of magnitude in length scale. He showed that self-affinity at small scales results from the “smaller is stronger” dependence of yield strength on the size of the deforming volume, which he measured on actual fault surfaces via nanoindentation. Chris was also a major contributor to a paper that placed new constraints on the strength of the Earth’s lithosphere by considering the size dependence of the yield strength of olivine. Chris also provided fundamental constraints on the physical mechanisms of rock friction by measuring the nanoindentation creep rate of quartz in near-zero versus comparatively high humidity environments. Previous friction experiments on quartz rocks and powders for the same range of humidity showed that the time dependence of friction disappears at low humidity but is conspicuous at higher humidity. Chris’s experiments revealed no difference in the nanoindentation creep rate of quartz at low and high humidity, demonstrating that the time dependence of the frictional strength of quartz rocks cannot be due solely to asperity creep, the standard view of the past 40 years. Finally, Chris demonstrated how nanoindentation can be used to determine the bulk rheological behavior of rocks by conducting days-long nanoindentation creep experiments on halite single crystals; the resulting data agree remarkably well with those for polycrystalline halite deformed in macroscopic experiments.
Chris Thom has already had a remarkable impact on the field of mineral and rock physics for a scientist at this early stage of their career. On behalf of the AGU Mineral and Rock Physics section, I am very pleased to present the 2019 Mineral and Rock Physics Graduate Research Award to Christopher Thom.
—David L. Goldsby, University of Pennsylvania, Philadelphia
I am greatly honored and humbled to receive the 2019 Graduate Research Award from the Mineral and Rock Physics section of AGU, and I am grateful for the wonderful people I worked with during my time at the University of Pennsylvania.
I would first and foremost like to thank my Ph.D. adviser, David Goldsby, for giving me an opportunity to succeed and for providing constant encouragement along the way. He allowed me to pursue a wide range of research topics with unique methods such as nanoindentation. His guidance and years of experience tackling difficult issues related to rock friction paved the way for my work on the physical origins of frictional aging and scale-dependent plasticity.
I would also like to thank several individuals who have influenced my approach to science during my Ph.D. Rob Carpick introduced me to the world of tribology, which has affected how I approach rock friction problems at small scales. Emily Brodsky introduced me to measurements of fault roughness and always encouraged me to think about how my work related to the bigger picture. George Pharr was instrumental in teaching me nanoindentation methods and providing in-depth technical support whenever I needed it. A number of other collaborators such as Lars Hansen and Katie Kumamoto provided stimulating discussions on many topics related to plasticity, which I will continue to work on in my future career.
—Christopher A. Thom, University of Oxford, Oxford, U.K.