University of Minnesota, Minneapolis
David L. Kohlstedt was awarded the Hess Medal at the AGU Fall Meeting Honors Ceremony, which was held on 10 December 2003, in San Francisco, California. The medal honors “outstanding achievements in research in the constitution and evolution of Earth and sister planets.”
“The official ‘short’ citation by AGU notes that David Kohlstedt receives the Hess Medal ‘for his fundamental contributions to understanding the Earth’s upper mantle rheology.’ The short citation is short-sighted: it misses the larger point of David’s contribution to the geological/geophysical community, which is the broad—albeit exacting—application of solid-state physics and solid-state chemistry, theory and experiment, to better understand chemical, mechanical, and microstructural evolution of the materials that constitute the terrestrial planets. David has turned effectively his creative attention to nanometer-scale physics in order to understand kilometer-scale phenomena, to human-timescale experiments in order to characterize geological-timescale events.
“David pursued his doctorate in solid-state physics at Illinois in the late 1960s, when that community was the hotbed of innovative studies of mechanical and chemical dynamics in crystalline solids. Upon entering Earth sciences as a research associate with Chris Goetze and Bill Brace at MIT (1971-1975), David’s Illinois-solid-state perspective came to the fore: with Goetze, David performed pioneering experiments on the rheology of olivine single crystals. At the time, the experiments—which employed Earth-like deviatoric stress and non-Earth-like elevated temperature—were controversial. The problem of mantle viscosity and its mechanisms, however, demanded an experimental approach that paid attention to atomic-level phenomena: only a temperature-based extrapolation could ‘capture’ the planetary-relevant physics. This early-career illustration is archetypical: to David, the physics of the planet-scale problem dictate the solid-state physics that create the experimental approach.
“Two faculty appointments later (Cornell, 1975 to 1989; Minnesota, 1989 to present), here is an incomplete list of David’s contributions: proof of a mechanical equation of state for dislocation plasticity in ionic and covalent solids; characterization of the impact of oxygen and oxide activities on dislocation and diffusional flow of olivine; characterization of the role of partial melting on the structure and plastic/anelastic rheology of mantle assemblages, on melt permeability, on scaling in melt segregation, and on interaction of metal melts with crystalline silicates; characterization of point-defect thermodynamics, diffusion kinetics, and the storage of ‘water’ in ‘anhydrous’ mantle minerals; and characterization of the crystal structure, chemical composition and dynamics of grain boundaries in mantle assemblages and other oxides and silicates. A thoughtful look at the literature reveals that David and his group have been at the forefront in all of these efforts, posing exacting questions concerning the physical mechanisms underlying geophysical processes and then designing equally exacting experiments based on simplifying assumptions that are rigorously defensible.
“David Kohlstedt leaves a wake of goodwill wherever he passes. Kindness and gentle good humor are David’s hallmarks: he values good relations among people and seeks always to promote understanding between individuals and groups. His work and interactions are uniformly more concerned with shedding light than with creating heat. Maintaining such an outlook in high-stakes academia is challenging; David nevertheless perseveres—and because of it, he delights.
“Harry Hess’s observational research encompassed geology, geophysics, and petrology, and focused on the physical and chemical dynamics of the mantle. David Kohlstedt’s experimental research shares fully both scope and purpose. And while David Kohlstedt’s ‘atoms-up’ perspective contrasts with Harry Hess’s ‘global-down’ approach, the quality and impact of David’s work matches beautifully that of the scholar for whom this award is named.”
—REID F. COOPER, Brown University, Providence, R.I.
“Thank you, Reid, for the warm and generous citation. My adventures in the Earth sciences have been particularly rewarding because of scholar friends like you, Brian Evans, Greg Hirth, and Andreas Kronenberg; your eloquent prose has prevailed. I am profoundly honored and almost overwhelmed to receive the Hess Medal.
“With limited space, it is impossible to do more than touch on a few defining moments and acknowledge a few fellow travelers.
“How does one move from studying physics of the solid state to exploring dynamics of the fluid Earth? Family ties are foundational. Without Sally, my wife, a respected historian of science, I would undoubtedly be an actuary in Appleton. (If you don’t get it, don’t worry; it’s a Lutheran joke.) Kris and Kurt, our sons, still challenge me on the ski slopes and join me in exploring South Dakota, my homeland.
“Outstanding teachers energized my early exposure to physics. Arnold Studtmann drew me into physics with his exciting demonstrations, Manuel Bretscher stimulated my interest with his clear physical insights, and Wendell Williams instilled in me the possibility of using principles of solid-state physics to attack problems in other fields.
“Earth sciences entered my life when Bill Brace brought a young materials physicist from Cambridge to Cambridge, from the banks of the Cam to the shores of the Charles, with a postdoc position at MIT. Bill quickly discovered that I knew nothing about stick-slip, not to mention about rocks. So he sent me to the other end of the corridor to work with Chris Goetze, a brilliant experimentalist, an enthusiastic mentor, and an intrepid explorer. Research was itself a constant adventure and continual education with Chris, who instilled in me a deep sense of excitement for intellectual exploration.
“Once a materials science faculty member at Cornell, a talented faculty helped me explore new territory and attract a venturesome team of students. With Reid Copper and Bart Riley, we traveled into the world of partially molten rocks, while with Daniel Ricoult, Quan Bai, and Duane Dimos we started to map the domain of point defects.
“In the early 1980s, I encountered Herman and Mervyn. Hermann Schmalzied educated me on the finer details of point defects and supplied the theoretical framework essential for the task. Synchronously, Mervyn Paterson enticed me to Australia to work on water-weakening in olivine and provided the equipment for doing so. Oh, yes, Mervyn subsequently supplied a young postdoc, Steve Mackwell, who ventured fearlessly into experiments on the role of water on the viscosity of mantle rocks.
“A bit over a decade ago, Minnesota brought me firmly into geophysical territory. Surrounded by supportive faculty and stimulated by inquisitive graduate students, the last decade has taken my quest in persisting, though sometimes unforeseen, directions. Here, Mark Zimmerman laid down the law for partially molten lherzolite, David Goldsby remapped the flow law for ice, Sue Ginsberg discovered deformation-driven melt segregation, and Shenghua Mei quantified the dependence of viscosity on water content. Amazingly creative, if not exceptionally tall, postdocs included Take Hiraga, who explored partitioning of incompatible elements to grain boundaries, and Greg Hirth, who investigated the interplay between water and melt in the formation of the compositional lithosphere. Current students continue the spirit of adventure. While Ben Holtzman discovers sweet music in melt segregation, Sash Majumder explores the physics of fluid migration. As Shushu Chen leads us from the mantle up into the crust, Justin Hustoft and Nate Groebner venture from the mantle down into the core. And Ted Scott, not being satisfied with adventures on Earth, explores partial melting on Io.
“Although my contributions to geophysics may not rise to the scientific or aesthetic level of the geopoetry embodied in Harry Hess’s theory of seafloor spreading, I hope that at least some will now hear the harmonics of geomusic in the intermittent flow of melt and water deep within the Earth and perhaps elsewhere in the solar system.
“For the countless adventures throughout my career in geophysics, I thank you all.”
—DAVID L. KOHLSTEDT, University of Minnesota, Minneapolis