Don L. Anderson (1933 - 2014)

Don Lynn Anderson, Eleanor and John R. McMillan Professor Emeritus of Geophysics at the California Institute of Technology, passed away peacefully at his home in Cambria, California, 2nd December, 2014, aged 82. Don was born March 5, 1933 at Frederick, Maryland. He worked for most of his career at the California Institute of Technology, where he gained his Ph.D. degree under the tutelage of Frank Press. In turn, Don advised numerous graduate students of his own, many of whom went on to become eminent in their fields.

Among Don's many leadership roles were Director of the Seismological Laboratory, Caltech, from 1967- 1989, principal investigator on the 1971 Viking mission to Mars, and President of the American Geophysical Union. He was honored with numerous awards including the Crafoord Prize (1998, with Adam Dziewonski), the National Medal of Science (1998), the Bowie Medal of the American Geophysical Union (1991), the Gold Medal of the Royal Astronomical Society (1988), the Arthur L. Day Gold Medal of the Geological Society of America (1987), the Emil Wiechert Medal of the German Geophysical Society (1986), and the NASA Exceptional Scientific Achievement Medal (1977). He held Fellowships of the American Philosophical Society (1990), the American Association for the Advancement of Science (1988), the National Academy of Sciences (1982), and the American Academy of Arts and Sciences (1972).

In a career spanning more than half a century, Don made pioneering contributions to understanding the large-scale structure of the Earth, taking on undaunted anisotropy, anelasticty, asphericity and anharmonicity. One of his great strengths was integration of physics, thermodynamics, petrology and geochemistry. He investigated the behaviour of mantle materials at high pressures and temperatures, the phase transformations of mantle minerals, and the generation of earthquakes. He and his colleagues developed the theory of wave propagation in complex media and he introduced the term "tomography" into seismology. He made major contributions to understanding plate-tectonic motions and convection in the Earth's mantle. In collaboration with Adam Dziewonski he developed the Preliminary Reference Earth Model (PREM), a cornerstone of modern global geophysics. In the latter part of his career, Don became most famous for ideas that depart from conventional wisdom, but which he felt are more consistent with thermodynamics and classical physics. He challenged standard geochemical and evolutionary models for the Earth, and presented alternative theories for the mineralogical and isotopic composition of the mantle. He viewed the Earth as being chemically stratified into layers, the deeper ones being refractory, convecting sluggishly, and having essentially no direct involvement with surface magmatism. He considered the mid-mantle to be pyroxene- and garnet-rich, not composed of olivine-dominated peridotite. These ideas led him to challenge the hypothesis of deep-mantle plumes, convective upwellings that are widely assumed to explain volcanic oceanic islands such as Hawaii and Iceland. Instead, he considered such volcanism to be fed from the shallow mantle through extensional fissures induced by plate tectonics. Don considered plate tectonics to be a natural result of a planet cooled from above, and for essentially all volcanism on Earth to result from this process.

I first met Don at the AGU Fall Meeting in 1999. After that, life was never the same again. Don had discovered that email made the world one big Department. He loved the Internet and embraced it with huge enthusiasm, supporting and contributing to his favourite site www.mantleplumes.org. He devoted countless hours to mentoring young scientists the world over, some of whom were never destined to meet him. He inspired numerous papers, projects and collaborations with his startling ideas, radical challenges, and infectious out-of-the-box thinking. And he couldn't hide the fact that he loved every minute of it. Don bequeathed to his colleagues a commitment to the total, unrestricted and free sharing of resources, leading from the front by example. In the last months of his life, when he knew he would soon have to shut his laptop down for the last time, he worked tirelessly to finish his papers in progress and to make free and unrestricted to everybody his legacy to science. This includes over 300 published papers, his books Theory of the Earth and New Theory of the Earth, videos, web pages, blogs, hundreds of presentation slides and his tongue-in-cheek metaphorical voyage into minds and planets What Planet Do You Live On Anyway? All this is available unrestricted from his personal resources webpage at www.mantleplumes.org/DLA.html. The many details of his extraordinary life and career that are absent from this brief tribute are accessible from his Wikipedia page at http://en.wikipedia.org/wiki/Don_L._Anderson.

Gillian R. Foulger 12th December, 2014