Many would agree that the recognition of plate tectonics has been the most significant development in the geosciences since Darwin and Wallace proposed evolution by natural selection. Reduced to its essence, plate tectonics includes seafloor spreading, transform faulting, subduction of oceanic lithosphere, and rigid-body motion of lithospheric plates. No one has made a greater contribution to our understanding of the subduction of oceanic lithosphere than Bryan Isacks.
With Jack Oliver, Isacks reintroduced the concept of the lithosphere and showed how its subduction explained a plethora of peculiarities of island arc structures. Isacks, Oliver, and Lynn Sykes wrote definitive papers showing how many key aspects of plate tectonics are defined by earthquake seismology. In these papers Bryan demonstrated that fault plane solutions of intermediate and deep-focus earthquakes require that those earthquakes occur within the downgoing slab of lithosphere, and he used those solutions to place constraints on the forces that drive plate motion. With Muawia Barazangi and others, he showed that the deep structure of back-arc basins implied seafloor spreading there.
Like most major contributors to plate tectonics, Bryan moved away from it in the 1970s, and he turned to subduction beneath a continental margin, the Andes, where the idealized rules of plate tectonics fail. With Barazangi and in a later elaboration with Teresa Jordan and others, he pointed out the geologic similarity between portions of the Andes where subduction occurs at a gentle angle and what geologists had inferred for the tectonic development of the western United States from 80 to 50 million years ago. His leadership in this area of research made Cornell a major center of Andean research.
Then 25 years ago, Isacks was one of the first to exploit digital topography to understand both geodynamics and erosion. He combined the fact that glaciers form at high altitudes with the widely accepted notion that glaciers erode more rapidly than rivers, and he coined the term “glacial buzz saw” to explain the hypsometry with seemingly flat high terrain despite many deep glacial valleys.
An unusually humble man, Isacks has received only one important accolade, the respect and appreciation of many students; ~35 of the ~45 graduate students whom he had advised attended a celebration of his 70th birthday. Until now, Bryan Isacks may have been AGU’s most outstanding scientist who had never received a medal or formal recognition of his contributions. We are delighted that this oversight has now been set right.
I thank Peter Molnar and Frank Richter for their very kind and generous citation.
In the 1960s I was lucky to have been immersed in the exciting and enabling culture of collaborative research at Lamont when the ideas of plate tectonics emerged, seemingly, by a process of “self-organized criticality” involving the interactions of numerous scientists in England, Canada, and the United States. In that network of interactions at Lamont I particularly linked with my thesis advisor Jack Oliver and colleagues Lynn Sykes, Peter Molnar, Muawia Barazangi, and Walter Mitronovas.
In the 1970s, after moving to Cornell, Muawia Barazangi and I came upon the segments of alternating steep and flat dipping plates that are subducting beneath the Andes. We were taken by the remarkable correlation between plate dip and Andean volcanism and topography. In the early 1980s, Rick Allmendinger and Terry Jordan came to Cornell with ideas about the role of flat subduction in the Laramide tectonics of the western United States. We were amazed at the analogy between the Laramide western United States and the late Cenozoic tectonics of the central Andes. Sharing this amazement were Suzanne and Bob Kay, who were working on subduction-related volcanism in the Aleutians, and Art Bloom, who was involved in NASA’s Landsat and Shuttle Imaging Radar programs. The six of us started the Cornell Andes Project in the early 1980s, and it continues to this day.
The close relationship between the dip of the subducted plate and upper plate tectonics led me to the outstanding signal of Andean tectonics, the Central Andean Plateau. As revealed by digital topography, a picture emerged involving plateau uplift by lower crustal shortening, a crustal-scale monocline defining the seaward edges of both the plateau and the volcanogenic asthenospheric wedge, and the enhanced bending of the Bolivian Orocline. In NASA’s Earth Observing System (EOS) and spaceborne imaging radar-C (SIR-C) programs I worked on satellite remote sensing of glaciers past and present and the coupling between mountain building and climate. I was fortunate to have very talented and enthusiastic graduate students, who worked as colleagues and often led the way, as in the old days at Lamont. They deserve a significant piece of the medal.
Recently, I’ve used digital topography to show how ice sheets have so beautifully sculpted the Finger Lakes’ landscape. The resulting video is narrated by my wife, Marjorie Olds, who, as my life coach, also owns a piece of the Walter Bucher Medal.
—Bryan L. Isacks, Cornell University, Ithaca, N. Y.
Citation: AGU (2015), Bryan L. Isacks receives 2014 Walter H. Bucher Medal, Eos, 96, doi:10.1029/2015EO021835.
Text © 2015. The authors. CC BY-NC 3.0
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