Bryan Isacks, geophysicist who helped shape theory of plate tectonics, dies at 90

Bryan L. Isacks, the William and Katherine Snee Professor of Geological Sciences Emeritus in the Cornell Duffield College of Engineering who transformed the understanding of Earth's surface by providing fundamental evidence for the theory of plate tectonics, died Sept. 9 in Ithaca. He was 90.

In his landmark 1968 study, "Seismology and the New Global Tectonics," Isacks - along with co-authors Jack Oliver, a now deceased Cornell professor of earth and atmospheric sciences, and Lynn Sykes of Columbia University - used seismology to connect earthquake patterns to the movement of massive slabs on Earth's crust. The work provided evidence for the movement of tectonic plates and the process of subduction, turning what had once been a controversial idea into a foundation of modern geology.

"Earth sciences has lost a giant," said Richard Allmendinger, professor emeritus of earth and atmospheric sciences in Duffield Engineering. "Bryan was an unassuming genius. His 1968 paper is widely recognized as one of the most important in the plate tectonic revolution, yet he never boasted about himself or his many, singular accomplishments."

Isacks continued to publish in seismology into the 1980s and his work on the segmentation of the Nazca-South America subduction zone became a modern analogue for understanding plate tectonics in the western U.S., said Allmendinger, who worked with Isacks and their Duffield Engineering colleagues Teresa Jordan, Suzanne Kay and Art Bloom to grow that research into the long-running Cornell Andes Project.

"He produced the first ever digital elevation model of the Andes Mountains and wrote a classic paper linking the topography to lithospheric scale processes," Allmendinger said. "That paper was one of the first to employ continent scale digital elevation models anywhere and cemented Bryan's leadership in the brand new field of quantitative analysis of topography."

Isacks later turned to satellite remote sensing, including as principal investigator for a NASA Earth Observing System investigation of climate in high mountain systems. He was a co-investigator on a proposal in the 1990s for an Earth-orbiting radar satellite that was partly the inspiration for the NASA-ISRO Synthetic Aperture Radar satellite that launched into orbit in 2025, according to Matthew Pritchard, the Sidney Kaufman Professor of Geophysics in Duffield Engineering.

"Bryan was a very supportive colleague and a great mentor to junior faculty," said Pritchard, who is a member of the Operational Science Team for the NASA-ISRO satellite along with several other Cornell faculty and alumni. "He gave me a lot of good professional and scientific advice over the years, including on other projects that used satellite data to study magma chambers, geothermal resources and Alaskan glaciers. His impact on the field and the department was immense."

Isacks was born on July 25, 1936, in New Orleans, according to a family obituary. He attended Columbia University as an undergraduate and graduate student before beginning his career there as a geophysicist.

Isacks joined the Cornell faculty in 1971 and eventually became director of the university's Institute for the Study of the Continents. He chaired the Department of Geological Sciences from 1994 to 2003 and played a critical role in the merger that created the Department of Earth and Atmospheric Sciences - recognizing the need to academically connect Earth's different systems to better understand and solve pressing 21st century challenges.

Locally, Isacks applied digital topography to study the landscape of the Finger Lakes region and the forces that shaped it. He was an advocate for the creation of the Museum of the Earth in Ithaca, where he helped curate a model glacier exhibit that illustrates how retreating glaciers created the Finger Lakes.

Isacks retired from Cornell in 2008 but remained connected to colleagues and students whose work had grown from the research communities he helped build.

Among other accolades, Isacks was a Fellow of the American Geophysical Union and the American Association for the Advancement of Science. In 2014, he was awarded the Walter H. Bucher Medal from the American Geophysical Union, which described plate tectonics as "one of the most significant developments in the geosciences since Darwin and Wallace proposed evolution by natural selection." The award citation singled out Isacks' contributions to understanding the fundamental processes of plate tectonics, noting "No one has made a greater contribution to our understanding of the subduction of oceanic lithosphere than Bryan Isacks."

He is survived by his wife, Marjorie Olds; children Lillian Isacks, Katherine Isacks, Susan Isacks, Bryan Isacks Jr., Brett Olds and Robert Olds; and several grandchildren.

Syl Kacapyr is associate director of marketing and communications for Duffield Engineering.