Born in Quinhon (Quy Nhơn) on June 18, 1937; died on March 22, 2025. Xavier Le Pichon was a pioneer in research on seafloor spreading and continental drift, ranging from an understanding of our planet’s overall functioning to the study of its local manifestations, such as earthquakes. He held the Chair of Geodynamics at the Collège de France from 1986 to 2008.
Xavier Le Pichon defended his dissertation in 1966 in Strasbourg on the structure of the Mid-Atlantic Ridge. While at the Lamont-Doherty Observatory (USA) as part of Maurice Ewing’s team in the late 1960s—at a time when systematic observation of the ocean floor was revealing mid-ocean ridges, trenches, and what would soon be called transform faults—where continental drift and seafloor spreading had been proven by paleomagnetists—he followed in the footsteps of Harry Hess, Fred Vine, Drummond Matthews, Tuzo Wilson, Dan McKenzie, and Jason Morgan to propose the first global quantitative model describing the relative movements of the major tectonic plates and reconstructing the evolution of the Atlantic since the Cretaceous, in a seminal article published in the *Journal of Geophysical Research* in 1968. The book he subsequently published with Jean Bonnin and Jean Francheteau, titled “Plate Tectonics,” in 1973, remains an unsurpassed compendium chronicling this major scientific revolution that established the geodynamic framework within which we have all been working ever since.
Upon his return to France, he continued to study the movements and deformations of the lithosphere, making major advances in the mechanisms of rifting, subduction, and collision; in seismic coupling in subduction zones; and in recognizing the importance of space geodesy for understanding the active deformation of continents. He played a major role in the restructuring of French oceanography, which quickly became one of the best in the world. Starting with the founding of Ifremer’s predecessor in Brest, and later as a professor at Pierre-and-Marie-Curie University and the École normale supérieure, he organized a large number of oceanographic expeditions to further explore the ocean floor, all of which yielded significant results. To name just three of these projects organized as part of international collaborations, we can mention the FAMOUS expedition—a Franco-American program and the first exploration of the Mid-Atlantic Ridge using the CYANA and ALVIN submersibles— the HEAT expedition to explore the Hellenic Trench—the first diving expedition into a subduction zone—and the Franco-Japanese Kaiko and Kaiko-Tokai expeditions to explore the trenches around Japan, combining surface geophysics with dives using a new submarine, the Nautile, which could descend to -6,000 m. His unwavering dedication to the study of the oceans made him one of the great explorers of the 20th century. France owes much of its preeminent position among nations in the fields of tectonics and oceanography to him.
A member of the Academy of Sciences, Xavier Le Pichon ended his career as a professor at the Collège de France, where his lectures on geodynamics over the years remain fondly remembered. Long before this recognition, he was a renowned professor who inspired many students at UPMC (now Sorbonne University) with his passion for lithosphere dynamics and the study of the physical processes occurring within it. He was also a brilliant and demanding mentor, always encouraging his students and collaborators to follow their intuitions and providing them with the means to work and carve out a place for themselves in the highly competitive world of research.
His scientific work was recognized with numerous national and international awards and medals, including the Wollaston Medal from the Geological Society of London, the Japan Prize, and the Balzan Prize. He chronicled his experiences at sea in several books, including *3,000 Meters Below the Atlantic* (Albin Michel), about the FAMOUS expedition, *Voyage aux extrémités de la mer* about the Kaiko program, as well as more philosophical works on death, *Aux racines de l’homme: de la mort à l’amour* (Presses de la Renaissance) and *La Mort* with Tang Yi Jie (Desclée de Brouwer).
He had a major impact on French Earth sciences. His students carry on his approach to oceanic research, and many other teams benefit from the exploration tools he played a major role in developing.
Source: CNRS-INSU, 2025.