Explorer of Deep Earth Wins Vetlesen Prize

Explorer of Deep Earth Wins Vetlesen Prize

David Kohlstedt’s pioneering experiments have shown how processes at inaccessible depths drive what happens on the planet’s surface.

Most geologic processes on the Earth’s surface—the rise of mountain ranges, opening of ocean basins, eruption of volcanoes, shaking of earthquakes—have their origins far below, in the recent, malleable region generally known as the mantle. However the mantle is just too distant for humans to directly observe. In recent many years, physicist David Kohlstedt and colleagues have found a way around this: recreating the mantle’s temperature, pressure and chemical conditions within the lab, observing what happens on microscopic levels, after which scaling up the outcomes to real-world size. Their findings underlie much of recent geophysics, structural geology, volcanology, seismology, glaciology, and even the study of other planets.

Kohlstedt, a professor emeritus on the University of Minnesota, has been awarded the 2023 Vetlesen Prize, considered by many to be the Earth sciences’ highest honor. Endowed by the Recent York-based G. Unger Vetlesen Foundation and administered by the Columbia Climate School’s Lamont-Doherty Earth Observatory, the 70-year-old award is bestowed “for scientific achievement leading to a clearer understanding of the Earth, its history, or its relations to the universe.” Kohlstedt will receive $250,000 and a gold medal at a ceremony at Columbia in April.

The Earth’s crust is a tenuous little cloak, making up only about 1 percent of the planet’s volume. Directly below, the mantle comprises about 85 percent. While it seems solid, over time much of it behaves as a viscous fluid. Like a slowly simmering stew, material rises and falls by convection, and in some places, it melts. It’s the moving mantle that makes the Earth what it’s, by pushing around the large tectonic plates that make up the planet’s surface. It’s the mantle that cycles carbon from profound depths to the atmosphere, and back again. Mantle-derived lavas continually create latest sections of ocean seafloor, and drive volcanoes on land where the seafloor is thrust beneath continents. Mantle-driven deformation of near-surface rocks is the final word source of most earthquakes.

When Kohlstedt was starting his research within the early Nineteen Seventies, earth scientists had already adopted the overarching theory of plate tectonics, which explains all of those phenomena. But they still had no way of quantifying how briskly or under what conditions material within the mantle deformed, flowed or melted. That made it difficult to accurately model the planet’s history, along with the shorter-term processes that create deadly natural hazards. Kohlstedt’s lab produced many studies that greatly clarified the image.

Kohlstedt (far left) with colleagues on the University of Minnesota rock and mineral physics lab in 2021. (Courtesy University of Minnesota)

Kohlstedt got here on the job from an unusual angle. Son of a Lutheran minister and an elementary school teacher, he spent his childhood in rural South Dakota. His father, son of a farm family, was good along with his hands and will fix anything—cars, washing machines, lawnmowers—and the younger Kohlstedt developed the identical skills. Excelling at math, he considered studying to be an actuary, but got sidetracked into physics because of an inspiring high-school science teacher. After college at Indiana’s Valparaiso University, he followed with a 1970 PhD. on the University of Illinois.

With no training in Earth sciences, Kohlstedt gave the impression to be on course for a profession creating industrial ceramics or other useful materials. But he was sidetracked again during a 1971-1975 research stint on the Massachusetts Institute of Technology with William Brace, a path-breaking geophysicist who was subjecting crustal rocks to extreme stresses within the lab—experiments that soon improved the understanding of how earthquakes start. Kohlstedt said later that he moved to MIT not due to subject material, but because his wife, Sally, a science historian, had gotten a job in Boston, and he needed a job nearby. It modified the direction of his work.

“Coming into one field with expertise in something else, sometimes it really works to your advantage,” said Kohlstedt. Much of his subsequent work was motivated by sheer curiosity, he said. “Understanding  how lava gets to the surface tells us loads concerning the evolution of the Earth.”  On a more practical level, “One reason to care concerning the deep Earth is, volcanoes can come up and kill people and bury cities.”

Kohlstedt within the badlands of his native South Dakota. (Don Benson)

After MIT, Kohlstedt spent some 15 years teaching and doing research at Cornell University. In 1989, he moved to the University of Minnesota, where, over the subsequent three many years, he and a protracted line of scholars designed, built and operated systems that simulated the intense conditions of the upper mantle. Many experiments involved the mineral olivine, the region’s most abundant substance. In complex gas-filled pistons, they subjected samples to various combos of pressure and temperature—as much as 1300 degrees C—together with additions of other natural substances, to see how all of the aspects would interact. They observed the outcomes on an atomic level using electron microscopes, then used equations to scale them as much as sizes that could possibly be applied to real-world problems.

One in all Kohlstedt’s early achievements was a 1980 paper offering a comprehensive algorithm governing stresses within the lithosphere, an area on the very top of the mantle. The paper has since been cited in hundreds of other studies.

In perhaps his most central finding, Kohlstedt investigated the onetime presumption that the mantle holds small amounts of water, but not enough to play any necessary role. In actual fact, he showed that just somewhat water, counted in parts per million, dramatically weakens the strength of mantle rocks, spurring them to flow or melt on each long- and short-term scales. “More water means more movement. Water drives all the pieces in plate tectonics,” he said. Amongst other things, the role of water in volcanic eruptions continues to be being vigorously studied.

Studies by Kohlstedt and colleagues also showed the sequence of events that drives volcanism at mid-ocean ridges. They found that the method starts 100 kilometers or more under the ocean floor, where modest amounts of melted material filter through porous masses of tiny, crystalline grains, much like water seeping through sand. Because the melt moves further up, it gains traction by melting adjoining areas of rock and creating channels through which it will probably flow ever more voluminously and rapidly.

Kohlstedt’s work has also been applied to glacial ice flow, and to the planet Venus, which appears to lack the dynamic tectonic qualities of Earth resulting from a scarcity of water. Kohlstedt is now technically retired, but is working on several newer projects, including an evaluation of the conditions inside Jupiter’s highly volcanic moon Io.

One in all the various letters supporting Kohlstedt’s nomination puts him “head and shoulders above everybody else in his field: within the breadth and profundity of his work and within the clarity of its exposition. Anyone who thinks concerning the dynamics of the solid Earth [has] David’s work continually of their minds.” Others pointed to his generous mentorship of dozens of scholars who contributed to his work, and who often went on to influential careers.

Kohlstedt will receive the 2023 prize together with the 2020 winner, French geophysicist Anny Cazenave, who couldn’t accept in person resulting from the COVID pandemic. Cazenave received the prize for pioneering the usage of satellites to chart ongoing sea-level rise around the globe.

The Vetlesen Foundation, a significant supporter of Earth-science research, was established in 1955 by Norwegian sailor, naval engineer and shipbuilder George Unger Vetlesen. During World War II, Vetlesen played key roles within the resistance against the Nazis, and later in expanding shipping and air travel between Scandinavia and North America.

The Vetlesen Prize is given every three years. Other recipients have included astronomer Jan Oort, who elucidated the architecture of the outer Solar System and galaxies; geochemist Wallace Broecker, a founder of recent climate science; geologist Walter Alvarez, who convinced the world that dinosaurs were exterminated by an extraterrestrial impact; and atmospheric scientist Susan Solomon, who identified manmade chemicals because the source of the “ozone hole” that has hovered over Antarctica in recent many years.

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