Deep explorer wins Wittelson award
David Kohlstedt’s groundbreaking experiments show how processes at inaccessible depths drive what happens on Earth’s surface.
David Kohlstedt of the University of Minnesota has been awarded the 2023 Wittelsen Prize for his work in the earth sciences. (Courtesy of University of Minnesota)
Most geological processes on Earth’s surface—the rise of mountains, the opening of ocean basins, the eruption of volcanoes, the shaking of earthquakes—originate in a hot, malleable region far below the surface called the mantle. But the mantle is too far away for humans to observe directly.In recent decades, physicists David Colstedt and colleagues found a way to solve this problem: recreate the temperature, pressure and chemical conditions of the mantle in the laboratory, observe what happens at the microscopic level, and then scale up the results to real-world size. Their discoveries are the basis for modern geophysics, structural geology, volcanology, seismology, glaciology, and even other planetary studies.
University of Minnesota Professor Emeritus Kohlstedt awarded 2023 Class of 2023 Whitson Award, considered by many to be the highest honor in earth sciences.by the New York-based G. Unger Vetlesen Foundation Managed by the Columbia Climate Institute Lamont-Doherty Earth Observatory, the 70-year-old award is honored “for scientific achievements that lead to a clearer understanding of Earth, its history, or its relationship to the universe.” Kohlstedt will receive $250,000 and a gold medal at an awards ceremony at Columbia University in April.
The Earth’s crust is a thin, small cape that only makes up about 1% of the Earth’s volume. Directly below, the mantle makes up about 85 percent. Although it appears to be a solid, over time most of it behaves as a viscous fluid. Like a slow-cooked stew, the material rises and falls by convection, and in some places, it melts. The shifting mantle is what makes Earth what it is by pushing on the giant tectonic plates that make up the Earth’s surface. It is the mantle that cycles carbon from the depths into the atmosphere and back again. Mantle-derived lava continually creates new ocean floor sections and drives volcanoes on land where the seafloor is pushed beneath the continents. Mantle-driven deformation of near-surface rocks is the ultimate source of most earthquakes.
When Kohlstedt began his research in the early 1970s, geoscientists had embraced the overarching theory of plate tectonics, which explained all of these phenomena. But they still haven’t been able to quantify how quickly or under what conditions material deforms, flows or melts in the mantle. This makes it difficult to accurately model Earth’s history, and the short-term processes that lead to deadly natural disasters. Kohlstedt’s lab has conducted many studies that have greatly illuminated this picture.
Kohlstedt (far left) with colleagues at the University of Minnesota’s Rock and Mineral Physics Laboratory in 2021. (Courtesy of University of Minnesota)
Kohlstedt took on the job from an unusual angle. The son of a Lutheran pastor and elementary school teacher, he spent his childhood in rural South Dakota. The son of a farm family, his father had good hands that could fix anything — cars, washing machines, lawnmowers — and young Kohlstedt mastered the same skill set. Good at math, he considered studying to be an actuary, but switched to physics thanks to an inspirational high school science teacher. He received his Ph.D. in 1970 after completing his undergraduate studies at Valparaiso University in Indiana. at the University of Illinois.
With no training in earth sciences, Kohlstedt appears to have embarked on a career path of creating technical ceramics or other useful materials.But during his research at MIT from 1971-1975, he strayed again william brace, a pioneering geophysicist who subjected crustal rocks to extreme pressures in his lab—experiments that quickly improved understanding of how earthquakes start. Kohlstedt later said he moved to MIT not because of the discipline but because his wife, Sally, a science historian, had found a job in Boston and he needed nearby a job. This changed the direction of his work.
“It’s to your advantage sometimes to go into one field with expertise in other fields,” says Kohlstedt, who says much of his later work was out of sheer curiosity. “Understanding how lava reaches the surface can tell us a lot about the evolution of the Earth.” On a more practical level, “One reason to care about the depths of the Earth is that volcanoes pop up to kill people and bury cities.”
Kohlstedt in the badlands of his native South Dakota. (Don Benson)
After graduating from MIT, Kohlstedt taught and researched at Cornell University for approximately 15 years. In 1989, he moved to the University of Minnesota, and over the next three decades, he and a large group of students designed, built and operated systems that simulated extreme conditions in the upper mantle. Many of the experiments involved olivine, the most abundant mineral in the region. Inside the complex gas-filled piston, they subjected the samples to different combinations of pressure and temperature (up to 1,300 degrees Celsius) with the addition of other natural substances to see how all the factors interacted. They observed the results at the atomic level using an electron microscope, then used equations to magnify them to a size that could be applied to real-world problems.
One of Kohlstedt’s early achievements was the 1980 paper Provides a comprehensive set of rules to manage pressure in the lithosphere, the topmost region of the Earth’s mantle. This paper was later cited by thousands of other studies.
In perhaps his most important discovery, Kohlstedt investigated what had been assumed that the Earth’s mantle contained a small amount of water, but not enough to play any significant role. In fact, he showed that even small amounts of water, measured in parts per million, can greatly weaken mantle rocks, causing them to flow or melt on long- and short-term scales. “More water means more movement. Water drives everything about plate tectonics,” he said.Among other things, the role of water in volcanic eruptions is still under intense research.
The study by Kohlstedt and colleagues also shows the sequence of events This drives volcanic activity at mid-ocean ridges. They found that the process begins at depths of 100 kilometers or more on the ocean floor, where a moderate amount of molten material is filtered through a porous mass of tiny crystalline particles, similar to water seeping through sand. As the melt moves further up, it gains traction by melting adjacent regions of rock and creating channels through which it can flow in larger quantities and more rapidly.
Kohlstedt’s work has also been applied to glacial ice streams and to Venus, which appears to lack the dynamic tectonic properties of Earth due to lack of water. Kohlstedt is now technically retired but is working on several new projects, including an analysis of conditions inside Jupiter’s highly volcanic moon Io.
One of the many letters in support of Kohlstedt’s nomination stated that he was “ahead of others in his field: in the breadth and depth of his work and the clarity with which he articulated it. Anyone who thinks about the dynamics of the solid Earth [has] David’s work was always on their minds. Others point to his generous mentorship of the dozens of students who contributed to his work and who often went on to influential careers.
Kohlstedt to receive 2023 prize with French geophysicist, 2020 winner Anne Cazenave, unable to receive in person due to the COVID pandemic. Cazeneuve was awarded for being the first to use satellites to map the world’s continuing sea level rise.
A major supporter of Earth science research, the Vetlesen Foundation was founded in 1955 by Norwegian sailor, naval engineer and shipbuilder George Unger Vetlesen. Wittelsen played a key role in the resistance against the Nazis during World War II and later in the expansion of shipping and air travel between Scandinavia and North America.
The Vetlesen Prize is awarded every three years. Other honorees include astronomer Jan Oort, who elucidated the structure of the outer solar system and galaxies; geochemist Wallace Broecker, founder of modern climate science; and geologist Walter Alvarez, who convinced the world The dinosaurs were wiped out by an alien impact; and Susan Solomon, an atmospheric scientist who has identified man-made chemicals as the source of the “ozone hole” that has been circling Antarctica in recent decades.
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