Tony Watts on the Mechanics of Tectonic Plates

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By the end of the 1960s, plate tectonics had been widely accepted, but it rested on an untested assumption: that the plates are strong enough to move as rigid slabs. Tony Watts describes how, as a postdoc at the Lamont-Doherty Earth Observatory in the early 1970s, he helped measure that strength by treating the lithosphere like an elastic beam bending under a load, first at ocean trenches and then at seamounts. The same approach has since been applied to sedimentary basins, where it called into question some estimates of past sea-level rise, as well as to ice sheets and to volcanoes on Mars. He closes with the questions that remain open, including why the plate seems thicker over short…