Harriet Lau on the Dynamics of the Earth from Hours to Millennia
Harriet Lau is an Assistant Professor in the Department of Earth and Planetary Sciences at the University of California at Berkeley. She studies the motions of the Earth over intermediate timescales, from the diurnal ones induced by tidal forces to millennial accommodations to the arrival or disappearance of ice sheets. She views these intermediate timescale responses of the Earth as manifestations of the interior structure and composition of the deep Earth. Here she is looking at large olivine crystals in a sample of the San Carlos Olivine from Arizona. She describes experiments performed on samples such as this to measure deformation in conditions that mimic deep Earth conditions.
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Podcast Illustrations
Images courtesy of Harriet Lau
The timescale of the motions in the mantle determines the nature of the mantle’s behavior - from elastic at the second timescale at one end, to viscous at the million-year timescale.
The rate of change in sea level today due to the large Laurentide ice sheet that completely melted by ~ 7,000 years BP. Sea-level change is negative in places that are rebounding today. In other places, the land is sinking as a bulge caused by the weight of ice in a neighboring area relaxes.
A simulation of the kinds of sub-millimeter-level deviations across the planet in solid Earth tide deformation. Top panels show the up and down motion over a tidal cycle. The simulation at top left includes structures like the large low-shear-velocity provinces (LLSVPs), and the one on the top right assumes a symmetrical structure without LLSVPs in the mantle. They look identical at first glance, but the bottom figure shows the difference between the two. This indicates that measuring the actual Earth deformation can tell us something about the interior structure and composition of the Earth, at least on ~1000-km scales.