Long after the disappearance of the glaciers that once covered much of North America, the land they rested upon is still recovering from their weight – and the slow movement of this recovery includes horizontal motion never seen before, say Purdue scientists.
The research team, led by Eric A. Calais, has found that a large swath of territory in the Northeast is slowly moving southward in relation to the rest of the continent. This region, once covered with massive ice sheets heavy enough to deform the very stone they rested upon, has long been known to be rising slowly in response to the glaciers’ retreat, but this response has now been observed to have a horizontal component as well. The southward movement does not appear to be dramatic – in most places it is on the order of a millimeter per year or less – but it calls into question a view that earth scientists have held about crustal plates for three decades, namely that these large, rocky chunks of the planet’s surface are rigid objects.
"Our findings do not disprove this view entirely, but they encourage us to see that deviations to the rule can occur," said Calais, an associate professor of geophysics in Purdue’s College of Science. "We are now in a position to measure just how rigid these plates are, and in some areas, such as those still rebounding from the glaciers, we are finding movement we had never seen. This movement contains critical clues regarding the viscosity of the earth’s interior, which is impossible to measure directly. The movement may even influence seismic activity in places such as Quebec, which is from plate boundaries but has nonetheless suffered from strong earthquakes."
Chad Boutin | EurekAlert!
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