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Geophysics

Going halves over Hudson Bay

Nature volume 390, pages 445–447 (1997)Cite this article

Regional variations in the gravitational pull at the Earth's surface can provide glimpses into the Earth's internal structure. One such anomaly (a negative one) is centred over Hudson Bay in North America (see cover), and has a maximum amplitude of roughly 1 part in 20,000 of the surface gravitational acceleration — which as anomalies go is quite sizeable. A definitive explanation for this anomaly has proved elusive. But on page 500of this issue1 Simons and Hager describe a fruitful new approach to the question, which not only provides the most direct answer yet, but should also be invaluable in understanding dynamic processes shaping the Earth.

There are at least two different explanations for the large Canadian anomaly, and they are not mutually exclusive. One stems from the remarkable correlation between its spatial form and the geometry of the Laurentide ice sheet during the last glacial maximum. This massive ice sheet covered northern North America for tens of thousands of years until its retreat some 10,000 years ago. The ice load would have caused compression and outward viscous flow of the Earth beneath it — an event from which the Earth is still recovering in a process known as post-glacial rebound, and which is plausibly reflected in the gravity anomaly.

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  1. the Department of Physics, University of Toronto, 60 St George Street, Toronto, M5S 1A7, Canada

    Jerry X. Mitrovica

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  1. Jerry X. Mitrovica
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Mitrovica, J. Going halves over Hudson Bay. Nature 390, 445–447 (1997). https://doi.org/10.1038/37231

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