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Free-air gravity anomaly

Hudson Bay and the associated structural basin lie within the centre of a large free-air gravity anomaly that lies within the Canadian Shield. The similarity in areal extent of the free-air gravity anomaly with the perimeter of the former Laurentide ice sheet that covered this part of Laurentia led to a long-held conclusion that this perturbation in the Earth's gravity reflected still ongoing glacial isostatic adjustment to the melting and disappearance of this ice sheet. Data collected over Canada by the Gravity Recovery and Climate Experiment (GRACE) satellite mission allowed geophysicists to isolate the gravity signal associated with glacial isostatic adjustment from longer–time scale process of mantle convection occurring beneath the Canadian Shield. Based upon this data, geophysicists and other Earth scientists concluded that the Laurentide Ice Sheet was composed of two large domes to the west and east of Hudson Bay. Modelling glacial isostatic adjustment using the GRACE data, they concluded that ≈25 to ≈45% of the observed free-air gravity anomaly was due to ongoing glacial isostatic adjustment, and the remainder likely represents longer time-scale effects of mantle convection.