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isostatic anomaly A gravity anomaly on a scale of more than 100 km that is associated with areas previously loaded, e.g. by ice (see GLACIO-ISOSTASY), lakes, etc., or where recent tectonic activity has loaded the crust, e.g. mountain formation, volcanic loading, etc. It is generally removed from Bouguer anomalies as part of the regional gradient, but it can also be calculated. See AIRY MODEL; and PRATT MODEL.