Gravitic anomaly explained

Rizwana Z. sent this link to one of my mailing lists: Satellites solve mystery of low gravity over Canada:

If it seems Canadians weigh less than their American neighbours, they do — but not for the reasons you might think. A large swath of Canada actually boasts lower gravity than its surroundings.

Researchers have puzzled for years over whether this was due to the crust there rebounding slowly after the end of the last ice age or a deeper issue involving convection in the Earth's mantle — or some combination of the two.

Now, ultra-precise measurements taken over four years by a pair of satellites known as GRACE (Gravity Recovery and Climate Experiment) reveal that each effect is equally responsible for Canada's low gravity. The work could shed light on how continents form and evolve over time.