Experience Canada’s Gravity Anomaly: How Hudson Bay’s Unique Phenomenon Makes You Weigh Less

Gravity Anomaly in Hudson Bay, Canada

Gravity is not the same everywhere on Earth. In Canada’s Hudson Bay, gravity is slightly weaker than the global average. This anomaly has been studied by scientists since the 1960s.

Why is Gravity Weaker in Hudson Bay?

The Earth’s mass is not perfectly distributed, causing variations in gravity. Here are two main reasons for the weaker gravity in Hudson Bay:

The Laurentide Ice Sheet Theory

About 20,000 years ago, the Laurentide Ice Sheet, a massive glacier over 3 kilometers thick, covered much of North America. Its weight compressed the land beneath it, pushing down Earth’s crust. Although the ice melted quickly at the end of the Ice Age, the crust has been rebounding slowly, at a rate of about 12 millimeters per year. This slow rebound means there is less mass in the Hudson Bay region, resulting in slightly weaker gravity.

Mantle Convection Theory

Beneath the Earth’s crust lies the mantle, a layer of molten rock that circulates in currents heated by the Earth’s core. These currents push and pull on the crust, affecting the land above. In Hudson Bay, this downward pull reduces the area’s mass, contributing to the weaker gravitational pull.

Combining Both Theories

Satellite data from the Gravity Recovery and Climate Experiment (GRACE) confirmed that both theories are correct. The lower gravity in Hudson Bay is due to a combination of the crust’s slow rebound from the Ice Age and the mantle currents beneath the surface. The ice sheet’s rebound effect accounts for 25-45% of the gravitational variation, while mantle convection accounts for the remaining 55-75%.

Impact on Gravity

The difference in gravity is subtle, about 0.004 percent less than Earth’s average. This means you would weigh slightly less in Hudson Bay compared to other parts of the world, though this difference is too small to notice without highly accurate scales.