Why a scale reads slightly lower near Hudson Bay
A person standing in the Hudson Bay region is pulled downward by gravity a little less strongly than someone standing in many other parts of Earth. A scale responds to that pull, so it would register a tiny reduction in weight. The change is far too small to feel, and an ordinary bathroom scale is not precise enough to reveal it.
The reason is not that Earth’s surface is simply “missing” a layer. Gravity depends on how much mass lies nearby and how that mass is arranged. Beneath Hudson Bay, the distribution of rock and denser mantle material produces a weaker-than-average gravitational field—a feature called a gravity anomaly.
The lingering effect of an enormous ice sheet
During the last ice age, a vast sheet of ice covered much of what is now Canada. Its immense weight pushed the land downward and displaced some of the slowly flowing mantle beneath it. When the ice melted, the crust began rising and the mantle began shifting back. That adjustment is still under way, thousands of years later.
The rebound changes the shape of the crust, while the slow movement of rock below it changes where mass sits underground. Together, these shifts contribute to the region’s unusually weak gravity. The ice itself is long gone, but its geological aftereffects remain.
So the “strange” experience on a scale is real in principle, not a sensation: your weight would be minutely lower because Earth’s mass is arranged differently beneath your feet.
