Gravity is directly proportional to mass. So higher the mass so does the gravity and vice versa.Large portions of Canada, particularly Hudson Bay region are missing Gravity. Wait! people are not flying around in this region but the gravity is slightly lower.
This peculiar phenomenon in Canada was first discovered in 1960 when the gravity fields of Earth were being .So if Canadian regions have less gravity then they must have less mass also. Scientists have proposed two explanations for this.
First one deals with flow of molten magma below the Earth’s crust, the process is known as convection of magma. Below the solid crust on about which we have continents and oceans there’s a layer of molten rocks which flows and with it(100 to 200 km below the surface), the continental plates are dragged downwards thereby reducing the mass in the area and consequently, gravity.
Second hypothesis talks of Rebound effect. In the Ice Age the Canadian regions were covered with a over 3km thick sheet of ice. It was heavy and weighed down the ground. When it melted away, it left a deep indentation on surface. Now the ice is gone the mass is lesser so does the gravity. Now the ground is trying get its shape slowly at a rate of an inch per year. This rebound effect can be demonstrated as if you were poking a sponge in the middle makes a depression and when you release it the sponge regains its shape, the same thing is happening with the ground there but at a much slower rate.
It seems that both the given theory is correct. According to data gathered by the Gravity Recovery and Climate Experiment (GRACE) satellites, it turns out that the ice sheet theory only accounts for 25 percent to 45 percent of the gravitational variation and the remaining 55 percent to 75 percent of gravitational variation is likely due to movement of molten rocks in mantle.
Enjoy reading and be open to the things that world has to offer.
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