Portal:Geophysics/Did you know/3

• ... that a world map by Gerardus Mercator attributes the Earth's magnetic field to a magnetic mountain (pictured) above the Arctic Circle?
• .. that tectonic subsidence, the sinking of the Earth's crust, can be caused by extension, cooling, or loading?
• ... that tectonic plates in the Earth's crust are not completely rigid but can be deformed by the melting of an ice cap?
• ... that substorms were first described in 1964?