Geological processes tend to be slow. But in 1995 a discovery by a group of scientists shocked the world when they announced they had found evidence of a rapid geomagnetic reversal. Before then, geophysicists believed that a complete flip would take around 5000 years.
The observations come from Steens Mountain, I layer of lava flows almost one kilometer thick and 16.2 million years old in the Eastern Oregon desert. Rob Coe, Michel Prevot and Pierre Camps published evidence that at the time the lava flow was solidifying, the geomagnetic pole shifted as much as six degrees a day over a period of 13 successive days.
The earths magnetic field is believed to be created by the convection currents of metallic fluids in the hot outer core. Scientists generally estimate that currents within the core flow somewhere between 10 and 30 kilometers a year. Flow rates during a reversal cannot be much greater, theorists believe, because there appear to be feedback effects that limit the flow rate. If the outer core moves more quickly it generates stronger magnetic forces that tend to slow it back down again.
At Steens Mountain, they calculated based on their observations that the fluid in the outer core would have had to move around 3000 kilometers in just this short period of time to produce this change. Coe agrees ”These rates are a thousand times faster than people would like to see.”
Bergeron, L. (1996). When north flies. New Scientist, 2023, 24-28