The Earth has two different sets of poles: the geographic north and south poles (the endpoints of the Earth's rotational axis) and the magnetic north and south poles (based on the Earth's magnetic field). The magnetic poles are not fixed; instead, they move in circular patterns that may travel up to 50 miles (80 kilometers) in a single day. We calculate the position of the magnetic North Pole by taking an average of its positions over a period of time. The average position of the magnetic North Pole has moved about 685 miles (1,102 kilometers) in the past 150 years. The magnetic north and south poles can even trade positions - - it's not especially uncommon. Scientists believe that this has happened about 400 times in the last 330 million years, with the last switch taking place about 780,000 years ago. The reversal process takes about 1,000 years to complete. Because the magnetic field has weakened by about 10 percent in the past 150 years, scientists think there might be a flip in progress. But what causes magnetic poles to move around and trade places?
The Earth's magnetic poles shift because of changes in the convection patterns near the center of the planet's mass. A phenomenon called the dynamo effect, characterized by currents and convections within the Earth's core, occurs because the inner core (made of solid iron) spins at a different rate than the outer core (made of a molten material). The behavior of the Earth's solid iron core works to create the Earth's magnetic field, but how the dynamo effect changes the magnetic field is not well understood. It probably has to do with shifts in the core's spinning rate and the currents within the Earth's molten material. Changes to the Earth's crust (like earthquakes) and irregularities where the mantle (the layer between the inner core and the crust) and the core meet can also cause changes in the magnetic field.
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