Whirlpool occur when two opposing currents meet. They cause the water to spin round and round very rapidly. Huge whirlpools at the sea are normally caused by powerful tides.
The most famous whirlpool is the Maelstrom, which appears between two islands off the coast of Norway. sometimes this whirlpool is even strong enough to destroy small ships.
The ancient Greeks believed that the Charybdis whirlpool in the Mediterranean was caused by a monster.
