There are many interesting and awesome natural phenomena. Some of them need certain condition to appear that makes it rare to happen, others come up regularly. Some are very dangerous and can be deadly if we get trapped in it. However, all those phenomena naturally happened and available to be studied and understood. So that, we can make it useful and avoiding the damage of it.
Whirlpool are found in various parts of the world, three of the famous are Maelstrom located off the coast Norway, Charybdis occurred in a narrow strait between Italy and Sicily, and in the downstream of Niagara Falls. The original maelstrom was Moskstraumen, which is caused by a very powerful tidal current. Some people depict it as a giant vortex that leads to the bottom of the ocean where it is in fact a crossroad of underwater currents. Well, they were a bit off, but still, it’s quite a view to catch.
The second type is even more fantastic. Some called it ice pans, these formations that form in the middle of the river are basically surface slabs of ice. They’re explained by sudden shifts of temperature. As the water cools off, it gives away heat that creates frazil ice. These ice particles can of course form an ice pan, and if the lake has enough frazil ice and the current is slow enough, the ice pan can reach the sizes that baffle people and even become a hanging dam.