One of the world's most famous examples of an isthmus is the Isthmus of Panama. The Florida Museum of Natural History reports that this isthmus was formed over millions of years by the Earth's tectonic plates slowly colliding with the sea floor raised by the Pacific Plate sliding beneath the Caribbean Plate.
NASA reports the formation of an isthmus is due to a number of islands breaking the surface of the ocean or sea. When the ocean rises and falls, sediment is trapped between the islands eventually forming a land mass over millions of years.
According to the Water Encyclopedia website, isthmuses are usually found connecting a peninsula to a larger land mass. Before being pushed against the land mass of South America, the Isthmus of Panama was a Central American peninsula.
