Volcanic activity in the Paraná Plateau occurred over 150 million years ago. Then seismic events about 200,000 years ago created this sensational series of two-step waterfalls. The steps range in size from 115 to 130 feet. The latter is equivalent to a 12 floor high-rise. The exposed cliffs are basalt, a form of igneous or magmatic rock. The shape, strength and positioning of the basalt columns dictate the flow of water. The edges are constantly eroding at about .5 to .8 inches a year. Iguaçu Falls is an evolving work of art by Mother Nature.