Iguazu Falls: A history of differential fluvial incision

The Iguazu Falls are one of the most beautiful in the world because of the combination of a high and wide structural step across a fluvial system with large water discharge and the tropical environmental location that sustains an exuberant forest and high biodiversity. The geology of the area consists of three layers of basalts that give a staircase-type shape to the falls. The Iguazu River is about 1,500 m wide above the falls and forms many rapids between rock outcrops and small islands. The falls have a sinuous arch-like head 2.7 km long, and part of water volume enters a canyon 80–90 m wide and 70–80 m deep, forming the spectacular “Garganta do Diabo” (Devil’s Gorge). Part of river water enters the canyon by its left side and generates a front with 160–200 individual falls that form a unique wall of water during floods. Although no absolute ages exist on the evolution of the fluvial system, it has been suggested that the falls have been continuously wandering upstream to its present position by progressive headwater erosion at a rate of 1.4–2.1 cm/year in the last 1.5–2.0 million years. The falls are recognized as UNESCO World Heritage property and regarded as a Geomorphological Site by the Brazilian Commission of Geologic and Paleobiological Sites – SIGEP.