Iguazu Falls: 275 Cascades of Water Carved by 130 Million Years of Geology
Iguazu Falls, which straddles the Brazil-Argentina border and includes a lesser cascade in Paraguay, is made up of around 275 separate waterfalls spread across a 2.7-kilometre (1.7-mile) crescent of breathtaking natural power. The falls discharge approximately 1,500 cubic meters of water per second during normal flow (with seasonal variations ranging from 250 cubic meters during the dry season to 13,000 cubic meters during floods), making it one of the world's most volumetrically powerful waterfalls despite not being the tallest (the Salto Angel (Angel Falls) in Venezuela reaches 979 meters, while Iguazu's tallest individual cascade measures approximately 82 meters). What distinguishes Iguazu is the sheer number of waterfalls that provide a panoramic spectacle, with the Garganta del Diablo (Devil's Throat) being the most powerful cascade, with water falling 82 meters amid thundering roars and mist visible for kilometres.
Iguazu Falls' geological basis dates back 130 million years, to the Cretaceous epoch. The Paraná Plateau is a large basaltic lava plateau that covers southern Brazil, northeastern Argentina, and eastern Paraguay. It was generated by remarkable volcanic eruptions that released fluid tholeiitic basalt lava in repeated cycles over millions of years. These eruptions deposited basalt layers over 1,000 meters thick across large areas. The separate basalt flows cooled, forming discrete strata with different mineral compositions and mechanical qualities. When the Iguazu River, which is fed by streams from Brazil's Serra do Mar mountains, reached this volcanic plateau around 5 million years ago, it began to erode preferentially along the softer, more erodable shale strata beneath the resistant basalt cap rock.
The waterfall's continual evolution shows dynamic geologic processes. Water continuously weakens the basalt cap by eroding the underlying shale, producing periodic collapse of the overlying resistant rock, resulting in the characteristic amphitheatre-shaped form. Iguazu Falls retreats upstream at a rate of around 1 metre every decade, eventually retreating south to its source. Geological models indicate that the falls have migrated around 30 kilometres upstream since formation, with more upstream migration projected if current erosion rates continue. The Iguazu River's remarkable erosive capacity is due to its enormous water volume and the abrasiveness of sediment-laden water. UNESCO classified the falls as a World Heritage Site, recognising both their geological significance and the richness of the surrounding rainforest ecosystems. Iguazu Falls is thus not a static wonder, but rather a dynamically changing geological formation formed by water, gravity, and resistant rock layers interacting over millions of years.
