Iguazu Falls: a history of differential fluvial incision

STEVAUX, J. AND LATRUBESSE, E

Geomorphological Landscapes of the World

Springer Verlag

Lugar: Berlin; Año: 2008;

Located at the border between Brazil and Argentina, the world famous Iguazu Falls are one of the most beautiful because 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 mean annual discharge of the Iguazu River at the falls is  1413 m3s-1, but discharges as high as 35,600 m3.s-1 had been recorded. The geology of the falls consists of three layers of basalts that give a staircase-type shape to the falls. The columnar disjunction  and the trapp sequence and the orthogonal pattern of fracture on the basalts produced a peculiar design for the erosion and fall formation. Vertical fractures are related to more recent unloading conditions and became more important while the canyon was excavated. The Iguazu River has about 1500m in width above the falls and runs and forms many rapids between rock expositions and small islands. The river channel changes abruptly its direction from south to N-NW and precipitates vertically from a height of 80m. The falls have a sinuous arch-like head of 2.7 km in length where part of water volume enters in  a canyon 80 to 90 m width and 70-80 m depth through 21 km upstream the confluence of Iguazu and Paraná rivers forming the spectacular “Garganta do Diabo” (Devil’s Gorge). Part of river water enters in the canyon by its left side and generates a front with 160 to 200 individual falls that forms during floods a unique front. Although no absolute ages exist as well as no detailed knowledge is available on the evolution of the fluvial system, it has been suggested that the falls were continuously wandering upstream to its present position by progressive headwater erosion at a rate of 1.4 to 2.1 cm/year in the last 1.5 to 2.0 my. The falls are part of the Bi-National Park of Iguazu (Argentina and Brazil) that spread on near 2500 km2.  The Argentinean area was recognized as UNESCO World Heritage in 1984 and in 1986 the site was extended to the Brazilian side. Iguazu Falls are regarded as a Geomorphological Site by the Brazilian Commission of Geologic and Paleobiological Sites – SIGEP.