The Iguazu Falls were formed by the erosion of the Iguazu River, which runs along the border between Brazil and Argentina. The river is fed by numerous tributaries and originates in the Serra do Mar mountains of Brazil.
Over millions of years, the powerful force of the river’s water has eroded the underlying rock and soil, creating a series of steep cliffs and channels that make up the falls. The Iguazu River flows over a wide plateau made of basalt rock, which is covered by a layer of softer sandstone. As the river erodes the sandstone layer, it undercuts the harder basalt, creating the dramatic cliffs over which the waterfalls cascade.
The falls themselves are made up of hundreds of individual cascades and channels, ranging in height from 60 to 82 meters (197 to 269 feet). The most famous of these is the Devil’s Throat, a U-shaped chasm 82 meters (269 feet) high and 150 meters (492 feet) wide that marks the border between Argentina and Brazil. The falls are surrounded by lush rainforest vegetation and are home to a rich array of plant and animal species, making the area a UNESCO World Heritage Site.
Iguazu Falls: the origins and the geology
The formation of the Iguazu Falls is closely tied to the geologic history of the region. The falls are located on the Paraná Plateau, which is an extensive basaltic lava plateau covering much of southern Brazil, eastern Paraguay, and northern Argentina. The plateau was formed by a series of volcanic eruptions that took place during the Cretaceous and Paleogene periods, about 130 to 50 million years ago.
The basaltic rock that makes up the plateau is extremely hard and resistant to erosion, which is why it forms the steep cliffs over which the waterfalls cascade. However, the basalt is covered by a layer of softer sandstone and other sedimentary rocks, which have been more easily eroded by the Iguazu River and its tributaries.
Over time, the river has carved a deep channel through the sandstone layer, which has undercut the harder basalt above it. This process has created the dramatic cliffs and steep drops that make up the falls. The falls themselves are constantly changing due to ongoing erosion and geological processes. In some areas, the river has cut through softer layers of rock, creating narrow channels and canyons. In other areas, the basaltic rock is more resistant, resulting in wider cascades and pools.
The geologic features of the region have also had a significant impact on the ecology of the area. The plateau’s extensive basaltic soils support a diverse array of plant life, including the lush rainforest vegetation that surrounds the falls. The falls and surrounding forest are home to a rich variety of animal species, including numerous rare and endangered species. The Iguazu Falls are thus not only a spectacular natural wonder but also an important ecological hotspot.
