Physical Geology 2004


Click here to read about the other natural wonders of the world

Related Links:

Click here for a link to a site that has a video stream of Iguaçu Falls


The falls are situated in the middle of the national park Parque Nacional Foz do Iguaçu (founded in 1939) and bridges connect the Brazilian city of Foz do Iguaçu with the Argentinean town of Puerto Iguaçu and the Paraguayan city of Ciudad del Este.







Basalt is a volcanic rock formed by the melting of pre-existent material deep in the layer of the earth called the lithosphere. When reaching the surface, basalt spreads out and becomes lava. Composed almost entirely of dark, fine-grained silicate minerals, chiefly plagioclase feldspar and pyroxene, and magnetite, basalt is usually dark-gray in color, and often has a vesicular texture, preserving vestiges of bubbles produced by expanding steam as lava cools and solidifies.






Covering 185 thousand hectares, the Iguaçu region is the largest remaining sub-tropical forest in South America. Trees such as Brazilian walnut, silk-cotton tree, jaracatiá, angico, canella, guacumbu, ipê, and secular peroba all flourish in the lush forest. Wildlife that calls the area home include the macaw,toucan, parakeet, monkey, crocodile, otter, jaguar and armadillo.






The Guarani Aquifer has a preliminarily defined total extension of approximately 1.2 million square kilometers. The Guarani Aquifer is made up of many arenaceous layers that were deposited in the Paraná Sedimentary Basin during the Mesozoic Era (during the Triassic, Jurassic and Cretaceous Periods) between 200 and 132 million years ago.


Arial view of the Guarani Aquifer, the Parana River, Iguacu Falls, and the Iguacu River. The upper photos shows the convergence of theregion around the borders of Brazil, Argentina, and Paraguay, and the bottom one shows the geologic topography of the area.


Iguaçu Falls

"Great Water"

One of the World's Natural Wonders:

- Iguaçu Falls are counted among the greatest natural wonders of the world and are by far the most overwhelming and spectacular waterfalls in South America. The map at the left indicates where this and other natural wonders of the world are.

Where in the World are They?

- Iguaçu Falls are the result of the confluence of the Iguaçu river (a river which crosses the western highlands of the Brazilian states of Paraná and Sao Paulo, and the Paraná River. The Falls discharge water at the edge of the massive flood basalts (where the borders of Brazil, Argentina, and Paraguay meet) at a rate of up to 2,300 cubic yards per second.

Click here for link to full map of South America

What Makes Iguaçu Falls Unique?

- There are approximately 160 to 270 waterfalls (depending on the water flow during the rainy season). There are 19 major drops with the best view of the falls on the Brazilian side.

- Due to the high humidity caused by the spray from the falls the park is very rich in superb flora and fauna. Within the semi-tropical forest where you can see orchids, bamboo, begonias growing among the pine trees and palms. Colorful birds and butterflies are found everywhere in this dense jungle. The roar of the falling waters can be heard from afar and at the falls you will see rainbows.

Ancient Folklore

- Although geologic research proves that the Iguaçu falls were formed over 100 million years ago due to massive volcanic eruptions, the falls are steeped in myth and legend according to Native Guarani Indian legend, Iguaçu Falls were formed when a jealous forest god, enraged by two young lovers who fled down the river in a canoe, made the river's bed collapse in front of the couple. Legend has it that the girl plunged over the edge and turned into stone. The warrior, it claims, survived as a tree overlooking his lost love.

Geologic Formation of the Falls

- The formation of Iguaçu Falls dates back to two hundred million years ago, when the first rupture in the super continent Pangea took place between Africa and South America.

- One hundred million years ago, eruptions of basaltic lava broke through chasms in the Earth’s crust, forming spillways several kilometers high in layers several meters thick. The Iguaçu Falls are formed by three of these spillways mostly covered by water; a larger one, between 141 and 180 meters high, a smaller one, between 116 and 141 meters high, and an even smaller one, less than 116 meters high. The falls are formed in three steps by these spillways; one smaller fall and two higher ones.

- Horizontal and vertical movement of the continental plates created vertical cracks in the basalt rock. These big cracks are called faults. A system of these faults runs through the Iguaçu region. The principal channel of the Iguaçu River runs through one of the faults where erosion has been more intense.

- Thus, what we see today are falls cascading over one of the largest flood-basalt provinces in the world, with the falls themselves stretching four times wider than Niagara Falls. While drilling in Brazil, Petrobrás (Brazil's national petroleum company) has found basalt layers of more than 5,000 feet. In the Iguaçu Falls region there is approximately 1,000 meters (3,250 feet) of basalt. According to geologists from the Itaipu Dam, the Iguaçu region has between 8 to 10 layers of basaltic rock. To learn more about basalt, see the left column.

Unearthly Geologic Creations

- Waterfall "fingers" are created by the rifts in the basalt that allow the water to break off into smaller waterfalls which ultimately empty into the Devil's Throat (see below). See left for an example of the waterfall "fingers.

- Devil's Throat is a semi-circular bowl that is hundreds of yards across, into which the river plunges on its descent 200 feet down into a mist-filled abyss. Here, 14 separate falls join forces, pounding down the 350ft cliffs, emitting violent turbulence and spray.


-Vesicles result from preserved gas bubbles that form when magma rises and then decompresses. They normally range in diameter from millimeters to a few centimeters, but those found in the Paraná Basin have been found to reach a meter in length.

- Amethyst accumulations - due to water percolating through the basalt, spectacular amethysts (purple quartz) have formed, in spite of millions of years of chemical weathering, these mature minerals have withstood tropical tests of time.


-Tourism has become increasing prevalent in the Iguaçu Falls region, especially with the rise of eco tourism, which draws tourists from around the world to the surrounding cities on the Brazilian, Argentinean, and the Paraguayan sides.

- Some of the Ecologic factors involving the Iguaçu Falls address how best to utilize the huge quantity of water that flows over them in order to lessen the impact of human habitation of the region. Hydro power and aquifer water supply are two of the ways Iguaçu Falls helps ecologically sustainable development.

- The Itaipú dam, on the Río Paraná 12 km (7.5miles) north of the falls, is the site of the largest single power station in the world, built jointly by Brazil and Paraguay. It was built in 1892, and began operating in 1984. The dam produces enough electricity to power the whole of Southern Brazil and much of Rio de Janeiro, São Paulo (one of the largest metropolitan cities in the world) and Minas Gerais.

- The Guarani Aquifer is where is the sixth biggest under ground reservoir of water in the world. It is located under the Iguaçu Falls region. The Guarani Aquifer is the largest trans frontier underground sweet-water reservoir in the world. It extends from the Paraná Sedimentary Basin located within the countries of Brazil, Paraguay and Uruguay to the Chaco Basin located principally in Argentina. To see a map and read more about the Guarani Aquifer, see the left column.


Literature Cited (translated from the Portuguese by Rachel Graville)

Author: Rachel Graville
Creation/revision date: April 17, 2004


Link to other Student Webpages for 2004 Earlham Physical Geology

This website was prepared as an assignment for Geosciences 211 (Physical Geology) taught in the spring of 2004 at Earlham College, Richmond, Indiana.

Earlham College Geosciences Department Earlham Geosciences 211: Physical Geology

Copyright 2004 Earlham College. Revised April 20, 2004 . Send corrections or comments to