Canyons are deep valleys with almost vertical slopes, which can extend for hundreds of kilometers and reach up to 5 thousand meters in depth. At first sight, those who observe these gigantic notches on the surface of the planet could imagine that they were created from one moment to the next by some catastrophic phenomenon, such as an earthquake capable of opening the earth and creating a precipice.
None of that: in general, the canyons have a slow deepening, which can last millions of years. The main authors of these works of art are the rivers. “Depending on the declivity of the land, the amount of water and the fractures in the relief, a watercourse has the capacity to carve the rocks of the bed through which it flows, giving rise to the walls”, says geographer Lylian Coltrinari, from the University of São Paulo (USP).
However, a river does not build a canyon alone. In this process, the so-called uplifts also play an important role, processes of shock and displacement of plates inside the Earth’s crust that gradually raise the relief of the region. As the terrain rises, the rivers running on the surface begin to gain speed and deepen their beds, increasing the height of the walls.
For scientists, the canyons make it possible to understand the origin of the rocks and relief of a region. In an approximate image, if we compare the Earth with an onion, a canyon is like a knife cut that reveals some layers of the skin of the rocky “vegetable” in which we live. But today’s canyons are not exact portraits of the past. “In addition to continuous river erosion, the action of heat, wind, ice and Earth’s gravity itself, which causes landslides, has modified the appearance of these features over time”, says Lylian.
dive into it
At the bookshop:
A Terra, João Guizzo (editing) and Lylian Coltrinari (translation), Ática, 1994
The action of millions of years of river erosion exposes rock walls up to 1,800 meters deep. For a long stretch, the canyon is predominantly red. In other sections, each layer of rock has its own specific color, composing a watercolor that includes bands of light yellow, gray, green, pink and violet.
NATURAL EXCAVATOR
Carrying sediments for 6 million years, the Colorado River is the great sculptor of the place. Its erosion capacity is impressive: before the inauguration of the Glen Canyon dam in its bed, in 1963, researchers estimated that the river dragged about 500 thousand tons of sediment per day. Completing the work, dozens of tributaries dig their own valleys, fed by rain or snow from higher regions.
AUDIENCE CHAMPION
Carved out of a plateau, the Grand Canyon stretches for 445 kilometers in northwestern Arizona, in the United States. The site is one of the most popular natural attractions in the country. Every year around 5 million people visit the national park that is home to the deep valleys.
REVEALED GEOLOGY
For most of its length, the walls of the Grand Canyon are composed of so-called sedimentary rocks, which are characterized by layers that are deposited one on top of the other over time and tell the geological history of the place. Just to give an idea of the “age” of the region, suffice it to say that the rocks in the deepest layers were formed around 2.5 billion years ago.
Explored only in the 90s, this canyon stole the position of the largest on the planet from the Grand Canyon. In 496 kilometers long, the walls reach 5,000 meters in height
Itaimbezinho (Brazil)
In Tupi-Guarani, the name of the most famous canyon in the country means “cutting stone”. Located in Rio Grande do Sul, it is 6 kilometers long and has walls 700 meters high
Fish River (Namibia)
Dug in the south of the African continent, this canyon is one of the longest in the world, measuring 160 kilometers. Its canyons, however, are not that big and are on average 500 meters high.
Colca (Peru)
Considered the deepest example of erosion in the Andes, this canyon is over 100 kilometers long and has canyons up to 3,000 meters deep.
Barranca Del Cobre (Mexico)
This valley system located in a mountainous area near the US border encompasses six main canyons. The deepest has walls of 1840 meters