How did the Grand Canyon come about

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Grand Canyon: the window into the history of the earth

The Grand Canyon is located in the US state of Arizona and is one of the most spectacular natural wonders on earth. The great gorge was cut into the rocks of a plateau by the Colorado River over millions of years. Thus, the erosive history of the canyon is significantly different from that of the East African Rift Valley.

Most of the Grand Canyon is protected in a national park. Grand Canyon National Park was established in 1919, but was declared a National Monument 11 years earlier.

The gorge got its name from the river: the Colorado River was formerly called the "Grand River". The Grand Canyon itself is a superlative: 450 km long, between 6 and 30 km wide and up to 1,800 m deep. Every year 5 million people visit the national park. Early traces of settlement are 3000 years old.

The history of the creation of the Grand Canyon is no less spectacular than its dimensions. Geoscientists assume that the Colorado River began to cut into the subsurface 5-7 million years ago. In doing so, it cut through the most diverse rocks of the Colorado Plateau and created what is probably the most powerful outcrop in the world. A stroke of luck for the geologists!
First the sediments were eroded. At greater depths, the Colorado River ate (and eats) its way through the metamorphic basement. This consists of very hard granite which is also very old at around 1.8 billion years. The exposed layer sequence is not constant, but rather shows 2 discordances: the most striking layer gap is found in the deposits of the Cambrian.
Geoscientists can also reconstruct the speed at which the river dug into the rock: during the ice ages, the Colorado carried a particularly large amount of water and the rate of erosion was correspondingly high.
A good 1 million years ago there was a series of striking volcanic eruptions at the Uinkaret Volcano Field on the western edge of the gorge. The volcanic deposits clogged the canyon and formed a natural dam behind which the water accumulated to form a gigantic lake. When the water pressure got too high, the dam burst and a flash flood rushed through the canyon. It brought severe flooding downstream. We also know this scenario from the Rhine, which was also dammed near Andernach by a natural dam after the eruption of the Laacher See volcano.

In the upper reaches of the Colorado River there are other canyons such as Glenn Canyon, which has now been flooded by Lake Powell, and the canyons of Canyonland National Park. Numerous tributaries of the Colorado River also cut gorges into the Colorado Plateau. These are known as slot canyons and are an insider tip.

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