The Grand Canyon Geology
The Grand Canyon features one of the world's most studied geologic histories anywhere, because it possesses the most complete sequence of rock that represents two billion years of Earth's geologic history in North America. There are 40 identified rock layers and 14 major unconformities that indicate where there are gaps in the geologic record. It is by far one of the most fascinating and easily accessible places for geologists to catalog the Earth's major events and delve into our planet's veiled past.
How Was the Canyon Made?
Scientists cannot be completely sure how the canyon was created and there are still theories evolving, but they do have a very educated guess. Erosion is what most target as the main contributor to the creation of the Grand Canyon. This was caused mostly by water, ice and wind, however; continental drift, weather and climate changes, and even volcanoes were also contributing factors to the formation of the Grand Canyon. Most scientists agree that the largest component in the creation of the canyon was water and the path of the Colorado River. Water is one of the most powerful forces on Earth, with the ability to build and destroy.
The first contributor in granting water the ideal components to complete such a great feat as carving out the Grand Canyon was the Laramide orogeny, which also formed the Rocky Mountains. This event occurred 75 million years ago and caused an estimated 10,000 ft. (3,000 m.) of uplift, which granted the Colorado River a steeper slope to carve its way into the four plateaus that make up this area. A river alone with its steady ebb and flow could not carve out a canyon so massive without a little help from Mother Nature.
Flash Floods and the Arid Desert
Flash floods are one of the most destructive forces on our planet, with the power and force to move boulders, uproot trees, obliterate buildings, wash out roads, and destroy bridges. The floods also take many lives because of how suddenly they can occur. They move quickly with the ability to possess walls of water 10 - 20 ft. high and can carry debris in their front: it is easy to see how they can carve out rivers and canyons.
The reason flash floods occur in places like the Grand Canyon, is because of the desert climate. The Grand Canyon is situated in an arid desert that only receives an average of 26 inches (66 cm) of rain each year. Since the ground receives so little moisture, it bakes under the sun each day, which makes it difficult and almost impossible to absorb water easily. When the skies open up and rain pours down, the water falls at such a rate that the ground is not able to absorb it fast enough and this causes a flash flood. Since the water cannot be absorbed it goes wherever it can; moving fast downhill and picking up debris along the way.
Today's flash floods are powerful, but they are nothing compared to the floods that helped shape the canyon! When the Earth was young its climate, weather and geology was very unstable. From the little history we can find locked away in fossils, old and petrified trees, rocks, magma, soil and the ocean, scientists are able to document that the worst, largest, and most catastrophic natural occurring disasters were during the time when the Earth was young. Everything was more extreme; tsunamis, volcanic eruptions, storms, droughts and earthquakes. The climate and the Earth itself were exceptionally unstable.
Droughts lasted longer and so did storms, which made the effects of floods that much more devastating. In fact, amidst the many layers of rock that the canyon holds there are breaks and some gaps where time periods are missing or an uneven spread of sediment; this is called an unconformity. Throughout the 40 layers of rock there are 14 unconformities that have geologic history gaps as large as 165 - 250 million years and 12,000 feet of sediment washed away in some places. Scientists can only speculate about how large these natural disasters must have been to cause so much damage; one theory is that large floods either caused by storms or glacier melt.
Geology
The canyon's major exposed sedimentary rock layers range in age from 200 million to two billion years old! The canyon's oldest layer is called the Vishnu Group; it is made of thousands of feet of sand, ash, mud and silt and is the dark-colored, garnet-studded layer at the bottom of the canyon in the Inner Gorge. This layer was created two billion years ago in the Precambrian time period when all land mass on earth was comprised of a few islands that plate tectonics caused to slam into each other and form the first few growing continents.
The canyon was formed only five to six million years ago and is much younger than the lowermost layers. In fact, most of the canyon walls are deposited marine sediment from when ocean covered the land. Each layer of rock responds differently to the erosion qualities of the Colorado River. Some rocks become cliffs and others form slopes or erode faster than different layers, this creates the variety of textures you will find at the Grand Canyon. The vivid hues that the canyon features originate because most of the rock layers contain iron and other mineral deposits.
The Grand Canyon Today
Today the canyon is one of the world's most amazing natural wonders, where people come from all over the world to marvel at its beauty and mystery. The Grand Canyon is 277 miles (446 km) long, between 4 - 18 miles (6.4 - 29 km) wide and over a mile deep (1.6 km), which makes it the largest canyon on land. Erosion is still occurring and will continue to do so, but at a much slower rate than in the past. This is mostly due to the Glen Canyon Dam. The dam is harnessing the hydroelectric power of the Colorado River, controlling how much water is put in the river and filtering out much of the sediments that erode before it hits the canyon.
The Grand Canyon National Park is a place of wonder and beginning, where learning about our geologic past is being used to ensure a better future.
