Deciphering the Grand canyon
For geologists, the Grand Canyon is one of the most spectacular natural laboratories on our planet. The canyon's formations embody the enormity of geological time, and its vast size and intricately structured towers and walls demonstrate the immense power of erosion. Geologists closely inspect every face of the canyon, and read the layers of its rocks like the page of a book. They construct detailed maps and determine its three-dimensional structure to understand how the canyon and the rocks exposed in it formed.
The Grand Canyon Region
The Colorado Plateau is an uplifted area of flat plains, broad mesas, great canyons, and spectacular vistas. As the plateau rose, the Colorado River cut its way downward, creating the mile-deep chasm of the Grand Canyon. This extraordinary depth resulted from the powerful erosion of the river. Its power to erode is a consequence of its steep drop combined with the rapid uplift of the plateau. These processes continue today.
Carving the Canyon
The Grand Canyon has been eroding at the geologically rapid rate of 3 centimeters every hundred years. The erosion is rapid because the Kaibab Plateau, a high tableland that encompasses northern Arizona, is rising quickly. In addition, the river drops more than 600 meters from Lake Powell to Lake Mead, and thus its rapid current has great power to erode. Boulders from the cliffs fall into the river, where the water breaks them down to pebbles, sand, and finally, silt.
About 70 million years ago, the region of what is now northern Arizona started to rise.
The Shivwits Plateau, just to the north of the Grand Canyon, contains gravels deposited by rivers flowing from the southwest.
When the layers at the bottom of the Grand Canyon formed 1.7 billion years ago, Arizona was at the western edge of North America.
The upper walls of the Grand Canyon reveal sedimentary rock layers formed in marine and continental environments between 550 and 260 million years ago.
The size of rock fragments in sedimentary rocks indicates the amount of energy needed to deposit them.