Grand Canyon

[ edit ] Image of the Grand Canyon and surrounding area taken from the International Space Station The Grand Canyon from an airplane, with the Colorado River visible Grand Canyon, Arizona, Nevada, Lake Powell to Lake Mead , June 27, 2017, Sentinel-2 true-color satellite image. Scale 1:450,000. The Grand Canyon is a river valley in the Colorado Plateau that exposes uplifted Proterozoic and Paleozoic strata , and it is also one of the six distinct physiographic sections of the Colorado Plateau province. Even though it is not the deepest canyon on land in the world ( Kali Gandaki Gorge in Nepal is much deeper ), the Grand Canyon is known for its visually overwhelming size and its intricate and colorful landscape. Geologically, it is significant because of the thick sequence of ancient rocks that are well preserved and exposed in the walls of the canyon. These rock layers record much of the early geologic history of the North American continent. Uplift associated with mountain formation later moved these sediments thousands of feet upward and created the Colorado Plateau. The higher elevation has also resulted in greater precipitation in the Colorado River drainage area, but not enough to change the Grand Canyon area from being semi-arid. The uplift of the Colorado Plateau is uneven, and the Kaibab Plateau that the Grand Canyon bisects is over one thousand feet (300 m) higher at the North Rim than at the South Rim. Almost all runoff from the North Rim (which also gets more rain and snow) flows toward the Grand Canyon, while much of the runoff on the plateau behind the South Rim flows away from the canyon (following the general tilt). The result is deeper and longer tributary washes and canyons on the north side and shorter and steeper side canyons on the south side. : 406 T

[ edit ] Main article: Geology of the Grand Canyon area Diagram showing the placement, age and thickness of the rock units exposed in the Grand Canyon Rockfalls in recent times, along with other mass wasting , have further widened the canyon The Grand Canyon is part of the Colorado River basin, which has developed over the past 70 million years. For more than 150 years, scientists have gathered data, proposed new ideas, and debated sometimes contentious theories about the geologic origins of the Grand Canyon and the Colorado River. Formation of the Grand Canyon and the Colorado River may involve a complex history in which multiple factors and geologic processes have interacted over time and in different locations. In the most recent round of "old river" vs. "young river" controversy, researchers have challenged estimates that had placed the age of the canyon at 5–6 million years. The research has aroused considerable controversy because it suggests a substantial departure from prior widely supported scientific consensus. In a 2008 study, Victor Polyak examined caves near the Grand Canyon and placed their origins about 17 million years ago. The study, which was published in the journal Science in 2008, used uranium-lead dating to analyze calcite deposits found on the walls of nine caves throughout the canyon. In another 2008 study, Rebecca Flowers reported on apatite (U-Th)/He thermochronometry results suggesting that parts of the Grand Canyon had reached a depth near to the modern depth around 20 million years ago. In a subsequent study published in the journal Science in 2012, she suggested that the western part of the Grand Canyon could be as old as 70 million years. The emerging scientific consensus is that the canyon is made up of multiple segments which formed at d

[ edit ] Ribbon Falls, near the North Kaibab Trail , is produced by ground water reaching the surface Groundwater flow in the Grand Canyon region is an active area of study. Groundwater forms when rain soaks down into the earth and reaches the water table . The composition of the earth in a given area determines its permeability , the ease with which water flows through it. Sand is more permeable than clay. Less permeable rock layers composed of clay can block the passage of water and are known as aquitards . More permeable areas of rock that hold and transport groundwater underground are known as aquifers . An area of water bounded by two aquitards is called a confined aquifer, while water below the surface and above an aquitard is called an unconfined aquifer. The different geologic levels of the Grand Canyon have created two major aquifers where groundwater collects. The higher C-aquifer is an unconfined aquifer. It collects groundwater that seeps through the Kaibab and Toroweap Formations into the Coconino Sandstone. Below it, the Permian Hermit Formation and Supai Group provide a dense barrier. Groundwater from the C-aquifer can flow laterally, appearing as seeps along the canyon walls at the base of the Coconino Sandstone but can also descend vertically through fault zones to recharge the underlying confined R-aquifer. The R-aquifer, also known as the Red Wall Muav aquifer, is a karst aquifer. It involves an area of substantial fracturing through the Redwall Limestone, Temple Butte Formation and Cambrian Muav Limestone of the Tonto Group. Five individual systems flow through the R-aquifer and compose the regional groundwater-flow system which drains into the Grand Canyon: Kaibab, Uinkaret-Kanab, Marble-Shinumo, Cataract, and Blue Spring. The flow of groundwater in