![]() Similarly, the massive Ogallala Aquifer of the Great Plains in the United States no longer receives the water recharge from the Rocky Mountains that formed it during the Pliocene Epoch (5.3 million to 2.6 million years ago). Radioisotope dating techniques have shown that this water is many thousands of years old. The water is being used extensively for water supply and irrigation purposes. A good example is the water of the Nubian Sandstone Aquifer System, which extends through several countries in an area that is now the Sahara. When the water table is deep underground, the water of the aquifer may be exceedingly old, possibly a result of a past climatic regime. Rates of groundwater recharge are greatest when rainfall inputs to the soil exceed evapotranspiration losses. This drainage is referred to as groundwater recharge. The water found in aquifers is replenished by drainage through the soil, which is often a slow process. As opposed to a confined aquifer, the water table in an unconfined aquifer system has no overlying impervious rock layer to separate it from the atmosphere. SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!Ī groundwater aquifer is said to be unconfined when its upper surface ( water table) is open to the atmosphere through permeable material.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century.Britannica Beyond We’ve created a new place where questions are at the center of learning.100 Women Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians.COVID-19 Portal While this global health crisis continues to evolve, it can be useful to look to past pandemics to better understand how to respond today.Student Portal Britannica is the ultimate student resource for key school subjects like history, government, literature, and more.Demystified Videos In Demystified, Britannica has all the answers to your burning questions.This Time in History In these videos, find out what happened this month (or any month!) in history.#WTFact Videos In #WTFact Britannica shares some of the most bizarre facts we can find.Britannica Classics Check out these retro videos from Encyclopedia Britannica’s archives.Britannica Explains In these videos, Britannica explains a variety of topics and answers frequently asked questions. ![]()
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