artesian well, deep drilled well through which water is forced upward under pressure. The water in an artesian well flows from an aquifer, which is a layer of very porous rock or sediment, usually sandstone, capable of holding and transmitting large quantities of water. The geologic conditions necessary for an artesian well are an inclined aquifer sandwiched between impervious rock layers above and below that trap water in it. Water enters the exposed edge of the aquifer at a high elevation and percolates downward through interconnected pore spaces. The water held in these spaces is under pressure because of the weight of water in the portion of the aquifer above it. If a well is drilled from the land surface through the overlying impervious layer into the aquifer, this pressure will cause the water to rise in the well. In areas where the slope of the aquifer is great enough, pressure will drive the water above ground level in a spectacular, permanent fountain. Artesian springs can occur in similar fashion where faults or cracks in the overlying impervious layer allow water to flow upward. Water from an artesian well or spring is usually cold and free of organic contaminants, making it desirable for drinking. In North America, the Dakota sandstone provides aquifers for an artesian system that underlies parts of the Dakotas, Montana, Wyoming, Kansas, Nebraska, and Saskatchewan and supplies great quantities of water to the dry Great Plains region. Many East Coast cities derive their water supplies from aquifers that are exposed along the edge of the Piedmont and dip downward toward the Atlantic coast. The largest artesian system in the world underlies nearly all of E and S Australia. Other important artesian systems serve London, Paris, and E Algeria.

See Great Artesian Basin for the water source in Australia.

An artesian aquifer is a confined aquifer containing groundwater that will flow upwards through a well without the need for pumping. Water may even spurt out of the ground if the natural pressure is high enough. An aquifer provides the water for an artesian well. An aquifer is a layer of soft rock, like limestone or sandstone, that absorbs water from an inlet path. Porous stone is crushed between impermeable rocks or clay. This keeps the pressure high, so when the water finds a hole, it overcomes gravity and goes up instead of down.

In recharging aquifers, this happens because the water table at its recharge zone is at a higher elevation than the head of the well.

"Fossil water" aquifers can also be artesian if they are under sufficient pressure from the surrounding rocks. This is similar to how many newly tapped oil wells are pressurized.

Origin

Artesian wells were named after the former province of Artois in France, where many artesian wells were drilled by Carthusian monks since 1126. The technique was also known much earlier in Syria and Egypt, although whether the monks of Artois learned of it from outside sources or discovered it independently is unknown.

Examples of artesian wells

Australia

• The Great Artesian Basin is the largest and deepest artesian basin in the world, occupying 23% of the continent.

North America

Some towns in the United States were named Artesia after the artesian wells in the vicinity. Other artesian well sites include:

• Pahrump, Nevada
• Fountain Point, Michigan
• Olympia, Washington
• Memphis, Tennessee
• Smoke Hole Caverns, Seneca Rocks, West Virginia
• Evamor, Goodbee, Louisiana
• Black Belt (region of Alabama)
• Potomac, Illinois

See also

• Drinking water
• Fluid mechanics
• Great Artesian Basin
• Hydrogeology
• Qanat
• Voss water

Notes