The artesian well, discovered in the 12th century in Artois, is a well from which water springs spontaneously.
Principle of the artesian well
This phenomenon is due to the pressurising of an aquifer when the slope of the impermeable geological layer above it forces it under its piezometric line (line of equal pressure in subterranean water). If this layer is bored, thewater gushes up the bore following the principle of communicating vessels.
Because these deep subterranean waters can be hot, artesian wells are also used in geothermalheating systems.
Artesian well at the Butte aux Cailles in Paris. © Hugues Mitton CC by-sa 2.5