A well that taps confined groundwater. In
many regions, a permeable layer, typically sandstone, is confined
between two impermeable beds, creating a confined
aquifer. In these situations, water only enters the system in a
small recharge area, and if this is in the mountains, then the
aquifer may be under considerable pressure. This is known as
an artesian system. Water that escapes the system from a
fracture or well reflects the pressure difference between the
elevation of the source area and the discharge area (hydraulic
gradient) and rises above the groundwater level in the aquifer
as an artesian spring, or artesian well. The water may or may
not rise above the ground surface. Some scientists use the
term artesian well only to refer to wells in which the water
does rise above the ground surface. Some of these wells have
made fountains that have spewed water 200 feet (60 m) high.
One example of an artesian system is in Florida, where
water enters in the recharge area and is released near Miami
about 19,000 years later. Other examples are abundant east
of the Rocky Mountains of the western United States, in the
fens of the United Kingdom, and in some desert oases of
Egypt and North Africa.
See also GROUNDWATER.
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