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What is an artesian aquifer? What natural features need to be present for an artesian aquifer to exist?

Submitted by:	Angela
Date:	2003-07-06
Answered By:	Jon Hill (University of Edinburgh)

Before we can get to an artesian aquifer, we first need to define some terms:

Porous rock - rock that has pore space and can store water, similar to a sponge.
Permeable Rock - rock that allows the passage of fluid. This could be along fractures or cracks, or through pore space. A permeable rock is not necessarily porous. If a rock does not let fluid pass, the rock is impermeable.
Aquifer - an aquifer is a porous rock body that contains water.
Hydraulic pressure - pressure caused by a difference in height between two places.
Artisan well - a well that has a water level higher than the water table due to hydraulic pressure. This also means that the water could squirt out of the ground!

An artesian aquifer (also known as a confined aquifer) is an aquifer that is trapped between two impermeable layers. An unconfined aquifer is recharged rapidly from surface water. A confined aquifer takes much larger to recharge, but this also means it is not responsive to daily, annual or even millennial changes. An example of an artesian aquifer is South Dakota, USA. Figure one shows the South Dakota aquifer. Note how the Dakota sandstone (the aquifer) is bounded top and bottom by an impermeable rock.



	Figure 1: The geological setting of the artesian aquifer in South Dakota.

Why not come and discuss this further in the forums?

References

C. Plummer, D. McGeary, 1997. Physical Geology.

http://water.usgs.gov/pubs/FS/OFR93-643/

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