It's the Water
Artesian Geology
When a well is sunk deep in the earth, water sometimes flows up naturally, as it does from a spring. Such flowing wells are called artesian wells, from Artesium, the Latin name for the old French province of Artois, where many wells were drilled by Carthusian monks in the Middle Ages.
Most of the rain and snow which falls to earth sinks into the soil or porous rock beneath the surface. It flows out again at some point lower down, forming an ordinary spring. It is only where this water gets caught beneath great layers of watertight earth or stone and remains imprisoned there, under the accumulated pressure of the water higher up, that artesian wells are possible.
Leopold F. Schmidt, who visited the Olympia and Tumwater area in the 1890s, heard of artesian wells here. He tasted the water from an artesian spring and found it to be of superior quality—perfect for making beer. Tests performed by a laboratory confirmed his suspicions. His brewery was eventually supplied by 26 artesian wells.
The Tumwater area is underlain by a layer of porous rock called the Deschutes Valley Aquifer. This rock acts like a sponge and holds water. But what makes it an artesian aquifer? It’s bounded above and below by non-porous layers. Layers of basalt bedrock (which you can see in the Deschutes River canyon) provide one boundary for the aquifer; the other boundary is a dense layer of old lake sediments. These non-porous layers contain or confine the aquifer. As the amount of water in the aquifer is recharged, or added to, by rain and snow, the pressure on the lower part of the aquifer increases. When a well penetrates this lower part, the pressure above causes water to squirt out, forming a flowing artesian well. No pump required!
An aquifer exists where the groundwater is confined between two layers of impermeable substances like clay or dense rock. When tapped by a well, water in a confined aquifer is forced up, sometimes above the soil surface. This is how a flowing artesian well is formed.
Porous or permeable: a rock that has holes in it and can hold water like a sponge. Examples are limestone, chalk, or sandstone.
Impermeable: a substance that will not let water pass easily through it. Examples are clay and granite.
Groundwater: water that’s stored naturally underground in an aquifer
Aquifers and Wells
After entering an aquifer, water moves slowly toward lower lying places and eventually is discharged from the aquifer from springs, seeps into streams, or is withdrawn from the ground by wells. Groundwater in aquifers between layers of poorly permeable rock, such as clay or shale, may be confined under pressure. If such a confined aquifer is tapped by a well, water will rise above the top of the aquifer and may even flow from the well onto the land surface. Water confined in this way is said to be under artesian pressure, and the aquifer is called an artesian aquifer.
Visualizing artesian pressure
Here’s a little experiment to show you how artesian pressure works. Fill a plastic sandwich baggie with water, put a straw in through the opening, tape the opening around the straw closed, DON’T point the straw towards your teacher or parents, and then squeeze the baggie. Artesian water is pushed out through the straw.
