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Rock doc: Powerful pressures and special waters

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From page A4 | February 13, 2012 |

E. Kirsten Peters mug

Peters

It does seem like there’s something magical about artesian wells. Digging down to a level in the Earth from which water then spurts unaided is like a dream come true for some. And, after all, why pay the electric company for power to run a pump if Mother Nature will do all the work herself?

From times immemorial people have thought that water gushing from artesian wells must have different medicinal or even spiritual properties from plain ol’ water in a creek or a typical well. And since artesian water can be “mineral water” with a distinctive taste, that early point of view was easy to hold. Tthe water tasted different, might even be fizzy with bubbles, and rose out of the solid Earth of its own accord. Artesian water must be special stuff, right?

Don’t get me wrong. I like to drink artesian mineral water, but not because it’s artesian. I simply like the unusual taste of various mineral waters — and many commercial mineral waters come from artesian sources. Still, with a glass of good artesian mineral water in hand, it’s easy for me to reflect on the pressures within the Earth that can make water flow upwards.

One clue about the pressure that normally holds artesian water down is the bubbles found in some artesian wells. The bubbles are in the water in your glass because you have depressurized — lowered the pressure — of the water by opening the bottle. That’s the same thing you do when you pour cola out of a closed container. Bubbles immediately form in the soda-pop because the gases that were dissolved in the sweetened water at higher pressures come out of solution and make the tiny bubbles — which then float upward to join the atmosphere.

We know of the pressures within the Earth from a couple of different angles beyond artesian waters. One is from the evidence of certain rocks. There are three great classes of rocks, one of which is metamorphic rock like marble and high-grade coal called anthracite or “hard coal.”

Metamorphic rocks are created with other pre-existing materials are exposed to high pressures through long periods of time. For example, limestone that’s shaped by high pressures becomes marble. Normal or “soft coal” that’s exposed to high pressures become anthracite — and that material, if exposed to more heat and pressure can even become graphite (the material in the center of pencils).

Pressure in the Earth surely isn’t anything to sneeze at. That’s perhaps one of the lessons of the oil spill caused by the Deepwater Horizon in the Gulf of Mexico a while back. Unlike the Exxon Valdez spill in Alaska, where oil poured out from a ship, in the Gulf of Mexico the spill came from where we were drilling for oil deep under the seas where it is held at high pressure.

Normally, if all had gone according to plan, the drilling rig searching for oil would have intercepted petroleum and natural gas at high pressure — and been able to control that pressure in several ways. First, Deepwater Horizon was pumping mud at high pressure down the drill hole as it went. That high-pressure mud, in itself, is normally able to hold down the oil and gas the drill bit cuts through. Beyond that, the Blow Out Preventer (or BOP) is meant to cut off flow from the well, either automatically or manually, if that’s needed.

A surge in natural gas concentrations likely contributed to the failure of all the mechanisms meant to hold the gas and petroleum mixture in the Earth. The light-weight natural gas rocketed up the drill hole, hit the drilling rig itself, and created the explosion and fire that took the lives of the 11 workers on the Deepwater Horizon.

The Earth’s pressurized zones gives us both blessings and curses — from artesian waters and minerals like graphite to the greatest oil spill in U.S. history. All of those factors come to my mind when, on occasion, I raise a glass of bubbling mineral water with my evening meal.

Dr. E. Kirsten Peters, a native of the rural Northwest, was trained as a geologist at Princeton and Harvard. This column is a service of the College of Agricultural, Human and Natural Resource Sciences at Washington State University. Peters can be reached atepeters@wsu.edu.

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