The Geyser’s inner workings
A cold-water geyser works quite similar to a bottle of effervescent mineral water fizzing over. The pressure inside the bottle is much higher than outside of it. The high pressure is what keeps the carbon dioxide dissolved in the water and prevents it from gassing out. Upon opening the bottle, the pressure is released suddenly and the CO2 forms bubbles rising to the surface very quickly. The bubbles stir up the water, carrying it along their way upwards and make it spout out of the bottle like a little fountain.
CO2 of volcanic origin
The carbon dioxide fuelling the Andernach Geyser originates in a magma chamber below the eastern Eifel region, a fairly young volcano from a geological perspective. Significant fault zones that intersect near the Namedyer Werth peninsula in the river Rhine cause deep trenches and fissures to form in the rock underneath, and this creates the rising channels in which the CO2 can rise within the otherwise non-permeable slate. At a depth of several hundred metres below the surface, the gas comes in contact with deep ground water tables. The high pressure prevailing at these depths allows for a large volume of CO2 to dissolve in the 25 °C / 77 °F warm water.
The Geyser erupts
A geyser needs a rising channel to blow a water fountain. All cold-water geysers - including the Andernach Geyser - use drilled wells as their rising channels. Carbonised water from different ground water tables starts to collect in these channels and makes the water column rise slowly to the surface along the drilled well. By the time the well of approx 350 metres depth is all filled up with water, the pressure at the bottom has increased to around 35 bars at the bottom of the well.
The high pressure at the lower end of the water column means that huge quantities of CO2 are dissolved in it. The continuing flow of carbonised ground water continues to build up the CO2 levels to a critical point where no further gas can be dissolved in the water - the point at which the water is saturated with CO2. The excess CO2 now begins to rise upwards into areas where the pressure gradually decreases. The small gas bubbles expand as they rise higher, and that expansion displaces some of the water. The geyser well eventually overflows and slowly releases pressure, which in turn results in even more CO2 to degas from the water.
This additional CO2 again rises towards the surface and displaces even more water. A domino effect has been started, the degassing intensifies rapidly, gas bubbles of several metres length are forming and pushing the water with it towards the surface. The cold-water geyser erupts by blowing a continually growing water fountain, which can reach a height of up to 60 metres in the heaviest of eruptions. The eruption has exhausted the water in the well after around 6-8 minutes and the cycle begins again when carbonised water flows back into the drilled well.
This rare natural phenomenon keeps repeating itself like a clockwork every 115 to 120 minutes.