Functioning cold water geyser

A natural phenomenon of volcanic origin


Welcome to the Andernach geyser. Usually, you would visit the Geyser Centre with its fascinating permanent exhibition before the boat trip to the geyser, to discover and playfully learn hands-on how the cold-water geyser works and how it is connected to the Eifel volcanism.
But this year (2020) the museum in the Geyser Centre cannot be opened due to Corona related restrictions. However, in order to help you become a geyser expert before your visit, you will find a crash course on how the geyser works below.


You are visiting a cold-water geyser. It is different from the classic geysers that are known in Iceland, New Zealand or even those in the Yellowstone National Park in the USA. In contrary to these hot-water geysers, whose functions are based on the transformation of water into steam, the driving force behind the cold-water geyser in the Middle Rhine valley is the gas carbon dioxide (CO2).

CO2 from Magma

The Eifel region, which borders the Rhine valley to the west, is geologically a very young volcanic region. Volcanic eruptions have occurred repeatedly over the last 600,000 years. Their origins found in the magma deposits under the Eifel. Fluid rock either rises to the surface (volcanic eruption) or it collects in the Earth’s crust several kilometres deep. From these magma reservoirs of molten rock escape upwards highly volatile gaseous components, one being CO2. In the process, they use geological fault zones that cause cracks and fissures to form in the rock. This creates ascending “pathways” for the CO2 in the otherwise relatively impermeable slate rock.

Several hundred metres below the Earth’s surface, the gas encounters groundwater, flowing through the slate in partially porous quartz veins. Due to the high ground pressure, a large amount of CO2 can dissolve in the water, which is just over 20°C warm.

Wells as a Requirement

A cold-water geyser needs an ascending channel for a water eruption. In all cold-water geysers, including the cold-water geyser on the Namedyer Werth, this is achieved by a drilled well. Ground water saturated with Carbon dioxide, found in the various layers of quartz veins, that have been cut by the borehole, accumulates, and slowly fills up to the surface, the 350 metres deep well. When the well is filled with water, the weight of the water in the well pipe (1 litre of water = 1 kg) creates a pressure of about 35 bar at the bottom of the well.


A cold-water geyser can be compared best to a bottle of sparkling mineral water. The two consist of a mixture of CO2 and water, the composition of which reacts to changes in pressure. If the mineral water bottle is opened the pressure in the bottle is reduced. This can be clearly heard in the hissing sound when the lid is being opened. At the same time, small gas bubbles form in the water and rise to the top. When the pressure in the bottle decreases, part of the CO2 separates from the mineral water in which it was absorbed. If the bottle has been shaken beforehand, and then opened, not only do gas bubbles form, but a fountain of gas and water also form, which shoots out of the bottle like a bolt of lightning.

Geyser eruption

With the cold-water geyser, you do not have to shake the bottle or take off the lid. While the bottle of mineral water, only contains a certain amount of CO2, the gas concentration in the cold-water geyser continues to rise due to the constant inflow of water containing CO2 until complete saturation occurs. This in turn, prevents the inflowing CO2 from being absorbed in the water and therefore it begins rising to the surface in forms of bubbles.

And so, begins the eruption of the cold-water geyser. The gas bubbles rise upwards in the geyser well and begin to push the water out of the pipe. This causes the weight of the water column in the pipe to decrease and simultaneously reduces the pressure in the water column. This reduction of pressure (unscrewing the lid on a mineral water bottle) causes more and more CO2 to be released from the water.

The CO2 rises and pushes even more water out of the pipe. This domino effect leads to an increasingly rapid degassing, in which the water is carried upwards by the gas bubbles. At the surface, the well-known geyser fountain appears, which varies in height between 40-60 metres depending on the wind conditions.

An eruption lasts 12-15 minutes. Then the geyser pipe is almost empty, and it takes about 2 hours until the well is filled with water and saturated with CO2, so that the next eruption can take place.