What is a fumarole volcano

Volcanoes for schoolchildren

Hissing gas escapes: fumaroles and mofets

Image: A mofette bubbles in this pool and lets gas rise from the bottom.

Hissing, hot gas leaks called fumaroles can often be observed in volcanic areas. Several hundred degrees of hot gas flows from them, the majority of which consists of water vapor. Depending on how hot the gas is, small quantities of chemical substances such as chlorides, alkalis, iron, carbon dioxide and hydrogen sulfide are also contained in the gas.

The fumaroles at the bottom of the picture on the left are an example of gas leaks at 100 - 350 ° C. In addition to water vapor, the gas also contains carbon dioxide and hydrogen sulfide. Such a fumarole smells like rotten eggs. When the gas escapes to the surface, the gas is cooled. The water vapor becomes water, which forms a sulphurous acid with the hydrogen sulphide. This acid is so aggressive that it attacks and decomposes the surrounding rock. Yellow sulfur is deposited around the fumarole. In some volcanoes, sulfur is extracted as a valuable raw material.

But there are also fumaroles that emit gases up to 1000 degrees Celsius. Such high gas temperatures are a sign that the volcano could erupt again soon.
In contrast, there are relatively cool gas outlets. These are called mofettes. They have temperatures lower than 100 degrees. Such mofettes are also available in Germany. In the Eifel, cold gases escape on the banks of the Laacher See volcano. Despite their low temperature, mofets are not safe. The gases carbon dioxide and carbon monoxide flow from them. The gases are odorless and heavier than air. Therefore, the gas can collect in hollows and displace the breathing air. As a result, there is a risk of suffocation for humans and animals.
In the border area between Germany and the Czech Republic there are mofettes that emerge in small pools. These bubbles and look like the water is boiling, but it is very cold. But cold mofets are also signs that a volcano is not yet completely extinct.