As mentioned above about the Laacher See, it seems that there is unusual seismic activity going on for a few years now.
However, from the text that i can find, the discoveries are partially based on the finding of gasses in the water.
I am not aware of the composition of the gas.
But assume that there are methanogens and other gas producing bacteria in that lake.
This lake seems to be the right type for to hold at least methanogens.
Think for example about Lake Kivu.
Methanogens are microorganisms that belong to the Euryarchaeota of Archeobacteria and have the ability to convert inorganic organic compounds into methane and carbon dioxide.
They exist in various natural and non-natural ecosystems and are characterized by their strict anaerobic nature, slow growth rate, and dependence on simple compounds for nutrition.
Their major end product is biogas, which primarily consists of methane and carbon dioxide.
But there is also real seismic activity going on.
Anyway, read the to text yourselfs, you have manually translate to English, google translate does not work with this site (At least where i live) :
De Vulkaan-Eifel, een regio van het Duitse Eifelgebergte die gevormd werd door vulkaanuitbarstingen, vertoont opnieuw activiteit. Dat melden geologen in een studie die werd gepubliceerd in het vakblad Geophysical Journal International. Subtiele, ongewone bewegingen onder het aardoppervlak wijzen...
www.hln.be
Small excerpt from (to English translated) text :
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The last volcanic eruption in the region is estimated to have occurred around 11,000 years ago. Although many scientists assumed that the volcano beneath the Eifel is extinct, a handful of studies have shown that this may not be the case.
For example, the maars - another name for crater lakes - still release significant amounts of gases that some researchers believe originate from the Earth's mantle - the geological layer just below the Earth's crust.
A study published last year also found evidence of volcanic activity. For example, the scientists discovered small earthquakes under the Laacher See, the largest crater lake in the region, not far from Koblenz.
According to the authors, this could be explained by movements of fluid, possibly magma, in the lower parts of the Earth's crust.
"If you connect the dots, it seems clear that something is brewing in the heart of northwestern Europe," said Corné Kreemer, lead author of the study and professor at the University of Nevada, from the Netherlands, in a statement.
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and
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Mantle plume
The discoveries could possibly be explained by a mantle plume exerting pressure on the Earth's surface from below. Mantle plumes are a theoretical upward flow of hot, solid rock from the Earth's mantle to the Earth's surface.
Geologists suspect that these mantle plumes are responsible for volcanic hotspots such as Hawaii.
Many seismologists believe that there is a mantle plume directly beneath Eifel Volcano that extends to a depth of more than 400 kilometers and was probably responsible for volcanic activity in the region.
Whether that plume is still active is a matter of debate, but Kreemer and his colleagues suspect that it is.
Don't panic
In the long term, it is possible that more volcanic activity will be observed in this part of Europe, although according to the researchers this does not mean that we should expect a volcanic eruption or earthquake soon - or even ever.
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