Summary
Several hundred volcanoes lie dormant beneath the Eifel in western Germany. They are typical examples of what is known as distributed volcanic fields. To better understand their formation and activity, researchers from the GFZ Helmholtz Centre for Geosciences and partner institutions conducted Germany’s largest seismological voolcano experiment in this region between September 2022 and August 2023: With over 500 measuring stations and a 64-kilometre-long fibre optic cable, it was possible for the first time to produce a high-resolution image of the structures beneath the Eifel volcanoes. The new data show the most accurate representation to date of the magma reservoir that caused the eruption of Lake Laach 13,000 years ago. It is deeper and differently oriented than previously assumed. There are also surprising findings regarding thousands of recent microearthquakes and possible fluid accumulations in the crust. The results provide an important basis for more accurate assessment of volcanic processes and potential future hazards in the region. The researchers led by Prof. Dr Torsten Dahm have summarised the initial results of their studies in three publications in the journals Seismica,Journal of Geophysical Research and Geophysical Journal International.
Background: Distributed volcanic fields
Distributed volcanic fields are a little-studied form of volcanism within continental plates. They are characterised by a large number of volcanoes and maars spread over an area of 1,000 to 10,000 km². They can be found, for example, in the Eifel in western Germany, in the Massif Central in central France (e.g. Chaîne de Puye), in Arizona, USA (San Francisco Volcanic Field), but also in China or New Zealand (Auckland Volcanic Field). In most cases, each of the volcanoes is only active once; subsequent eruptions then take place at a different location. In order to better assess the danger posed by this type of volcanism, it is important to map the magmatic system from the mantle depth to the upper crust and to map reservoirs where magma can accumulate and rise, potentially leading to individual eruptions.
Large-scale seismological experiment in the Eifel
To investigate these questions, the GFZ Helmholtz Centre for Geosciences, together with universities and earthquake services from Germany and Luxembourg, conducted a large-scale seismological experiment in the volcanic fields of the Eifel from September 2022 to August 2023. The researchers call this type of experiment “Large-N” because it involves a large number of seismic measuring stations. In this case, there were more than 500. Their data was combined with that from another innovative method, called acoustic sensing technology (DAS – Distributed Acustic Sensing) using a 64-kilometre-long, unoccupied fibre optic cable. This method exploits the fact that light signals travelling through fibre optic cables are very sensitive to even the slightest tensions in the fibre, which might be caused by mechanical stresses or temperature changes in the environment.
The Large-N experiment in the Eifel region is, in fact, the largest of its kind ever conducted in Germany. It made it possible to place stations less than two kilometres apart in some cases. This enabled high-resolution subsurface investigations to be carried out directly beneath the volcanoes of the Eifel region for the first time. The results now published confirm previous assumptions about the structure and condition of the volcanoes in the Eifel region, but also reveal some unexpected findings.
Surprising new insights into the structures beneath Lake Laach
High-resolution tomographic images of the subsurface show for the first time the location, position and depth of the magma reservoir that caused the eruption of Lake Laach 13,000 years ago. The main phase of the eruption, which lasted only a few days, was highly explosive and produced massive ash and pyroclastic flow deposits near Mendig, south of Lake Laach. Until now, the size and depth of the magma chamber beneath Lake Laach could only be inferred indirectly from studies of the Mendig tephra layers, i.e. volcanic ash deposits accessible above ground.
Seismic tomography shows an anomaly in seismic velocities beneath Lake Laach at a depth of up to ten kilometres, which is significantly deeper than previously assumed. Surprisingly, the anomaly does not fall vertically downwards, but diagonally towards the Neuwied Basin, where most of the microquakes in the Vulkaneifel region are concentrated.
Localisation of over a thousand microquakes
With the help of this extraordinary data set, more than a thousand microquakes were localised in one year. Most of these quakes occurred along a narrow, vertical zone between Ochtendung and Lake Laach. However, there are also earthquake clusters that occurred at the edges of the seismic velocity anomalies. This surprised the scientists, as it could indicate an increased temperature in these areas.
“The strong reflections of seismic waves at layer boundaries in the upper and lower crust beneath the Neuwied Basin are also unusual,” says Torsten Dahm, head of the Eifel Large N Experiment. “The strength of the reflections indicates that fluids have accumulated in these layers. Whether these are magma or magmatic fluids has not yet been clarified and will be investigated using improved evaluation methods.”
Original publications:
Dahm, T., Isken, M., Milkereit, C., Sens-Schönfelder, C., et al (2025). A seismological large-N multisensor experiment to study the magma transfer of intracontinental volcanic fields: The example of the Eifel, Germany. Seismica, 4(2).
https://doi.org/10.26443/seismica.v4i2.1492
Zhang, H., Dahm, T., Haberland, C., Isken, M. P., Lauman, P., Buyukakpinar, P. (2025): The upper crustal structure of the Eifel volcanic region (southwest Germany) from local earthquake tomography using Large-N seismic network data. - Journal of Geophysical Research: Solid Earth, 130, 11, e2025JB031338.
https://doi.org/10.1029/2025JB031338
P Laumann, T Dahm, G Petersen, P Buyukakpinar, H Zhang, M Isken, B Schmidt, Microseismicity Reveals Fault Activation and Fluid Processes Beneath the Neuwied Basin and Laacher See Volcano, East Eifel, Germany, Geophysical Journal International, 2025; ggaf475
https://doi.org/10.1093/gji/ggaf475
