What’s bubbling below the Eifel plateau?

7 November 2022

A seismological campaign, the first of its kind in Germany, is being carried out to determine the status of the roughly 800 essentially dormant volcanoes in the Eifel region. The objective of the new project is to find out whether any of these volcanoes could again become active and what exactly is happening below the surface. What do we have to expect in the future? Professor Luca De Siena of the Institute of Geosciences at Johannes Gutenberg University Mainz (JGU) is a member of the survey team. He is to generate computer models from the newly obtained data to understand future volcanic activity in the Eifel region.

"We do know more about outer space than we do about the Deep Earth under our feet," says Professor Luca De Siena. The geophysicist makes his dissatisfaction with this situation all too clear during our interview. He's a specialist in Geophysics and Volcanology. "What I do is collect the signals made by a volcano in order to reconstruct a computerized model of its deep-lying structures."

At present, De Siena is participating in a large-scale survey being undertaken under the lead of the German Research Center for Geosciences (GFZ) in Potsdam. Experts from the universities of Frankfurt, Kiel, Cologne, and Mainz join with specialists of the State Seismological Survey of Rhineland-Palatinate (LGB-RLP) to assess the state of the volcanoes in the Eifel region. The massive undertaking, headed up by Professor Torsten Dahm, is appropriately entitled Large-N. The symbol "N" represents a number of arbitrary size while the "Large" refers to the vast quantity of seismic-detection instruments that have been installed in recent months in the districts of Ahrweiler and Mayen-Koblenz. These 350 geophones are to measure any seismic waves generated deep inside the Earth.

Volcanology – a high-potential research area at Mainz University

"It was no surprise that our colleagues in Potsdam decided to get in touch with us here at JGU," adds De Siena. "After all, the Eifel is practically on our doorstep." However, there is also more to that: "At Mainz University, we're establishing a major hub of the discipline of volcanology. At present, there are only two chairs in this field in Germany. One of these is held by Jonathan Castro here at JGU. Moreover, Mainz University in collaboration with the universities of Frankfurt and Heidelberg launched the TeMaS research platform." As a so-called high potential research area at JGU, TeMaS – short for 'Terrestial Magmatic Systems' – coordinates interdisciplinary research into how magmatic processes impact on various environments, such as the atmosphere, the Earth's crust, and its mantle.

Mainz has become such an important center of volcanology over the last years not least because Professor Boris Kaus, head of the Geophysics Group at the JGU Institute of Geosciences, received one of the prestigious fellowships of the Gutenberg Research College (GFK). This in turn enabled the establishment of a temporary W2 professorship for Luca De Siena. "Boris was very committed to this cause and I gladly accepted his offer." De Siena's research group focuses on volcano seismology. He himself has developed a computer program known as Multi-Resolution Seismic Attentuation Tomography (MuRAT) that employs recorded seismic waves to create 3-D models of volcanic structures.

"I come from a region where volcanoes represent a very real threat," De Siena explains. He was born in Salerno and after obtaining his diploma in physics from the University of Naples Federico II he went on to Bologna, where he was awarded his doctorate in Geophysics before returning to Naples. Hired by the Osservatorio Vesuviano monitoring institution, De Siena investigated the various volcanoes in the vicinity of the city. "The residents of Naples quite literally live on the edge of a volcano. From time to time, toxic gases are escaping, making whole blocks of houses uninhabitable. You might well think that people are crazy to accept this but they seem to have learned to live with the risk."

A magma plume like that in Yellowstone

The volcanism in the Eifel appears far less exciting. The last known eruption was 13,000 years ago. Since then, very little has occurred although some deep underground tremors have been registered in recent years. "The Eifel region is nevertheless particularly interesting," adds De Siena. "The volcanic processes in the Eifel are fundamentally different from those in Italy. There the volcanoes came into being because tectonic plates moved one over the other. In the case of the Eifel, we likely have a kind of volcanic phenomenon similar to that in the Yellowstone National Park in the United States." There, over a very long period, a kind of gigantic, mushroom-shaped pool of magma – known technically as a 'plume' – has gathered beneath the surface being fed by a channel reaching deep into the Earth. "At some point there will be an eruption – but that could be thousands if not hundreds of thousands of years in the future." It is thus time for the Large-N experiment.

"I spend most of my working time in front of my computer, but in the case of this project my team and I traversed the Eifel region to install geophones." De Siena shows images of the tiny detectors that are thrust into the ground. "These register only a relatively narrow range of acoustic waves. They are not particularly expensive and are easy to put in place. At the same time, we were also distributing larger broadband geophones. These, on the other hand, need to be very carefully positioned in holes filled with sand." Where possible, these were sited on private land or in the cellar vaults of old castles. De Siena himself set up 35 of the 350 instruments that are now scattered across the Eifel region.

All he can do now is sit back and wait for the first recorded data to start coming in. Recordings have to be collected manually from each individual geophone. Even in the era of the Internet and widespread cabling systems, this is the most inexpensive and reliable method of gathering the data. "The long-wavelength oscillations will tell us something about what is likely to happen at larger scale. These are very stable and not particularly susceptible to interference. But it is the short-wavelength data, producing higher details on shallower structures, that will have my attention." De Siena will be using these for his computer simulations.

"These will not be just in 3-D, they are actually 4-D models because I also factor in the parameter time. I look at the volcanic activity in the past and then try to predict what could occur in the near future. It's like weather forecasting although the results are not as dependable because we know more about the weather in general." However, De Siena will be able to compare his prognoses with continuously collected data sets and thus make his predictions increasingly accurate.

The economy, climate, and volcanoes

"What we find could be extremely relevant even though it is doubtful we'll be seeing any spectacular eruptions in the foreseeable future. The economy could be seriously impacted as, for example, the Eifel is a source of mineral water and a well-known brand of German beer is brewed here. It would be a major problem if toxic substances entered the groundwater because of magmatic activity."

De Siena is convinced that research into volcanism is vital – be it in the Eifel region, in the Yellowstone National Park or in Italy. "We forget about the potential danger because in our lifetimes there has never been a really overwhelming volcanic catastrophe. While it's true that the volcanic eruption in Iceland ten years ago paralyzed air traffic for several days, that was nothing in comparison with what has previously transpired on our planet. The extinction of the dinosaurs may well have been triggered by an asteroid strike, but it was mainly volcanic activity that resulted in the disappearance of their habitats. Even in the Holocene, volcanic eruptions have led to several phases of Little Ice Age-like conditions in Europe. There were dreadful crop failures in the mid-15th century and later there was the unprecedented wave of emigration to America."

"The problem is somewhat similar to that of global warming. When people can't actually see or feel the effects of a particular phenomenon, it is difficult for researchers to make clear why their investigations are relevant," says De Siena. "In Italy, the risk is both clear and apparent and so volcanology there gets the support it deserves. Yet volcanism plays an important role for the world as a whole – not least as a factor that can have significant effects on the Earth's climate."