Think of one thing that has interested you for as long as you can remember, or at least for so long the level of factual knowledge you have of it is almost ridiculously vast. That one thing that always brightens up your day when you hear or read something about it, no matter how busy you are or down you feel. A passion that goes beyond the level of having an ordinary hobby, because you don’t grow tired of spending time on it and learning more about it. It could be anything. Maybe a football club, or collecting fossils. Perhaps a specific model of a car brand. Or when you pick up your camera for yet another round of bird photography. It doesn’t truly matter what it is, because it hits home with anyone who has that bizarre enthusiasm for something seemingly trivial in the eyes of most people. To me, that one thing that stands out above all my other interests, is the Eifel volcanism.
The volcanic fields of the Eifel
Take some of the bigger names in the world of volcanoes. Etna, Mount St. Helens, Pinatubo, Vesuvius, Krakatau and of course any one pit, mountain or crack spewing lava or ash that happens to make the news. Not many people actually know the relevance of those names from a historical, let alone geological perspective. Yet they do ring a bell. What volcanic area most certainly isn’t on that list? Yes, the one I’m going to describe to you. The Eifel is located in the west of Germany, and is comprised of three different volcanic areas, located on the Rhenish Massif. One of those, the Hocheifel Volcanic Field, is of Tertiary age and lies between the much younger West and East Eifel Volcanic Fields. Scattered across Germany are many volcanoes of Tertiary age, but for the sake of not turning in this article into a book, I’ll stick to a series of facts regarding the youngest products of volcanism that can be found in this part of the world. That means the aforementioned volcanic fields west and east of the Hocheifel, where volcanism took place between approximately 700,000 years ago and 11,000 years ago.
So what are we talking about then, as these volcanoes seem to mean so little in the world of what can arguably be seen as the most visually impressive of natural hazards? All of the volcanic vents in the area are part of so-called ‘monogenetic volcanic fields’, meaning they tend to erupt only once before going extinct. That is, the individual vents, not the volcanism in the field in its entirety. In most cases, a very small amount of magma makes it to the surface, producing an eruption that is often over as quickly as it started. The magmas that erupt onto the surface do so mostly in the form of small ash plumes, scoria and lava flows, only affecting an area directly surrounding the vent. The resulting volcanic edifice: a ‘scoria cone’. When this magma comes into contact with ground water, a hydrothermal explosion occurs, known as a ‘phreatomagmatic eruption’, which is explosive, short-lived and leaves behind an often circular crater known as a ‘Maar’, but again, the effects of such eruptions are mostly of a local nature. Both of these types of volcanoes can be found in great abundance in the Eifel volcanic fields, and maars even got their name from the regional, Eifel name for ‘lake’. All in all, the fields consist mostly of these fairly tiny edifices. Some 200 scoria cones and about 70 maars in the West Eifel Volcanic Field (WEVF) and mostly scoria cones of the ~100 volcanoes in the East Eifel Volcanic Field (EEVF).
What does this mean for the landscape? What does it look like? The volcanoes aren’t hard to spot in quite a few cases, but don’t expect any enormous mountains of the likes seen in the Cascade Mountains, the Andes or Japan. In fact, the scoria cones of the Eifel quite often do count as ‘mountains’, depending on what definition one might apply, but their prominence is rarely more than just a few hundred meters over the surrounding, elevated terrain of the Rhenish Massif. Scoria cones formed by a single eruption just don’t grow that tall. Maars are often hard to spot, but in all cases they are depressions in the landscape, in some cases surrounded by a ring of tuff produced by the Maar-forming eruption. Most however, are very hard to spot, and the same can be said for the majority of the scoria cones; they’re just too tiny to stand out, whether that is the result of having been produced by a comparatively small eruption, the effects of the exogenic forces of weathering and erosion or both. In other words, the volcanoes are there for those who know what to look for, but that’s pretty much it. The Eifel isn’t densely populated, especially not the Westeifel, but its far-from-dramatic undulating terrain and mix of forests and agricultural land give it a very friendly looking, photogenic charm that many tourists appreciate quite a lot.
The threat of eruptions: an unwelcome surprise?
So it’s a fact that the Eifel has been relatively recently been volcanically active, but what does that mean? No activity even came close to there being any sort of historical records of it, at least not of actual eruptions. In geological terms, for an area not to be volcanically active for just over ten thousand years, means nothing. The actual cause of the formation and rise of magma under an area is very likely still present after such a relatively very short time, and in the case of the Eifel it truly is, although I’m not going to delve into that in this article.
So are we to expect an eruption anytime soon? My answer is ‘Yes!’, but that doesn’t mean we’re currently aware of any magma making its way to the surface at such a velocity that we can detect it and that we should panic about it right now. Monogenetic volcanoes are being fed by tiny amounts of magma, often rising directly from the Earth’s mantle in a matter of hours to days. Types of magma that are very ‘primitive’, which means they didn’t really have their chemical compositions changed by what we call ‘magmatic differentiation’. Processes like cooling down somewhat and absorbing a lot of materials from the Earth’s crust. The presence of very primitive lavas on the surface indicate a few important things: matters can change quickly and without a lot of warning, although the effusive and intrinsic mildly explosive nature of the molten rock means any threat is likely to remain local.
However, geoscientists, authorities and the local population are fairly ill-prepared for an eruption if it were to happen anytime soon. Those with any degree of responsibility often tend hide behind statistics and often meaningless facts like the number of years that have passed since the most recent eruption. Being aware and ready for an event that is likely going to happen at any time in the near geological future is being smart about it.
Taking both statistics and the speed at which things can go from ‘Nothing going on at all’ to ‘Oh Scheiße…’, the WEVF seems to be the most likely candidate for the next eruption. There’s reason enough take action on this specific threat, but it doesn’t really exist in the minds of most locals. It doesn’t mean that there’s no attention for any potential future volcanism in the Eifel. Without going to great lengths, one can easily find information on something stirring in the EEVF, where a completely different kind of beast snores in its slumber.
The East Eifel Volcanic Field: a story of evolving magma
About a hundred volcanoes, most of them monogenetic scoria cones. Pretty much the same as the WEVF, just containing just over a third of the amount of vents that once produced lava and ash. The East Eifel Volcanic Field sounds like smaller sibling of its counterpart about 30 kilometers to the southwest, but you’d be wrong to assume the differences stop there. In fact, the EEVF is much larger when we look at the volumes of the erupted volcanic materials we find there. That’s because, among the scoria cones, a few monsters are present.
Located in what is the middle of the volcanic field, are several volcanoes that have been fed by variants of a magma called phonolite. Mafic magmas like basanite and tephrite, which are generally fairly hot, effusive and typical for producing the small eruptions that are common in volcanic field like those of the Eifel, have formed numerous scoria cones that are still clearly visible in the landscape today. In some places, though, these magmas rose to form large magma chambers that have taken tens of thousands of years to grow before erupting. At the same time, the magma partially cooled down and only the minerals that didn’t solidify remained eruptible, becoming phonolite. Phonolite is a so-called intermediate rock, which means it has its place between mafic and felsic. Its viscosity is substantial, which allows for pressure to build up inside it quite efficiently, turning it explosive in most cases. That also happened on a small number of occasions in the EEVF over the last few hundred thousand years. Two of the phonolitic magma chambers have produced eruptions that were even large enough to create calderas.
Going big: the first caldera
After an initial phase of erupting ultramafic magmas occurring in the EEVF between 650.000 and 450.000 years B.P., the Phonolitic eruptions started in what is now called the Rieden Volcanic Complex between 450,000 and 350,000 years ago, which was long considered to have its own caldera, but the depression there is likely to be of an erosional nature than of anything that has to do with the collapse of a magma chamber. Numerous lava flow-producing vents and even lava domes formed in this phase of volcanic activity in the Eifel, before eruptions stopped for about 135,000 years, producing a total volume of ~10 km3 of volcanic deposits. Then, around 215,000 B.P., the ‘Hüttenberg Tephra’ was erupted. It is currently assumed this eruption may have been a high-end VEI5, having erupted a bulk volume of phonolitic ash and pumice that quite possibly lies somewhere between five to ten cubic kilometers. Another substantial, explosive eruption occurred from this volcano about 150,000 years ago, covering the landscape with the ‘Glees Tephra’, which has been produced by an eruption maybe reaching low-end VEI5 with an estimated 1 km3 of ejecta. Very few volcanoes have magma chambers that will not collapse after such events, and this volcano is no exception. Now known as ‘Wehrer Kessel’, which basically means ‘Wehr’s Cauldron’, the volcano is named after the village that can be found in the western half of the almost two-kilometer wide caldera. Currently, the volcano only produces amounts of CO2 that can be expected from extinct volcanoes, but since 2015 unexpected subsidence has been observed within the crater. More on that later.
Earning true infamy: how one volcano took it to the next level
As nasty as Wehrer Kessel’s behavior has been, its next door neighbor is the true beast of the lot. It is currently assumed phonolitic magma started accumulating between five and eight kilometers deep from approximately 30,000 years ago. After a series of large intrusions it accumulated to possibly 18 cubic kilometers (v. d. Bogaard & Schmincke, 1984) before an eruption finally took place an estimated 13,078 years ago (remember that date). And what an eruption it turned out to be. It started with large, phreatomagmatic explosions taking place at the southern end of what is now known as the crater of this volcano. Ash of these events was mainly blown towards the southwest. The main phase of the eruption commenced not long after, opening up a new vent just to the north of the one that had previously formed. The most powerful of the explosions produced ash columns that rose to an altitude of possibly 40 kilometers, before being dispersed toward what is now Scandinavia and Italy. It took an estimated eight to ten days before the eruption was over, and what was left was a vast area that was buried beneath tens of meters of pyroclastic flow and tephra fall deposits. Approximately 6.3 km3 worth of phonolitic magma expanded into some 20 km3 of mostly ash and pumice. The nearby Rhine valley was blocked by two natural dams formed by pyroclastic flows, blocking the river Rhine and causing the flooding of the Neuwieder Becken, a wider valley east and southeast of the volcano. The resulting lake was about 20 meters deep before it catastrophically drained due to the breaking of the dams. At the site of the eruption itself, a caldera formed that measures 2.5 by 3.5 kilometers from rim to rim, still visibly featuring the two different, but now merged explosion craters from which the eruption took place.
Comparing the eruption to well-known events
What happened in the EEVF just over 13,000 years ago is an event of a magnitude that occurs globally no more than a few times every century. Between the years 1900 and 2000, only three events of a similar magnitude occurred, using the logarithmic Volcanic Explosivity Index as a standard to work with. The first eruption at Wehrer Kessel was in all likelihood, as stated above, a large VEI5. But its big brother to the southeast went VEI6, having produced a bulk volume of ~20 km3 and placing it firmly between the 10 and 100 km3 which define an eruption of such magnitude. In 1902, Santa María volcano in Guatemala erupted 10 km3. In 1912, in Alaska, the Novarupta vent formed as part of the Katmai volcano, blasting out between 25 and 30 km3 of ash and pumice and in 1991 Pinatubo in the Philippines produced the world’s most recent VEI6 by erupting 11 km3 of volcanic materials. These events live in infamy because of their destructive legacies, on a list that features Krakatau, Huaynaputina and Ilopango as well, to name just a few exceptionally nasty monsters that have violently erupted over the last few thousand years. Although there was a number of much larger eruptions during the Holocene, ranking as VEI7, a VEI6 is by no means a small event, definitely earning its status of being ‘colossal’. Any event of this size would dominate the news on a global scale for at least days, if not weeks.
A deceptive serenity
After the EEVF eruption of 13,078 years BP ended, the caldera got partially filled up by water, forming a lake that is now 2 by 2.3 kilometers in diameter. This lake, known as Laacher See, gives the volcano its name. The crater walls are covered by a beech forest, an abbey dating back to the 11th century can be found in the southwest of the caldera and the lake is being used for all kinds of recreational purposes. Many paths stretch far and wide in and around the volcano, allowing hikers to enjoy a fine bit of nature. A campsite is located on the northwestern shore, as well as a hotel on the northern crater rim as one next to the abbey, enabling a stay of more than one day for anyone who’d be interested in doing so. Directly surrounding the caldera are numerous villages, various museums and castles and a very fine brewery. The area is bustling with anything and everything that has to do with having a good time. The volcanism of the area is mostly something nice for tourists to be entertained by. Shapes of volcanoes can be seen in the landscape, as well as rock quarries featuring layers of ash and lava. CO2 is being emitted visibly in a few places, like the ‘Andernach Geyser’, which is the result of a borehole blasting out CO2-pressurized ground water to a height of 30 to 60 meters every 90-110 minutes, making it the world’s tallest cold-water geyser. Spectacular and fun, as is underscored by the many signs in the field explaining the geological importance of the volcanic features of the area. The ‘Lava-dome’ volcano museum in Mendig helps to make things more understandable for those of a younger age. It would be easy to think of the Eifel volcanism to be done and dusted, as many have done who live and have lived in the area and those who visit it for work, recreation or social reasons.
One would expect I’m going to state that nothing could be further from the truth than the perceived serenity that is present in both Eifel volcanic fields. Although going to spice things of a bit, it has to be said that nothing even close to the activity of well-known volcanoes like Etna has ever been detected in the Eifel. I mentioned before that things can change quickly in the WEVF, but does the same thing apply to the other field? For both areas we can state that the most recent eruptions have occurred long before there ever could’ve been historical records of it, not to mention not having modern geosciences to our aid to help understand things. There are plenty of other volcanoes around the world which feature much more acute signs of unrest that require monitoring and everything that comes with it, and not every country can easily come up with enough cash for such a project. So does it make sense to invest some time, effort, know-how and money on a topic like the volcanism of the East Eifel Volcanic Field? In my opinion, that is most certainly the case.
Another building with a religious purpose was present within the Laacher See caldera, located on its eastern shore. This ‘villa’ was built in 1870 for a group of Jesuits, but in 1871 things started going wrong. On no fewer than eight occasions, a young Jesuit was found dead in his bed at the start of a new day. At the time, these deaths remained a mystery. Nowadays, it is being assumed they were poisoned and suffocated in their sleep by volcanic CO2 rising up from the partially collapsed magma chamber, through the ring faults and into the bedrooms on the ground floor of the villa. CO2 has a higher density than oxygen, and can kill quickly and without any sort of stress when it fills of room to a level that is higher than that of someone sleeping in a bed. No visible traces of the villa can be found in the landscape today, but the Jesuits are still interred in the grounds of the nearby abbey of Maria Laach.
One might say the Laacher See volcano has already killed several people in fairly recent times, earning a bad reputation. CO2 can still be seen near the eastern shore in the form of so-called ‘Mofetten’, where bubbles are visible and audible in the lake. A smell of rotten eggs, pointing out the presence of Hydrogen sulfide (H₂S), is a common occurrence on a day with little to no wind. But does CO2 output mean this volcano can erupt in the near future? No, not really. Magma chambers, especially larger ones, tend to take some time to cool down, all the while the system inevitably degasses. We’d have to look for other signs to figure out if there’s a more substantial volcanic threat coming from this rather big hole in the ground. Think of earthquakes and tremors formed by the motion of magma, or changes in the amounts and compositions of volcanic gasses emitted. Ground deformation, and especially localized rising of the Earth’s surface, is something to be concerned about. Is any of that going under or close to Laacher See? There’s a score of at least two out of three for the EEVF.
Coming to grips with reality
For plenty of geoscientists, getting to do research on a quiet, yet young volcanic field like the ones of the Eifel, especially when they contain nasty beasts like Laacher See and Wehrer Kessel, would be a very interesting project, to say the least. It might surprise you that until recently, nothing substantial had ever been undertaken to get a better perspective of the potential threats of future volcanism in the area. As part of a study (Hensch et al, 2018), using an array of both permanent and temporarily installed sensors, so-called ‘Deep low-frequency earthquakes’ have been detected below the EEVF for the first time between 2013 and 2018. These tiny earthquakes are typical for the motion of magma within the Earth’s crust. Quite a few of these events have been observed at four distinct zones ranging between 44 and 8 kilometers below the surface, most of them being too deep to be of a tectonic origin, although tectonic quakes occur frequently in the area as well. The shallowest of the microquakes were located almost right under… Laacher See. The findings of the very important study concerning this topic caused a bit of a stir, but no major amount of attention by the public formed as a result of this research.
How about very localized ground deformation? I’m not referring to the steady rising of the entire Eifel and surrounding areas by about 1 millimeter per year (Kreemer et al, 2020), which also happens to be quite relevant for the volcanic activity of the region, but the upward motion of the ground in and near the village of Glees. This place, counting about 600 inhabitants, lies a few kilometers northwest of Laacher See and northeast of Wehrer Kessel. The ground on the northern side of the village has been rising quite a bit since 2015, which is when measurements started. The most recent available data, dating from the end of 2020, shows an increase of about 3.5 centimeters, in some places more than 4 centimeters, since early 2015. Again, this is close to nothing compared to what’s currently going on at volcanoes like Campi Flegrei or Edgecumbe, but an area that has always been thought to be extinct or at least very quietly dormant by many, it’s a fact that has caused the raising of some eyebrows over the last few years. Several clusters of tectonic earthquakes near Glees have been observed (Hensch et al, 2018), which may be attributed to the formation of sill-like intrusions of magma and/or increased, CO2-produced pressure. And might there be a connection to the very local subsidence in Weher Kessel? As it stands, magmatic inflation under the Glees area cannot be ruled out, but more research is needed to get a much-needed understanding of what actually is going on, which leads me to a concerning, yet exciting conclusion: we don’t know enough. To my current knowledge, no extensive monitoring is being done in the area, apart from keeping tabs on the deep low-frequency earthquakes and ground deformation. How about gas measurements? Is there still no eye being constantly kept on what’s coming out of the ground? As you will likely understand, I’m quite keen to be kept informed on whatever is going on beneath the feet of those who live in the Eifel and visit that fascinating place for whatever reasons one may have.
Not just interesting for future eruptions
So far for the most exciting volcanic region of Europe north of Naples, which should be mandatory for any European geology class. It is one for the future. But is also helps to understand the past, as will be shown in part II. Stay posted.
Gijs de Reijke, April 2022
Hensch, M., Dahm, T., Ritter, J., Heimann, S., Schmidt, B., Stange, S., Lehmann, K. (2019). Deep low-frequency earthquakes reveal ongoing magmatic recharge beneath Laacher See Volcano (Eifel, Germany), Geophysical Journal International, 2019; DOI: 10.1093/gji/ggy532
Schmincke, Hans-Ulrich (2007) The Quaternary volcanic fields of the East and West Eifel (Germany). In: Mantle plumes – a multidisciplinary approach. , ed. by Ritter, R. and Christensen, U.. Springer, Heidelberg, pp. 241-322.
Schmincke, H.-U., 2006. Environmental impacts of the Lateglacial eruption of the Laacher See Volcano, 12.900 cal BP. In: von Koenigswald, W., Litt, T. (Eds.), 150 years of Neanderthal Discoveries. Terra Nostra, Bonn, pp. 149- 153.
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Kreemer, C., Blewitt, G., Davis, P.M., Geodetic evidence for a buoyant mantle plume beneath the Eifel volcanic area, NW Europe, Geophysical Journal International, Volume 222, Issue 2, Aug. 1, 2020, pp. 1316–1332, https://doi.org/10.1093/gji/ggaa227
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