[Guest article by Gijs de Reijke.]
Well, the big word is out. The results of a study (‘Deep low-frequency earthquakes reveal ongoing magmatic recharge beneath Laacher See Volcano (Eifel, Germany)’, Hensch et al.) have been published on the 7th of January, pointing out the presence of magmatic movement beneath the East Eifel Volcanic Field, Germany. Many people are oblivious to the fact there are volcanoes in this part of Europe. Geoscientists are now telling them there is evidence for the volcanism in the area to be ‘alive’. Time for real estate prices to plummet and for the area’s inhabitants to run and scream? Hardly.
[Video credits: Marc Szeglat]
Before I get to what the new findings are all about, I want to provide you all with some background information on the Eifel Volcanic Fields. Volcanism has been occurring in Germany for tens of millions of years. Tertiary volcanism have been taking place in volcanic centers like the Kaiserstuhl, Hegau, Rhön, Vogelsberg and even Eifel. The volcanic fields of the East and West Eifel are of Quaternary age, however, so that is what I’ll be focusing on for this article.
The West Eifel Volcanic Field
For an estimated 700,000 years the West Eifel Volcanic Field (from here on ‘WEVF’) has been volcanically active, producing some 270 scoria cones and maars with a fairly modest total volume of about 3 cubic kilometers, quite common for this type of volcanic field. The mostly small, monogenetic (one eruptive episode per volcano) vents produced very primitive magmas (e.g. variations of leucitite, nephelinite, melilite etc.) and a few volcanoes produced more evolved, intermediate phonolite coming from polygenetic (several eruptive episodes per volcano) complexes. The WEFV is the type location for the Maar volcano type: the word ‘maar’, which stems from the Eifel dialect, means as much as ‘lake’.
The most recent eruption in the WEVF took place as little as ~11,000 years ago, when the formation of Ulmener Maar took place, also making it the most recent eruption in Germany.
The East Eifel Volcanic Field
The other volcanic field is that of the East Eifel (from here on ‘EEVF’). Since about ~650,000 years this area has been volcanically active, with the formation of monogenetic scoria cones and a maar or two, totaling about 100 volcanic vents. The average size of the volcanoes is somewhat larger than that of the cones and maars of the WEVF, which could be the result of larger faults allowing for more magma to rise from the top of a plume or plume-like anomaly in the Mantle (Ritter et al., 2001). The most significant differences between the EEFV and WEVF volcanoes do not lie within the sizes of the scoria cones, but in the composition of the volcanic rocks and the types of volcanoes that are to be found in these fields. Where the volcanoes of the western field seem to lack magma chambers, being fuelled by magma coming straight from a region of partial melt at the base of the Earth’s crust, the volcanoes of the eastern field do have, in some cases, significantly sized magma chambers, allowing for long-term storage of magma and therefore more evolved magmas (various types of phonolites and trachytes). The evolution happens mainly due to processes that fall under the term of ‘magmatic differentiation’, which basically means that magmatic compositions is being influenced by factors such as cooling, absorbing materials from the Earth’s crust (assimilation) and replenishment by younger magma. In most of the EEVF, basanitic lavas are produced by the scoria cones, but in some cases the aforementioned phonolites and trachytes leave much larger scars in the landscape. At least two calderas are to be found in this volcanic field, one of them being the caldera of Wehrer Kessel, which is approximately 2 kilometers wide and was formed by explosive eruptions (trachyte) some 215,000 and 150,000 years ago, of which the first event was the largest (‘Hüttenberg Tephra’), possibly having been a VEI5-sized eruption: ~2 km³ DRE (Schmincke). There is still debate about the larger and older (450,000 – 350,000 years BP) Rieden complex being an actual caldera and not being composed of overlapping, smaller craters and erosive features. Most of the literature still points towards this volcanic complex to have undergone (several phases?) of caldera formation, possibly initiated by multiple events that could have been fueled by up to ~1 km³ of erupting magma (DRE) each.
The Big One
The second of the calderas, at least of those of which are certainly present in the EEVF, is one that makes the others almost look insignificant. After having undergone an estimated ~20,000 years of magma emplacement and magmatic differentiation (Schmitt et al., 2011) , the violent eruption of the Laacher See volcano took place, an estimated 12,900 years BP. Some 6.3 km³ (DRE) of zoned, phonolitic magma (evolved from basanite) was erupted out of the volcano in the form of mostly ash and pumice, after which an 8-shaped caldera (two overlapping vents) formed. The brunt of the eruption is assumed to have lasted eight to ten days, with three distinctive phases being recognized in the voluminous deposits: the Lower Laacher See Tuff (partially phreatomagmatic, vent-breaching phase), the Middle Laacher See Tuff (the main, ultra-Plinian phase) and the Upper Laacher See Tuff (weaker, Vulcanian explosions being fuelled by increasingly mafic phonolite). During the main event, ash columns might have reached altitudes of up to 40 kilometers above the Earth’s surface, dispersing large quantities of ash over large parts of Europe. Traces can still be found in Sweden, Italy and France. Large ignimbrite sheets now fill up the valleys surrounding the caldera, sometimes being many tens of meters thick. The nearby, narrow valley of the Rhine river was blocked for a while, forming a natural lake in the plain of Neuwied (Neuwieder Becken), which may have reached a depth of up to 20 meters. After a while, the weak, natural dams composed of pyroclastic deposits gave way to the pressure of the water behind them and unleashed a destructive flash flood into the lower parts of the Rhine. The SO2-traces of this event, which are significant in volume, can still be found in ice cores from Greenland. It is assumed that the Laacher See eruption was a weather-changing event, possibly making the already cold, last phase of the most recent ice age even colder, limiting the size at which vegetation grow, which can be seen in the narrower rings of trees from that time.
An eruption of this size and with such impact was new to the Eifel. The largest eruption from Wehrer Kessel is not to be underestimated (probably significantly larger than the infamous 1980 eruption of Mount Saint Helens), but is dwarfed by the Laacher See event. The estimated bulk volume of the erupted materials lies between 16 km³ and 25 km³ (VEI6), making the eruption larger than the one from Pinatubo (1991, Philippines) and possibly about the same size as the one produced by Novarupta/Mount Katmai (Alaska, 1912), maybe even getting fairly close to Krakatau (Indonesia, 1883). If an event comparable to the 12,900 year BP eruption were to take place now, or even something of a size comparable to what Wehrer Kessel or the Rieden volcano produced, the consequences for the Eifel area and the German and European economy would be devastating.
The current situation
So what is the new publication concerning Laacher See’s magma all about? Is something happening that should have us worried? The answer is actually both yes and no, but to make one thing clear: what is going on beneath the volcano is ‘business as usual’. For a long time it has been known that the Eifel contains young volcanoes. So young, in fact, that we should consider the volcanism in the area dormant rather than extinct. Add to that the fact one of the youngest volcanoes there also happens to be the most violent and destructive we’ve seen on this side of the European mainland, north of the Alps for millions of years and there is plenty of reason to at least ‘keep an eye on things’. The study by Hensch et al. came after several geoscientists within the volcanological community, including German volcanologist Hans-Ulrich Schmincke, emphasized the fact that the Eifel volcanoes were not properly monitored. They still aren’t, but since 2013 there have been some important changes, now allowing for just enough insight in the seismic processes taking place below the EEVF to be able to tell what is and what isn’t seismicity caused by tectonic processes. The findings: swarms of tiny earthquakes, often too deep to be tectonic in nature, occur on a regular basis below the volcano. The conclusion: magma is on the move, likely to slowly recharge the magma chamber of Laacher See that can be found between 5 and 8 kilometers below the volcano. And that is all there is to it. It is what we should consider business as usual. Reason for a healthy amount of concern, but it lies well within the possibilities that this process has been steadily going on since the cataclysmic eruption of 12,900 years ago and will do so for thousands if not tens of thousands of years to come. Yes, it is true that Laacher See has also been producing CO2 emissions longer than any records have been kept, but magma chambers tend to degas at any stage of their life cycle, including dormancy and even during their slow decay into definite extinction. It may well be the case the tiny, rising bits of magma will never be able to contribute to another eruption of Laacher See, because they might cool down too much on their way up or simply aren’t large enough to have a serious influence on the ~50 km³ of viscous, crystal mush that is now the magma ‘chamber’.
Then again, what do we know? We can’t look back into what happened at depth since the only eruption Laacher See has produced so far without the right data, nor can we foresee the subterraneous behavior in great detail. Maybe a large intrusion of magma will occur. Maybe several. Maybe large quantities of magma have been emplaced slowly, not causing too much disturbance or any at all for us humans.
There are two very important things we’ve learned. The first concerns Laacher See and other volcanoes that are fueled by strongly evolved magmas. Magma evolution takes a long time. A few thousand years is short, tens of thousands of years is common, longer is well possible. We know this slow process has been the case for the thus far only Laacher See eruption (Schmitt et al., 2011). Slow cooling of the magma body, solidifying the mafic minerals and keeping the more felsic minerals to remain in a fairly liquid state, enabling the formation of potentially eruptive and explosive magma in the center of the chamber, seems to be the main factor in magmatic differentiation below Laacher See and many other volcanoes. This can change when the old magma is abruptly replenished by younger magma making its way up in vast quantities, but as already stated: such events have not yet been observed, nor do we know if this intrusive behavior will occur at any time in the future.
To conclude the first important point: what has now been observed for the first time, is an ongoing process of magma being in motion. Not in a way that points toward an eruption any time soon, but more toward one, simple conclusion: we now have solid evidence of the East Eifel Volcanic Field, and in particular the Laacher See volcano, being in a dormant and not an extinct state.
The second matter of importance is that of monitoring. The monitoring of processes that might lead to an eruption, at any time in the future. To quote directly from the publication by Hensch et al.:
“So far, no direct observations could be made indicating ongoing recharge in the magmatic plumbing system beneath the LSV. The location of magmatic feeding channels and active crustal magma reservoirs is unknown. However, although the volcanic hazard in the Eifel is assumed to be low, the risk in case of an eruption would be high due to the dense population and high damage potential of this region in Central Europe (Leder et al. 2017). Thus, volcano-related seismic activity requires thorough monitoring and analysis.”
More specific examples are given when it comes to much-needed research concerning Laacher See’s ongoing magmatic processes.
“Ultimately, the present volcanic hazard posed by the LSV cannot be assessed solely based on the findings of our study. But bearing in mind that the LSV already experienced an explosive eruption 12.9 kyr ago, a deeper analysis of the magmatic/volcanic activity in the region and the resulting hazard is recommended. Despite of the close seismic monitoring, high resolution seismic and geophysical experiments are required to image potential shallow and deep crustal magma reservoirs. For example, large S-wave residuals on single stations close to the LSV (e.g. station DEP02 for the Glees 2 cluster) might reflect low velocity zones, possibly linked to shallow crustal fluid batches, which can only be resolved by a shallow seismic tomography. Further, geodetic measurements would help to constrain potential shallow volume changes, either during DLF sequences or during episodes like the Glees clusters. Continuous geochemical measurements would be another valuable enhancement to better understand CO2 emissions and potential changes in gas flux during episodes of seismic unrest.”
At this moment, Laacher See is an ideal destination for recreational purposes. The crater itself looks magnificent, with a lake covering the majority of the crater’s bottom and the walls being covered by a lush beech forest. The old monastery of Maria Laach can be found at the southwestern shore of the lake and camp sites and hotels dot the area. Whenever the weather is good, hundreds, if not thousands of people will walk and cycle their way through the area. At the eastern shore of the lake, the volcanic CO2 emissions can be seen in the form of bubbles rising through the water, which is both fun and of great educational value. Just south of the crater, the impressive deposits of the Laacher See eruption can be seen in a quarry known as ‘Wingertsberg’. Hopefully this will remain the case for a long time to come, but the geology of the Eifel should still be taken seriously, if only to know nothing unusual is going on. That goes for the WEVF just as well, where the presence of very primitive magmas indicates the warning time for an eruption might be very limited (hours to days) anyway; these magmas can only be present at the surface when there hasn’t been sufficient time for any sort of significant magmatic differentiation.
I think it is a safe bet to say the Eifel will have eruptions again in the future. When that will be, or if any will occur at all, no one knows. It might be a small, cone-forming eruption from a monogenetic vent. It might be the formation of a maar through a phreatomagmatic event. Maybe a phonolitic lava dome will form. Maybe a large, caldera-forming eruption will occur. Immediate fear for any of these events, especially in a time that points out the area is showing perfectly normal behavior considering the volcanism is dormant, only does more harm than good. But as a society it can never hurt to be awake before a volcano will be, meaning we should know what is going on, to the best of our capabilities.
Gijs de Reijke, January 2019
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.
Ritter, J.R.R., Jordan, M., Christensen, U.R., Achauer, U., 2001. Mantle plume below the Eifel volcanic fields, Germany. Earth Planet. Sci. Lett. 186, 7–14.
Schmincke, Hans-Ulrich (2009). Vulkane der Eifel – Aufbau, Entstehung und heutige Bedeutung, Spektrum-Akademischer Verlag 2009, ISBN 978-3-8274-2366-5.
Meyer, W. Geologie der Eifel, Schweitzerbart, Stuttgart, 4th edition (2013).