the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 06 Aug 2025
Assessment of possible volcanic hazards in Germany with regard to repository site selection
Abstract. In the context of selecting a site for the long-term disposal of radioactive, heat-generating waste in deep geological formations, the potential for future volcanic activity within the next 1 million years must be systematically evaluated. This assessment draws upon an integrated analysis of geological, geochemical, and geophysical datasets, as well as isotopic measurements of crustal and mantle-derived gases. Relevant data sources include teleseismic imaging, long-term seismic and microseismic monitoring—particularly deep earthquake patterns—and geodetic observations of vertical crustal movements. Additional insights are provided by geological and mineralogical studies that inform the spatial distribution and petrogenesis of volcanic rocks. When combined with geophysically derived mantle anomalies and radioisotopic age data for volcanic centers, these datasets enable the delineation of areas with an elevated probability of future volcanism. Special focus is given to the Quaternary volcanic provinces of the Eifel and Vogtland, which are identified as regions with a significantly increased likelihood of renewed activity. The outermost volcanic centers in these regions are used to define preliminary hazard perimeters. A conservative safety buffer of 25 km beyond these limits is adopted to define the exclusion zone boundary for deep geological repositories. In the Vogtland region, known for its characteristic earthquake swarms, seismic epicenters are equated with volcanic centers to delineate zones of potential recurrence. The extent of this area is adjusted accordingly based on seismic swarm distribution and geophysical data. A major secondary hazard associated with volcanism in the Eifel is the potential damming of the Rhine River within its narrow Middle Rhine Valley by lava flows or tephra deposits. Prolonged blockage of the river would result in extensive upstream flooding, affecting the Upper Rhine Graben and its tributary valleys. Two regions in Germany—north of the Westerwald and east of the Black Forest—are classified as having a low probability of future volcanism within the next 1 million years. In the Tertiary volcanic fields, no volcanic activity is expected within the next 1 million years due to their advanced age and normal mantle and gas compositions.
Competing interests: I declare that neither I nor my co-authors have any competing interests.
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RC1: 'Comment on sand-2025-2', Andreas Klügel, 27 Aug 2025
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General comments
This manuscript is a very nice summary of the extent of Quaternary volcanism in Germany, along with related features such as CO2 degassing, underlying mantle structures, and tectonic framework. These aspects are discussed to clarify possible causes for volcanic activity, and are projected to the next 1 million years to assess potential volcanic hazards relevant to repository site selection. The authors show that volcanic hazards exist not only for the active volcanic fields in the Eifel and Vogtland, but also along the upper Rhine River due to potential damming, and to a minor degree for the area between Stuttgart and Lake Constance.
Overall this manuscript is very well written, well organized, and I enjoyed reading it. It is accompanied by a number of figures and tables as electronic supplement, all of which were taken directly from the literature. What I am missing, though, is a more detailed map of the West and East Eifel volcanic fields in the main manuscript, as this region makes up much of the text. I am also missing an appropriate consideration of the review of Eifel volcanism by Schmincke (2007), because a considerable part of the present manuscript is dealing with aspects discussed in detail by him (see below). Apart from this, I have only a few specific and technical comments, and suggest the manuscript to be published after a minor revision.Specific comments
Lines 192-194: I think the conclusions that 1) the formation of a new volcanic field within the next million years is unlikely, and 2) there will be only minor lateral shifts in volcanic activity within the established Quaternary fields, are valid and important. In this context it could be noted that the spatial orientation and rough age progression of the west and east Eifel volcanic fields (younger volcanism to the southeast) do not agree with the direction of plate motion. I would also add the important observation that Cenozoic volcanic fields in Central Europe in general do not show any age progression related to plate motion, as was shown in the review and synthesis by Schmincke (2007). This review touches much of the current contribution, and therefore is an indispensable source that should really be considered and cited in this work:
Schmincke H.U. (2007): The Quaternary Volcanic Fields of the East and West Eifel (Germany). In: Ritter, J.R.R., Christensen, U.R. (Eds.) Mantle Plumes. - Springer, 241-322.Lines 269-270: this is a bit confusing, as the early (explosive) and the final stage of a volcanic eruption are typically no more than weeks to months apart. If a phreatomagmatic maar formation substantially predates the age of a spatially related lava flow then we essentially speak of two distinct eruptions. But do you know of any example in the Eifel where earlier maar deposits substantially predate an overlying scoria cone? Usually, as judged from the deposits, both reflect one single eruption without a prolonged break.
Chapter 4.4, Volcanoes of the West Eifel: actually, more than half of this short chapter deals with general processes related to magma ascent, but unspecific to the West Eifel. On the other hand, much of the preceding chapter describes the age distribution of West Eifel volcanoes. This could be re-organized: I suggest to move the West Eifel stuff of chapter 4.3 into 4.4 and move the more general part of 4.4 (which applies to young Eifel volcanism in general) to 4.3.
I also suggest to add recent findings on the existence of fluid-filled lenses beneath the West Eifel on the base of the old DEKORP seismic reflection data, as this is highly relevant for this contribution: Eickhoff D., Ritter J.R.R., Hlouaek F., Buske S. (2024) Seismic Reflection Imaging of Fluid-Filled Sills in the West Eifel Volcanic Field, Germany. Geophysical Research Letters 51, e2024GL111425. doi:10.1029/2024GL111425.Line 323: there are more recent works that shed light into the temporal evolution of the Laacher See magma chamber. These suggest periodic recharge events throughout the magma reservoir’s entire lifespan of ~24 ky. As these works are relevant to the main topic of this contribution, their main findings should be included here:
- Sundermeyer C., Gätjen J., Weimann L., Wörner G. (2020) Timescales from magma mixing to eruption in alkaline volcanism in the Eifel volcanic fields, western Germany. Contributions to Mineralogy and Petrology 175, 77. doi:10.1007/s00410-020-01715-y.
- Rout S. S., Wörner G. (2018). Zoning and exsolution in alkali feldspars from Laacher See volcano (Western Germany): constraints on temperature history prior to eruption. Contrib. Mineral. Petrol. 173, 95. doi: 10.1007/s00410-018-1522-x
- Rout S. S., Wörner G. (2020). Constraints on the pre-eruptive magmatic history of the Quaternary Laacher See volcano (Germany). Contrib. Mineral. Petrol. 175, 73. doi: 10.1007/s00410-020-01710-3Lines 335-336: very interesting discussion on the volcanological assessment of the Laacher See system, yet I think it needs to add two important points. (1) The growth model and extreme crustal deformation invoked here are based on gradual accumulation of magma at crustal levels. However, the works by Sundermeyer, Rout and co-workers show that magma can accumulate at much deeper levels and gradually fill a shallower reservoir during rare and discrete recharge events. Hence, large present-day deformation would not necessarily be observed. (2) The discussion seems to imply that the Laacher See eruption will be followed by a similar scenario, preceded by re-filling of the reservoir. This may happen at some time, but not necessarily now. The preceding volcanic phases (Rieden and Wehr) have shown that large eruptions were commonly followed by volcanic activity producing scoria cones in the wider vicinity. Again, in that case, large present-day deformation would not necessarily be observed.
l.538-539: It is not clear why a constant helium concentration observed in mantle-derived gases over a few years is sufficient to infer a decoupling between gas transport and active magmatism. What precisely do we know about this active magmatism, how frequent are potential recharge events by primitive melts from depth? If these occur at timescales of thousands to ten thousands of years, then there is little change in active magmatism and degassing in the last years/decades, hence no decoupling is evident. This casts doubt on the conclusion that the mantle source may be either waning or no longer actively replenished in this area. I suggest to remove this conclusion or provide a more conclusive reasoning.
Technical corrections and comments
Generally: a number of local town names appear in the text, but not all are shown or referred to in a map. This is particularly evident for the Eifel volcanic fields, of which a detailed map is lacking. Maybe the existing maps can be modified accordingly?
l.63: explosive, effusive, or a combination of both
l.124-125: for better clarity you could change "helium isotope composition ..." to "3He/4He ratio (R) ..."
l.129-134: I assume that most R/Ra data listed here were measured as part of CO2-dominated gases; maybe this could be explicitely stated. As for the highest value at Glees, it would be useful to state the kind of gas emission: was it diffuse CO2 degassing from the ground?
l.180, "magmatic conditions in the underlying mantle": I am not sure what is meant by this expression: the proportion of partial melt in the mantle? Or the melting conditions?
l.184, "...uplifted to a depth of approximately 50 km": please provide reference.
l.185: suggest to change to "the plume top is encased by lithospheric mantle", as it is not the entire conduit that is meant here.
l.189: it is confusing to write "forming a separate intrusion" here, as this may be understood by less specialized readers as a magmatic intrusion. Some readers may even think that a plume consists of melt rather than ductile crystalline material... I suggest to remove this subclause.
l.256, l.280, and others: I suggest to replace all references to the two popular textbooks by Schmincke ("Volcanism" and "Vulkane der Eifel") by his 2007 review, which is a much more appropriate source.
Line 349: why not providing the source for the 300 ka dating of Rodderberg: Paulick H, Ewen C, Blanchard H, Zöller L (2009) The Middle-Pleistocene (~300 ka) Rodderberg maar-scoria cone volcanic complex (Bonn, Germany): eruptive history, geochemistry, and thermoluminescence dating. Int J Earth Sci 98:1879–1899.
l.510: sentence is incomplete: "is located"?
l.515-516: I don't think that a popular textbook (Schmincke 2009) is a citeable source for the initial consideration of a mantle plume. I suggest to remove this subclause.
l.553. repetition of l. 547.
l.557: for clarity change to "elevated 3He/4He ratios of mantle-derived helium."
l.562: do you mean the volcanic / volcanological evolution?
l.594-607: this is a duplicate of lines 580-593; delete.
l.559, geophysical modelling: this is quite broad; it would be helpful to the reader to specify this briefly in the sentence: modelling of gravity data, deformation data...?
Figure 2, caption: for the reader not familiar with the Walker et al. (2005) paper it would be helpful to explain the abbreviations of this figure (e.g. APM, Pn) and also the grey shaded areas in the caption.Citation: https://doi.org/10.5194/sand-2025-2-RC1
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