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.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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- RC1: 'Comment on sand-2025-2', Andreas Klügel, 27 Aug 2025 reply
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CC1: 'Comment on sand-2025-2', Axel Schmitt, 03 Sep 2025
reply
Community comment of Schreiber and Jentzsch (submitted)
The manuscript by Schreiber and Jentzsch (Sch&J, submitted) addresses Germany’s volcanic hazard potential in the context of long-term nuclear waste storage. By its own description, it represents an integrated analysis of existing research. This includes the distribution, timing, and eruptive styles of late Quaternary volcanic fields, with particular emphasis on the Eifel. Within this scope, it is essential that sources are cited comprehensively and accurately, and that data and conclusions from prior work are represented fairly and correctly.
For time reasons, I primarily concentrate on sections 4.3–4.5, where I am most familiar with the current state of research. In these chapters, I find that Sch&J (submitted) frequently omit essential references to original work, misrepresent published findings, and rely on untested interpretations. In many places, nearly every other sentence requires a citation. A few of the most critical issues are highlighted below:
Line 253: No source cited for “Remnants of Eocene volcanic activity.”
Line 257: Tables S3 and S4 lack proper attribution in the text. Tables and figures are frequently reproduced at low-quality from published work, with Table S1 not even being translated into English. Captions were in part verbatim adopted form the originals without proper attribution. Overall, efforts in synthesising published data are minimal.
Lines 257/258: Numbers given for “256 and 100 volcanic centers for East and West Eifel” lack a source.
Line 268: The term “current geochronological dataset” is unclear. Mertz et al. (2015), the only cited study, covers only a limited number of sites.
Line 270: The phrase “substantially predate these ages” requires quantification. As existing geochronological methods are incapable of resolving annual, decadal, and even centennial age differences within the relevant timescale, this statement is nonsense.
Line 271: “One notable outlier—a lava flow near Gerolstein—has been dated at 32 ± 13 ka”: attribution missing.
Line 272: “Modern techniques” are invoked without specification. As Mertz et al. (2015) is the sole reference provided, then only ~3% of West Eifel volcanoes would be reliably dated, not 15%.
Line 278: The Late Pleistocene is incorrectly defined as “<100 ka.”
Line 282: No source for the “100–80 ka eruption age for Hohe Buche” is provided. It is concerning when unsubstantiated statements like this are propagated here and in popular media. Such unfounded claims diminish serious research efforts in geochronology.
Line 288: The section on supercritical fluids is speculative and disconnected from the chapter title. It fails to explain why maar craters are not universally produced. Again, substantive recent studies on this topic are ignored (e.g., Rausch et al., 2015; Schmincke et al., 2025).
Line 290: The claim regarding lava flows in “half of these cases” lacks attribution.
Line 295: A relevant publication on magma ascent in the Eifel based on hydrogen diffusion (Denis et al., 2013) is omitted.
Line 307: This section neglects scoria cones and maars, especially those surrounding Laacher See. It only briefly mentions important evolved complexes (Rieden, Wehr). Wehr is important as it shares compositional similarities with Laacher See, and its eruption ages approach the inferred onset of Laacher See mafic magma accumulation (Sturm et al., 2024; Bourdon et al., 1994). Instead, this section recycles an unpublished opinion regarding the Laacher See eruption volume, while published data on the timing of magma accumulation at Laacher See are overlooked or misrepresented (Bourdon et al., 1994; Schmitt F. et al., 2023).
Line 311: The interpretation of structures as collapse calderas lacks reference.
Line 314: Recent references for the precise age of the Laacher See eruption are absent (Reinig et al., 2021; Warken et al., 2025).
Line 321: More recent work on zircon crystallisation and magma residence conditions (Rout & Wörner, 2018; Rout & Wörner, 2020; Schmitt F. et al., 2023) is not cited.
Line 332: Mismatched reference: Demoulin et al. (2009) is cited in the text, while Demoulin & Hallot (2009) appears in the reference list. Demoulin & Hallot (2009) cite “estimated ~0.05–0.1 mm/yr displacement rates during the upper Pleistocene and the Holocene” for boundary faults of the Rhenish Massif. In addition to the unclear attribution of the stated 0.06–1.7 mm/yr displacement rates in Sch&J (submitted), it is difficult to see how regional faulting far removed from Laacher See can be related to viscoelastic magma emplacement, where long-lasting magmatism has modified the thermal and rheological structure of the crust for over 200,000 years.
Line 341: “Collapse volume at Laacher See is only ~0.5 km³.” A citation is given (Viereck & van den Bogaard, 1986), but the content is misrepresented. Viereck & van den Bogaard (1986, p. 70, translated from German) state:
“…the volume deficit of ca. 6 km³ was only to a small degree compensated by the Laacher See caldera (based on the dimensions of the collapse structure to a maximum of 10–20%), which is another indication for possible replenishment of the partially erupted magma chamber by ‘fresh’ basanite magma.”
Thus, a collapse volume of 0.5 km³ appears incorrectly attributed. Moreover, the cited work already presents an explanation for the difference between eruption and collapse volumes. Sch&J (submitted) either overlook or ignore this, as they do with existing research that demonstrated late basanite magma recharge into the Laacher See system (Wörner & Wright, 1984; Sundermeyer et al., 2020).
Line 443: “Topographic analysis suggests that a lava-induced barrier could reach over 200 m above sea level.” The reader is left uninformed about what this topographic analysis entails. Proposing such a scenario (which also features prominently in the abstract) without explanation and attribution to existing research on the damming of the Rhine River after the Laacher See eruption is unacceptable (Park & Schmincke, 2020a; 2020b).
In summary, the parts in Sch&J (submitted) reviewed here fall short of scholarly standards in both form and content. The pervasive omission of references and misrepresentation of prior research, while introducing oversimplified, untested, and in some cases already refuted hypotheses, undermines its credibility as a scholarly work.
Lastly, although not the focus of this community comment, I am surprised how state-of-the-art research on quantitative hazard assessments for distributed volcanism could be ignored in such a study (e.g., Bertin et al., 2019; Ang et al., 2020; Alohali, 2022, and references therein). I perceive this as a lack of methodological rigor. The conclusions by Sch&J (submitted) are thus at best qualitative guesswork and should be disregarded as basis for policy decisions for nuclear waste disposal.
Axel Schmitt
Curtin University
Additional references
Alohali, A., Bertin, D., de Silva, S., Cronin, S., Duncan, R., Qaysi, S., & Moufti, M. R. (2022). Spatio-temporal forecasting of future volcanism at Harrat Khaybar, Saudi Arabia. Journal of Applied Volcanology, 11(1), 12.
Ang, P. S., Bebbington, M. S., Lindsay, J. M., & Jenkins, S. F. (2020). From eruption scenarios to probabilistic volcanic hazard analysis: An example of the Auckland Volcanic Field, New Zealand. Journal of Volcanology and Geothermal Research, 397, 106871.
Bertin, D., Lindsay, J. M., Becerril, L., Cronin, S. J., & Bertin, L. J. (2019). MatHaz: a Matlab code to assist with probabilistic spatio-temporal volcanic hazard assessment in distributed volcanic fields. Journal of Applied Volcanology, 8(1), 4.
Bourdon, B., Zindler, A., Wörner, G., & Widom, E. (1994). U–Th systematics of a young basanitic volcano from the Eifel, Germany: Implications for melting and melt transport. Earth and Planetary Science Letters, 128(1–2), 1–17.
Denis, C. M., Demouchy, S., & Shaw, C. S. (2013). Evidence of dehydration in peridotites from Eifel Volcanic Field and estimates of the rate of magma ascent. Journal of Volcanology and Geothermal Research, 258, 85–99.
Park, C., & Schmincke, H. U. (2020). Boundary conditions for damming of a large river by fallout during the 12,900 BP Plinian Laacher See Eruption (Germany). Syn-eruptive Rhine damming II. Journal of Volcanology and Geothermal Research, 397, 106791.
Park, C., & Schmincke, H. U. (2020). Multistage damming of the Rhine River by tephra fallout during the 12,900 BP Plinian Laacher See Eruption (Germany). Syn-eruptive Rhine damming I. Journal of Volcanology and Geothermal Research, 389, 106688.
Rausch, J., Grobéty, B., & Vonlanthen, P. (2015). Eifel maars: Quantitative shape characterization of juvenile ash particles (Eifel Volcanic Field, Germany). Journal of Volcanology and Geothermal Research, 291, 86–100.
Reinig, F., Wacker, L., Jöris, O., Oppenheimer, C., Guidobaldi, G., Nievergelt, D., ... & Büntgen, U. (2021). Precise date for the Laacher See eruption synchronizes the Younger Dryas. Nature, 595(7865), 66–69.
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. Contributions to Mineralogy and Petrology, 173(11), 95.
Rout, S. S., & Wörner, G. (2020). Constraints on the pre-eruptive magmatic history of the Quaternary Laacher See volcano (Germany). Contributions to Mineralogy and Petrology, 175(8), 73.
Schmincke, H. U., Sumita, M., Chakraborty, S., & Hansteen, T. H. (2025). Origin of maar clusters at the type locality Eifel (Germany): H2O or CO2? Bulletin of Volcanology, 87(3), 1–8.
Schmitt, F. H., Schmitt, A. K., Gerdes, A., & Harvey, J. C. (2023). Magma accumulation underneath Laacher See volcano from detrital zircon in modern streams. Journal of the Geological Society, 180(1), jgs2022-064.
Sturm, A., Schmitt, A. K., & Danišík, M. (2024). Updating the Eifel record: Zircon double-dating of tephras from Wehr volcano (East Eifel, Germany) as marker horizons for the European Pleistocene loess stratigraphy. Quaternary Science Reviews, 338, 108810.
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(8), 77.
Warken, S. F., Schmitt, A. K., Scholz, D., Hertwig, A., Weber, M., Mertz-Kraus, R., ... & Sigl, M. (2025). Discovery of Laacher See eruption in speleothem record synchronizes Greenland and central European Late Glacial climate change. Science Advances, 11(3), eadt4057.
Wörner, G., & Wright, T. L. (1984). Evidence for magma mixing within the Laacher See magma chamber (East Eifel, Germany). Journal of Volcanology and Geothermal Research, 22(3-4), 301-327.
Citation: https://doi.org/10.5194/sand-2025-2-CC1 -
CC2: 'Reply on CC1', Ulrich Schreiber, 05 Sep 2025
reply
Comments on A. Schmitt's Statement
Basis of the Work and Number of Citations
The basis of the discussed paper is a 150-page report on the assessment of potential volcanic activities in Germany over the next 1 million years. For publication, a summary of the key arguments within a maximum of 30 pages, including references, was required. This led to the avoidance of in-depth discussions on detailed questions that would not have altered the outcome. As a result, several pages of citations had to be omitted.
On Certain Details:
The remnants of the lava flow of the Hohe Buche still lie on gravel from the younger middle terrace (Meyer, 1988; Mangartz, 1998). Therefore, it cannot have the K/Ar age of 366,000 ± 40,000 years determined by Schmincke/Mertes (1979), but is more likely around 100,000 years. Age determinations are only approximations and must be considered as probabilities due to the limited sample and analysis numbers. Different methods always yield varying results. For high probabilities, a large number of measurements would need to be conducted, which is understandably rarely feasible.
Supercritical Fluids and Eruption Mechanisms:
The section on supercritical fluids is based on physicochemical data. From the deep drilling at Windisch-Eschenbach, we know that significant amounts of water with high salt concentrations can also be found at depths of 6,000 meters. Strike-slip faults provide fast ascent paths for magma, and water can infiltrate from above. The necessary temperature of 374.12 °C for the supercritical state is immediately reached in contact with magma at depth. The required pressure of at least 221 bar may suffice to about 1,000 meters without ascent. Maintaining critical pressure beyond that, at the tip of the rising magma, is a logical consequence of the tectonic stress conditions. Only the depth of the initial eruption cannot be specified, as the local tectonic conditions must be known for this.
What is interesting about this process is the change in the solubility of water for polar substances when it becomes supercritical. The solubility for salts is lost, and they essentially precipitate out, becoming incorporated into the magma (NACHRICHTEN - Forschungszentrum Karlsruhe Year 33 1/2001 p. 59-70). If there is insufficient water at depth, no scH2O-triggered initial eruption will occur. This relationship has not yet been considered and is an important factor to take into account due to its own dynamics.
Why not every eruption point in the Eifel was addressed has been explained above.
The Laacher See Eruption:
Statements regarding the eruption volume of Laacher See have already been presented and extensively discussed at conferences (Görlitz, EGU). The entire discussion regarding the caldera, magma chamber volume, and fictitious supporting basanite intrusion is based on data from a doctoral thesis, which incorporated data from diploma theses. From this, an eruption volume was derived, which has been cited in all subsequent publications with small deviations (> 6 km³, 18 km³ due to pumice formation). According to the author, this result only represents an initial approximation. However, it has never been critically questioned, despite numerous inconsistencies. For example, there is no geophysical evidence (using various methods) of a relictic magma chamber of the size that would be required for the erupted volume. Models of a magma chamber have been proposed without a tectonic basis.
Request for Explanation:
How do you interpret the opening of the magma chamber of at least 9 km³ (including remnants) in the brittle zone of the crust within the few tens of thousands of years you have determined? The tectonic movement rates are not nearly sufficient for this.
Attempts at Explanation:
Instead of addressing the root cause of the problems, namely the original collection of tephra, explanations were offered that are not substantiated (e.g., influx of 6 km³ of magma during the eruption phase of a few weeks; as evidence, basanitic streaks in phonolitic tephra, which are very common and do not provide any indication of the volume of the intrusion). Lava output volumes, for example, at Etna range between 10 and 20 m³ per second. This amounts to 1,728,000 m³ per day with a 20 m³ discharge rate. To fill a 6 km³ hole, this would take slightly over 9.5 years.
The reflection seismic data from the Laacher See sediments, by the way, show undisturbed stratification (Bahrig's thesis), which does not suggest turbulent developments of magma intrusions in the underground.
How Valid is the Data Foundation?
Two examples illustrate why the studies of Laacher See volcanism are based on a false foundation: A large part of the magma volume was calculated based on distal fans. One of these fans extends far to the south, beyond the Alps. Only one point, located near Turin, was cited. The citation given was Schneider 1978. However, a search for evidence of Laacher See tephra in this work is unsuccessful. On the contrary, it is stated on page 65, third paragraph:
"To establish the chronological transition II/III in the northern Italian region, we are dependent on radiocarbon dating, as to date no Alleröd-period volcanic ash from the Laacher See area (Germany) has been found in this region that could be used as a welcome chronological marker north of the Alps." (Original: „Um den Übergang II/III im norditalienischen Raum zeitlich festlegen zu können, sind wir auf 14C angewiesen, da bis heute in diesem Gebiet keine allerödzeitliche Vulkanasche aus dem Laachersee-Gebiet (Deutschland) gefunden werden konnte, die nördlich der Alpen als willkommene Zeitmarke genutzt werden kann.“)
Further points concern unverified occurrences that were adopted from the literature. For example, there is an isopach for the total thickness of proximal Laacher See tephra that extends southeast beyond the Mosel. Only one site is cited, from Stöhr 1963, west of Waldesch. Stöhr's sketch clearly shows that these tephra must be older than those from Laacher See, as ice-wedge pseudomorphs are documented. The remnants of Laacher See tephra are found in a debris fan at the start of the adjacent steep valley (own investigations), where layers of only a few centimeters have been washed together.
Furthermore, it was not considered that the Laacher See tephra, due to the lack of vegetation, remained exposed for many years, and any significant storm could have swept away material. The resulting deposits can hardly be distinguished from the primary ones. There is no consideration of error analysis. The isopach maps used for calculations are based on free interpretation by the author and are substantiated by few or no data over most of their extent. They do not meet the required scientific standards.
For the assessment of future volcanic development in Germany, a reliable data foundation is a prerequisite. Since this is not provided for the Laacher See volcano, against which all other magma volumes (East Eifel) are compared and assessed, works based on this foundation have been noted but not always given full consideration.
Ulrich Schreiber
Citation: https://doi.org/10.5194/sand-2025-2-CC2 -
CC3: 'Reply on CC2', Axel Schmitt, 09 Sep 2025
reply
The scientific method relies on data and hypotheses being critically evaluated through peer review. When peer-reviewed data are incompletely or in a biased manner attributed, as in Sch&J (submitted), this must be criticized. The timely reply is appreciated, but it does not invalidate this criticism for the following reasons:
Basis of the Work and Number of Citations
Sch&J (submitted), even if derived from a longer report, does not absolve the authors of the duty to properly attribute prior research. Scholarly diligence also extends to relevant references that appeared between completion of the report and submission of the manuscript. Space would not be an issue had Sch&J (submitted) concentrated on established data. Furthermore, a report available online (Schreiber and Jentzsch, 2021, 132 p.) shows the same disregard for existing research as Sch&J (submitted). For example, none of the additional references listed in CC1 were included in that report.
Age of Hohe Buche Scoria Cone and Lava
The stated age of 100,000 years is speculative. Re-dating of Hohe Buche is underway as part of ongoing research (DFG Project number 450662246; Sturm et al., in prep.).
Supercritical Fluids and Eruption Mechanisms
The model advocated is neither quantitative, nor substantiated by observations relevant to the Eifel, nor validated through peer review.
Volume of the Laacher See Eruption
Sch&J (submitted, and reply to CC1) call for downsizing the Laacher See eruption volume, arguing that 1) published data foundations are faulty, 2) basanite recharge is “fictitious,” and 3) accumulation of the reported magma volume is physically impossible within allowable timescales.
Although some of these allegations are more than a decade old (e.g., Schreiber & Berberich, 2013, EGU2013-5908), none have been published following peer review. Introducing them into a report on volcanic hazards in relation to nuclear waste storage circumvents scholarly diligence.
Moreover, the arguments by Sch&J (submitted, and reply to CC1) are easily refuted:
- The presence of Laacher See tephra in northern Italy has been confirmed (Finsinger et al., 2008). Even if this were not the case, any resulting volume change would be negligible, owing to the logarithmic scaling of tephra thickness with distance and the dominance of the NW fan and proximal deposits. Alleged discrepancies with published data for one site out of 643 in the Laacher See tephra distribution database (https://www.tephrabase.org/structure.html), even if valid, are inconsequential.
- Petrologic evidence for basanite recharge is unequivocal (e.g., Sundermeyer et al., 2000). The mass ratios of basanite parent to differentiated phonolite magmas are quantitatively constrained in previous peer-reviewed studies (Wörner et al., 1983; Wörner & Schmincke, 1984a, b). Similar parent-to-evolved magma mass relations have since been documented in numerous other studies. Inferring basanite recharge durations from comparison with Mt. Etna lacks justification. Nonetheless, documented output rates there reach 100 m³/s (Harris et al., 2011), sufficient to fill a Laacher See-sized system in less than two years. As an aside, a 6.3 km³ phonolite eruption volume for Laacher See is consistent with published scaling relationships between caldera diameter and eruptive volume in other volcanoes (Geshi et al., 2014). Likewise, crater volumes smaller than erupted volumes are common (e.g., the 2 km³ lake filling the crater from the 30 km³ DRE Millennium eruption of Changbaishan; Wei et al., 2013).
- The exclusive focus on tectonic opening in a putative pull-apart structure ignores other mechanisms such as viscoelastic deformation, uplift, and stoping, which permit magma accommodation in the upper crust. Integrated filling rates of 0.0006 km³/year (combining the basanite volume in Wörner and Schmincke, 1984a, with the onset of basanite-phonolite differentiation at Laacher See from Bourdon et al., 1994) are well within the range of eruption rates reported for intraplate mafic volcanic fields worldwide (van den Hove et al., 2017).
This response maintains that Sch&J (submitted), intended as a volcanic hazard assessment for nuclear waste disposal sites, disregards substantial literature and misses its target by repeatedly advancing idiosyncratic opinions untested by peer review while ignoring essential research by others. Sch&J (submitted) is therefore unsuited for publication in its present form.
Additional references
Finsinger, W., Belis, C., Blockley, S. P., Eicher, U., Leuenberger, M., Lotter, A. F., & Ammann, B. (2008). Temporal patterns in lacustrine stable isotopes as evidence for climate change during the late glacial in the Southern European Alps. Journal of Paleolimnology, 40(3), 885-895.
Geshi, N., Ruch, J., & Acocella, V. (2014). Evaluating volumes for magma chambers and magma withdrawn for caldera collapse. Earth and Planetary Science Letters, 396, 107-115.
Harris, A., Steffke, A., Calvari, S., & Spampinato, L. (2011). Thirty years of satellite‐derived lava discharge rates at Etna: Implications for steady volumetric output. Journal of Geophysical Research: Solid Earth, 116(B8).
van den Hove, J. C., Van Otterloo, J., Betts, P. G., Ailleres, L., & Cas, R. A. (2017). Controls on volcanism at intraplate basaltic volcanic fields. Earth and Planetary Science Letters, 459, 36-47.
Wei, H., Liu, G., & Gill, J. (2013). Review of eruptive activity at Tianchi volcano, Changbaishan, northeast China: implications for possible future eruptions. Bulletin of volcanology, 75(4), 706.
Citation: https://doi.org/10.5194/sand-2025-2-CC3 -
CC4: 'Reply on CC3', Ulrich Schreiber, 11 Sep 2025
reply
Hohe Buche
The lava of the Hohe Buche is exposed along the Rhine, overlying gravels of the Lower Middle Terrace. The outcrop is easily accessible and clearly identifiable. In this respect, I agree with you that the age determination involves a speculative component, since the given value only represents a maximum age with reference to the outcrop. Due to Rhine erosion and Roman quarrying, it remains unknown how far the lava flow extended into the Rhine. This implies that the lava may in fact be significantly younger. It is therefore most welcome that a dating effort is planned—please share the results once available.
Initial Eruption of the Maar Volcano
Which contradictory values regarding supercritical water as a trigger of the initial eruption are available to you that lead you to question the model?
Laacher See
To clarify the situation once again: for the Laacher See tephra we are discussing a volume of 18 km³. This corresponds to a column with a base area of 2.5 km × 2.5 km (approximating the caldera diameter) and a height of 3000 meters. Such a value does not align with the relatively low tephra thicknesses in the immediate vicinity of the Laacher See, where the maximum of proximal deposits should be expected.
For the refilling of the Laacher See system (caldera with a volume of 0.5 km³ or magma chamber with 6 km³?), you suggest a timespan of two years (assuming high, but realistic, flux rates). However, the eruption cycle of the Laacher See volcano has been estimated by Schmincke and others to last only a few days to weeks. What, then, occurred in the interim with the >6 km³ void in the crust?
At this point it is unclear whether you indeed defend the scenario of refilling the >6 km³ magma chamber as an argument supporting subsidence. If so, the implications would need to be explained. According to your own investigations, the initial filling required several tens of thousands of years, during which the magma evolved towards a phonolitic composition. If, however, a replenishment occurred 13,000 years ago, then continued magma evolution should still be expected today, given that no subsequent eruption has taken place. Pure cooling without further magmatic differentiation would not yet be completed. Does this imply that there is currently an active magma chamber beneath the Laacher See, the activity of which remains undetected? However, no geophysical measurements provide evidence for this, nor do other indicators exist.
A simple estimate of caldera depth, derived from the erupted volume, would result in depths exceeding 1000 meters for the given diameter. This is clearly unrealistic, since at the same time the caldera area would have significantly expanded laterally due to normal faulting. Neither of these processes is observed.
The determined depth of magma generation clearly lies within the brittle failure domain of the upper crust, which is not a matter of speculation. The lateral extent of the postulated magma chamber is limited for thermal reasons. A viscoelastic deformation model to explain the space problem is excluded at this depth.
Uplift? In which area, by what magnitude, how documented?
Erosion? Of what, in which area, how documented?
Involving structural geologists in clarifying these questions would be highly beneficial.
Data Density
643 sites over an area exceeding 500,000 km² are of primarily statistical significance. They suffice for a qualitative statement. It is unrealistic to assume that a value at a single locality is uniformly valid across the entire area up to the next point with equal thickness. These may instead represent very locally constrained wind plumes transporting material. Turbulent wind transport is far too dynamic, particularly since it cannot be established whether these are late storm deposits occurring long after the eruption ended. The involvement of meteorologists in such discussions would therefore be essential.
At that time, based in Bonn and in cooperation with the Geological Survey of Rhineland-Palatinate (Mainz), we mapped the Westerwald sheets of Westerburg, Selters, and parts of Montabaur and Meudt. With considerable personnel effort, several hundred 1-meter soil profiles were recorded and the Laacher See pumice layers identified. The results are documented in diploma theses. It quickly became apparent that distribution was highly variable, with morphology-dependent differences: some areas contained no or only very minor proportions. With few exceptions, the profiles fitted within the 1-meter fan of van den Bogaard, as can be seen on the map below. No occurrence exceeded 0.5 m thickness, except for one site representing an alluvial fan. In the southeast, the map shows the only point that led to extending the 1 m contour significantly further SE—an erroneous interpretation as explained above.
This reveals a fundamental methodological problem: the size of the study area requires a large number of investigators in order to obtain reliable conclusions regarding tephra distribution. Inferring the size of the Laacher See magma chamber from the much-cited isopach map is therefore not tenable.
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CC3: 'Reply on CC2', Axel Schmitt, 09 Sep 2025
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CC2: 'Reply on CC1', Ulrich Schreiber, 05 Sep 2025
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CC5: 'Comment on sand-2025-2', Lothar Viereck, 17 Sep 2025
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I read the paper and found many points to be commented, e.g. references cited in the text are missing in the reference list, e.g. Kreemer et al 2020, but the major point is, that the authors pretend that the old volcanic fields in Germany are underlain by "normal" mantle. This is not the case! All volcanic fields up to an age of 70 ma in question are underlain by "anomalous" mantle (Legendre et a 2012 and Meier et al. 2016). This indicates that the probability of renewed volcanic activity is given for all Cenozoic volcanic fields. Or would anyone have 1 Ma ago predicted that volcanism would start again in the old fields of the Eifel or Vogtland? No! The most likely fields would have been Lower Hessia or the Hegau.
The other point is, that not only in the volcanic field of the East Eifel the Rodderberg, Bonn, is located about 30km away from the Laaher See. The Dike at Sandebeck near Horn-Bad Meinberg, most probably part of a volcanic system, occurs 30 km north of the northernmost group of volcanic edifizes in the volcanic field of Lower Hessia near Warburg. Thus, a probability radius of 10 km is too short ! This short distance may be correct in direction of the strongest extension but not in the direction of elongation of the field, NW-SE (variscan A-C cleavage) in the case of the Eifel and the mesozoic "eggische" NNW-SSE direction in the case of the NW-part of the Lower Hessian volcanic field.
ps: if the authors are interested in the text with all comments, please let me know and I send a pdf
Citation: https://doi.org/10.5194/sand-2025-2-CC5 -
CC8: 'Reply on CC5', Ulrich Schreiber, 05 Oct 2025
reply
The studies by Legendre et al. (2012) and Meier et al. (2016) reveal extensive regions of S-velocity anomalies in the upper mantle beneath Germany, which, however, do not allow any reliable conclusions regarding future magmatic activity. The anomalies are too unspecific for such interpretations; the previously cited studies were more suitable in this regard. The Cenozoic volcanic fields are not evenly distributed across the area affected by the S-velocity anomaly of the Central European mantle but are instead confined to a narrow east–west-trending belt. This indicates that additional conditions must have been required for their formation.
The anomalous mantle beneath the Tertiary volcanic fields was only taken into account if the depth was so shallow that an uplift with melt release could occur within the next 1 million years. Deeper mantle sections were therefore excluded from consideration. If geophysicists with today’s methods and instruments had existed 1 million years ago, it is likely that they would have been able to predict the magmatic development beneath the Eifel region.
The mandatory 10 km safety distance is a legal requirement. The delineations determined in this study correspond to the mantle anomalies discussed in the literature. The comparison with the volcanic conduit at Sandebeck near Horn-Bad Meinberg refers to a Miocene occurrence and therefore cannot be directly compared with present-day conditions. The mantle conditions at that time remain unknown. Compared to today, there was a much more extensive volcanic belt extending from the Netherlands to Poland.
Citation: https://doi.org/10.5194/sand-2025-2-CC8 -
CC9: 'Reply on CC8', Lothar Viereck, 06 Oct 2025
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It's my impression that none of your arguments neither against the relevance of the anomalies reported in Legendre et a. 2012 and Meier et al. 2016 nor against the 30km safety distance in direction of the elongation of a volcanic field is valid.
Citation: https://doi.org/10.5194/sand-2025-2-CC9
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CC9: 'Reply on CC8', Lothar Viereck, 06 Oct 2025
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CC8: 'Reply on CC5', Ulrich Schreiber, 05 Oct 2025
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CC6: 'Comment on sand-2025-2, TECTONICS', Klaus Reicherter, 29 Sep 2025
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I would like to draw the attention of the authors to recent or neotectonic studies in the Lower Rhine Graben (D, NL, B). Interestingly, the normal faults of the Lower Rhine Graben (LRG) end in the Eifel plume area, this means displacements there are minor and even slip rates are very slow. Furthermore, seismic activity as outlined by Hensch et al. (2019) indicates strike-slip faulting along the enigmatic Ochtendung Fault, that was already identified by Schmicke earlier. As a general observation of normal fault systems, the tips of the faults tend to show strike slip movements (however at both tips in opposite sense), see Roberts (2007). The focal mechanisms of the Ochtendung area are mainly sinistral on NW-SE trending faults, and hence perpendicular to the basin-bounding faults of the Neuwied Basin. Like the Eifel volcanism, since 800-700 ka, we observe coeval incision of the Moselle and Rhine evidenced by fluvial terraces. So, climatic pulses of ice ages (base level drop means incision) are partly influcence by the formation of forebulges and the decay of forebulges during glacial isostatic adjustment (Brandes et al. 2025). The questions arising are: has the late Quaternary Eifel volcanism a trigger in ice ages? And to what amount is fault activity triggered by glacial rebound (Houtgast and van Balen, 2005)? If so, when does Ice Age stadium (the Pleistocene) comes to an end? How long is the duration of the post-glacial aftermath by adjustment, is it still ongoing as GPS rates suggest? And what are the effects on volcanic and fault activity. Probably not like Sirocko (2012) suggested in times of iceshield growing more volcanic activity but during the decay and release of vertical crustal stresses. Sirocko employed the Siegen thrust as main conduit for magma (like Schmicke did), a mechanically impossible theory, as the Siegen Thrust is flat in depth and a mid-crustal fault. In my opinion the GIA is a topic worth to be discussed in the frame of the search for a Nuclear Waste Deposit, especially for the Eifel and the faults in the LRG.
Citation: https://doi.org/10.5194/sand-2025-2-CC6 -
CC7: 'Reply on CC6', Ulrich Schreiber, 05 Oct 2025
reply
The Cenozoic tectonic evolution of the Eifel region and the Rhenish Massif has been only poorly investigated. It is characterized, among other features, by a shear system that originated during the Cretaceous or possibly even earlier. The exposure conditions are generally unfavorable for identifying continuous strike-slip faults. In the northern region, mining activities in the Ruhr area have revealed a system of strike-slip faults striking approximately 105–110° (Loos, J., Juch, D., Ehrhardt, W., 1999: Äquidistanzen von Blattverschiebungen), which occur regularly at intervals of a few kilometers. This well-documented fault system continues southward into the Lower Rhenish Group and the Rhenish Massif, where it can often be traced by quartz dikes. It was likely partially reactivated under Cenozoic stress conditions.
A dextral fault striking ~105° passes directly through the Laacher See area. It was probably structurally involved in the development of the magma chamber system and the caldera architecture. The structural models of Holohan et al. (2008: Analogue models of caldera collapse in strike-slip tectonic regimes, Bulletin of Volcanology) show remarkable similarities to this setting. Along the fault zone toward the west, the calderas of Wehr and Spessart as well as the phonolite dome of Brenk are located. Farther west, the fault zone, several tens of meters wide, was clearly exposed in the Holzmülheim limestone quarry. Toward the east, near Plaidt, a relatively young seismic center with an area comparable to that of the Laacher See is situated, into which the Ochtendung fault zone merges from the south. A new magma chamber system could potentially develop in this area. Further east, the fault crosses the Lahn valley, where more than seven mofettes occur, extending as far east as Bad Ems. In Bad Ems, CO₂ degassing is observed that is comparable in intensity to that at Laacher See.
The Sieg overthrust clearly played no role in the magmatic evolution of the region. The idea that glacial retreat could have influenced the crustal stress regime is plausible; however, its effect on volcanic activity is likely negligible, as both the regional stress field and local magmatic–tectonic conditions are the dominant factors. The observed uplift rates in the Eifel region are best explained as a combination of the current stress field (Hinzen, 2003, Tectonophysics 377) and mantle dynamics.
Citation: https://doi.org/10.5194/sand-2025-2-CC7
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CC7: 'Reply on CC6', Ulrich Schreiber, 05 Oct 2025
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RC2: 'Comment on sand-2025-2', Gerhard Wörner, 16 Oct 2025
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Publisher’s note: a supplement was added to this comment on 21 October 2025.
Assessment of possible volcanic hazards in Germany with regard to repository site selection by Ulrich Schreiber and Gerhard Jentzsch
submitted to “Safety of Nuclear Waste Disposal”
Introductory Remarks
This manuscript provides a review-style aggregation of what is known about the history, distribution and style of volcanism in volcanic fields that were active during Quaternary times in Germany and the geophysical conditions and state of their mantle source regions. The motivation is to provide a scientific foundation for estimating volcanic hazards at potential sites within Germany for safe repository of spent radioactive waste.
This task is important and requires sound reasoning at the current state of the art of science (“aktueller Stand von Wissenschaft und Forschung”). Furthermore, the topic is of fundamental significance for any future political decisions of critical importance for safety in the realm of nuclear technology.
My own field of expertise includes magmatic petrology, geochemistry and volcanology with >40 years of research focus on, but not restricted to, magmatic activity in the Eifel region. I have more limited background on geophysical methods but I am familiar with interpretations of geophysical data with respect to mantle and magmatic processes. Therefore, my comments below refer mostly to aspects of volcanology, magmatic processes and regional geology.
The authors, in their introduction, describe the fundamental types of data and observations that are relevant to assess volcanic hazards (and partly risks) in general.
The focus of this study is on the two Quaternary volcanic fields (Eifel and Vogtland) and in this regard, the overall conclusions with respect to potential of renewed volcanic activity in these regions are reasonable but incomplete (see below).
In order to evaluate this manuscript for publication within the context of its title, motivation, and relation to safe disposal of nuclear waste defines, three main issues need to be considered:
- Is this manuscript at the current state of research and are the conclusions and recommendations with respect to volcanic risk and hazards for sites for safe disposal of radioactive wastes based on sound reasoning?
- Does this manuscript address and focus on all relevant scientific matters of importance for the overarching motivation?
- Are the authors qualified and respected in the research field(s) that are relevant for the research area, especially given the high stakes involved.
As a summary of my evaluation of this manuscript, and as argued in detail below, I feel that this manuscript fails with regard to all three accounts above and therefore should be rejected. In the political process of defining geological risks of future safe disposal of radioactive waste, the outcome of the review process for this manuscript needs to be considered with respect to the expert report on which this manuscript is based.
In the following, I am summarizing my critical comments with respect to the issues and questions raised above. For details and comments direct on the manuscript, please refer to the annotated PDF of the manuscript. These comments, will not be repeated again here.
- Current state of research and sound reasoning
As indicated by comments on the manuscript, and also by several “community comments“ of the interactive discussion of the manuscript, there are sections in the manuscript that lack proper citation and discussion of previously published work, some citations are irrelevant or misleading with respect to the original authors statements and conclusions. Lack of references and discussion of existing publish research concern the following topics (examples below). In addition, several lines of discussion of previously published research are either unsupported by published data (as would be expected in a review paper) or not sufficiently relevant for the overall focus and motivation of this manuscript.
- The geochronology of eruptions in the East- and West-Eifel volcanic fields, the magmatic evolution of the Laacher See magma reservoir. Regarding arguments based on geochronology, magma mass balance and size of the Laacher See crater result in erroneous calculations with respect to the emplacement of magma below the Laacher See volcano (see comments on annotated manuscript and community comments by A. Schmitt). Further, there is no evidence that the crater of the Laacher See volcano is anything like a simple (sag-) caldera, mass proportions of parent and evolved magmas are firmly established by trace element modelling in published literature, the depth, composition, volume and temporal evolution of the magma reservoir from which the phonolite magma erupted is well documented in the published literature. Given the erroneous magma recharge rates calculated be the authors (based on false or incomplete reference to published geochronological data) and with respect to the unknown spatial arrangement of magma reservoir(s) below the Laacher See volcano, all arguments regarding the relation between size and magma volume put forward in this manuscript are mute. The simple observation of the composition and volume of erupted magmas require that a magma system of the reported volume must exist, even though we know little about the emplacement processes. I agree, however, that a better reconstruction and understanding of the transcrustal magma system below the Laacher See volcano would be an important topic for future research.
- Consideration of and reference to the cause, timing, and consequence of crustal deformation and current crustal uplift, in particular with respect to (i) inducing stresses with consequences for (new?) passways for magma ascent, (ii) melting in the underlying mantle, and (iii) style of deformation (see also comment by Reicherter). I agree with the authors that glacial isostatic adjustment (GIA) and related post glacial rebound will not have any significant effect and increase partial melting region below the Quaternary volcanic fields. However, this topic deserves a much more up-to-date and informed discussion.
- I am not a structural geologist and I do not know the geological sites and evidence put forward here with respect to the relations between the (a) the crustal structure, tectonic lineaments, stress and strain and (b) the formation of crustal magma reservoirs. I can only observe that none of these observations and ideas have ever been subject of previous publications by other authors and experts in structural geology. Given that the geological structure of the Rhenish Schield has been studied by a multitude of structural geologists, this is reason for doubting the authors proposed models for magma emplacement. Within this context, I observe that the authors arguments are put forward here in this manuscript for a review-publication the first time. This indicates, that none of these proposed observations and interpretations have passed prior scrutinization by structural geology experts as part of a review process.
- Defining a “safe” distance from volcanic risk is an issue of major concern for the research topic. In general, as stated elsewhere in my review, I agree with the overall conclusions of the authors with respect to the areas in Germany where eruptions are expected to occur within the next 1 Ma. In detail, however, the recommendations are partially flawed. One example is the section in the manuscript where the eastern margin of risk from a Laacher See – style eruption is discussed. This requires to define a ”safety-buffer”. The details of this definition are highly questionable and the 55 km limit is highly questionabel in regard to the potential effects of tephra fall out. Given the thickness of Laacher See tephra deposits at 55 km (100 cm observed) and then at 65 km distance (ca. 80 cm as calculated from models similar to those discussed in Daggitt et al, 2014). Deposits even much further away from source still are observed to be at ca. >75 cm. Why should that 100 cm of Tephra deposit a hazard and a tephra layer of 80 cm (10 km further from source) irrelevant for „disruptions“ that would be more manageable? While this consideration makes the area of risk from a Laacher See-type eruption in the future 1 Ma very much smaller, but this reasoning makes no sense to me. In addition to this, the geographical distribution of tephra from the past Laacher See eruption (and thus the area of risk) is just one of many scenarios which depend on the actual direction of atmospheric winds at the time of eruption which, as we certainly must take into account, could be in any direction out from the Eifel volcanic field. Changing atmospheric conditions were identified by the authors to impact hazard assessment of tephra deposits. However, in their hazard analysis, this has not been considered and the assumption that any future tephra deposition from a Laacher See-type eruption in the Eifel would follow the exact same pattern of atmospheric distribution is not a reasonable assumption. In the absence of any tephra dispersal models to reconstruct the tephra distribution across Germany and an assessment of other atmospheric conditions (compared to those during the eruption of Laacher See volcano 13.000 years ago, the evaluation of future risk and hazard of tephra deposition from renewed Laacher See – style eruptions is incomplete.
- The above considerations require that the authors of a review article of volcanic risk across Germany need to evaluate current state of tephra dispersion data, as compiled on the highly useful TephraBase website with relevant data found here: https://www.tephrabase.org/cgi-bin/tlay_1.pl. TephraBase is not mentioned in this study.
- A rather critical topic for consideration in the context of this review is the statistical estimation of the probability of future eruptions in the Quaternary volcanic fields in Germany (Eifel and Vogtland). This has in fact been attempted at various levels of confidence by Ritter et al (2025) and Jaquet et al (2000). These studies are not considered.
- Focus and topics of importance for the overarching motivation
Yes, most research results compiled in this review-article contribute to an understanding of magmatic and volcanic activity in the Quaternary volcanic regions in Germany. However, there are also details and additional issues treated here, that may be of local interest but do not contribute to the motivation and scope related to potential future activity and volcanic risks.
This manuscript is only concerned with volcanic regions in Germany that were active during the past 1 million years. Obviously, this is a reasonable first order approach and the most significant issue to be considered. At a first glance, any geologist knowing the geological map of Germany could have drawn reasonable (and similar) boundaries around regions were recent (< 1 Ma) volcanic activity occurred and therefore, where future eruptions are to be expected with considerable probability within the next 1 Ma. The present authors provide such a valid assessment (with some critical aspects as detailed above).
On the other hand, for risk evaluation for all of Germany (which is and must be the motivation given the title and relevance of this study), this implies that there would be no other region that could possibly volcanically active and therefore would not pose any volcanic risk during the next 1 million years.
In order to address this issue, and possibly exclude and volcanic risks outside the “safety zone around the two Quaternary volcanic fields, the authors should have compiled all available geochronological data for volcanic rocks and eruptive events in Germany during Cenozoic times. Existing age compilations (for a recent one see Binder et al, 2022) indicate that volcanism has been active at time scales of several millions of years in many regions in Germany, some with rejuvenation after extended or shorter periods of times (e.g. Eifel), others have developed in areas where previously no volcanic activity has been recorded in the geological. Therefore, at timescales of consideration for this manuscript (+ 1 Ma to - 1 Ma) and the purpose of estimating volcanic risks, past volcanic activity in Germany must be considered at much larger temporal and spatial scales (than just Eifel and Vogtland). This would have to involve a careful consideration of published age data, their uncertainties and a discussion of temporal evolution of Cenozoic volcanic activity in Germany based – at least – on a probability-density distribution of known ages.
Again, while an assessment of future volcanic eruptions in the known Quaternary volcanic fields is an essential first step, the history and distribution of past volcanic activity during Cenozoic times all over central and southern Germany needs to be included into such a report. Existing data indicate that the probability of a future eruption in these areas is presently unknown but certainly not zero.
In fact, this same issue has been raised by a “Community comment in the interactive discussion” on the manuscript (L. Viereck).
With respect to the question of whether all relevant research questions are considered and fully discussed, my answer is “no”.
Further, some topics that were discussed here are superfluous, some are even irrelevant to the research question and motivation of this study. For example, the discussion on the relation between the size of the Laacher See crater (note, it is NOT a simple sag-down caldera) and the discussion about the erupted magma volume (and volume of parent basanite magmas) based on crater volume appears (at least to me) irrelevant to the overarching research question. Rather, it is the actually documented erupted volume and dispersal of tephra that is relevant here.
Concluding remarks
The comments in this review are in no way complete and, obviously, comprehensive. I have not commented on many other aspects (and critical issues) on the full range of topics treated in this review. Rather, I concentrated on the most problematical aspects which alone already provide sufficient arguments for me and a final evaluation whether or not this manuscript should be published. Any further remarks could only be additional but would be no more decisive.
I have further observed the various “community comments“ and interactive discussion of the manuscript and found all critical remarks quite useful, in particular the detailed critical analysis by A. Schmitt. These highlight, some in much more detail, critical issues with this publication, how previous research is neglected or falsely interpreted and where reference to published work has been ignored. In fact, her has provided a detailed list of relevant literature references that clearly drive this point home and there is no need to repeat this list here. Comments by Reicherter and Klügel also document the lack of reference to previous work, which cannot be accepted in a review-style publication.
Given these community comments have already pointed out many (other) critical issues similar and additional to mine, I will not repeat or dwell on these here in my review.
I found the rebuttals by Schreiber in part worth consideration, but the major problems of this manuscript could not be discussed away by this author.
The relevance, consequences as well as potential effects and impact of a science-based scrutiny of geological risks and hazards for sites of safe disposal of nuclear waste require, in my mind, that the authors of any publication or expert report on related topics are credible and trustworthy. The first author has a history of appearing in the media via books, films, commentaries, that repeatedly resulted in flashy reports. There is nothing wrong for a scientist to interact with media. However, given the relevance of the topic of the expert report and this manuscript, an evaluation of the author’s scientific standing, accomplishment in the research field, and integrity are also essential.
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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/s00410-020-01710-3
Lines 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.