AK-NERO: Working Group Nerochytic Speleogenesis

Nerochytic Speleogenesis as a new concept for karstification

The hypothesis

The working group nerochytic speleogenesis (short: AK NERO) is dedicating research efforts to a hypothesis which we believe is highly relevant for the understanding of karstification. The core of the hypothesis is that CO2 in karst is not only in a passive transport with the flowing water (Bögli, Dreybrodt, Klimtschuk), but it has in addition to that a mobility and dynamics of its own (thus NERO from greek nerochytis/sink). This inherent mobility in vertical direction is coupled to the cave ventilation in summer times in the vadose zone. At the karst water interface, the CO2 dissolves enhanced by convection which is induced by an increased density of the water.

This karst water, “inoculated” with additional CO2, contributes to new subsurface flow paths with their typical round-shaped, phreatic shapes at cave walls as they can be found in many fossile caves.

The location

The Swabian Alb belongs to the so-called green karst. A soil layer produces CO2, the vadose zone is up to 200 m thick. More than 2.500 caves are known. A number of karstic springs have their sources in in caves at the edges of this low mountain range. The karstification is still ongoing. The underground is mainly massive compact limestone. The history of rivers and landscape allows rough estimates on the history of karstification.

How the thesis came up

Exploring caves and the experience of visiting caves is popular since the late 18th century. The members of cave clubs and associations were citizens with interests in caves and speleogenesis, but also archaeology, geology, or hydrology.

The discovery of huge cave halls by Jochen Hasenmayer in the Blautopf underwater cave in 1985 has revealed a presumed or real contradiction between karstification processes and the ages of caves. This discussion amongst scientists and citizens is since then followed by an interested public. Arguments are exchanged, observations are shared or rejected.

The aspect NERO with mobile CO2 originated from a flash of inspiration during a discussion among cavers in October 2013.

State of the work and planned activities

Preliminary work has been done in the laboratory, by means of numerical simulation models, as well as in caves on the Swabian Alb. This indicates that the hypothesis can be plausible. Many questions are open, and we want to address them in the future. In order to increase the attention for the topic in the karst community, it is now important to open up research fundings, to generate measurement data and to interpret them with appropriate models, to publish, to be present at conferences and workshops.

The AK NERO is so far an informal association of scientists and cavers (or cave researchers), welcome are also interested citizens.

Please, contact us if you like to get regular updates or if you want to participate actively. You can be part of AK NERO even without your name mentioned below.



  • Harald Scherzer, Höhlen- und Heimatverein Laichingen
  • Holger Class, University of Stuttgart
  • Andreas Länge, Arge Grabenstetten
  • Wieland Scheuerle, Arge Grabenstetten
  • Bettina Strauch, German research centre for geosciences, Potsdam
  • Oliver Trötschler, University of Stuttgart
  • Wolfgang Ufrecht, City of Stuttgart/ Höhlen- und Heimatverein Laichingen
  • Kilian Weishaupt, Universität Stuttgart
  • Johann Westhauser
  • Martin Zimmer, German research centre for geosciences, Potsdam
  • UNESCO Geopark Schwäbische Alb


as well as a number of student theses supervised by Holger Class, Kilian Weishaupt, and Oliver Trötschler


Contributions to conferences and workshops

  • Class H.; Weishaupt K.; Trötschler O.; Scherzer H.: Density-induced CO2 dissolution – approaches to test a new hypothesis on a process relevant for epigenetic karstification, EGU General Assembly 2020, 4-8 May 2020.

  • Scherzer H.; Class H.: Nerochytische Speläogenese, Übergang von CO2 aus Höhlenluft (vadose Zone) in Karstwasser (phreatische Zone). Stand der Forschung 2019, 10. Symposium Verkarstung in Süddeutschland, 23. November 2019, Laichingen.

  • Scherzer H.; Class H.: Mobilität von CO2 in der phreatischen Zone des bedeckten Karstes – eine Abschätzung zur Bedeutung für die Höhlenentstehung. Inspiriert aus Beobachtungen in Höhlen der Schwäbischen Alb. Tagung des Verbands der deutschen Höhlen- und Karstforscher (VDHK), 15.-18. Juni 2017, Laichingen.


This image shows Holger Class
apl. Prof. Dr.-Ing.

Holger Class

Akademischer Oberrat

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