Natural carbon dioxide emissions as mofettes in Slovenia

Natural CO2 springs and mineral water springs are frequent only in north-east Slovenia. They occur mainly in the alluvial valleys of the Slovenske gorice hills area, at elevation between 200 and 300 m a.s.l. but their number is not unified. The attempts to perform their systematic overview were done in 2016 when elaborating the Geological Atlas of Slovenia (many of its maps are freely available at portal eGeologija:

The last extensive fieldwork was performed in 2014–2015 (Gabor & Rman, 2016) when we investigated 11 springs. We were able to distinguish among mofettes and mineral waters. Two were classified as wet mofettes (Polička slatina and Slepice) and three as dry mofettes (Rihtarovci, Strmec, mofette at Lokavska slatina). These constantly emit cold CO2, hold acid surface or meteoric water, and bare soil or changed vegetation may also be present. Mineral water consisting of more than 1 g/l of total dissolved solids outflows at Ihovska, Ivanjševska and Radvenska slatina, and Žekš. It is rich in free CO2 and has a strong free gas flux. Two, Verjanska slatina and Ujterska slatina, were neither mofettes nor mineral waters. The first, like most others, may be a »slatina« (=soda spring), having more than 250 mg/l of free CO2. We found no connection between the depth of the springs and the intensity of gas emissions.

Up to now, the research has shown that several sites between towns Lenart-Benedikt-Radenci-Nuskova have lots of geogene gas. It is predominately very pure CO2, but methane may also be present locally. The isotope signatures of gases indicate an origin of helium and CO2 predominantly (>75%) in the subcontinental mantle. The measured 3He/4He ratios range from 4.62 to 5.97 Ra and include the highest ones recorded in the whole Pannonian Basin system, while the gaseous δ13C is between -5.1 to -3.5 ‰.

In May 2019, a new opportunity for field work occurred. Geomanifestations are being investigated within the GeoConnect³d project, and the topic coincided with investigation of the Dipartimento di fisica e geologia (UniPer) of University of Perugia on carbon degassing of the Balkans as part of a Deep Carbon Observatory project, “Improving the estimation of the tectonic carbon flux”. Therefore, dr. N. Rman, dr. A. Ionescu and C. Pop jointly visited some of most interesting sites in Slovenia. We took water samples, dissolved and free gas samples, which will be analysed in laboratories in Hungary, Italy and Romania, as well as measured the free gas flux at several mofette locations.

Already in the field, we have had new surprises. As it was a rather rainy May in Slovenia, both, before and during the sampling, emitting gas bubbles could easily be observed at flooding water on the ground. Based on this »method« we have found new diffuse gas emissions at two sites – at mofettes Žekš near Benedikt and Polička slatina near the Ščavnica River valley.

Some of the photographs below show our most interesting features.

Dr. Nina Rman
GeoZS – Geološki zavod Slovenije / Geological Survey of Slovenia


Gabor, L., Rman, N. 2016: Mofettes in Slovenske gorice, Slovenia. Geologija 59/2, 155-177. DOI: 10.5474/geologija.2016.009

Brauer, K., Geissler, W., Kampf, H., Niedermann, S., Rman, N., 2016. Helium and carbon isotope signatures of gas exhalations in the westernmost Pannonian Basin (SE Austria/ NE Slovenia): evidence for active litospheric mantle degassing. Chem. Geol. 422, 60–70.

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