Acta Carsologica

Groundwater dilution and flow conditions in sulfuric acid caves: the case study of Frasassi (Italy)

Sandro Galdenzi — Wed, 13 Dec 2023 00:00:00 +0100

This study analyzes the dilution process of the sulfidic groundwater in the Frasassi caves due to the recharge of O₂-rich freshwater and its influence on the sulfuric acid speleogenesis and morphogenesis. The drainage pattern and the seasonal changes of the chemo-physical characteristics of the groundwater through a year-long monitoring and the measurements of the groundwater levels are presented. The inflow of water infiltrating from the karst surface influenced the sulfidic groundwater parameters, reflecting the seasonal meteoric cycle. On the contrary, the Sentino River, which represents the local base level, directly influenced the groundwater only in the most external part of the cave. The water level measurements evidenced a low hydraulic gradient (~3‰), due to the high karstification, and also some differences in the permeability depending on the drainage direction. Most cave pools are isolated on the surface and connected to each other through a network of submerged passages. In the present conditions, a surface layer of bicarbonate water forms above the sulfidic water in a large part of the cave, where it impedes subaerial corrosion by released acidic gases. Conversely, the distribution of residual gypsum deposits and corrosional wall features in the upper old cave levels demonstrate that large interfaces between sulfidic water and cave atmosphere existed during some periods of the cave history. Here, the release of acidic gases (CO₂ and H₂S) and the production of H₂SO₄ from H₂S oxidation caused the widespread subaerial corrosion which significantly contributed to the morphogenesis. The comparison between these residual morphologies and the active processes shows that morphogenesis in the cave has evolved through time, influenced by hydrodynamic conditions, in turn depending on the general morphological and hydrogeological setting of the whole karst area.

Karst Rock Relief of Qara and White Desert (Western Desert of Egypt)

Martin Knez, Tadej Slabe, Magdy Torab, Noura Fayad — Wed, 13 Dec 2023 00:00:00 +0100

The karst rock relief clearly reveals the ways in which the karst surface and caves have been shaped and how they have developed. The oldest traces are the rock features of old karst caves, which were formed under climate conditions entirely different from the current ones, i.e., in the Pleistocene, and which have been dry for a longer period of time. Today, the wind is the prevailing factor in shaping the rock on the surface and in the karst of the White Desert near Farafra in particular, where we can witness the development of an entire range of wind rock features which helps us sort and classify them logically. However, in the wadis near the Qara Oasis a unique rock relief is forming, in which traces of water flow and dissolution of the rock under the sandy deposits are utterly predominant. The rainfall volume is low, however, the heavy rainfall events lasting short periods of time are enough to shape the less resistant rock. The rock features dominating the walls are co-shaped by dissolution and aeolian erosion. Crust forms on those parts of the rock surface that come in contact with water. The bare surfaces, on the other hand, are carved out by the wind. In the places where the crust has flaked off, the wind carves out cups.

Geomorphological units in Arcos-pains karst region, Minas gerais, Brazil

Mariana Barbosa Timo, Luiz Travassos — Wed, 13 Dec 2023 00:00:00 +0100

The Arcos-Pains Karst Region is approximately 850 km2, formed by massive carbonate rocks that host hundreds of caves, rock shelters and shafts. Many fossil discoveries exist in the region; one can also find rock paintings and other archaeological remains. A ruiniform landscape, weathered caves and continuous or isolated outcrops characterize the karst. They are cut by diaclasis, fractures and fissures, separated by flattened relief with dolines, uvalas, ponors and blind valleys. The evolution of karst morphology in the region reflects pluviometric and paleoclimatic variations, with faults and fractures from neotectonics events exerting control over water flows. One can observe four geomorphological compartments in this region, each with specific characteristics. The region is an outstanding example of the Brazilian intertropical karst and one of the most important Brazilian mineral deposits of limestone and dolomite. So, delimitating its geomorphological units can facilitate understanding the speleological heritage and guide strategic decisions for sustainable use.

Unraveling the functioning of the vadose zone in alpine karst aquifers: New insights from a tracer test in the Migovec cave system (Julian alps, NW Slovenia)

Wed, 13 Dec 2023 00:00:00 +0100

The aquifers of alpine karst and high karst plateaus are abundant water resources. They are difficult to characterise due to their complex, partly glaciokarstic, evolution in active tectonic environments, and an unsaturated zone up to two kilometres thick. We present and discuss the results of a tracing test in the alpine karst of the Julian Alps (Slovenia), more precisely in the Migovec System, the longest cave system in Slovenia (length = 43 km, depth = 972 m). The cave extends below a mountain ridge that separates the Soča and Sava Valleys, thus forming a topographic divide between the Adriatic and Black Sea basins, which gives the test greater regional significance. In early September 2019, three kilograms of uranine were injected into a perched lake in a remote part of the system, approximately 900 metres below the plateau and 100 metres above the low water table. All known springs in the valleys on either side of the mountain were monitored by manual or instrumental sampling and a field fluorometer. Due to the unexpectedly dry season, no tracer was detected at any site for two months until a heavy rainfall event in early November. Subsequently, about 60-65 % of the tracer mass appeared within 60 hours in the Tolminka River. No tracer was detected at other sites, either because
it was not present or because it was highly diluted. The study suggests that the lake containing the tracer is bypassed by the vadose flow and that the tracer was only mobilised during large events when the lake became part of the epihreatic flow. The linear peak flow velocity from the injection site to the Tolminka Spring was only about 1.7 m/h. However, assuming that the tracer was only mobilised by the large rain event, the velocity would be 70 m/h. The study highlights the challenges and pitfalls of water tracing in alpine karst systems and suggests ways to avoid them.

The vertical electrical sounding (VES) of the epikarst: A case study of the covered karst of the Bakony region (Hungary)

Veress Márton, György Deák, Zoltán Mitre — Wed, 13 Dec 2023 00:00:00 +0100

The epikarsts of five covered karst areas in the Bakony region are compared. The comparison is based on the specific resistances of the bedrock resistance averages measured by vertical electrical sounding (VES). The average largest specific resistance differences (per area) and the mean values (per profile) were calculated to investigate the characteristics of the epikarst. The mean values of specific resistance were compared using analysis of variance (ANOVA) to determine whether the specific resistances of the areas showed significant differences. The studied karst areas can be categorised as high or low specific resistance areas, and the ANOVA method could be applied to three areas based on the available data. It can be concluded that the mean values of their specific resistances are significantly different. The mean values and standard deviation of the specific resistances of the different areas were analysed. It is described that the karst receives less water in the case of areas with lower specific resistance, while it receives more water in the case of areas with higher specific resistance. Areas with a high specific resistance are less karstified, while areas with a low specific resistance are more karstified. Low specific resistances and small mean values indicate a higher degree of cavity formation in the epikarst, while the decrease in mean values and standard deviation indicates increasing uniformity of the degree of cavity formation in the epikarst. The different degree of cavity formation is explained by the different karstification rates and the exposure of different time of certain areas.

Integrated geomorphological analysis of a Mediterranean temporary pond priority habitat: the Lago del Capraro doline (Salento peninsula, Italy)

Francesco Gianfreda, Sergui Negri, Paolo Sansò — Wed, 13 Dec 2023 00:00:00 +0100

The Lago del Capraro doline (Salento peninsula, southern Italy), a valuable Mediterranean Temporary Pond (MTP), has been investigated aiming to define its geomorphological features and to collect data about the local hydraulic regime. At the bottom of the Lago del Capraro doline, in fact, a small temporary pond appears soon after major precipitation events as that one of autumn 2013. The morphological survey shows that this solution doline is placed on a karst plain surface stretching at about 70 m of altitude; the doline has an elliptical shape with the major axis 130 m long whereas the length of the minor axis is about 100 m. It shows a flat bottom, placed at about 65 m above m.s.l., due to the presence of a colluvial sandy clays filling, bordered by steep limestone slopes about 5 m high. Geophysical surveys and a cone dynamic penetrometer test allowed a detailed geological model to be realized. In particular, ERT and seismic refraction models revealed the geometry and the thickness of doline filling deposits as well as the preferential infiltration zones of surface waters. Interestingly, the cone penetrometer test reveals that resistance decreases downward in the filling lower part, most likely because of the active solution process at the doline bottom. The results of this study suggest an increase of surface water infiltration at doline bottom in the next future so that the development of a pond will be an increasingly rare event, partly compensated by the clustering of rainy periods during autumn months as expected in the future by climate models.

Contrasting Approaches to the Study of Subterranean Life: Biospeleology and Speleobiology

David C. Culver, Tanja Pipan — Wed, 13 Dec 2023 00:00:00 +0100

The study of subterranean life in general and cave life in particular has been given several names, most especially biospeleology and speleobiology. Historically, biospeleology came first, and signalled that biological study was part of speleology, the science of caves. Speleology itself has come to have several meanings beyond the science of caves, but as a discipline it has not fully developed. Speleobiology emphasizes the connection with biology, especially ecology and evolutionary biology. Biospeleology can be construed as the taxonomic and distributional aspects of the biology of caves while speleobiology can be construed as the aspects pertaining to general biological principles such as evolution.

New locality of Proteus anguinus in the area of the Tabor Ridge near Grosuplje, Central Slovenia

Nataša Ravbar, Damjan Viršek, Magdalena Năpăruş-Aljančič — Wed, 13 Dec 2023 00:00:00 +0100