Stanka Šebela

Evidence of a plate-wide tectonic pressure pulse provided by extensometric monitoring in the Balkan Mountains (Bulgaria)

Abstract The EU-TecNet monitoring network uses customized three-dimensional extensometers to record transient deformations across individual faults. This paper presents the first results from two newly established monitoring points in the Balkan Mountains in Bulgaria. The data from Saeva Dupka, recorded across an EEN-WWS striking fault, show sinistral strike-slip along the fault and subsidence of the southern block. Much of the subsidence occurred around the time of the distal MW = 5.6 Pernik Earthquake. An important transient deformation event, which began in autumn 2012, was reflected by significant compression and following extension, across the monitored fault. The data from Bacho Kiro, recorded across a NE–SW striking fault, show sinistral strike-slip along the fault and subsidence of the north-western block. The same important deformation event was reflected by changes in the strike-slip, dip-slip, and horizontal opening/closing trends. These results have been compared to data from other monitoring points in the Western Carpathians, External Dinarides, and Tian Shan. Many of the sites show evidence of simultaneous displacement anomalies and this observation is interpreted as a reflection of the plate-wide propagation of a tectonic pressure pulse towards the end of 2012.

Characterization of black deposits in karst caves, examples from Slovenia

Karst caves are important tourism and natural heritage destinations. Within dry cave passages otherwise notable for their rich flowstone decoration, areas with a characteristic black color can sometimes be observed on cave walls and floors and on speleothems. To determine the origin of these black deposits, mineralogical and chemical analyses were carried out in two caves (Postojna Cave and Črna Jama (Kočevje), Slovenia). Qualitative chemical composition was obtained by scanning electron microscopy in conjunction with energy dispersive X-ray spectrometry (SEM/EDS). Organic matter in black deposits was confirmed by the Walkley–Black (wet burning) and loss-on-ignition (LOI, dry burning) methods. Results showed that black deposits from the caves studied could be attributed to natural and anthropogenic causes. Natural causes are related to Mn–Fe oxide precipitation and are probably dependent on microorganism activity. Anthropogenic sources are related to historic (or/and prehistoric) human activities such as cave visitors using torches and fires, events outside the caves such as forest and settlement fires, and recent air pollution. Black deposits show the effect of long-term environmental impact on karst caves and could be included in guided tours of show caves along with a scientific explanation of their causes and origin.

Analyzing climate change and surface-subsurface interactions using the Postojna Planina Cave System (Slovenia) as a model system

Worldwide, there are at least 12 ILTER sites with an emphasis on karst, landforms arising from the combination of high rock solubility and well-developed solutional channel porosity underground, but the study of cave ecosystems has been largely neglected. Only two ILTER sites, both in Slovenia, are primarily caves. Caves are under-represented for several reasons, but especially because of the overall difficulty of access and the lack of a clear research agenda for cave ecosystem studies. We review several aspects of long-term studies in Postojna Planina Cave System (PPCS), proposing our approach as a model for ILTER research in caves. In PPCS, analysis of short-term temperature data shows a muted daily cycle and seasonality, and analysis of long-term temperature data shows an increase, largely the result of climate change. Changes in drip rate of epikarst aquifers above the cave are correlated with rainfall but with lags and complications resulting from differences in longer term rainfall patterns. Analysis of discharge rates indicates a rapid response to precipitation not only in the Pivka River at its sinking, but also at Unica Spring, where discharge is augmented from other parts of the aquifer, including epikarst. Quantitative analysis of the obligate epikarst-dwelling copepod community shows that, unlike most cave communities, complete sampling of the fauna is possible. Finally, organic carbon levels in PPCS indicate likely carbon limitation in the system. These five factors (temperature, drip rate, river discharge, epikarst copepod fauna, and organic carbon) are the appropriate variables for capturing the essential long-term trends in cave ecosystems and their causes.

Impact of Motorways on Karst Waters

Impervious surfaces of road networks accumulate contaminants and pollutants, which are washed off during rain and snowstorm events into nearby waters and lands. Especially in areas with a developed traffic network, runoff from motorways is a significant source of pollution. Various protection and remediation measures were developed and implemented for preventing or at least diminishing its negative influences. Three major sources of pollution are associated with the road network: vehicles (emissions of motor vehicles, spilled and released oil, tires’ particles, de-icing agents), road characteristics and paint markers, and atmospheric depositions influenced by the adjacent land use. Besides pollutants directly associated with traffic, the impermeable surfaces can collect and drain a negligible quantity of organic waste, nitrogen and phosphorous, herbicides, pesticides and faecal pathogens. Soil infiltration treatment, building of collection basins and constructed wetlands are used as protection and remediation measures. In karst areas, motorway runoff has an amplified impact on ground water, compared to other types of landscapes. The soil layer is commonly thin or non-existent and thus soil infiltration treatment is practically inexistent. Stormwater runoff may immediately flow into the aquifer through subsurface conduit networks, fractures, sinkholes and sinking streams, which makes karst groundwater especially vulnerable to pollution. Accidents that cause greater quantities of hazardous substances to flow into the karst, for whatever reason, endanger our environment, karst waters, and even in smaller quantities also the quality of the karst springs that have been captured for drinking water supply. Especially dangerous are spills of oil derivatives, since we know too little about the flow of such substances that do not dissolve in water and are lighter than it. Based on observations of Globocec spring following the accident near Ortnek and of the Rižana Spring following the spillage near Obrov and other similar cases, we anticipate a longer retention time and washing away of oil derivatives due to the possibility of adsorption on sediments and retention in siphons.

Application of Scanning Electron Microscopy/Energy-Dispersive X-Ray Spectroscopy for Characterization of Detrital Minerals in Karst Cave Speleothems

Micro-scale observations in karst caves help to identify different processes that shaped local morphology. Scanning electron microscopy/energy-dispersive X-ray spectroscopy inspection of speleothems from two karst caves in Slovenia, Predjama and Črna Jama, confirmed the presence of sub-angular to sub-rounded detrital fragments of clay minerals, feldspars, quartz, Fe-oxides/hydroxides, rutile and Nb-rutile, xenotime, kassite, allanite, fluorapatite, epidote, ilmenite, monazite, sphene, and zircon, between 2 and 50 μm across. These occur in porous layers separating calcite laminae in the clayey coating on the layer below the surface of the speleothems, and are also incorporated within actual crystals. It is likely that they are derived from the weathered rocks of the Eocene flysch. Probably they were first transported into the caves by floodwaters forming cave sediments. Later, depending upon the climate conditions, they were moved by air currents or by water to the surface of active speleothems. They might also be redeposited from overlying soils enriched with wind-transported minerals from the flysch, or from higher passages filled with weathered flysch sediment, by drip water percolating through the fissured limestone. As some of the identified minerals are carriers of rare earth elements, Ti and Zr, their presence could affect any palaeoclimatic interpretations that are based upon the geochemical composition of the speleothems.

Caves and Hydrology of the Contact Karst of Beka and Ocizla

The Beka-Ocizla cave system extends at the contact between Palaeocene limestone and Eocene flysch at an altitude of 350 m in a shallow depression called Loke. Six known caves are connected to this cave system: Ocizeljska jama (Ocizla cave), Blažev spodmol (Blaž’s rock shelter), Maletova jama s slapom (Maletova jama cave with waterfall), Jama z naravnim mostom (Cave with the natural bridge), Jurjeva jama v Lokah (Jurjeva jama cave in Loke) and S-4/Socerb. Three larger streams and a smaller one flow into the depression from flysch and sink into marly limestone. Together, they drain the flysch surface of approximately 3.5 km2. Some of the cave entrances function as periodic sinks of the surface waters that flow in from beneath the villages of Beka, Ocizla and Petrinje. The water from the entire cave system flows towards the Boljunec spring. Hydrological observations conducted in the cave include mapping of traces of the past flood events and continuous monitoring of the water level and temperature at five different locations in the cave system. A few flood events happened in past years: an extreme flood event between 17 and 19 September 2010, and flood events between October 2012 and March 2013. Special hydrological conditions during these events are also described.

An evaluation of structural analyses of discontinuities in carbonate rock

The main goal of the study was to compare two methods of structural analysis, based on different principles: an engineering method and the Eraso method. The first one was developed with the intention of studying geotechnical and hydraulic properties on freshly exposed rock surfaces, while the second one is based on microtectonic analysis and is mainly applied on surface outcrops. Structural analysis of discontinuities in fractured and karstified rock at one experimental field site in Slovenia was performed. Measurements were carried out on surface outcrops and in an underground artificial tunnel, twice in two different seasons (autumn 1999 and summer 1996), but by the same personnel. Both methods were found to be more or less repeatable and applicable both on the surface outcrops (weathered rock) and on freshly excavated rock surfaces (artificial tunnels and quarries), and on a macroscale. The results have shown that we can infer from the macroscale data set to the (regional) mega-scale. Copyright

Periodical Measurements of VLF Radio Signals and Noise Sounds in Črna Jama (Postojnska Jama)

In Crna Jama, which is part of Postojnska Jama, underground measurement of VLF (Very Low Frequency) radio signals was periodically carried out in 2012 and 2013 for detection of possible pre-seismic and/or other anomalies and to ascertain suitability of VLF monitoring in a natural cave environment. The modulation of the VLF signal was connected with a powerful atmospheric front and changes of the precipitation level. VLF data showed day and night changes and also significant changes between dry and rainy periods when water from the surface reached the cave chamber through about 30 m of limestone roof. During VLF monitoring we did not receive earthquake precursor signals. VLF monitoring in a karst cave could be an option for future research in understanding pre-seismic and other anomalies. On-line connection with other VLF surface or cave monitoring sites in Europe is necessary in future VLF registration. Results of preliminary VLF monitoring showed Crna Jama to be a suitable place for future studies. Key words: VLF radio signals, noise sounds, pre-seismic anomalies, Crna Jama, Slovenia.

Unroofed Caves Provide Important Clues to the Karst Development

Unroofed caves are old caves that were revealed on account of the lowering of the karst surface. They are preserved by their infill—mostly alluvium and flowstone. It became clear during the motorway construction undertaking in Slovenia that unroofed caves constitute a relatively common karst landform. In fact, more common than karstologists had imagined before the karst surface was uncovered through earthworks. The various types of notches occurring on the surface have long been interpreted as types of dolines or as the result of the lithological properties of rock and its fracturing. 75 km long and, on average, 25 m wide stretch of the motorway across the classical Karst gave up 350 caves, of which 90 are unroofed caves. Some of them make up the same cave system. New findings prompted karstologists to become more aware of these unique surface karst forms. In the process, numerous unroofed caves filled with all types of alluvium were discovered. There were several attempts at typification of the characteristic shapes of unroofed caves and to design partial models to explain their typical formation processes. The surface and subcutaneous dissolution of carbonate rock and its disintegration from back in the Ice Age, brought about the lowering of the karst surface. Old caves, which were formed by erstwhile water flows and are partly intersected by shafts which drain water from the permeable karst surface, pop up as either empty or filled with alluvium. The caves were formed as a part of a system of cavities in a period when impermeable rocks had enclosed the aquifer higher up, causing the underground water in the aquifer to be at a higher level. The hypothesis was that the karst topography and its remarkable systems of valleys can be traced back to former surface water throughflow. However, revealing the surface did not provide the evidence to support this hypothesis, instead obvious signs of former water throughflow in carbonate rock were identified—manifested as open and cut through old caves.

Unroofed Caves Near Kozina and Their Identification

Unroofed caves are an important karst form that makes up a part of the karst surface and epikarst, and provides us with valuable evidence of the karst development. They are old caves that became exposed by the lowering of the karst surface. In fact they are preserved by their fill—mostly fine-grained alluvium. It is also often that they feature preserved flowstone and an intact rock rim. During earthworks preceding the motorway construction, this important karst feature, also characterizing the surface, attracted special attention. Earthworks revealed that the karst surface is scattered with several distinct types of unroofed caves, which in itself are not an uncommon phenomena. The typical shapes of unroofed caves found on karst terrain could be singled out, i.e. individual doline-like forms that occur in strings, and oblong notches. Because the surface of the Karst region has lowered so dramatically, there are old caves and shafts opening up all the time in the course of the construction of the motorways. Old caves are either void or filled with alluvium. The caves were formed as a part of a system of cavities in a period when impermeable rocks had enclosed the aquifer higher up, causing the ground water in the aquifer to be at a higher level. But karstification gave rise to a drop in the water table in the aquifer—today it is 200 m and more below ground, and the karst surface is still lowering. Unroofed caves are therefore regarded as distinct surface karst forms which were in part reshaped by surface processes that make up an important part of epikarst. In the course of the earthworks for the construction of the Kozina motorway, the typical shapes of unroofed caves, passages and large cave systems carved in horizontal or inclined karst surfaces were discovered.