Karst terrains, sinkholes
Karst is a process and a type of topography formed from the dissolution of soluble rocks (limestones, chalks, gypsum, salts, dolomites) by underground (and surface) waters. There are two main types of karst: surface and subsurface. Surface (visible) karst includes characteristic features like sinkholes, depressions, dolines, poljes, swallow holes, ponors, and dry and blind valleys. Sinkholes are the most characteristic landforms of karst topography. Other types of landforms such as karren, clints and grikes are typical for barren karst (holokarst).
Subsurface (subterranean) karst is represented by caves. Meantime, in karst areas there are many underground voids and channels cannot be entered as they have no entrances. Many caves consist of multiple levels of passages that extend horizontally as much as 3-5 km and vertically as much as 80-90 m. Some of voids and galleries are located within the vadose zone, storing the water or re-directing it to the underground basins. Rarely, voids may open to the surface, cause catastrophic damage of properties and infrastructure.
Overall, 340 to 380 million people in Europe, United States, Asia (China, Indonesia, Vietnam, Malaysia, Thailand), Brazil, Caribbean islands, Australia as well as significant amount of infrastructure are exposed to karst processes. These processes pose a complex set of engineering, land use, and environmental problems. Site selection and construction in karst areas require a detail studies and comprehensive work plans to manage sinkholes and caves. But the most complex and problem that has to be studied is the detection and locating of underground voids.
The major karst-prone countries and regions in Europe: Slovenia; Bosnia and Herzegovina; Croatia; Switzerland; Ireland; Limestone Alps and Styria in Austria; French Prealps (Préalpes); Wallonia in Belgium; Emilia-Romagna, Sicily and Apulia in Italy; Almeria and Garraf in Spain; Podillya in Ukraine; Sussex, Yorkshire, Hertfordshire, and Isle of Wight in England.
The major karst (sinkhole) prone states in the United States are Florida, Alabama, Missouri, Kentucky, Indiana, Texas, Arkansas, Oklahoma, Tennessee, West Virginia.
Karst topography and water regime are very dynamic and may lead to the following processes:
- sinkhole development and collapse (the most karst-related hazard)
- earth subsidence (another common phenomena; diameters of depressions can reach several hundred meters)
- sinkhole flooding
- cave roof collapse
- collapse of carbonate cliffs, caves and other coastal landforms
- rockfalls caused by open karst fracture and dissolution (although limestone slopes are considered to be stable, localized failures in fractured and weathered zones do occur)
- failure of industrial facilities, quarries and retention ponds (including bauxite and potash mining and processing facilities)
- strong oscillation in the water-table levels, increasing and decreasing of spring output
- surface water level changes — lake drying, or flooding of the normally dry valleys and depressions
- sea water intrusion along the seashore consisting of limestones, chalks or dolomites.
Zesmill carries out surveys and takes part in national and international programs in karst areas both in developed and developing countries. We employ methods based on the latest researches in karst geology, geomorphology, karst hydrogeology, geophysics, remote sensing, and GIS.
Geology
Lithology and speleogenesis studies; structural and tectonic analysis; fault assessment and fracturing analysis; geological and environmental related drilling services (including cave roof drilling out).
Geomorphology
Clear definition of present and ancient sinkholes, dolines, poljes, ponors; identification and mapping of the karst landforms and their changes over time; morphometric analysis of digital elevation models; piping karst / suffusion karst assessment.
Geophysics
Electric resistivity surveys over sinkholes, dray and water saturated voids (although ambiguities in the electrical resistivity signature of karst features happen, this method resistivity remains the most effective); low frequency (VLF) surveys.
Zesmill collaborates with companies and academic institutions that provide micro-gravity surveys; self or spontaneous potential prospecting; geo-electrical tomography. Among them are ISCA and Politecnico di Milano.
Hydrology
Measurement of fresh and mineral springs flow; hydrochemical observations; defining the karst catchments (karst contributory areas); watershed mapping.
Remote sensing
Interpretation of multi-temporal, multi-spectral satellite and aerial imagery, and SAR images; Digital Elevation Models (DEM) generation; submarine karst spring detection using infrared imagery.
Cartography and GIS
Maps of karst areas; 3D models; maps of sinkhole distribution, density, and typology; karst regionalization.