Covered Karsts

The chapter presents the characteristics of karst, karst hydrology, mor‑phology and typology. In the hydrological overview, karst water zones are identified and described; surface karst features (karren, dolines, poljes, etc.) are defined broken down to their main varieties with their brief characterisation. The main genetic types of caves are presented. Karst types are identified according to their geological conditions (such as covering, structure), and then the types by hydrology and cover are described. In the classification by climatic environment, tundra, temperate, mediterranean, tropical and high-mountain (glacio)karst are identified and described.

This chapter presents the locations where investigations and observations were made. The following karst regions studied in detail are described: Aggtelek Karst, Asiago Plateau, Bakony Mountains, Bükk Mountains, Durmitor, Northern Limestone Alps, Madagascar, Mecsek Mountains and Pádis plateau. The areas from where observations derive are the Atacama Desert, Biokovo mountains, Cerkniško polje, Crimean Peninsula, Dolomites Iceland, Middle Lena, the Lunan area and Parajd.

This chapter presents the goals and descriptions of the investigations per‑formed and the description of the sites of field studies. Methods included morphometric analyses, study of bedrock structure for karst features, mapping (topographic, karst morphological, denudational), aerial imaging, preparation of cross-sections, oblique views and block diagrams. For the investigation of the cover, engine-driven helical borer, geophysical techniques were applied and exploration pits were excavated in order to establish its thickness, structure and type. Changes in karst landforms were measured (mass movements, changes of depth). At some localities the particle size, clay and carbonate contents of the cover were analysed. Model experiments were run to reveal interactions between grike development, subsidence doline formation, capillary rise, settling velocity and water level sinking as well as to collect data on the sedimentation properties of subsidence dolines.

Covered karsts are classified according to the character of the cover (cryptokarst if the cover is impermeable and concealed karst if it is permeable), to the origin of cover deposits (locally deposited or transported there) and to the age of karstification (syngenetic if the depression in the cover and the form in the bedrock are of the same age and postgenetic if not). Covered karsts may develop in structural landforms (synclines, tectonic graben, horsts of various elevations) and in depressions formed by the powers shaping the surface, which could be of karstic origin (doline, ponor, polje, fengcong depressions and intermountain plains of fenglin karst) or of non-karstic origin (valley, abrasional platform and river terrace). The appearance and pattern of covered karst depend on the type of karst. When characterising pattern geosyncline or glaciokarst (folded-nappe structure), block mountains, platform, salt diapir, tundra, taiga, temperate, mediterranean and tropical covered karsts are distinguished. The geosyncline (glaciokarst) and block mountains karst types mainly occur under temperate climate, while the platform and salt diapir may appear on any climatic karst type. According to pattern, covered karst developed from allogenic karst (which can be recent allogenic, rejuvenating allogenic or semi-allogenic), nappe allogenic, horst, cirque, glacial trough, polje, karst hill, cueasta, tropical depression, polygonal, intermountain plain, petrified forest, platform and salt diapir covered karsts are identified. On the recent allogenic karst, in slope direction from the bordering non-karstic surface, cryptokarst, mixed and open karst zones are found. On the rejuvenating allogenic karst, in slope direction from the former terrain of sediment supply, open, mixed and buried karst zones follow each other. On the semi-allogenic karst, in lack of the accumulation of fluvial deposits, the cover sediment does not derive from the non-karstic terrain bordering the karst and is of continuous distribution. On the nappe allogenic karst, buried karst, cryptokarst (with karst windows), concealed karst and open karst zones occur. On horst covered karst, on the neighbouring blocks, concealed, crypto and buried karst terrains alternate (in patches or in continuous distribution). On the glacial trough covered karst, striped or striped-patchy patterns are typical. On the polje karst, continuous or zonal (so-called internal zonal) covered karst develops. On the karst hill covered karst, the patches of covered karst may coalesce, while on cueasta covered karst, the patches of covered karst are arranged in stripes parallel to the cuestas. The tropical depression covered karst and the polygonal covered karst show patchy distribution, while the intermountain plain covered karst is continuous, but can show internal zonation with crypto and concealed karst zones. No or poor zonation can be identified on the platform karst. The covered karst of salt diapir shows patches and develops on the cover uplifted by the rising salt diapir.

The landforms of covered karst, originated in cryptokarst or concealed karst environment, are presented. Cryptokarst landforms include caprock dolines, ponors, blind valleys, epigenetic valleys and remnant caves. Typical concealed karst landforms are subsidence dolines, closed gullies (blind gullies) and blind suffosion gullies. On both types of covered karst, karren, depressions of superficial deposit and covered karst ponors occur. Numerous varieties of covered karst landforms are distinguished. According to their morphology, karren represent 15 varieties. According to their origin, caprock dolines represent 3; according to size, dropout dolines represent 8; and according to size, morphology and environment, suffosion dolines represent 8 varieties. Subsidence dolines are characterised by morphological parameters (distinguishing between features of karstic and non-karstic origin), ground plan, cross-section and shape of slope. The patterns of doline groups and their morphological environments are demonstrated as well as some varieties of subsidence pseudokarst depressions. Ponors are grouped according to their positions occupied in the karst into karst marginal and karst interior ponors. Karst interior ponors show four varieties according to the position of the rock boundary, while covered karst ponors have three varieties. Depressions of superficial deposit are characterised and grouped according to their position, bedrock morphology, cover sediments and degree of coveredness. Where it is reasonable, covered karst landforms on evaporites are presented separately (karren, salt step, solution subsidence trough, solution-induced depositional basin). The pseudokarst-covered karst landforms are also described.

In this chapter the activity and processes related to covered karst depressions, particularly during floods, the associated phenomena and deposition are demonstrated. The reasons for activity are taken into account. Activities are typified by character and modes of water inflow. The phenomena related to activity (flood lake, overflow, throughflow, intermittent springs, onfilling) and types of activity (surface inflow, seepage, latent activity, composite activity) are identified. A typology of flood lakes, the deposits of lakes of various durations (series with plant waste, laminite), is proposed with explanations of their origin, from which conclusions are drawn to the conditions of depressions at the time of deposition. The deposits (charcoal, limonite, etc.) of fossil dolines are presented and the environments of their origin are analysed. Sedimentation from various types of suspensions in flood lakes was modelled in the laboratory. Landform evolution in dolines was classified according to its duration, and factors associated with the date and duration of landform evolution are considered. The changes in the depth of depressions over several years have been measured and the resultant landforms described. Comparing these two data series, the depressions were classified according to their material budget.

In this chapter, the development and further evolution of subsoil karren, caprock dolines, subsidence dolines, ponors, DSDs and remnant caves are represented. For the above landforms and their varieties, the influencing geological, morphological and hydrological conditions are presented, and the origin, evolution and transformation of landforms are demonstrated. In the presentation of the development of karren, the role of the cover (mainly its grain size) and water movement in the cover is detailed. The classification of caprock dolines relies on the depth of stoping pipes. When studying subsidence dolines, the influence of terrain slope, elevation, karst water and the properties of the cover sediment (grain size, CaCO₃ and clay contents) are investigated. The contribution of landform development on the bedrock and processes in the cover (piping, compaction) to the formation of the depression is analysed. In the genetic classification of ponors, the distribution of non-karstic rocks and the position of karst water are considered. In the description of the evolution of DSDs, the karstic and non-karstic influences are overviewed, and it is investigated from what landforms (subsidence doline, ponor, katavothron) the studied features developed.

This chapter presents the evolution of covered karst surfaces. On karsts which develop from bare karst into covered karst, geomorphic evolution (increasing or decreasing extension of the covered karst) depends on the ratio between the inward transport of cover upon the karst and outward transport (removal of material). Here two-phase landform evolution takes place as on recent allogenic covered karst and renewed allogenic covered karst. On other types of covered karst, the cover formed independent from bare karst, and surface evolution has a single phase, such as in the case of horst covered karst, mantled allogenic covered karst, covered karst of glaciokarst and platform covered karst. Surface evolution begins with covered karst stage. In the latter group, a type (horst covered karst) also occurs where surface evolution is differentiated as a consequence of different evolution and different present elevation of karst horsts. Covered karst is continually reproduced where intensive karstification happens. Such type is tropical karst. In an overview of geomorphic evolution, the role bare karst plays in covered karst formation, the phases of bare karst development and the contribution of karstic and non-karstic landforms in landscape evolution are presented. When describing the various paths of evolution, the properties of cover rock are also taken into consideration.