Introduction
The uvala is a karst landform name that originated as a local toponym across parts of the Dinaric region (Slovenia, Croatia, Bosnia and Herzegovina, Montenegro and Serbia) to denote a closed depression. In geomorphological usage the term designates closed karst basins that are typically larger than individual sinkholes (dolines) and often display irregular, elongated or compound planforms measurable at the kilometre scale. Uvalas occupy an intermediate size class between dolines and the much larger poljes; a representative Dinaric example is Veliki Lubenovac in the Velebit massif (approximately 1 km across). Although the label was coined regionally, analogous large closed karst hollows occur on all continents, which has supported adoption of ‘uvala’ in global karst literature.
Classical treatments of uvalas emphasized simple genetic models—most notably the coalescence of adjacent dolines—but these definitions were often underpinned by limited empirical evidence and provoked debate, with some authors arguing the term was ill‑defined and dispensable. A reassessment beginning around 2009 proposed a more robust delimitation: uvalas are kilometre‑scale, irregular or elongated closed depressions whose origin is tied to intensified solutional denudation focused along tectonically fragmented zones. This contemporary view distinguishes uvalas from dolines and poljes not only by size but by characteristic morphology and a distinct suite of formative (genetic and structural) controls, restoring the uvala as a discrete karst relief type.
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Uvalas in early karstology
Jovan Cvijić (1865–1927), a Serbian geographer trained under Albrecht Penck of the Vienna School, was instrumental in converting local Dinaric terms — including karst, dolina, uvala and polje — into an internationally recognized karst lexicon. Regarded as a founding figure in karst morphology and hydrogeology, Cvijić advanced a systematic framework for karst studies based initially on European fieldwork and later illustrated with examples worldwide. In his influential formulations (notably 1921) he proposed a cyclical genetic sequence for closed karst depressions in which small dolines enlarge into uvalas, which in turn develop into poljes.
Accumulation of empirical observations and comparative studies from all continents, however, challenged the simplicity and universality of this linear scheme. Global research emphasized the decisive role of climate as a genetic control on karst development, showing that climatic regime and related processes can produce divergent morphologies that do not conform to a single doline→uvala→polje trajectory. Consequently, karstologists have questioned the sufficiency of the early cyclic model and argued for revised frameworks that accommodate multiple genetic factors and environmental contexts.
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The mainstream definitions of uvala
Contemporary karstology has largely moved away from classical cyclic models of karst evolution, and this shift has led some authors to reject the uvala concept or the term itself (e.g., Lowe & Waltham 1995). Major English-language syntheses sometimes omit uvalas from their typologies altogether (Ford & Williams 2007), while influential textbook treatments continue to define uvalas mechanically as compound closed depressions produced by lateral enlargement and coalescence of dolines (Sweeting 1973; Williams in Goudie 2005). This persistent “coalescing-dolines” formulation effectively retains an element of the older cyclic framework even as many commentators claim to abandon that paradigm, producing an internal inconsistency within mainstream treatments.
Herbert Lehmann’s critique redirected attention away from the Mediterranean/Dinaric model as a universal template for karst and emphasized that the Dinaric karst is exceptional rather than normative (Lehmann 1973, 1987). In practice, a geographic and disciplinary split has emerged: broad, often English- and German‑language textbooks tend either to reduce uvalas to very large dolines or to omit them, whereas detailed, regionally focused monographs—predominantly from European (notably Dinaric/Mediterranean) contexts and frequently published in other languages—document a distinct uvala type that cannot be explained simply as doline aggregation.
The divergence matters for classification and geomorphic interpretation: one approach integrates uvalas as a separate landform category supported by field-based European studies, while the other subsumes them under enlarged dolines within simplified, non‑regional models. Resolving this divide requires reconciling mechanistic textbook definitions with the empirical evidence provided by localized monographs and acknowledging the geographic bias that has shaped prevailing conceptualizations.
New contributions of technical sciences
Large closed karst depressions constitute a globally distributed geomorphological class distinct from smaller dolines: they form extensive, enclosed basins that are integral to regional karst systems and serve as important sedimentary archives. Their origin and morphodynamic trajectories over geological timescales are, however, poorly constrained because much research has concentrated on smaller, individual dolines rather than on these broader basins.
Disentangling whether a given depression developed primarily by solutional widening, episodic collapse, structural control, or by a combination of these processes requires an integrated approach that couples surface geomorphology with subsurface data and robust temporal constraints. To reconstruct early stages of development and place karst evolution in a regional framework, multidisciplinary synthesis is essential: precise geochronology must be linked with tectonic, seismotectonic and paleoclimatic information to reveal interactions among uplift, faulting, seismic events and climate-driven hydrology.
Recent advances in analytical and measurement techniques now deliver high‑precision ages spanning hundreds of thousands to millions of years, enabling quantitative chronological frameworks that were previously unattainable. Such temporal resolution is only meaningful when sample selection minimizes post‑depositional disturbance: undisturbed sediment cores and fossils shielded from surface denudation, weathering or corrosion better preserve primary depositional ages and environmental proxies.
Reworked or allochthonous materials—sediments and objects transported into cavities, fissures or caves—are particularly valuable as indirect archives of early karst activity and nearby tectonic phases. Proper recognition, stratigraphic placement and dating of these inputs can provide constraints on the timing of landscape change and structural events even where in situ deposits are absent or altered.
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When dated allochthonous records are integrated with stratigraphy, subsurface geophysical and tectonic data and paleoclimatic indicators, it becomes possible to reconstruct the sequence of karstification, subsidence or collapse and the external forcings (tectonic uplift, seismicity, climate change) that modulated them. This integrated, multi‑proxy strategy opens a practicable window onto the long‑term evolution of large closed karst depressions.
Dating of karst sediments and landforms in the Swabian Alb, exemplified by the Karls- und Bärenhöhle system, demonstrates the need for integrated chronologies that combine isotopic, palaeontological and landscape-evolution evidence. Karls- und Bärenhöhle is a former river cave now perched well above the modern valley floor, a position that implies substantial long-term incision and denudation within the local lithological framework. Modern investigations at the site employed a multi-method approach: uranium–thorium (U–Th) isotope dating was applied to cave sediment beddings in tandem with palaeogeological and palaeontological analyses of probe cores and fossil material to constrain depositional ages and the wider palaeoenvironmental context.
U–Th analysis of sedimentary material from inside the cave produced an age of approximately 450 ka, providing a direct radiometric constraint on cave-fill deposition. However, when this isotopic result is interpreted alongside fossil evidence, empirical denudation-rate estimates, regional lithology, and the cave’s present perched geometry, the inferred timing of cave development is substantially older. Palaeogeomorphic reconstruction yields a cave-origin age on the order of ~5 Ma, indicating multi-million-year karst evolution preceding the younger isotopic ages of infill.
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Complementary work in the Middle Swabian Alb has produced independent palaeobiological constraints: unroofed-cave sediments dated in 2006 contained large mammal remains representing seven genera, which, by lithostratigraphic and biochronological assessment within the European Land Mammal Mega Zones (ELMMZ), span MN1–MN17. The only common overlap among those genera corresponds to MN9 (~11 Ma), signalling that at least some fossil-bearing deposits in the region are early to middle Miocene in age.
Together these data reveal a time-transgressive, polyphase history of karstification, sedimentation, faunal accumulation and valley incision on the Swabian Alb. U–Th ages of cave fills (~450 ka), palaeogeomorphic estimates of cave initiation (~5 Ma) and biochronological signals from unroofed-cave fossils (~11 Ma) indicate that different elements of the karst record formed at markedly different times. Accurate chronological interpretation therefore requires synthesising isotopic dating with palaeontological evidence and quantitative landscape-evolution models to resolve the multi-million- to multi-tens-of-million-year development of karst relief in the region.
Recent geochronological and paleoenvironmental studies in the Dinarides, particularly in Slovenia, demonstrate a long-lived and multi-phase history of karstification and speleogenesis. Cosmogenic, paleomagnetic and paleontological analyses have yielded chronologies that span from the early Pliocene to the Middle Pleistocene: combined paleomagnetism and faunal evidence from the Postojna system indicate primary cave formation on the order of ~3.4 Ma (early Pliocene), while younger sedimentary fills in Slovenian caves and unroofed conduits include deposits dated to ~450 ka, showing that Pleistocene phases of sediment accumulation are preserved within the subterranean record. Together these age signals record protracted cave development followed by episodic infill and reworking through Quaternary times.
The regional geological framework facilitates this longevity and complexity. The Dinarides are underlain by exceptionally thick carbonate sequences—reported between ~4,500 and 8,000 m—that extend beneath present sea level. Such voluminous carbonate strata, coupled with tectonic uplift, provide both the lithological substrate and the hydraulic gradients necessary for extensive karstification and deep subterranean drainage over geologic timescales.
Speleological inventory and exploration support the scale and vertical extent implied by the geochronology and stratigraphy. The Dinaric karst contains thousands of caves produced by sustained speleogenetic processes; focused investigations on Mt. Velebit (Bakšić 2008) documented multiple deep vertical shafts, the deepest being Lukina Jama explored to 1,431 m, whose bottom lies ca. 83 m above mean sea level. Such systems demonstrate that karstification has operated across large elevation ranges, producing deep vadose and phreatic conduits and substantial subsurface storage.
In sum, Pliocene initiation of cave networks, Pleistocene sedimentary infill, very thick carbonate sequences, extensive cave inventories, and extreme vertical shafts together characterize the Dinarides as a regionally extensive, long-lived karst province with complex speleological evolution and considerable vertical and lateral subterranean development.
The proposition that karst depressions exceeding the typical size of dolines may originate prior to 2.6 Ma implies that some large karst hollows could have begun forming in the Pliocene or even the Miocene. If so, their earliest phases of dissolution and landscape incision occurred under Neogene climates that in much of Europe were warmer and more humid than present, so primary karstification in these basins may reflect (sub-)tropical pedoclimatic conditions rather than modern temperate regimes.
Distinguishing these large depressions from conventional dolines is essential for interpreting their geomorphic history: size-class is not merely descriptive but carries implications for longevity and developmental trajectory. However, age alone does not prescribe a unique morphotype. Identical genetic drivers of karstification—solutional enlargement along conduits, collapse, or cover-subsidence—can yield markedly different surface expressions depending on local controls.
Those controlling conditions include bedrock composition and purity, rock thickness and permeability, the pattern and intensity of fractures and bedding, the prevailing hydrological regime (phreatic versus vadose flow and oscillations of the water table), climatic parameters during and after formation, the nature and persistence of soils and vegetation, and the temporal continuity of karst processes. Variations in any of these factors can channel the same fundamental dissolutional mechanisms into divergent landforms, or preserve inherited morphology through subsequent environmental change.
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For geomorphic and paleoenvironmental interpretation this means caution is required: morphological resemblance does not guarantee contemporaneity. Robust reconstructions demand integration of chronological constraints with detailed lithostratigraphic, structural, paleoclimatic and hydrogeological evidence to separate deeply inherited basins from features that have been substantially overprinted or reworked in more recent times.
Uvala revisited: tectonics and accelerated corrosion along major tectonic corridors
Ćalić’s regional study of forty-three large karst depressions across the Dinarides (Slovenia, Croatia, Bosnia and Herzegovina, Montenegro, Serbia) used systematic sampling by shape, size and elevation to evaluate tectonic control on karst morphology (Ćalić 2011). The analysis combined morphometric techniques, structural‑geologic mapping, DEM analyses and fieldwork, with detailed structural mapping carried out in twelve depressions following the J. Ćar (2001) approach. Published in Geomorphology (Ćalić 2011) and building on earlier regional observations (e.g., Poljak 1951) and structural interpretations (Vlahović et al. 2012), the work identifies regional-scale “broken zones” — corridors of faults and fractures — as the primary structural template for uvala formation. These tectonic corridors enhance permeability and focus subsurface dissolution, conduit development and surface collapse, so that major uvalas develop preferentially along them. The Croatian Velebit range is highlighted as a particularly uvala‑rich sector, where specific lithologies and structural fabrics concentrate karstification. In Velebit, widespread carbonate breccias (locally termed Jelar breccia) are interpreted as the surficial expression of faulting dated to the Middle Eocene–Middle Miocene; their high permeability, together with Neogene tectonics, is invoked to explain intensified karstification. The pronounced Lomska Duliba uvala (length ≈ 7 km; summit elevation ≈ 1.25 km) exemplifies how tectono‑lithologic controls—notably Jelar breccia outcrops—produce deep, large‑scale karst depressions.
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Ćalić (2009, 2011) reconceptualizes the uvala as a kilometre-scale karst closed depression with an irregular to elongated planimetric shape whose origin is principally controlled by corrosion concentrated along major tectonic fracture zones. Under this definition uvalas are structural-landform features produced by distributed or linear solutional activity rather than by the coalescence of isolated, point-like dolines.
Morphologically, uvalas typically exhibit undulating or pitted floors studded with numerous dolines, are infrequently and only locally filled by colluvium, lie above the phreatic surface, and ordinarily lack perennial surface drainage; ephemeral sinking streams or seasonal ponds occur only as exceptions. These attributes distinguish uvalas from levelled karst plains and from single doline forms and require attention to both internal microrelief and planimetric outline.
Spatially and genetically, uvalas develop in dissected karst terrains where differential erosion and networks of tectonic fractures concentrate corrosion and guide elongation or areal enlargement. Thus, they should be recognised by scale (regional/linear rather than point), tectonic control, and characteristic planform, not by accidental or cyclic descriptive criteria used in some earlier treatments.
Ćalić’s revision corrects vague and inconsistent earlier definitions and gives the term a clearer morphogenetic basis. Subsequent authoritative works have largely adopted this rehabilitated concept: the second edition of the Encyclopedia of Caves (Culver & White, 2012) incorporated related terminology, Zupan Hanja (2012) indexed the concept in the context of Dinaric karst, and revisions by U. Sauro have further consolidated the clarified usage of uvala in contemporary karstology.
Global relevance of uvalas
Recent work by Ćalić demonstrates that Dinaric uvalas are genuine karst landforms, challenging Lehmann’s long‑standing assertion that the Dinaric Karst—and by implication its uvalas—are atypical of karst worldwide. That challenge leaves open a central question: are Dinaric uvalas regionally idiosyncratic, or do they exemplify a landform class that transcends particular tectonic or climatic settings?
The treatment of uvalas in major syntheses is ambivalent. Ford and Williams (2007) largely marginalize uvalas in theoretical karst models, yet repeatedly invoke the term to describe closed depressions appearing in different epochs, climates and regions. This simultaneous dismissal and lexical reliance highlights conceptual uncertainty in karst classification: uvalas are deemed important enough to name but are not consistently integrated into process‑based frameworks.
Empirical inventories indicate that uvala‑scale depressions occur beyond the Dinarides. A German survey (Bayer & Groschopf 1989) lists 57 named Karstwannen on the Swabian Alb and, with adjacent Franconian Jura features, yields some 70 large closed depressions. Roughly half of these have along‑axis dimensions of 1–4.5 km, placing them squarely within the size range typically associated with uvalas; the authors argue their morphology aligns more closely with uvalas than with poljes.
Regional studies nonetheless reveal taxonomic difficulties. Pfeiffer (2010) documents Karstwannen in the Swabian Alb, Franconian Jura and the Causses and treats them as distinct geomorphic entities recording episodes of substantial bedrock lowering. Yet he hesitates to classify them unequivocally as uvalas because of (1) wide plan‑form and morphological variability, (2) thick and regionally variable infill sequences (from Tertiary sediments to Quaternary periglacial deposits and colluvium), (3) mismatch with definitions derived largely from Dinaric examples, and (4) a limited Western/Central European literature base addressing such features.
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Alpine evidence is sparse but instructive. The Funtensee depression in the Steinernes Meer (Berchtesgaden Alps) measures about 2000 × 750 m, contains a pond with subsurface drainage, and has been analyzed as an uvala‑scale closed karst depression—an uncommon explicitly documented Alpine case. More broadly, many limestone belts of the Northern and Southern Limestone Alps have received extensive speleological and tectonic study but comparatively little focused work on large closed depressions, indicating a regional research gap.
Taken together, these lines of evidence reveal inconsistent taxonomy and uneven empirical attention to uvala‑scale depressions across Europe and in global karst literature. Inventories and well‑documented local cases demonstrate the morphological reality of such depressions outside the Dinarides, while major conceptual treatments oscillate between marginalization and terminological use. Resolving whether uvalas are a climate‑independent, globally applicable landform class therefore requires renewed, regionally comparative research that integrates morphology, stratigraphic history and process‑based modelling.
Europe — examples
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Large karst depressions, including uvalas, are widespread components of carbonate landscape morphology across Europe; the regional literature consists largely of field studies and syntheses that document their occurrence, morphology and spatial distribution. These accounts demonstrate that uvalas are not confined to a single karst province but occur in a variety of geological and climatic settings from lowland plateaus to high mountain massifs.
In western and northern Europe, classic treatments of British Isles karst record surface depressions and basin-scale forms (Sweeting 1972; Gunn 2004), while German Jurassic plateaus such as the Swabian Alb and the Franconian Jura exhibit well‑developed karst depressions akin to uvalas (Pfeiffer 2010). In the Alps and adjacent pre‑Alpine ranges, high‑elevation karst basins are documented, for example Funtensee in the Berchtesgaden area (Fischer 1985) and depressions in the Venetian Prealps (Sauro 2003).
Southwestern European carbonate plateaus also host extensive basin forms: studies from Spain document a range of karst depressions (Calaforra Chordi & Berrocal Pérez 2008; Palomares Martin 2012), while Portugal and the French Causses are treated as important examples of plateau karst (Nicod 2003). In eastern Europe and parts of the non‑Dinaric Balkans, regional treatments record comparable landforms in Romania and Greece (Ford & Williams 2007; Jalov & Stamenova 2005), and eastern Serbia’s Carpathian sector contains named uvala‑type basins (Rečke, Busovata, Nekudovo, Igrište, Brezovica) that attest to substantial basin development within that geology.
The Dinaric Alps provide one of the clearest demonstrations of the spatial extent and cross‑border continuity of uvalas: Ćalić (2009) compiles numerous named uvalas and large karst basins distributed across Slovenia (e.g., Kanji Dol, Mrzli Log), Croatia (e.g., Lomska Duliba, Veliki Lubenovac, Mirovo), Bosnia and Herzegovina (e.g., Rupa, Ždralovac), and Montenegro (e.g., Ljeskovi Dolovi, Ubaljski Do). Collectively, these European examples underscore that uvalas are a recurring and geographically extensive element of carbonate relief, varying in scale and form according to local lithology, structure and geomorphic history.
Exposed carbonate bedrock—chiefly limestone devoid of evaporites—outcrops across roughly 20% of the Earth’s ice‑free land surface, creating a broad substrate for karstification and carbonate‑dominated relief that spans a wide range of climates and latitudes. This global distribution underpins the occurrence of uvalas and other karst depressions in many continental and insular settings, with local morphology governed by regional climate, lithology and tectonic setting.
In North America karst and carbonate terrains are documented both in mountainous regions, notably the Appalachian chain, and in plateau and lowland contexts such as parts of the southwestern and central United States (e.g., New Mexico, Oklahoma), where limestone outcrops strongly control drainage and surface relief. Across Africa carbonate rocks and karst features occur broadly on the continent, with well‑known regional examples including Moroccan limestone landscapes; these range from isolated outcrops to extensive carbonate provinces. Asia hosts large, regionally important karst provinces (for example in Iran and China) and extensive tropical karst in Southeast Asia (Myanmar, Thailand, Cambodia, Malaysia), illustrating karst expression from arid to humid tropical regimes and on both continental and insular landforms. In Australasia, temperate island settings such as Tasmania and New Zealand show distinctive karst development and cave‑forming processes appropriate to cool‑temperate climates.
At a finer scale, intramontane examples demonstrate how uvalas and related features can vary within a single mountain system: the Velebit massif, for instance, contains named karst localities in its northern, middle and southern sectors (Veliki Lubenovac, Ravni Dabar, Duboki Dol), each representing localized limestone outcrops and associated karst relief. Collectively, these examples emphasize that where carbonate bedrock is exposed, a diversity of karst landforms—including uvalas—can develop, their specific forms reflecting interplay of climate, structure and lithology.