Uvala (landform)

Uvala is originally a local toponym used by people in some regions in Slovenia, Croatia, Bosnia and Herzegovina, Montenegro and Serbia. In geosciences it denotes a closed karst depression, a terrain form usually of elongated or compound structure and of larger size than that of sinkholes. It is a morphological form frequently found in the outer Dinaric Alps anywhere between Slovenia and Greece, but large closed karst depressions are found on all continents in different landscapes and therefore uvala has become a globally established term. It is also used to distinguish such depressions from poljes, which are many square kilometres in size. Definitions of uvalas are often poorly empirically supported. "The coalescence of dolines" (sinkholes) is the dominant and most frequently found definition. However, because of the ongoing dissatisfaction with this definition, the term 'uvala' has often been belittled – occasionally it was even proposed that the term be given up altogether.

However, recent empirical research (~2009) revised poor mainstream definitions, stating that "…uvalas are large (in km scale) karst closed depressions of irregular or elongated plan form resulting from accelerated corrosion along major tectonically broken zones." This is arguing for the "re-introducing of uvalas into modern karstology" – distinguishing them from dolines and poljes in size (typically) and "also in morphology and combination of genetic factors", which give them "a status of a particular karst relief form."

Uvalas in early karstology
Thanks to the research work of the Serbian geographer Jovan Cvijić (1865–1927), the protégé of Albrecht Penck (the Nestor of the Vienna School of Physical Geography), the word uvala – like the words 'karst', 'dolina' or 'polje', popular terms of the Dinarides – became an established international standard. As the father of Karst Morphology and Hydrogeology, Cvijić envisioned the phenomena of karstology in his publications, first in regions of Europe and then all over the world.

Early karstologists like Cvijić (1921) believed the long-term processes of evolution of each karst depression could be explained in cyclic theories: "Dolines evolve into uvalas, and uvalas into poljes."

However, the increasing body of literature and data collected on karst on all continents, and the global insight that climate ought to be considered as an essential genetic factor in all karst analysis, raised growing concern that this definition may be unsatisfactory.

The mainstream definitions of uvala
These days most authors consider theories of cyclic karst evolution as outdated or even as untenable. Some authors, while dismissing cyclic theory, at the same time discard the term uvala altogether: "…This mechanism is no longer accepted and the term uvala has fallen into disuse", Lowe&Waltham (1995). In the comprehensive primer 'Karst Hydrogeology and Geomorphology', written by Ford&Williams (2007) for the English oriented world, likewise in their contributions in English encyclopedias, the uvala is simply not a factor in their karst models (uvalas, they claim, are simply very large dolines).

With his influence and publications the internationally renown German morphologist, Herbert Lehmann, put an end to the focus of karstology on warm temperate climate. Lehmann in 1973: "Der mediterrane Karst, im engeren Sinne der Dinarische Karst, ist nicht das Musterbeispiel der Karstentwicklung überhaupt, sondern eher Ausnahme", Lehmann (1973/1987) (Dinaric karst is an exception).

Nevertheless, the mainstream position of karstology and especially non-European karstology still dominates with the somewhat singular, empirically unsupported, definition: "As solution depressions evolve, some enlarge laterally and coalesce, producing compound closed depressions known as uvalas." "Large closed depression formed by the coalescence of several dolines which have enlarged towards each other."

For most English textbooks and encyclopedias and additionally some German equivalents the term uvala is straightforward. When only briefly defined, one of the above cited definitions, in most cases Sweeting's (1973), is used. Yet, the definition 'dolines coalescing into uvalas' is logically the first part of the cyclic theory, claimed to having been little used or abolished!

Most scientific monographs however, such as comprehensive empirical studies, confirm the existence of the authentic type of uvala – yet most monographs analyze European objects only, and most are written and published in languages other than English.

New contributions of technical sciences
Large closed karst depressions are an important phenomenon on all continents, yet their analysis apart from and beyond dolines is rare. Assessing the potential of new knowledge, especially on the question of the genesis and evolution of large depressions, is very difficult. Possibly the studies of geological dating, interdisciplinary Tectonics, Seismotectonics and Climatology will open a window to look into earlier periods of evolution.

The recent progress in methods and measuring techniques in the sciences with the regard to geological objects allows 'dating' in dimensions of several hundred thousand or even million years – with high precision.

Some progress in dating was made by ensuring that examined sediment probes and fossils have not only been exposed to surface, where denudation, weathering or corrosion are in effect. Rather "allochthonous" objects, objects which were moved and washed into cavities, transported into fissures or caves might be archive elements of early karst activity and tectonic stages of nearby large closed depressions.

Dating with modern techniques in the Swabian Alb
Results for a reliable age were achieved, e.g., by combining uranium-thorium dating, paleo geological and paleontological dating in sediment beddings (probes and fossils) inside the cave de:Karls- und Bärenhöhle on the Swabian Alb, Germany. The isotope-method yielded an age of ca. 450 thousand years (ka). Taking into account fossil analysis, a denudation rate, the local and regional lithology and the position of the primeval river cave (now dry) high above the recent valley bottom, the age of the cave was determined to be roughly five million years (Ma), Ufrecht/Abel (2003).

In 2006 fossil remains in sediments of unroofed caves of the Middle Swabian Alb were successfully dated, Ufrecht (2006). The remains of large land-mammals of seven genera were lithologically and bio-stratigraphically (paleontologically) classified into the biozones MN1 to MN17 of the European Land Mammal Mega Zones (ELMMZ) table. These found genera overlapped only in MN9, which is ca. eleven Ma.

Dating with modern techniques on the Dinarides
Recent analysis of sediments in caves and unroofed caves of Slovenia produced in some cases ages of c. 450ka. In the Postojna Caves (Slovenia) the method of paleomagnetism in combination with paleontological studies yielded a dating comparable to that on the Swabian Alb. Thus those caves themselves were estimated to have an age of c. 3.4 Ma.

Carbonate rocks of the Dinarides are 4500 to 8000 m thick and thus reach deep below the current sea level. There are thousands of caves in the Dinarides. Bakšić (2008) published the systematic exploration of eight shafts on Mt. Velebit, the deepest, Lukina Jama, explored down to 1431 m, only 83 m above sea level.

Extremely retrospective views: The genetic and evolutionary issue
If an age of karst depressions larger than dolines beyond 2,6 Ma is possible, that is: depression development may possibly have started in Pliocene or even in Miocene, then depressions were already formed in Europe's (sub-)tropical climates.

However, even if a very high age of a depression is assumed, which karst form will emerge? "Very similar genetic factors can lead to the development of different forms, depending on the conditions within a karst area", Ćalić (2009) p. 166f.

Uvala revisited: Tectonics. Accelerated corrosion along major tectonically 'broken zones' of regional faults
The geographer Jelena Ćalić, chose to analyze large karst depressions using geomorphological (morphometrical) and structural geologic mapping methods. This way Ćalić gained more data of tectonically induced subsurface traces. Forty-three large karst depressions (potential uvalas), sampled by shape, size and elevation in the Dinarides of Slovenia, Croatia, 'Bosnia and Herzegovina', Montenegro, and Serbia were analyzed by digital elevation models (DEM) and field research. The results were published in English in the journal 'Geomorphology, Amsterdam, 2011', Ćalić (2011). In twelve of the forty-three studied depressions detailed structural-geological mapping (following the method of J. Ćar (2001)) was carried out. This mapping "revealed dominant development of uvalas along tectonically 'broken zones' of regional scale", the 'broken zones' being highly permeable.

The Croatian mountain chain Velebit is probably the richest area in karstic uvalas of the Dinarides, Poljak (1951) cited by Ćalić (2009) p. 70. The breccia in this chain – there known as Jelar breccia – show very extensive outcropping. These highly permeable carbonate breccias are a prominent feature of "Middle Eocene to Middle Miocene" age faulting activities in the Velebit area, Vlahovic et al. (2012). The deep incision of Velebit's most prominent uvala Lomska Duliba can be explained by the presence of the Jelar breccias, Ćalić (2009), p. 72.



New definition of uvala
Ćalić (2011) defines uvala as follows: "The term uvala must be excluded from such contexts," (cyclic concepts) "because they discredit its true meaning." [...] "At this stage of research, it can be concluded that uvalas are large (in km scale) karst closed depressions of irregular or elongated plan form resulting from accelerated corrosion along major tectonically broken zones. Their bottoms are undulating or pitted with dolines, seldom flattened by colluvial sediments and always situated above the karst water table." [(...] "…small seasonal sinking streams or, ponds are very rare, an exception rather than a rule." [...] "The depressions of this kind are not present on karst levelled surfaces, but only in areas with more or less dissected relief;" [...] they "are forms of accelerated corrosion – not as points as dolines, but 'linear' or 'areal' [...]."Ćalić (2009) and Ćalić (2011).
 * Ćalić in a nut shell: There are deficits in most previous uvala-definitions. The revision was overdue. It re-introduces uvalas into modern karstology!

The second edition of the 'Encyclopedia of Caves', Culver&White (2012), amongst others, added the keyword 'Dinaric Karst, Geography and Geology', Zupan Hanja (2012), while U. Sauro revised his keyword 'Closed Depressions' – in part, so that both authors now fully endorse Ćalić's revival of the term karstic uvala.

Global relevance of uvalas
Ćalić's work and resulting definition affirms that Dinaric uvalas are karst forms in their own right. The question remains whether this is relevant globally and in different climates. Possibly the postulate of Lehmann (1973/1987) that Dinaric Karst is not representative for karst worldwide (see above), with respect to uvalas must be re-examined.

In the comprehensive karst modelling of Ford&Williams (2007) uvalas are irrelevant. Yet, they consider the term uvala indispensable and use it no less than six times to describe karst phenomena found in different epochs, climates and regions of various continents, in some cases with reference to other authors.

A German publication lists fifty-seven 'Karstwannen' on the Swabian Alb, Bayer&Groschopf (1989). Together with a few more on the karstic Franconian Jura, there may well be about 70 large depressions, half of which are 1000-4500m in length. According to Bayer&Groschopf, p. 182 "[...] sind Karstwannen eher mit Uvalas denn mit Poljes zu korrelieren, [...] entsprechen von der geomorphologischen Ausformung dem Uvala Charakter." (They correlate with uvalas rather than with poljes, [...] they correspond to geomorphological forms of uvalas).

Pfeiffer (2010) discusses Karstwannen ("Karst depression","Uvala"," Polje") of the Swabian Alb, the Franconian Jura and those of the Causses (southern France). "Die Karstwannen sind eigenständige Formen, die eine zeitweise großflächige Tieferlegung der Gesteinsoberfläche belegen", S. 210 (Karstwannen are a distinctive form element, confirming, there was a phase of extensive lowering of the rocky plane). Yet considering the terms uvala or polje, he is undecided, mainly because
 * of his own findings of shapes,
 * "Die Wannen weisen zum Teil sehr mächtige Füllungen auf, die regional sehr unterschiedlich sind und eine Spanne von tertiären Sedimenten über quartäre periglaziale Schichten bis hin zu Kolluvium umfassen", S. 212 (Some of the Wannen have tremendous fillings. The size of the fillings differs from region to region. There are sediments of various ages, ranging from tertiary to quaternary periglacial sediments or even colluvium).
 * the lack of correspondence with the mainstream-definition,
 * the very sparse literature on a West- or Central European feature of the kind.

Large areas of the Alps, those flanking the central massive on the north and the south (Northern Limestone Alps, Southern Limestone Alps), geologically consist of limestone stratigraphy of various ages. A lot of geological research in speleology, tectonics and petrology has been done, but this rarely focuses on large closed karst depressions like uvalas. The 'Funtensee-Uvala' (Steinernes Meer of the Berchtesgaden Alps) is an exception, which was analyzed and published in the context of a project of the Berchtesgaden National Park.

Europe (examples)
Limestone Alps Spain Dinarides:
 * Germany (Swabian Alb, Franconian Jura), Pfeiffer (2010)
 * England, Sweeting (1972)
 * Ireland, Gunn (2004)
 * Funtensee, Berchtesgaden, Fischer (1985)
 * Venetian Prealps, Sauro (2003)
 * Calaforra Chordi&Berrocal Pérez (2008)
 * Palomares Martin (2012)
 * Portugal, Nicod (2003)
 * France, Les 'Causses', Nicod (2003)
 * Romania, (Ford&Williams (2007)
 * Greece, Jalov&Stamenova (2005)
 * Serbia, Rečke, Busovata, Nekudovo, Igrište, Brezovica (Carpathians, east Serbia)
 * Numerous uvalas in four countries, inter alia, Ćalić (2009):
 * Kanji Dol, Mrzli Log, Grda Draga, etc. (Slovenia)
 * Lomska Duliba, Veliki Lubenovac, Mirovo, Bilenski Padez, Duboki Dol, Ravni and Crni Dabar, etc. (Croatia)
 * Rupa, Ždralovac, Klekovačka Uvala, etc. (Bosnia and Herzegovina)
 * Ljeskovi Dolovi, Ubaljski Do, Illinski Do, etc. (Montenegro)

Other continents (examples)
America Africa Asia Australia
 * Appalachian Mountains, (Herak (1972)
 * New-Mexiko, (Ford&Williams (2007)
 * Oklahoma, Ford&Williams (2007)
 * various, Gunn (2004)
 * Marocco, Jennings (1987)
 * Iran, Bosák, et al. (1999)
 * China, Gunn (2004)
 * South east Asia (Burma, Thailand, Cambodia, Malaysia), Gunn (2004)
 * (Tasmania), Jennings (1987)
 * New Zealand, Jennings (1987)

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