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."Ćalić (2011), p. 41 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."Ćalić (2011), p. 32
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)Mainly Davis (1899), Grund (1914) and Cvijić (1921) believed the long-term processes of evolution of each karst depression could be explained in cyclic theories:
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,The German geographer, Herbert Lehmann, was the first (1939) to analyze and emphasize (sub-)tropic karst. 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).Some authors prefer to use the even less precise term "compound depression", e.g. White (1988) in his preface. The term uvala is devaluated, but maintained, due to a lack of studies focusing on uvalas.
With his influence and publications the internationally renown German morphologist, Herbert Lehmann,Herbert Lehmann was chairman for 12 years of the karst commission founded by the International Geographic Union (IGU) at its congress 1952 in Washington, D.C. 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)Karstphänomene im Nordmediterranen Raum, (1973), reprint 1987 in: Fuchs et al (1987), Ed. (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:
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.cf. Fairbridge (1968), Herak (1972), Chorley (1984), Jennings (1985), Trudgill (1985), Lowe&Waltham (1995), Goudie (2004), Gunn (2004), Ford&Williams (1989/2007); German: Ahnert (2009), Leser (2009) 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.French, Italian, German, languages of the countries of the Dinaridescf. Poljak (1951), Cocean&Petrescu (1989), Habič (1986), Šušteršič (1986), Frelih (2003), Nicod (2003), Sauro (2001), Čar (2001), Sauro (2003), Zupan Hajna (2012)One explanation might be: Karstology seldom has sufficient resources for manpower and equipment needed to proliferate or to implement costly methods of applied- or technical sciences.
Technical sciences progress in support of uvala as a particular relief form?
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 sciencesMeasuring Radionuclides, Nuclear chemistry, Climatology, Seismology, Information systems with the regard to geological objects allows 'dating' in dimensions of several hundred thousand or even million years – with high precision.The samples needed in physics- or chemical labs can be very small, but they must be extremely well purified. All measurements are usually very resource-consuming (expensive)Bosák (2003) lists no fewer than 64 dating methods. But he also describes their limited feasibility for certain geological objects and their variant span of time, which can be measured.
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.Thanks to a long tradition the Paleontology of Southwest Germany has a well developed infrastructure.
Dating with modern techniques on the Dinarides Recent analysis of sediments in caves and unroofed caves of Slovenia produced in some cases ages of . 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 .Mihevc (2010) and Zupan Hajna et al (2008)
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.The systematic exploration of many shafts, caves and unroofed caves started relatively late; explorations were most intensive in the last 20–25 years.In Lomska Duliba one of the most spectacular uvalas of the Velebit (in Pleistocene overprinted by temporary glaciation), the 536 m speleologically explored vertical shaft Ledena Jama drains a part of the uvala. Drainage is dispersed and there is no sinking stream. (information courtesy J. Ćalić)
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.This is why some authors imagine (Mediterranean) poljes may be Tertiary relics, "die unter einem warm-feuchteren Subtropenklima als heute entstanden." (whose development began in a climate warmer and more humid than today), Leser (2009), p. 322. Ford&Williams (2007) for Australia, p. 410
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.In some period of the past, the same type of tectonic movements could have resulted in formation of a polje, if a subsided (lowered) block reached the piezometric level, and development close to the water table followed; or a uvala might have developed if it stayed high in the vadose zone, with completely different surface processes. The dominant triggering factor for both of these hypothetical forms was tectonic activity, but the settings in which they continued their evolution were crucial for their present character. Ćalić (2009) p 166f.
Uvala revisited: Tectonics. Accelerated corrosion along major tectonically 'broken zones' of regional faults