Some rocks, such as limestone, gypsum, and halite, dissolve when encountered with carbon dioxide-rich fluids, and the morphological formations of these dissolved rocks on the earth are called karst. In addition, the ensemble of shapes formed by the Karstification is called “Karst Topography” (Ford and Williams, 2013). The main factors affecting the formation of karst areas can be listed as rock composition, climate, vegetation cover and elevation. Typical examples of karst formation and development in terms of Turkey is mostly within the Taurus Mountains, which is located in southern Anatolia (Sür, 1994). The karstic formations observed in the Anatolian geography can be listed as limestone pavements, ponols, dolines, uvalas, poljes, potholes, karstic valleys, natural bridges and underground streamtunnels, caves, travertine cones, traverten terraces, stalactites and stalagmites.
Although Turkey has quite rich in terms of the formation of karst geology, it has not yet been carried out serious work on these units. In this section, the main karstic occurrences observed in Anatolia will be examined.
2.1. Limestone pavements
The most common of these karstic formations are called limestone pavements. That structures can be described as microtopographpical units, that occur as a result of denudation and dissolution processes. They are generally truncated in the form of a groove or channel between sharp-edged miniature ridges. The shapes and arrangements of these structures vary depending on the morphological and lithological properties of the area, vegetation, percolation and dissolution. Additionaly, that kind of structures can be observed in Taşeli plateau, Gülnar district, highlands of Tarsus and Mersin provinces, Seydisehir, Kestel, and Dalaman Çayı Valley that are located in the Taurides system in Turkey (Alagöz, 1943).
Ponors transport the surface waters to the underground from the creek beds and poljes in the karstic regions. Ponor of Akgöl which is located net to Konya Ereğlisi is a beautiful example of that kind of karstic structures and they are found in the western Taurides and Central Anatolia (Sür, 1994).
2.3. Sinkholes (Dolines)
Sinkholes or Dolines are the closed depressions which occur because of karstification are very abundant karstic fectures in Anatolia peninsula. There is no definite limit to the distinction between larger karstic solution pits such as doline, uvala and polye. Generally, formations with a diameter of 200 mm or less are named as doline and the occurrences with a diameter that is greater than 200 mm are called as uvalas or poljes. A criterion in the classification is the combination of a karstic depression with another one. If a merger with another karstic pit is observed, this formation is called uvala, but in contrast, it is classified as doline. One of the doline formations in Turkey which is called Kırşehir Doline (Figure 1) can be represented as a good example for that kind of structures. (Sayhan, 1999).
The large depressions that are called uvala with irregular edged corners form result of the dissolution of slopes between the dolines close to each other. If there are sequential dolines in the valley bed in the karstic areas, they will merge to form the uvala after some time. Uvalas can be obserbed around southern part of the karaman, and northern side of the Mut districtes where the dolines are present. (Sür, 1994).
Poljes are the karst structures larger than uvalas and they occur due to karstification and result of tectonic events. They resemble a plain with their highly elevated surroundings and the alluvium cover. Depending on the condition of the groundwater level, the polje may become a temporary lake or marsh, but the water can pass to the underground by sinkholes or ponors (similar to Suğla Lake). Development of Poljes can be seen especially around southern part of Taurides. Kestel-Çeltikçi-Zivint- Bozova-Bademağacı-Korkuteli polje systems that are located in the west part of Antalya coast and extending in NE-SW direction, and Müren-Elmaı-Avlan-Kaş Çiftliği system that are extending in the same direction are the significant environments for poljes as an example (Sür, 1994). Besides, Mugla Polje (Figure 2) which known as the Menteşe region that is located in the western anatolia is quite striking for development of that structures.
Potholes are depressions that resemble collapse dolines but are usually larger in size. Dissolutions and collapses play an important role in the development of such structures. A large part of the potholes in Turkey took place in Konya in central Anatolia section and Kızraren, Timraş, Kuruobruk, Çıralıdeniz, Suluobruk, Eğil structures can be given as an example. In addition, the Cennet (Heaven) and Cehennem (Hell) potholes (Figure 3), located in the limestone plateau behind Narlıdere to the east of Silifke, are also quite large in size and are shaped by the collapse of the underground cave systems (Sür, 1994).
2.6. Karst valleys
Karst valleys are structures that result from the dissolution of soluble rocks such as tunnels, natural bridges, and caves. According to their characteristics, these valleys can be named as dry, dead, or blind valleys. Dry valleys are structures that can temporarily store water, but the valleys that do not contain any water are blind valleys. The valley which is completely surrounded by elevation, and having no any aperture is called Blind Valley or Karst Window (according to Turkish literature), and the valley with only one openness can be defined as dead valley. The Geyik Valley (Deer Valley) in the Muğla province (Figure 4) borders can be seen as an example of such karst valleys.
Tunnels can be defined as underground water channels between the ponors that are transmitting water to the groundwater and karst springs floating water to the surface.
2.8. Karstic belts (natural bridges)
Karstic belts are formed as a result of the partial collapse of the divisions between adjacent potholes or karst windows, and the formation of roof collapses of underground waterways (Figure 5). In Turkey, also the most prominent example of these shapes seen in karst area located in the Taurides system is called “Yerköprü” formation, present on the northwest of Silifke district (Ver, 1994).
Caves are karstic carvings of various sizes, which can grow in both horizontal and vertical directions (Figure 6), and some of them have multiple galleries, and they can be defined as basically constructions of underground water. There are approximately 40,000 karst caves in Turkey and are present in most of these karst plateaus in the Taurides system. These caves can be generally categorized as Antalya, Konya, Burdur, Isparta, İçel, Zonguldak caves. One of the most important karstic caves in Antalya is the Altinbesik cave located in north-east of Manavgat, the Karain cave located on the north side, and the Phosphorous Cave along with Damlataş Cave which developed in the same environment (Sür, 1994; Alagöz, 1984).
2.10. Travertines and travertine cones
Travertines are the forms of accumulation (Figure 7) that come into play as a result of the effects of groundwater. With the help of carbon dioxide, underground waters that dissolve rocks and contain excess amounts of calcium carbonate reach saturation due to different factors and precipitate these units. As the chemical reaction is repeated many times, travertines occur that are conformable to topography. The travertines in Antalya and Denizli, can be considered as the most remarkable structures in Turkey.
On the other side, these formations can also be observed in Göksu, Bursa, Çankırı, Maliköy, Bolu, Pınarbaşı, Reyhanlı, Erzincan, Malatya, and many other places around the Anatolia. In addition to all these, travertine cones (Figure 8) formed by similar mechanisms can also be considered as remarkable constructions, and typical examples can be found in Salt and Bolu Lakes of central Anatolia.
2.11. Gypsum karst
Gypsum karst is termed as depressions which are the result of dissolution of the gypsum rock with weaker strength than limestone. However, these types of karstification are more unstable than limestone karsts because they can be easily affected by external factors, and disappear or change shape over time. Remarkable examples of gypsum karst can be observed in the Çankırı and Sivas provinces (Figure 9), and especially in the Sarıkışla-Zara regions.
3. SEVERAL KARST AREAS IN ANATOLIA
In this section, general information about some karstic regions in Anatolia will be explained.
3.1. Gökpınar Karst Springs
Gökpınar karst springs located 8 km to the south from the Gürün district, Sivas, Turkey (Figure 10). Gökpınar-1 and Gökpınar are the two main outlets of the springs and the host rock of the outflows is Jurassic-Cretaceous aged Yüceyurt limestone.
The region is composed of allocthonous and autocthonous rocks which are having age from Upper Devonian to Quaternary. These rock units are composed of limestones, commonly and the Yüceyurt formation where Gökpınar karst springs outflowing, involves the karstified aquifer in the region (Figure 11). Karst system in the region includes karren, dolines, ponors, underground flowing tunnels and caves, and the fields are characterized by the presence of the characteristic karst features with different size and form. Most of the small scale solution carvings and big scale karstic structures are present in Yücelyurt limestones. Small sized solution carvings includes microkarren, karren, solution pits and solution pans. Karst landscapes in big scale in the field are sinkholes, ponors (swallow holes), and some closed depressions.
Additionaly, several cave formations are also observed in the field. Solution pits that are the most abundant karstic features in the field have circular, elliptical or irregular shape, and they show diameters from few centimetres to a number of decimetres. Dolines that occured by dissolution, collapse, suffosion, or subsidence processes are the most veriest karstic landscapes in the field. In the study area dolines are widely distributed karst landforms. Additionaly, dissolution or collapse dolins, are usually located in the south and west sides of the region with high elevatios, and they are following structural trends in general. Ponors (swallow holes) are the occurences where the meteoric water flows to the karst aquifer system and feeds the karst groundwater rechargings. In the field, ponors are located around the surroundings of the closed depressions, along the fracture zones, and the stream beds.
3.2. Hafik Gypsum Karst
The most important gypsum karst in Anatolia is present in Hafik, Sivas province (Figure 12) with 750 m thick and early miocene age. Moreover, the region involving a lot of specific karstic characteristics such as karrens, dissolution dolines, collapse dolines, blind valleys, karstic springs, swallow holes, caves, unroofed caves, natural bridges, and poljes. Gypsum is much more soluble than limestone cannot resist to the environmental factors as much as limestone, (Boğli, 1980).
Because of that reason, karstic event that are happening around the Gypsum terranes are developing rapidly than limestone ones (White, 1988; Ford and Williams, 1989). Karstic terrains are covering 30 % of Anatolia, but the regions that are composed of gypsum much more smaller than the other carbonate karstic terranes, and present in Central and Eastern Anatolia. Gypsum can be observed around Ankara, Çankırı, Çorum, Kırşehir, Kayseri and Sivas regions (Alagöz, 1967; Gunay, 2002; Doğan and Yeşilyurt, 2004), but the most significant gypsum occurrence in Anatolia, outcrops in Sivas province (Alagöz, 1967; Aktimur, 1988; Kaçaroğlu et al., 1997; Çubuk and İnan, 1998; Çiner et al., 2002; Doğan, 2002; Günay, 2002; Waltham, 2002, Doğan and Yeşilyurt, 2004).
The units that best represent early Miocene karstic properties are the gypsum outcrops ast of Sivas around Hafik, Zara and İmranlı. That outcrops include karrens, dissolution and collapse dolines (Figure 13.), collapse dolines, blind valleys, karstic springs, swallow holes, caves, unroofed caves, natural bridges, and poljes. Dissolution dolines can be observed in the younger karst areas between Sivas and Zara at the northern part of Kızılırmak valley, and the southern side of İmranlı. Additionaly, much more older karstic areas located between Hafik and Zara, andt he most beautiful occurrences of poljes and collapse dolines (Alagöz, 1967; Waltham, 2002; Doğan and Yeşilyurt, 2004).
Anatolian peninsula located within the borders of Turkey hosts to very important karstic structures. However, it is interesting to note that, despite the presence of so many geological units, there has not been enough work on karst geology. Tens of thousands of karstic caves and unique geological units, especially within the Tauride system, are suitable for new works on karst geology and hydrogeology. This article briefly summarizes the karst structures in Turkey, and the studies have been compiled with care.
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