Natural and induced sinkholes of the Obruk Plateau and Karapınar-Hotamış Plain, Turkey

Journal of Asian Earth Sciences 40 (2011) 496–508

Contents lists available at ScienceDirect

Journal of Asian Earth Sciences

journal homepage: www.elsevier .com/locate / jseaes

Natural and induced sinkholes of the Obruk Plateau and Karapınar-Hotamıs�Plain, Turkey

Ugur Dogan ⇑, Mutlu YılmazDepartment of Geography, Ankara University, Sıhhıye, Ankara 06100, Turkey

a r t i c l e i n f o a b s t r a c t

Article history:Received 24 April 2010Received in revised form 23 September2010Accepted 24 September 2010

Keywords:KarstSinkholeKarst hazardObruk PlateauTurkey

1367-9120/$ - see front matter � 2010 Elsevier Ltd. Adoi:10.1016/j.jseaes.2010.09.014

⇑ Corresponding author. Tel.: +90 312 3103280/124E-mail address: [email protected] (U. Dogan).

The number of sinkholes (locally known as obruks) has increased rapidly in recent years near Karapınar,located in the semi-arid Konya Closed Basin in Central Anatolia. Nineteen sinkholes have formed in thelast 33 years (1977–2009) as a result of the collapse of cavity roofs in the Neogene lacustrine limestone inthe Obruk Plateau and beneath Quaternary lake sediments in the Karapınar-Hotamıs� Plain. Of these, 13have formed within the past 4 years (2006–2009). The Obruk Plateau takes its name from the presence ofseveral hundred paleo-sinkholes which formed as a result of natural processes during the Quaternaryperiod. More recently, human activity has induced the formation of new sinkholes, which presents a haz-ard to life and property. Changing agricultural patterns have led to the opening of thousands of deepwells in recent years, and increased water pumping currently exceeds the sustainable yield of the aquifer.Thus the formation of sinkholes has been triggered by a combination of natural and human causes. Thegroundwater level has dropped almost 24 m in the vicinity of Karapınar during the last 26 years (1983–2008). Approximately 8 m of this drop occurred within the 4 years prior to the study (2005–2008).Legally-binding precautions must be taken to prevent further water table decline, in order to decreasesinkhole formation within the basin in the years to come.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction

Carbonate karst is estimated to cover over 10–15% of the Earth’sland surface and these karstic terrains provide essential groundwater to supply roughly 20–25% of the global population (Fordand Williams, 2007). Within these karst areas, sinkholes are amongthe most significant natural hazards threatening human life andproperty and lead to increasing expenditure each year (White,1988; Waltham, 1989; Waltham and Fookes, 2003; Walthamet al., 2005; Parise et al., 2008). The location and timing of sinkholescannot generally be predicted and they usually occur abruptly(Newton, 1987; Waltham et al., 2005).

Sinkhole hazards increase in cohesive alluvial cover on karstrocks (Dogan and Çiçek, 2002; Waltham et al., 2005) and on evap-orite karst, where dissolution is more rapid (Benito et al., 1995;Alberto et al., 2008; Gutiérrez et al., 2008a,b; Luzón et al., 2008;Galve et al., 2009) in comparison to carbonate karst (Bruno et al.,2008; Brinkmann et al., 2008) or caprock areas (Dogan, 2005). InTurkey, nearly one third of which is composed of karst terrains,most attention is focused on sinkholes formed in recent yearson lacustrine limestone and consolidated non-karst caprocks

ll rights reserved.

8; fax: +90 312 3105713.

overlying the limestones near Karapınar in the Konya Closed Basin(KCB) (Fig. 1), rather than on sinkhole hazards in evaporite karst,which are seen across a large area (Dogan and Yes�ilyurt, 2004;Dogan and Özel, 2005). The KCB is comprised of the Konya Plainsub-basin in the south, the Tuz Lake sub-basins in the north andthe Obruk Plateau, which is located between these two sub-basins(Fig. 1).

Obruk is the local name for sinkholes that may be of collapse orcaprock type; there are many that have been formed within theTaurus karst and in the KCB, and reach their greatest density onObruk Plateau, northwest of Karapınar.

In the Obruk Plateau, there are several hundreds of saucepan-like and cylindrical sinkholes, showing dimensions ranging froma few meters to tens of meters in width. Those which attract atten-tion are ‘‘cenote’’ type (Ford and Williams, 2007) sinkholes atdiameters of several hundred meters; depths can range from10 m to more than 100 m. A lake is often observed at the bottomwhere the sinkhole reaches the depth of the water table (e.g.Kızören, Çıralı, Meyil, Timras�, Apa) (Figs. 1 and 2).

Many geomorphologic and hydrologic studies have been con-ducted on the subject of the KCB especially regarding the ObrukPlateau sinkholes, which have attracted the attention of research-ers since the early 20th century (e.g. Erinç, 1960; Eroskay andGünay, 1980; Canik and Çörekçioglu, 1986; Erol, 1986, 1990;Biricik, 1992; Bayarı et al., 2009a,b). However, the hazard to life

http://dx.doi.org/10.1016/j.jseaes.2010.09.014

mailto:[email protected]

http://dx.doi.org/10.1016/j.jseaes.2010.09.014

http://www.sciencedirect.com/science/journal/13679120

http://www.elsevier.com/locate/jseaes

Fig. 1. Location map of the study area. Faults have been adapted from Koçyigit (2005) and Özsayın and Dirik (2007). Last Glacial Maximum (LGM) lake limits have beenadapted Fontugne et al. (1999) and Kashima (2002).

Fig. 2. The Çıralı Obruk, one of the giant paleo-collapse sinkhole located in theObruk Plateau. There are many man-made ancient caves in the sinkhole slopes(photo taken in 2004).

U. Dogan, M. Yılmaz / Journal of Asian Earth Sciences 40 (2011) 496–508 497

and property posed by sinkholes, which continue to form rapidly atthe present time, and which will continue to form in the future, hasbeen widely ignored.

The purpose of the present study is to determine the role of hu-man and natural causes relating to the formation of new sinkholesaround Karapınar.

2. Regional setting

2.1. Geological setting

The formation and spatial distribution of sinkholes are closelyrelated to the lacustrine _Insuyu Formation (Ulu, 2009a,b) and theaquifer in this formation (Figs. 3 and 4). The _Insuyu Formationwas formed as a result of an extension regime during The UpperMiocene–Pliocene (Koçyigit, 2005). It consists of thick limestonein the upper section, limestone, marl, clay, tuff and silt intercala-tion in the lower section (Ulu, 2009a,b). The thickness of fracturedlacustrine limestone, suitable for karstification has been docu-mented by boreholes to be over 200 m (Canik and Çörekçioglu,

Fig. 3. Stratigraphic column of the study area. Adapted from Ulu (2009a,b).

498 U. Dogan, M. Yılmaz / Journal of Asian Earth Sciences 40 (2011) 496–508

1986). Limestone, marl and clay intercalations are commonlyobserved in the boreholes in the Obruk Plateau (Fig. 5).

At the base of the _Insuyu Formation, there is the Upper Creta-ceous Karabögürtlen Formation consisting of calciturbitide, quartz-ite, calcschist, serpentine, dunite, gabbro, shale and marble (Ulu,2009a,b). The Karabögürtlen Formation overlies Mesozoic forma-tions. These Mesozoic formations consist of limestone, dolomite,marble and shale which are exposed in the study area (Figs. 3and 4).

Volcanic mountains and maars formed as a result of Miocene-Quaternary volcanism (Keller, 1974; Ulu, 2009a,b) are commonin the vicinity of Karapınar. These include Üzecek Mountain inthe south of Obruk Plateau and Karacadag, Meke Maar and Acı LakeMaar in the east.

Sedimentation in the _Insuyu Formation came to end with thelast compression that caused sediments deformation. Subse-quently, Konya Graben – one of the biggest neotectonic structurescharacterizing continental extension in the West-Central Anatolia– were formed (Koçyigit, 2005). The modern Konya Graben is alarge depression lying between Konya to the west, Nigde to theeast, Karapınar to the north and Karaman to the south (Fig. 1). Itformed through an extension regime which began in the Late Plio-cene. The western side of the Karapınar Graben, forming a part ofKonya Graben, is bordered by the Seyithacı Fault, extending in aNE–SW direction (Koçyigit, 2005) (Fig. 4).

Thick Quaternary sediments largely were formed during glacialperiods by the Paleo-Konya Lake and Tuz Lake. The Plaeo-KonyaLake approximately covered the areas where the Konya Plain is

Fig. 4. Geologic and hydrogeologic map of the study area. Geological formations were modified after 1/500.000 scale geological map of MTA; faults were adapted fromKoçyigit (2005) and Özsayın and Dirik (2007); 1968 groundwater contours were adapted from DS_I (State Hydraulic Works) (1975), and 2008 groundwater contours weredrawn according to some well observations taken from DS_I.


now situated and Tuz Lake, which covered a much larger area thanit does now (Erol, 1971; Fontugne et al., 1999; Kashima, 2002)(Fig. 1). Borehole data indicate that the Quaternary sediments are30–40 m thick near the edges of Karapınar-Hotamıs� Plain, increas-ing to be more than 100 m thick in the central areas of the plain(Fig. 5), in accordance with tectonic subsidence. The Karapınar-Hotamıs� Plain is one of the sub-sections of the Konya Plain. The_Insuyu Formation remains high between the Quaternary sedimentsin the south and north because of the above-mentioned tectonicmovement.

2.2. Hydrologic and hydrogeologic setting

The large KCB has a semi-arid climate. Most streams in the re-gion are seasonal, largely originate within the Central TaurusMountains to the south, and terminate in the Konya Plain. The

Obruk Plateau is largely devoid of runoff due to low precipitation,high evaporation and percolation.

Considering that average precipitation in the basin is �330 mm(Konya 322.2 mm, Karaman 333.3 mm and Aksaray 347.3 mm) andaverage evapotranspiration is around �1300 mm (Konya1305 mm, Karaman 1198 mm, Aksaray 1370 mm), it is clear thatthe Central Taurus Mountains are very important for the KCB. Ithas been known for many years that groundwater in the _InsuyuFormation aquifer flows from the high Central Taurus Mountains(2000–2500 m), the main recharge point in the south, towardsTuz Lake (�905 m) (Fig. 1), the main discharge point in the north(Eroskay and Günay, 1980; Canik and Çörekçioglu, 1986; Erol,1986, 1990; Bayarı et al., 2009a,b). This is also confirmed by thegroundwater contours around Karapınar in the periods 1968–2008 (Fig. 4). Radiocarbon dating determined that the age of thegroundwater in the basin varies between the present-day and

Fig. 5. Stratigraphies of wells shown in Fig. 4 (adapted from DS_I archive).


40 ka years; water flows at 3 m/year within the aquifer, and in-creases in age from the main recharge point to the main dischargepoint (Bayarı et al., 2009a).

According to Bayarı et al. (2009b), there are two main, largelyindependent, aquifers within the KCB, which are separated by aPaleogene aquitard. The lower aquifer consists of Paleozoic–Mesozoic rocks. The upper aquifer is part of the _Insuyu Formation,in which limestone controls the formation and the areal distribu-tion of sinkholes. The _Insuyu Formation aquifer contains Ca–HCO3 groundwater, and 10–70 lt/s water could be pumped fromdeep wells of 50–250 m depth opened to this aquifer (Bayarıet al., 2009b).

In recent years, a significant decline has occurred in the watertable throughout the KCB because of increasing aridity and exces-sive pumping from deep wells. According to official data, 70% ofnearly 100,000 deep wells are illegal (_Is�çioglu, 2008), and are boredin order to grow commercial crops which are highly waterdemanding (Göçmez et al., 2008a; Bayarı et al., 2009a,b). Approxi-mately 886 M m3/year of water is pumped from the aquifer in theKCB. It is estimated that this exceeds the sustainable capacity ofthe aquifer by 267 M m3/year (Göçmez et al., 2008a).

Comparison of the 1968 and 2008 groundwater contours showsthat water table declined about 24 m in the last 41 years. In fact,long-term data for groundwater level obtained from wells showthat, this water table decline occurred over a much shorter time(Fig. 6).

The series of groundwater measurements covering the longestperiod (1969–2008) was taken in the Gülfet Yayla well (well No.52258 or 220), located approximately 10 km to the west of Kar-apınar at the border of Obruk Plateau (Fig. 4). According to thisdata, no significant change occurred in ground water level between1969 and 1982, with the exception of minor climatic fluctuationsof a few meters (4 m maximum). However, from 1983 onwards,a decline trend started to be seen in the water table, which level�17.4 m in 1983 dropped to �41.1 m in 2008 (Fig. 6A). This lower-ing trend accelerated in 1990 (October �20.1 m) and 1999 (Octo-ber �26.5 m). The most rapid decline in the water table occurredbetween 2005 and 2008, when the water table fell about 8 m(�33.1 m to �41.1 m). This period coincided with the formationof many sinkholes.

The data set obtained from the Egilmez well (well No. 52268) inthe Hotamıs� Plain, in the southeast part of the study area (Fig. 4)indicates that the water table fell 22.5 m during the 35 years be-tween 1974 and 2008 (Fig. 6B). As in the Gülfet Yayla well, themeasurements from this well also indicate a declining trend inthe water table from 1983 onwards.

The only well within the Obruk Plateau for which long term (be-tween 1996 and 2008) measurements were taken is the Yenikentwell (well No. 38306), located 1046 m to the west of Meyil sink-hole (Fig. 4). The water table depth fell from �67 m in October1996 to �82.6 m by July 2008.

The recent dry period which has been influential in the regionsince 1980, has also contributed to the drop in groundwater levelthroughout the basin. Göçmez et al. (2008b) determined that 60%of the change in groundwater level in the KCB and 40% of thechange in groundwater around Karapınar has resulted from cli-matic variables; the remaining change was caused by excessivewater pumping. The years 1983, 1990 and 1999, when a subsi-dence trend was observed in the water table, coincided with theextension of irrigated farming, a period of climatic drought, andthe introduction of agricultural crops with greater water require-ments. The water table levels in Gülfet Yayla and Egilmez wellsstarted to show increased seasonal fluctuations, particularly from1990 onwards. These fluctuations have increased over time, andare related to excessive water extraction from the aquifer for agri-cultural purposes. This process caused the groundwater level in thebasin to drop. Accordingly, many shallow lakes, marshes and otherwater sources have dried up and the level of Tuz Lake has gonedown.

2.3. Geomorphologic setting

The Obruk Plateau is an extensive area (approximately 90 kmE–W and 80 km N–S), which is 40–100 m higher than the Tuz Lakesub-basin in the north and the Konya Plain sub-basin in the south.

The neotectonic regime, which is influential in the region, had agreat influence on the southern and southeastern morphologic out-line of the Obruk Plateau (Koçyigit, 2005). While the _Insuyu Forma-tion is covered with thick Quaternary sediments of Konya Graben,which has started to subside under the influence of the extension

Fig. 6. Long-term groundwater level changes around Karapınar: (A) Gülfet Yayla well (well No. 52258 or 220); (B) Egilmez well (well No. 52268). Water level measurementsin wells were performed by DS_I in January, April, July and October. Well locations are shown in Fig. 4.


regime in the south of the plateau, it has remained relatively highin the Obruk Plateau. The Tuz Lake sub-basin constitutes the low-est area of the Konya Basin topographically. For that reason,groundwater flows from the Konya Plain (�1000 m) towards TuzLake (�905 m).

Pluvial lakes covering hundreds of square kilometers andreaching depths of several tens of meters emerged in the KonyaPlain sub-basin during glacial periods and then largely or entirelydisappeared during warm periods (Erol, 1986, 1990). During theLast Glacial Maximum, the present Konya Plain was covered bythe Paleo-Konya Lake. The Paleo-Konya Lake reached its most re-cent highest level between 23 and 17 14C ka BP (Roberts et al.,1979). The lake covered an area of more than 4000 km2, and wasmore than 20 m deep (Fontugne et al., 1999; Karabıyıkoglu et al.,1999). The same process affected the Tuz Lake sub-basin (Erol,1971; Kashima, 2002).

Climate cycles during the Quaternary led to high amplitudewater table fluctuations in the Obruk Plateau because of the emer-gence and disappearance of lakes in the KCB. According to Erol(1986, 1990) caves at different levels must have been formed inthe _Insuyu Formation limestone in the Plateau. It would thereforebe reasonable to suppose that each climatic cycle was character-ized by the formation of new-generation sinkholes, which led todramatic water table drop and therefore the removal of the buoy-ant support of cavity roofs. Erol (1986, 1990) indicated the rela-tionship between distributions of sinkholes and changes in theQuaternary lake level with detailed geomorphologic maps.

The great majority of the sinkholes in the Obruk Plateau arelocated within the study area (Fig. 7). Of the more than 100 older

sinkholes, a few are located on the edges of the Karapınar-Hotamıs�Plain. Large sinkholes are easily detected on topographical maps.Tens of sinkholes several meters deep, ranging in diameter be-tween several meters and several hundred meters, could only bedetermined with the aid of aerial photographs and fieldwork, sincethey were too shallow or ruined and had become in filled to detectotherwise.

There are several significant, large sinkholes in the KCB thatcontain lakes, because they extend down to the water table. Ofthese, Meyil and Çıralı obruks are in the study area, while Kızören,Timras� and Apa are in different parts of the basin. In addition, thereare a number of large and deep sinkholes, such as the Ak, Potur,Karain, Kangallı and Kızıl obruks, located north of the study area(Fig. 7 and Table 1).

While some of the old sinkholes are collapse sinkholes, formeddirectly as a result of the collapse karstic void roofs in the _Insuyulimestone, some are caprock sinkholes (Lowe and Waltham,2002; Waltham and Fookes, 2003; Ford and Williams, 2007),formed in the non-karst rocks over the limestone in the plateau(A–A0 cross-section in Fig. 8). While some of the non-karst rocksin the plateau were deposited in lacustrine environments duringthe Neogene or Quaternary (Ulu, 2009a), some are composed ofterrestrial sediments such as alluvial fan, colluviums. Most of theterrestrial sediments are located in uvalas on the plateau (Erol,1990). Combined paleo-sinkholes, which have lost their character-istics to a great extent as a result of erosion and infilling and/orkarstic subsidence, have contributed greatly to the formation ofuvalas. Secondary and third generation caprock sinkholes wereformed in the uvalas (A–A0 cross-section in Fig. 8).

Fig. 7. Location of the sinkholes in the study area.

Table 1Morphometric features of the some huge old sinkholes.

Sinkhole name MeyilObruk

ÇıralıObruk

ÇiftelerObruk

KızılObruk

YarımObruk

DerinObruk

AkObruk

PoturObruk

KangallıObruk

Approximate shape at surface Circular Circular Circular Circular Circular Circular Circular Elliptical CircularDiameter at ground surface (m) 640–650 310–320 440–450 700–710 440–470 250–260 560–570 520–760 420–450Elevation at ground surface (m a.s.l.) 1053 1065 1078 1072 1062 1060 1073 1070 1052Diameter at lake surface (m) 300–320 138–140 – – – – – – –Elevation at lake level (m a.s.l.) 963 965 – – – – – – –Depth from ground surface (m) 90 100 73 88 49 33 69 82 66Bottom diameter of dry sinkhole (m) – – 130–150 150–170 180–190 60–70 210–270 200–260 150–180Dry sinkhole bottom elevation (m) – – 1005 984 1013 1027 1004 988 986


3. Results

Information gathered from local residents, publications, andofficial institutions suggests that the oldest sinkholes which areknown to have been newly formed in the vicinity of Karapınar date

from 1977. In the 33 years since then, 19 sinkholes have formed(Fig. 7 and Table 2).

Between 1977 and 2000, six sinkholes (Akviran, Nebili, Sekizli,Yirce, Kolca and Yavs�an Çukuru obruks) occurred in the vicinityof Karapınar. The first of these was Akviran Obruk, formed in

Fig. 8. Geologic and geomorphologic cross-section of the sinkholes.

Table 2Morphometric features of the sinkholes which was formed in the last 33 years (1977–2009).

Sinkhole name Formation date Coordinate (UTM) Altitude (m) Diameter (m) Depth (m) With lake

Akviran Obruk 1977 36537410E 4194381N 1048 19.3 78 +Nebili Obruk 1983 36546950E 4184955N 1090 18.5 23 �Sekizli Obruk 1983 36541216E 4192416N 1033 16.7 3.30 �Yirce Obruk 1985 36542625E 4185360N 1065 45 40 �Kolca Obruk 1995 36540780E 4193860N 1033 52 26 �Yavs�an Obruk 2000 36541960E 4178196N 1040 21 69 +Küpbasan Obruk 2006 April 36543359E 4176502N 1002 19 6 �Seyithacı Obruk I 2007 April 36551202E 4185732N 1009 15.25 1.06 �Seyithacı Obruk II 2007 June 36550685E 4185044N 1009 17.5 4.5 �Seyithacı Obruk III 2007 July 36550746E 4185470N 1009 24.95 7.8 �Akkuyu Obruk I 2007 August 36532443E 4177474N 1022 15.7 2.1 �Seyithacı Obruk IV 2007 November 36551147E 4185796N 1008 3.2 4.5 �Akviran Obruk I 2007 December 36537554E 4194085N 1045 2 0.5 �Akkuyu Obruk II 2008 August 36531546E 4175616N 1008 15 1 �Seyithacı Obruk V 2008 October 36551199E 4185647N 1008 11.6 2.5 �Seyithacı Obruk VI 2008 October 36550537E 4184508N 1011 4.5 6.6 �_Inoba Obruk 2008 November 36537746E 4159336N 1010 24 35 +

Akkuyu Obruk III 2009 February 36532232E 4174442N 1008 24.8 35.8 +Es�eli Obruk 2009 February 36545128E 4181330N 1036 15.9 0.85 �


1977. Among the sinkholes situated at elevations between 1033and 1090 m on the Obruk Plateau, the deepest is Akviran Obruk(78 m), and the widest is Kolca Yayla Obruk (52 m), formed in1995 (Fig. 9). All of these sinkholes are caprock sinkholes formedin relatively low-lying Quaternary sedimentary areas within theplateau, defined by Erol (1986, 1990) as uvalas. These sinkholesformed in and around the summer pasture settlements orroadsides.

Between 2006 and 2009, 13 sinkholes have formed in andaround summer pasture settlements in the vicinity of Karapınar.Two of these sinkholes, the _Inoba and Akkuyu (Yarımoglu) IIIobruks, were covered by the national media due to their large size(Table 2) and the hazards they presented.

Because these 13 sinkholes are situated in six different loca-tions, they will be discussed in groups; the six sinkholes formedin the vicinity of the Seyithacı settlement belong to the Seyithacı

Fig. 9. Kolca Yayla Obruk (caprock sinkhole) formed in the Obruk Plateau at adistance of 100 m to Karapınar-Kolca Yayla road.


obruks; the three sinkholes in the vicinity of Akkuyu settlementform the Akkuyu obruk group. The Inoba, Küpbasan, Es�eli andAkviran II obruks do not form part of a group and will be discussedseparately.

3.1. Seyithacı Obruks

Between April 2007 and October 2008, six sinkholes of variousdimensions formed in and around the Seyithacı settlement situ-ated on the adjacent part of the Obruk Plateau to the plain(1008–1011 m) (Figs. 7 and 10 and Table 2). This settlement wasseparated by faults from the Obruk Plateau (1100 m) and KarapınarPlain (1000 m). On the walls of Seyithacı sinkholes, there is greenclay (1 m thickness) overlying the limestone; and there is soil of0.5 m thickness above the clay. Seyithacı sinkholes formed in the_Insuyu limestone are defined as collapse sinkholes due to thin cap-rock despite this stratigraphic section.

Of the six Seyithacı sinkholes, four were formed in agriculturallands several hundred meters from the settlement (Fig. 10A, E, Fand G) and the remaining two (Seyithacı II and III sinkholes), whichare wider than the others, formed within the settlement (Fig. 10B,C and D).

Seyithacı II sinkhole formed 10 m west of the settlement accessroad in the middle of a pathway. It is situated 30 m from localhouses. 0.8 m clay above limestone, and �0.5 m soil is presentabove this sediment on the wall of the sinkhole.

Seyithacı III sinkhole formed in the north part of the settlement,at a distance of 30 m from both the road and houses (Fig. 10C andD). Circular tension fractures 20 cm in width extend 2 m from thesinkhole, and indicate that the diameter of the sinkhole is likely toenlarge to at least �4 m within a short time. The lithologic struc-ture of the sinkhole wall is the same as Seyithacı II.

3.2. Küpbasan Obruk

This sinkhole, which is on the Quaternary lake deposits on theedges of the Karapınar Plain, is situated at an elevation of1002 m. The sinkhole formed in the center of Küpbasan summerpasture settlement. Local people attempted to fill the 6 m deepsinkhole with back fill. It could be defined as a caprock sinkhole,because the non-karstic rocks in which it was formed are relativelythick compared to the Seyithacı sinkholes.

3.3. _Inoba Obruk

This sinkhole formed during late 2008 on the west side of _Inobasettlement, 30 km southwest of Karapınar. The sinkhole is 50 m

from the settlement houses (Fig. 11A) at the edge of the KarapınarPlain, which is 8 m higher than the plain bottom and surrounds thesettlement of _Inoba on the west. The sinkhole is 24 m in diameterand, since it is 35 m deep, it intersects the water table and a lakehas formed within it (Fig. 11B). Approximately 250 m to the southof _Inoba sinkhole, there is a larger old sinkhole.

_Inoba Obruk was formed in non-karst Quaternary lacustrinesediments composed of clay, marl, silt and red mudstone layersof various colors and thicknesses (C–C0 cross-section in Fig. 8).The thickness of some of the silt layers exceeds 1 m. Due to thischaracteristic, _Inoba Obruk is defined as a caprock sinkhole.

For 2 days prior to the formation of the sinkhole, local peopleheard noises underground. Intermittent sounds, originating fromunderground over a period of 2 days, caused villagers to leave theirhouses in the evenings for fear of an earthquake. Some local resi-dents mentioned that they heard these noises while they were intheir houses and that the frightening noises coming from under-ground sounded like a large mass falling into water (personal com-munication: Mehmet Köroglu, a resident of _Inoba Yayla). On themorning of the third day, a newly-formed sinkhole was observed.According to this piece of information, the dramatic fall of thewater table and high seasonal fluctuations caused both the in-crease in the effective weight of the karstic void span and the fallof rocks from the span. Thus, the karstic void roof could not bearthe load and collapsed.

3.4. Akkuyu Obruks

During 2007 and 2008, three sinkholes formed in the vicinity ofAkkuyu summer pasture. The first two were named Akkuyu ObrukI and Akkuyu Obruk II, according the order in which they formed.The third obruk was the largest and was named Yarımoglu Obrukby the local people. However, this sinkhole is referred to as AkkuyuObruk III in this publication.

Akkuyu Obruk I (which is located on the Plateau) and AkkuyuObruk II are caprock sinkholes with diameters of �15 m anddepths of 1 m. Since these sinkholes are not very deep, only soilis visible in their wall. They were formed due to the sag of thecaprock.

Akkuyu (Yarımoglu) Obruk III is 15 km west of Karapınar, sit-uated 200 m north of the Karapınar-Konya highway, and 500 mfrom farmhouses in Akkuyu (Fig. 12). It formed while maizewas being harvested in a field on the edges of the Hotamıs�Plain.

The sinkhole is 35.8 m deep; the mouth is 20.4 m wide in anorth–south direction and 24.8 m wide in an east–west direction.Many fractures are visible within several meters around the sink-hole. These fractures and the slope profile of the sinkhole indicatethat enlargement will occur in the future. There is a lake at the bot-tom of the sinkhole, which reaches the water table. This sinkhole isa caprock sinkhole formed in non-karstic sediments on the lime-stone (B–B0 cross-section in Fig. 8).

3.5. Es�eli Obruk

Es�eli Obruk is located in the northwest of Es�eli summer pasture,at an altitude of 1036 m (on the Plateau). Its diameter is 15.9 m andthe depth is 0.85 m. It is a shallow sinkhole, similar to the Akkuyu Iand Akkuyu II obruks.

3.6. Akviran Obruk II

This sinkhole was formed on the Obruk Plateau. Even thoughthe sinkhole formed south of Akviran Obruk is relatively verysmall, it is important in the sense that it indicates that there arestill hazards on the plateau.

Fig. 10. The Seyithacı obruks (2007–2009). (A) Seyithacı Obruk I, (B) Seyithacı Obruk II, (C and D) Seyithacı Obruk III, (E) Seyithacı Obruk IV, (F) Seyithacı Obruk V, and (G)Seyithacı Obruk VI.


4. Discussion

The sinkholes developed on karstic voids which were formedwithin the _Insuyu Formation limestone by karst groundwater.The increasing effective weight of the load on the roofs of thesevoids caused them to collapse, forming sinkholes. These small kar-stic voids (or cavities) have been documented by several boreholesin the Obruk Plateau. The groups of Seyithacı obruks are collapsetype and the other sinkholes are caprock types.

While changes in the groundwater level related to the Quater-nary climate cycles became influential in the formation of paleo-sinkholes, human activities together with natural karst processeshave triggered the formation of many new sinkholes (particularly

between 2006 and 2009 years). Excessive pumping from theunderground and climatic aridity has contributed to falling ofthe water table by approximately 24 m during the last 26 years.High amplitude progressive seasonal fluctuations of the water ta-ble (related to pumping of the summer months) have causedexisting karstic voids to migrate upward. In particular, breaks incaprocks have caused unsupported roofs to weaken from the bot-tom. Hydraulic support from groundwater on the cavity roofs dis-appeared as the water table dropped. This affected cavity roofs,increasing the effective load on the spans and causing roofs tocollapse. Therefore, unlike paleo-sinkholes, sinkholes formedrecently near Karapınar stem from both natural processes andhuman activities.

Fig. 11. The _Inoba Obruk sinkhole was formed near the _Inoba settlement.

Fig. 12. Akkuyu (Yarımoglu) Obruk III is the deepest of new sinkholes.


The altitudes and geographical distributions of the sinkholesformed in recent years support the concept that water table de-cline has induced the collapse of cavity roofs. Among the sinkholesformed in the last 33 years, all of those formed before 2000emerged on the plateau, but in the bottoms of the uvalas, whichare relatively lower; those formed after 2006 (except for AkviranII, Akkuyu I and Es�eli obruks) emerged on the low lying adjacentpart of the Plateau to the plain and edges of the Karapınar-Hotamıs�

Plain (�8–10 m higher than the lower part of plain). This spatialdistribution and time relationship show that the first sinkholesformed in the uvala bottoms – with relatively thin karstic voidroofs – between 1977 and 2000 when the water table was higher(�24 m and 13 m, respectively) than the present time. The watertable dropped further (�13 m) between 2000 and 2008, leadingto conditions under which cavity roofs collapsed largely on theedge of plateau and plain. The sudden fall (measuring up to 8 m)of the water table, particularly between the years 2005 and 2008,strengthens the evidence for a relationship between water tabledecline and the formation of new sinkholes. With the exceptionof Akrivan II, Akkuyu I and Es�eli obruks, sinkholes that have formedwithin the last 4 years (2006–2009) are situated at very similaraltitudes (between 1002 and 1011 m), further evidence for a rela-tionship between falling water table and cavity collapses.

The findings of the present research support the earlier conclu-sions by Erol (1986, 1990), suggesting that sinkhole formation inthe Konya Basin is triggered by changes in groundwater level. Erolstated that groundwater flowed from the Paleo-Konya Lake to theTuz Lake, which occurred during pluvial (wet) periods in the Qua-ternary, thereby enlarging the voids, and that sinkhole formationtook place during the period in at least in four stages, as a resultof the regression in lake levels (water tables) during the intergla-cial periods.

In addition, Canik and Çörekçioglu (1986) found that thegroundwater contained high levels of CO2 as a result of Plio-Qua-ternary volcanism. CO2 accelerates karstic dissolution, leading tosinkhole formation (Canik and Çörekçioglu, 1986). Bayarı et al.(2009b) proposed that sinkholes are formed through hypogenickarstification, in which particularly strong geogenic carbon dioxideoscillation is effective. In addition, slope profiles of newly-formedsinkholes invalidate previous evaluations (Erinç, 1960; Bayarıet al., 2009b) of the formation mechanisms based on the slope pro-files of giant paleo-sinkholes such as Kızören, Çıralı, Meyil and Tim-ras� obruks (Fig. 1). Therefore, it may be suggested that concave orconvex slopes seen in the slope profiles of sinkholes have devel-oped as a result of changes in the lithology of the bedrock formingthe sinkhole walls; partial collapses in the mouth and on the wallsafter sinkhole formation; and rock falls and erosion.

Many sinkholes have formed around Karapınar, on the ObrukPlateau and at the edges of the Karapınar-Hotamıs� Plain sincethe beginning of the Quaternary. However, increased human influ-ence is causing the dramatic water table decline in the KCB, whichmost likely has a more significant influence on the formation ofsinkholes in recent years in comparison to climatic factors. Accord-ingly, it appears that newly-formed sinkholes on the Obruk Plateauand plain were formed through a combination of natural and hu-man influences. In addition, considering the mostly random distri-bution of old and new sinkholes on the plateau and plain; and themany paleo-sinkholes intersecting one another, it can be suggestedthat sinkholes were formed on network or spongework type karstconduits developed in the horizontal lacustrine limestone of the_Insuyu Formation. On the other hand, it can be said that many ofthe sinkholes extending along the northwest–southeast directionon the plateau and located in a line between Meyil and Çıralıobruks were formed on the same conduit (Fig. 7; A–A0 cross-sec-tion in Fig. 8).

5. Hazard of karst collapse

Observation of sinkhole, those formed between the years 1977and 2000, and geomorphic–hydrographic data imply that sinkholesare less likely to be formed in the plateau compared to the plains,but that they have the potential to be larger. The hazard of sinkholeformation in central sections of the plains is greatly reduced by the


thickness of Quaternary sediment above the limestone (more than100 m thick in some sections) and the formation of karst is notgood because of the high water table.

Overall, sinkhole formation in the last 33 years has advancedfrom the plateau (relative altitude 40–100 m) towards the plainas a result of the falling of the water table.

It could be argued that if the water table continues to drop infuture years, the susceptibility of sinkholes will remain mainlyfor the edge of the Karapınar-Hotamıs� Plain, the low lying adjacentpart of the plateau to the plain and parts of the Obruk Plateau. Set-tlements in the Obruk Plateau (Akviran, Kolca, Sekizli summer pas-tures, etc.) may also face a slight hazard of collapse. Especially thehigh hazard levels might also occur at the edge of the Karapınar-Hotamıs� Plain and the low lying part of the plateau adjacent tothe plain (particularly in and around Seyithacı, Küpbasan, Akkuyu,_Inoba summer pastures). This prediction is corroborated by thepresence of the paleo-Atçukuru Obruk on the plain to the southof the Karapınar-Konya road (Erol, 1990) (Fig. 7) and also severalpaleo-sinkholes situated in the plain side, several meters belowthe new sinkholes in the vicinity of the _Inoba and Seyithacı. Thesepaleo-sinkholes must have been formed during periods when thewater table was close to its present level or lower.

The sinkholes prior to 2000 were generally formed in the vicin-ity of the summer pastures in the Obruk Plateau, where transpor-tation and human activities are not very dense and several familieslive, mainly engaged in stockbreeding. This situation decreasedhazard in terms of human safety and property security. However,new sinkholes formed in settlements and in the vicinity of high-ways have become a threat to life and property.

6. Conclusion

Nineteen sinkholes of various dimensions have formed duringthe last 33 years (most of them during the past 4 years, between2006 and 2009) on the Obruk Plateau and side of the Karapınar-Hotamıs� Plain. Formation of collapse and caprock sinkholes was trig-gered by natural processes, human-induced lowering of the watertable, and increased seasonal fluctuations in the water table level.

Recent sinkholes in the vicinity of Karapınar vary in age theyformed in succession on the Obruk Plateau and spread to the Kar-apınar-Hotamıs� Plain. This orientation indicates that sinkhole for-mation in the KCB has been triggered by drops of groundwaterlevel (around 24 m in the last 26 years) largely caused by humanactivities. The fact that the Obruk Plateau is 40–100 m higher thanthe adjacent plain allows the roof thickness above the voids to bethicker, thereby limiting the number of sinkholes formed in theseareas in contrast to the edge of the Karapınar-Hotamıs� Plain andthe low lying adjacent part of the plateau to the plain.

The results presented in this paper raise awareness and the lo-cal decision makers should take into account the collapses. There-fore, illegal deep wells must be closed, in order the loss of life andproperty to sinkholes and the cultivation of crops which are notnaturally able to withstand the climatic conditions of the basinshould cease. Subsequently, water pumping must be controlledvia licensed deep wells and reduced to the minimum level neces-sary, and further depletion of the water table must be prevented.In addition, immediate action must be taken to identify under-ground voids or conduits (using such methods as geophysics anddrilling), particularly in Seyithacı, Küpbasan, _Inoba, and the Ak-kuyu summer pasture settlements, in the vicinity of Karapınar-Konya road, and in some settlements in the plateau.

The immediate hazards of sinkhole formation might be reducedby recharging the aquifer using surface-water from within the ba-sin or from an adjacent basin. However, this approach is problem-atic, as there are insufficient water resources within the basin for

this operation; also, it is very difficult to divert water from adjacentbasins, due both to water stress in these areas and the high costsinvolved. Therefore, there is an urgent need to implement a watermanagement action plan in the KCB.

Acknowledgements

We would like to thank Musa Ceyhan and Mehmet Köroglu fortheir areal guidance in the study. We would like to thank MuratAtaol for his assistance. Also, We would like to thank Owen Doonanwho revised final English text of the manuscript. We are also grate-ful to Prof. Boris Natalin and to two anonymous reviewers for theirconstructive comments.

References

Alberto, W., Giardino, M., Martinotti, G., Tiranti, D., 2008. Geomorphological hazardsrelated to deep dissolution phenomena in the Western Italian Alps:distribution, assessment and interaction with human activities. EngineeringGeology 99, 147–159.

Bayarı, C.S., Özyurt, N.N., Kilani, S., 2009a. Radiocarbon age distribution ofgroundwater in the Konya Closed Basin, central Anatolia, Turkey.Hydrogeology Journal 17, 347–365.

Bayarı, C.S., Pekkan, E., Özyurt, N.N., 2009b. Obruks, as giant collapse dolines causedby hypogenic karstification in Central Anatolia, Turkey: analysis of likelyformation processes. Hydrogeology Journal 17, 327–345.

Benito, G., Pérez del Campo, P., Gutiérrez, M., Sancho, C., 1995. Natural and human-induced sinkholes in gypsum terrain and associated environmental problems inNE Spain. Environmental Geology 25, 156–164.

Biricik, A.S., 1992. Geomorphology of the Obruk Plateau and its Surroundings.Marmara University Publication, _Istanbul (in Turkish).

Brinkmann, R., Parise, M., Dye, D., 2008. Sinkhole distribution in a rapidlydeveloping urban environment: Hillsborough County, Tampa Bay area,Florida. Engineering Geology 99, 169–184.

Bruno, E., Calcaterra, D., Parise, M., 2008. Development and morphometry ofsinkholes in coastal plains of Apulia, southern Italy. Preliminary sinkholesusceptibility assessment. Engineering Geology 99, 198–209.

Canik, B., Çörekçioglu, _I., 1986. The formation of sinkholes (Obruk) betweenKarapınar and Kızören-Konya. In: Karst Water Resources (Proceedings ofAnkara-Antalya Symposium, July 1985). IAHS Publ. No. 161, pp. 193–205.

Dogan, U., 2005. Land subsidence and caprock dolines caused by subsurface gypsumdissolution and the effect of subsidence on the fluvial system in the Upper TigrisBasin (between Bismil–Batman, Turkey). Geomorphology 71, 389–401.

Dogan, U., Çiçek, _I., 2002. Occurrence of cover-collapse sinkholes (cover-collapsedolines) in the May Dam reservoir area (Konya, Turkey). Cave and Karst Science29 (3), 111–116.

Dogan, U., Özel, S., 2005. Gypsum karst and its evolution east of Hafik (Sivas,Turkey). Geomorphology 71, 373–388.

Dogan, U., Yes�ilyurt, S., 2004. Gypsum karst south of Imranlı, Sivas, Turkey. Caveand Karst Science 31 (1), 7–14.

DS_I, 1975. Hydrogeological Investigation Report of the Konya-Çumra-KarapınarPlain. State Hydraulic Works General Direction, Ankara.

Erinç, S., 1960. On the karst features in Turkey. Turkis Geographical Review 20, 83–106.

Erol, O., 1971. Geomorphological evidence of the recessional phases of the pluviallakes in the Konya, Tuzgölü and Burdur basins in Anatolia. Ankara UniversityAnnals of the Geographical Research Institute 3–4, 13–52.

Erol, O., 1986. The relationship between the phases of the development of theKonya- Karapınar obruks and the Pleistocene Tuzgölü and Konya pluvial Lakes.In: Karst Water Resources (Proceedings of Ankara-Antalya Symposium, July1985). IAHS Publ. No. 161, pp. 207–213.

Erol, O., 1990. The relationship between the phases of the development of theKonya-Karapınar obruks and the Pleistocene Tuzgölü and Konya pluvial lakes,Turkey. Bulletin of the Institute of Marine Sciences and Geography Bulletin 7, 5–50.

Eroskay, O., Günay, G., 1980. Tectonic classification and hydrogeological propertiesof the karst regions in Turkey. In: International Seminar on Karst HydrogeologyAntalya, 1979. Publ. by SHW, pp. 1–41.

Fontugne, M., Kuzucuoglu, C., Karabıyıkoglu, M., Hatte, C., Pastre, J.F., 1999. FromPleniglacial to Holocene: a 14C chronostratigraphy of environmental changes inthe Konya Plain, Turkey. Quaternary Science Reviews 18, 573–591.

Ford, D., Williams, P., 2007. Karst Hydrogeology and Geomorphology. John Wileyand Sons, Chichester.

Galve, J.P., Gutiérrez, F., Lucha, P., Bonachea, J., Remondo, J., Cendrero, A., Gutiérrez,M., Gimeno, M.J., Pardo, G., Sánchez, J.A., 2009. Sinkholes in the salt-bearingevaporite karst of Ebro River valley upstream of Zaragoza city (NE Spain):geomorphological mapping and analysis as a basis for risk management.Geomorphology 108, 145–158.

Göçmez, G., Dıvrak, B.B., Galena, _I., 2008a. Determination of the Groundwater LevelChanges in the Konya Closed Basin, Summary Report. WWF, Istanbul (inTurkish).


Göçmez, G., Genç, A., Karakoca, A., 2008b. Statistically assessment of groundwaterlevel change in the Konya closed basin. In: Conference on Groundwater andDrought in Konya Closed Basin, Konya, 11–12 September 2008, pp. 98–107 (inTurkish).

Gutiérrez, F., Guerreo, J., Lucha, P., 2008a. A genetic classification of sinkholesillustrated from evaporite paleokarst exposures in Spain. EnvironmentalGeology 53, 993–1006.

Gutiérrez, F., Guerreo, J., Lucha, P., 2008b. Quantitative sinkhole hazard assessment.A case study from the Ebro Valley evaporite alluvial karst (NE Spain). NaturalHazards 45, 211–233.

_Is�çioglu, A., 2008. An overview of groundwater use and allocation in Konya ClosedBasin. In: Conference on Groundwater and Drought in Konya Closed Basin,Konya, 11–12 September 2008, pp. 135–142 (in Turkish).

Karabıyıkoglu, M., Kuzucuoglu, C., Fontugne, M., Kaiser, B., Mouralis, D., 1999. Faciesand depositional sequences of the Late Pleistocene Göçü shoreline system,Konya basin, Central Anatolia: implications for reconstructing lake-levelchanges. Quaternary Science Reviews 18, 593–609.

Kashima, K., 2002. Environmental and climatic changes during the last 20,000 yearsat Lake Tuz, central Turkey. Catena 48, 3–20.

Keller, J., 1974. Quaternary maar volcanism near Karapinar in Central Anatolia. BullVolcanol 38, 378–396.

Koçyigit, A., 2005. The Denizli graben-horst system and the eastern limit of westernAnatolia continental extension: basin fill, structure, deformational mode, throwamount and episodic evolutionary history SW Turkey. Geodinamica Acta 18(3–4), 167–208.

Lowe, D., Waltham, T., 2002. Dictionary of Karst and Caves. BCRA Cave StudiesSeries 10, Buxton.

Luzón, A., Pérez, A., Soriano, M.A., Pocoví, A., 2008. Sedimentary record ofPleistocene paleodoline evolution in the Ebro basin (NE Spain). SedimentaryGeology 1–2, 1–13.

Newton, J.G., 1987. Development of Sinkholes Resulting from Man’s Activities in theEastern United States. US Geological Survey Circular 968.

Özsayın, E., Dirik, K., 2007. Quaternary activity of the Cihanbeyli and YeniceobaFault Zones: _Inönü-Eskis�ehir Fault System, Central Anatolia. Turkish Journal ofEarth Sciences 16, 471–492.

Parise, M., Waele, J.D., Gutiérrez, F., 2008. Engineering and environmental problemsin karst-an introduction. Engineering Geology 99, 91–94.

Roberts, N., Erol, O., Meester, T., Uerpmannn, H.P., 1979. Radiocarbon chronology oflate Pleistocene Konya Lake, Turkey. Nature 281 (5733), 662–664.

Ulu, Ü., 2009a. Geological Maps of Turkey Karaman-M30 Sheet. General Directorateof Mineral Research and Exploration, Ankara (in Turkish).

Ulu, Ü., 2009b. Geological Maps of Turkey Karaman-M31 Sheet. General Directorateof Mineral Research and Exploration, Ankara (in Turkish).

Waltham, A.C., 1989. Ground Subsidence. Blackie, Glasgow.Waltham, T., Bell, F., Culshaw, M., 2005. Sinkholes and Subsidence. Springer, Berlin.Waltham, A.C., Fookes, P.G., 2003. Engineering classification of karst ground

conditions. Quarterly Journal of Engineering Geology and Hydrogeology 36,101–118.

White, W.B., 1988. Geomorphology and Hydrology of Karst Terrains. OxfordUniversity Press, Oxford.

Documents

Natural and induced sinkholes of the Obruk Plateau and Karapınar-Hotamış Plain, Turkey