Karst Water Resources (Proceedings of the Ankara - Antalya Symposium, July 1985). IAHSPubl.no. 161

THE FORMATION OF SINKHOLES (OBRUK) BETWEEN KARAPINAR AND KIZÔREN - KONYA

Baki Canik Selçuk University, Faculty of Engineering - Architecture, Department of Geological Engineering, Konya, Turkey

ilhami Çôrekçiogiu DSl 4. Regional Directorate, Geological Engineer, Konya, Turkey

Abstract

Obruks constitute the most important karstic features within the carbonate rocks of Konya region in Central Anatolia. The most important of these has been formed within lacustrine limestones of Neogene, namely the Cihanbeyii Formation. In the region, obruks developed in Cretaceous limestones also exist. Between Karapsnar and Kizoren, the karstification of limestones and the related obruks development haye been continuing since the beginning of Quaternary up to now. Among these, internal karstification is very important. The most important factors affecting internal karstification are neotectonics of Centrai Anatolia after Pliocene, groundwater flow and increased corrosion of limestones due to dissolving of volcanic CQ2 and asidic gases in great quantities within the underground waters. The areas of horizontal sections are observed to be widened deeper in the new and undisturbed obruks, while the recent obruks are 70 m deep or more with dangerous appearence, the uvalas have been formed by joining of the oldest obruks. The ceiling of the cavities that have been formed as the result of the internal karstification, collapse because of heavy load. If the collapsing reaches the water table, water filled obruks develop; if on the other hand collapsing does not reach the water table, dry obruks are observed. Occasional out - coming of shocks and sounds from the underground which disturb local people must be the informer of the formation of a new obruk.

Introduction

Various karstic features have been formed within different aged limestones in Konya Plateau of Central Anatolia. The most important of these consists of sinkholes formed within lacustrine Neogene limestones. Approximately fifty sinkholes of different diameter and depth exist between Southern Nebili sinkhole and Northwestern Haciveli sinkhole within Karaptnar - Kizoren region which covers an area of 28 km length and 4 km width (Guidait, and §aroglu, 1983). The bottoms of a few of these have reached the water table. Their formation has been continuing since Middle Quaternary. The area of study is approximately 1800 km2 (Fig. 1).

193

194 B. Canik & 1. Çôrekçioglu

The average heights change between 1000—1080 m within the area, excluding Clzecek Mountain which approaches an altitude of 1293 m.

Data from the Karapmar meteorological station indicate that the mean temperature for the latest 7 years is 11.2°C and mean precipitation for the latest 16 years is 278 mm.

Geology

Upper Paleozoic : The oldest rocks in the region are marbles. They crop out in a narrow area at the South of Kizoren and Yellikuyu. They are grey coloured with abundant fractures and solution cavities. Agalede (1954) also attributes an age of Upper Paleozoic for these.

Neogene : Widespread lacustrine Neogene deposits consist of conglomerates, marls, silts, clays, limestones and silicified limestones.Their thickness around Sultanhani exceeds 1000 m in the drillings of Turkish Petroleums Ltd. and are named as Cihanbeyli formation. The thickness of the basal conglomerate reaches 90 m in the drill - hole Sultanhani - 1 which is situated at the East of the study area. Grey and beige coloured marls come above them. The marls consist of alternations of claystone and limestone, including a 20 m thick gypsum level. Solution limestones do not show an important thickness within the area. Their thickness in some petroleum drill - holes reach up to 300 m in the region (TPAO,

The formation of sinkholes in Konya 195

1076). Frequently marl, silt and clay exist in the uppermost part. They also contain 0.50 m thick limestone intercalations. Marls and silts are widespread between Ozecek Mountain and Çirah sinkhole. Here, the observed thickness is more than 70 m. Silicified limestone exists below these and in turn below the silicified limestone, karstic limestones take place.

Clay and marl levels and lenses have been observed within these limestones by geophysical studies. Upward increase in amount of dolomitic limestones is common between Çirah and Meyil sinkholes. Its appearent thickness within Çirali sinkhole is around 85 m. Within this, weakly cemented, brecciated 8-10 m thick silicified limestone levels exist. These levels can be seen at the northern skirts of Çirali sinkhole. The silicification of the limestone is related with the volcanisrn around Karapmar. Siliceous solutions which were related to the post Upper Pliocene volcanisrn, caused the silicium enrichment within the lake. Whitish and motley coloured marl, clay and silt deposits are widespread from Çirali sinkhole towards northwest and the various characteristics of the lithology can be observed in the sinkholes within the area. Marl and clayey levels are sometimes gypsious. MTA Tuz Lake studies (1982), give an age of Mio - Pliocene to the Neogene lacustrine deposits.

Volcanisrn : The volcanisrn of Ozecek Mountain should certainly have the same age with the young volcanisrn around Karapmar. Age of the extrusion is calculated to be 3 .2-1.1 million years by K/Ar method (Keller, J., 1974). Ozecek volcanisrn consist of basalt lavas, tuffites and pyroclastic materials. Mears which have been formed by gaseous explosions related to younger volcanisrn also exist in the region.

Factors That Control Sinkhole Formation

The formation of sinkholes within the study area has its own characteristics and it is difficult to observe similar features although similar circumstances happened to come together by chance. Therefore, conic and cylindiric karstic features with various depths and diameters occuring between Karapmar - Kizoren, should be defined as 'Obruk type karstification". 'The most important factors in Obruk type karstification are lithology of the rocks, effects of neotectonism within the region, flow direction of the underground water and its chemical composition.

A - Lithology of the Rocks : The lower levels of the Cihanbeyli formation in the region generally consist of limestones with clay and marl intercalations. They have fractures and solution cavities. The karstic structure has been well developed by the speeding up of limestone corrosion an by more dissolving of C0 2 and other asidic gases related with Kara­pmar volcanisrn within the underground water. Since the above pressure is decreased, part of the contaminated C02 evolves through the solution cavities during the flow of the under­ground water down to the spring. This, in turn, prolongs the effect of solution as it gains asidic characteristics within wet and moist environments at the surfaces of solution cavities and above the underground water table.

At the south, marl, clay and silt come over the limestone. These occurences which does not support the above pressure, are uncompact and sometimes contain thin dolomitic limestone beds. Nebili, Sekizli and Akviran obruks have been formed within them since

196 B.Canik & i.Çôrekçioglu

1977 (Fig. 2). Uniaxial compressive strength of marls and silts is found to be around 0.60 kg/cm2. Their cohesion is 0.30 kg/cm2, unit volume weight is 1.6-1.8 g/cm3 and elastic modulus is around 17—18 kg/cm2.

In the vicinity of Çirali, Karain, Dikmen and Meyil obruks, a few metres thick clay and marl stay above the lower limestone. The dolomitic limestones start from 980 m altitude and reach 85-90 m thickness at the surface (Fig. 3). These are generally intensely fractured and weakly cemented, and contain clay and marl lenses of a few metres thickness. The most important obruks that have been developed within dolomitic and silicified limestones are the above mentioned ones. The limestones had been silicified by mixing of siliceous solutions of Karapmar volcanic activities during Upper Pliocene. Formation of the karst features like Çirali, Karain or Akviran obruks by only surface solution of this type of rocks is seen to be impossible. But, deeper solution of the limestones underneath the dolomitic and silicified level, and collapsing of the incompetent marl, silt levels, prove the formation of "Obruktype" karst features.

Fig. 2 - Formation of Sinkholes (Obruks) Between Karapinar-Kizôren, KONYA.

The form

ation of sinkholes

in K

onya

c o

!/)

u

_o

o

to

BO

O

iZ

198 B.Canik & I.Çôrekçioglu

B - Origin of C02 : The most important factor in the solution of limestones that prove the formation of the obruks is the increase in the rate of CO, and the other asidic gases in the underground water. Volcanoes of Karapinar lake, Ozecek Mountain and Maar craters such as Meke Lake, Aci Lake and Yilan Obruk which have been formed by volcanic explosions indicate youngest volcanic activities in Quaternary (Keller, J., 1974). These activities which continued until the middle of Quaternary have caused emanation of C02

and other asidic gases. Volcanic C0 2 gase emanations can be observed even now around Yanmca, Nebili in the north and northwest of Ozecek Mountain and south of Gullukuyu. During the opening of wells of 60—70 m depth, special precautions are necessary in order to carry out the drilling against the C0 2 gases collected from 20—25 m on.

Fig. 4— Hydrogeological Map of The Area Between Karapmar-Kizôren, KONYA.

The formation of sinkholes in Konya 199

C—FJow of Underground Water : Here, some different views about the direction of underground water flow were obtained in the previous hydrogeological studies (DSI, 1975; Eroskay, 1976; MTA 1982), and hydrogeological map of the area has been prepared by measuring the underground water levels within present wefls in a 1800 km2 area during April 1985 (Fig. 4). The main direction of the underground water flow is seen to be from south and north at the map. The hydraulic gradient is around 5x10—4 between the south and north of the area. In addition, the asymmetrical ellipse of water isohips with the nort­herly sharp point, indicates basal water leakages at a point in the central part of the area where deeps obruks are widespread. The local movement direction of underground water at the northern half of the ellipse is toward the south because of these basal water leakages.The outflow of underground water of northerly movement is from the springs in the marshy place situated in the south of Tuz Lake. Most of the basal leakage is from two nearby spring areas in Baglica (Çôrekçioglu, 1969). No great change has been observed in the water yield withing the first 5 months period of 1985. Mean water yield of greater springs is 1.04 m3/s and of smaller springs is 0.23 m3/s. The movement of the underground water, from south to north has caused dissolving of C02 and other asidic gases of volcanoes in the underground water and turn, dissolving of the limestones through their way to the north.

The Tuz Lake fault is said to be a right lateral fault, formed during Middle - Uooer Miocene in the neotectonism of Central Anatolia (§aroglu,.et al., 1983), but the same fault is said to have at least 250 m of vertical tilt in Quaternary ,(Aziz, 1985; TPAO oral communication).This, in turn, indicates an underground water with greater paleohydraulic gradient from the vicinity of Hotamis. marshy area at the south to the Tuz LaKe at the north, during Quaternary period.

Characteristics of Obruks

Newly formed and shallow obruks are commonly called as "Opan". Akviran obruk that formed suddenly in 1977 has 15 m peripheral diameter and 60 m depth, and its bottom reaches the water table level. Its basal diameter is around 30-35 m. It developed within silts, clays and marls. Rubble and rock fragments exist at the bottom, because of landslides.

Nebili obruk, suddenly occurred in 1983 within silts and marls, situated 1.5 km west from Nebili hill. It has a mouth diameter of 10 m and depth of 70 m, and its horizontal sections get wider downwards. Its bottom has already reached the water table level but subsequenty broken rock fragments from the inside of the obruk have covered the bottom water.

Sekizli obruk, has started as a hole with 10-15 cm mouth diameter in 1983. In following few months, it suddenly collapsed within clays, silts, and marls in a rainy day. Its mouth diameter is now 5 m and its depth is 8.5 m.

A hole with a 8—10 cm diameter had developed within a footpath, 2 km NE of Yirce, in April 1985. Curious people without the knowledge of outcoming danger have enlarged the hole up to 40—50 cm diameter and deepened it to 40 cm. Here, a new obruk is to be formed at any moment.

200 B.Canik & L Çôrekçioglu

Formation of obruks within the study area has been continuing since the beginning of Quaternary and more effectively since the Middle of Quaternary. First formed obruks within marly and silty areas caused on occurence of uvala having the obruk relicts by increasing erosion between Dikmen and Sekizli. In addition, there exist many uvalas and poljes. Most typical example of poljes is the Meyil polje within which exist wet and dry obruks and settlements (Canik 1985).

Fig. 5— Map of the Area Sinkholes (Obruks) Intensively Distributed.

The formation of sinkholes in Konya 201

Most typical and good examples of oldest obruks constitute wet obruks of Meyil, Karain and Çirali and dry obruks of Dikmen, Yunus, Hamam, Kizil, Yanm, Derin, Ak, Fincan, Potur, Kangalh, Yilarili, Zincanca and Kayahbasj (Fig. 5). These are arranged in a NW-SE direction, having diameters of 8—700 m and depths of 10-80 m. Direction of obruks arrangement approximately corresponds to the joint systems (Fig. 6). Of these, Meyil, Dikmen, Karain, Kizil, Kangalli and Çirali obruks have formed within dolomitic limestones, whereas Çifteler and Ak obruks developed within marly and argillaceous rocks.

Underground solution cavities gradually get bigger and coalesce with each other and wide caves have been formed, as dissolving and transporting effects of underground water continue in the study area. The collapses begin when the cave ceilings get to support the above weight. These collapses do not always directly reach the surface. But, some sounds and quakes which occur as a result of great underground collapses can commonly reach the surface. These kinds of sounds from underground and sometimes slight earthquakes disturb the inhabitants of Hacihasip, Meyil, Uzuncakuyu, Egrikuyu, Haciveli, etc. Of course these are detectable events as the internal karstification and the collapsing of great blocks from the ceilings of underground caves continue. These events should be accepted as informers of formations of obruks at unexpected times and unexpected scales.

W 270 90 E

380 joints

50 joints

Fig. 6 — Joint Distrubition.

202 B.Canik & Î.Çôrekçioglu

Chemistry of Underground Water

Chemical compositions of the water samples taken from various locations have been correlated and their similarities with each other and origins of the ions have been examinated (Fig. 7). Lacustral Mio - Pliocene deposites which widespreadly occur within the area show vertical and horizontal differences. Volcanoes around Karapmar have also affected the chemical compositions of the waters. For example, the waters of Yellikuyu,Tilki§ar,Songul, Boriicek, Meyilyayla and Çirali obruk contain Ca, Mg and HC03. Well waters of Gumu§du-giin, Siileymanli, Çifte and Efeli yayla together with the water of Baglrca spring contain Ca, Mg, Na, HC03 and CL Well waters of Seyithaci, Yelekli, Çukurkuyu contain Mg, Ca, Na, HC03, S04 , CI and Tahir, Mezgitli yayla Mg, Na, Ca, S0 4 , HC03( CI.

Fig. 7 - Logarithmic Digram (after Scholler, 1935).

The formation of sinkholes in Konya 203

Chemical analysis of water samples in the investigation area :

Name of water

Sample location

Çukurkuyu

Seyithaci yayla

Yelekli "

Meyil obruk

Tahiryayia

Mezgitli yayla

Suleymanh yayla

Gumu|dtigiin "

Bagiica spring

E§eii yayla

Çifte "

Çirali obruk

Tilkijar yayla

Yelli kuyu yayla

Songiil yayla

Bôriicek "

Ca

3,9

4,8

4,3

2,5

3,4

4,4

4,8

5,9

5,3

4,0

5,5

4,7

3,1

4,2

5,3

5,8

Cations -

Mg

5,2

7,0

5,8

7,6

4,5

8,2

3,4

3,5

3,0

2,8

3,5

3,0

2,4

3,0

3,5

4,1

Meq/I

Na

2,35

3,70

4,22

5,85

3,40

6,65

2,75

3,1

2,5

1,78

2,60

0,80

1,25

1,35

1,15

0,60

K

0,09

0,56

0,25

1,02

0,05

0,07

0,17

0,29

0,05

0,05

0,07

0,09

0,08

0,07

0,09

0,12

Anions

CI

3,54

3,87

4,4

4,8

2,76

5,3

3,08

3,62

2,65

1,87

2,49

0,77

1,06

1,62

0,99

0,73

-meq/1

so4

3,60

4,60

4,70

3,04

5,40

9,3

0,87

1,36

0,60

0,38

0,59

1,20

1,18

1,52

1,36

1,10

HC03

4,4

7,6

5,4

9,1

3,1

4,8

7,15

7,85

7,65

6,4

8,6

6,6

4,6

5,5

0,99

8,8

204 B.Canik &Î.Çôrekçioglu

While waters with Ca, Mg and HC03 indicate the waters wandering in doiomitic and limestone areas, S04 contents also show the gypseous parts of the lacustrine ievels.

Conclusion

Internal karstification has been effective in the formation of obruks. The occurence of solution limestones below; clay, silt and silicified limestones above, the occurence of under­ground water flow direction from south to north and the abundant occurence of volcanic C02 and acidic gases within these waters constitute the most important factors.

Measured water levels within sinkholes and wells in the settled parts of the study area (April-1985):

Name of the Locality

Akçayazi Yelekli Demiryah Akkuyu Bôriicek Kiilfat Eseli Yantnca OimezH Guiiiikuyu Seyithaci B. Çukurca Ya§çayay!a Bursal B. Kôrin Çingiryayla S. Sekizli Akviranyayla Ortacebe Akobrukyayla Hacihasip Kabahasan Sivrioglu Acikuyuyayla Çukurkuyuyayl; Sinnelik Htiseyinbey Karakolyayla

Water lev. (m)

995.25 990.20

1001.40 990.45 994.47 986.50 990.98 988.58 991.80 990.90 987.92 990.55 991.85 999.10 992.27 988.87 987.68 987.00 989.30 989.20 985.75 987.00 987.55 984.50

Î 990.32 984J90 985.50 98639

Name of the Locality

Akçaçar Kepez Kizbogan B. Burnak Gôktuzla Oçkuyular §irinler Yeniyayla Elagôz Mezgitli Ko§k Ortakuyu Sicakyayla B. Sekeller Gôzerli GiinesJi Bozcamahmut Arifyayla Bayramdiigun Ba§gotiiren Siileymancik Yenice Bilezikli Acikuyu Egrikuyu Kuzukuyu Emirhaç Yiizbasjoglu

Water lev. (m)

993.22 988.40

978.60 978.17 979.22 981.43 987.90 97835 981.14 985.16 988.85 98132 981.58 983.95 984.55 983.00 963.68 971.10 98235 974.97 975.20 973.55 96638 972.05 989.80

1014.65 1012.20 1009.70

Name of the Local ity

HacayaySa Imiryayia Hacihimmet Yellikuyu Hacihasip Yedikulaç Yirce Hanyiktgi Yav§ançukuru Egrikuyu Apakyayla Kami§agil Ak obruk Uzuncakuyu Çukurkuyu Dikmenyayla Acikuyu Poturyayla Badink Yazikumca Kangalbogazi Oveçagili Tatarli Karaburun K. Sekeller Meyil obruk Çirali obruk Karain obruk Puthaciyayla

Water lev. (m)

1019.90 1018.50

992.60 985 SO 985.75 988.38 990.68 992.42 989.50 989.80 992.30 992.00 984.57 98730 987.89 983.65 983.90 981.45 986.63 992.68 988.10 983.68 981.44 984.06 98333 984.36 985.11 983.95 986.73

The formation of sinkholes in Konya 205

These karstic features having truncated conical or cylindrical shapes with various diamètres and depths are locally called as "OBRUK" by the native inhabitants. It has its own specific characteristics as such to be synonymous in every language in this branch of science.

The vicinities of these obruks which have special beauties of the nature should be protected as a national park.

REFERENCES

Agalede, H., 1954. Tuz gôliiniin bati ve giineybati kenarlannin jeolojik etiidii. MTA rapor no : 2371, yayinlanmamif. Ankara

Canik, B., 1985. Hydrogeologie karstique du polje d'irmene, Bodrum (Turquie). S.O. jeoloji Bôliimii, nun publie. Konya

Çôrekçioglu, L, 1969. Aksaray - Sultanhani - Kizôren (Obruk) havzasi hidrojeoloji etiid ra-poru. DSÎ 4. Bolge, yayinlanmami§. Konya

Eroskay, O., 1976. The factors influencing the Konya obruks and their groundwater potentials evaluation. i.Cl. Fen Fak. Mec. Seri B. 41 (1^t) : 5-14. Istanbul

Giildali, N., Çaroglu, F., 1983. Konya yôresi obruklan. TJK, Yeryuvan ve insan, Cilt 7, sayi 4. Ankara

Keller, J., 1974. Quaternary maar volcanism near Karapmar in Central Anatolia. Reprinted from Bulletin volcanologique, tome XXXVI11-2 p. 378-396. Napoli

Konya - Çumra - Karapmar ovasi hidrojeolojik etiid raporu, 1975, DSI Genel Mudiirlugii. Ankara.

§aroglu, F., Boray, A., Ozer, S., Ku§çu, Î., 1983. Orta Toroslar - Orta Anadolu'nun giineyi-nin neotektonigi ile ilgili goru§ler. Jeomorfoloji dergisi, sayi : 11, s. 35-44.

TPAO Petrol logs, Sultanhani, 1976.Ankara

Tuz Gôlii Proje Raporu, 1982. MTA Enstitusii, Endiistriyel Hammaddeler Dairesi. Ankara