Geotechnical and geoenvironmental characteristics of man-made underground structures in Cappadocia, Turkey

Underground cities and semi-underground settlements, most of which are 1500 years at least, exist in the Cappadocia Region of Turkey. These man-made rock structures are carved in soft tuffs and the best examples of long-term performance of man-made structures in the field of rock engineering. The tuffs also have good thermal isolation properties to be used as housing and storage of foods. In this article, the authors are only concerned with physical and short-term mechanical characteristics due to the wide-spectrum of the theme and the in situ characterization of the Cappadocia tuffs, and the results of investigations are presented. In addition, a critical overview on possible engineering geological problems at Cappadocia with mechanical aspects of historical and modern rock structures and their implications in rock engineering is made. From the experimental results in the field, it is evident that the engineering characteristics of these rocks do not show significant changes in vertical and horizontal directions. However, they are prone to atmospheric conditions. In addition, temperature and humidity measurements at different floors of the underground cities and various parts of semi-underground settlements indicated that variations in climatic conditions of the openings are very small when compared to those outside the ground surface.     

Assessment of environmental and engineering geological problems for the possible re-use of an abandoned rock-hewn settlement in Urgüp (Cappadocia), Turkey

The Cappadocia Region of Central Anatolia having a very distinct culture is one of the attractive touristic sites of Turkey due to its spectacular and unique landforms and historical heritages. In this region, the structures carved into thick to massive tuffs survived and kept their original integrity for a number of centuries. Environmental and anthropological factors at the Cappadocia Region have been the main reasons for extensive subsurface and multi-purpose use in the past and present. In addition, thermal insulation properties of the tuffs make these rocks suitable for use in underground openings. The Kayakapi Neighborhood, located in the town of Urgüp, is one of the famous historical sites. This site is situated within the “Göreme National Park and the Rock Sites of Cappadocia” which was inscribed on the World Heritage List in 1985. In order to develop the tourism potential of this abandoned site while preserving its cultural and natural values, a natural environmental conservation and revitalization project was initiated. As an integral part of this project, in this study, environmental and engineering geological problems, including rock fall potential and stability of about 1,200 rock-hewn structures, were investigated and an inventory was prepared for the possible re-use of the underground openings and other structures at the site, and remedial measures were recommended. The assessments based on observations and experimental studies indicated that the tuffs do not show significant changes both perpendicular and parallel to layering, and discontinuities and rock weathering seem to be more important factors controlling the stability of rock-hewn structures. The major stability problems threatening the re-use of the openings are structurally-controlled block instabilities, overbreaks, and erosion and shearing of the pillars made of tuff. On the other hand, the area at the entrance of the site requires some protection measures such as the construction of a retaining wall, systematic bolting of rock slabs and removal of some blocks having rock fall potential. The inventory for the openings suggests that there are a number of openings that can be re-used after necessary remedial measures.     

Development and morphometry of drainage network in volcanic terrain, Central Anatolia, Turkey

This paper presents the results of morphotectonic and morphometric research carried out in order to determine the neotectonic development of the volcanic mountains and a drainage network in SW Cappadocia. The study area extends among the Aksaray, Ni?de, and Nev?ehir Provinces. The study area comprises Hasanda?, Melendiz, Keçiboyduran, Göllüda? Mountains and the adjacent parts of these volcanic mountains.Data collected exclusively from 1:25,000 digitised topographic maps and 10 m-resolution DEMs were used to define parameters related to the longitudinal profile of streams. The study area was divided into 10 volcanic units. Longitudinal profiles of 20 streams and stream orders were analysed to determine a regional tectonic differentiation pattern in these units. The streams in the study area drain into four different tectonic depressions. These depressions are Aksaray plain controlled by the Tuz Gölü fault (TGF), Çiftlik plain controlled by the Keçiboyduran–Melendiz fault (KMF), Misli plain controlled by the Derinkuyu fault (DF), and Bor plain controlled by the Ni?de Fault Zone (NFZ). An analysis of morphometric parameters shows that the development of a drainage network is associated with faults and rock resistance. Occurrence of morphometric parameters with different values in units reveals that the volcanic mountains were not uplifted in the same period and were subjected to different morphologic processes. High total order number in the south of Hasanda? (unit 3) and Melendiz Mountains (unit 7) indicate that the uplift ratio of the southern part is much greater than that of the northern part. Moreover, development of the drainage network in the south is in a more advanced phase than in the north. Indeed, the drainage network in the north is in the youngest erosional phase of all parts of the study area. The increased stream length-gradient indices (SL), and stream gradients and an analysis of headward erosion show that the streams displaying the longest and highest reach of the erosional phase are all in the southern part of Keçiboyduran and Melendiz Mountains. The longitudinal profile (Lp) of the present thalweg of the streams is irregular. The irregular Lp are associated with four different causes. These are geological variations in resistance, tectonics, and volcanic topography and downcutting in response to stream incision. The beginning of the fluvial incision in the northern part is younger than in the south.     

Mio-Pliocene basin development in the eastern part of the Cappadocian Volcanic Province (Central Anatolia,Turkey) and its implications for regional tectonics

The Cappadocian Volcanic Province (CVP) comprises predominantly of a thick succession of volcanogenic rocks and interbedded siliciclastic sediments of Middle Miocene to Recent age in Central Anatolia, Turkey. The conditions of basin development in the eastern part of the CVP have been elucidated by using sedimentological and geomorphological approaches. The prevailing tectonic regime, its extent and causes are also discussed. Sedimentological analysis supported by geomorphological observations revealed a major NE-trending probably normal, border fault and its several synthetics. This tectonic element constitutes the SE margin of the basin and divided the CVP from the Tauride range during Middle Miocene to Pliocene. The basin fill in the study area comprises gravelly alluvial fans near the border fault, while fluvial clastics and lacustrine carbonates dominate towards the centre. Some pyroclastic rocks and lava flows are also made part of the fill. The southeastern basin margin is characterized morphologically by a number of uplifted basement blocks, probably associated with synthetic faults, and some deeply incised canyons in the footwall. These canyons were subsequently filled with a Mid-Pliocene ignimbrite sheet, and represent the sediment supply conduits to the basin. The cessation of filling in the basin was determined by strike-slip faults that uplifted and detached the basin about 2.6 Ma. This date also marks the onset of the neotectonic period in the region. The overall extensional tectonic regime inferred for the eastern CVP appears coeval with events recognised in the southern basins, i.e. Adana and Mut Basins and the eastern Mediterranean. Some physical connections between these basins also have been demonstrated. It is suggested that the CVP and the southern basins were all created during a phase of extension resulting from continued northward subduction of the African plate beneath the Eurasia during the Late Cenozoic.     

40Ar/39Ar dating of ignimbrites and plinian air-fall layers from Cappadocia,Central Turkey: Implications to chronostratigraphic and Eastern Mediterranean palaeoenvironmental record

Magmatism forming the Central Anatolian Volcanic Province of Cappadocia, central Turkey, records the last phase of Neotethyan subduction after ∼11 Ma. Thirteen large calc-alkaline ignimbrite sheets form marker bands within the volcano-sedimentary succession (the Ürgüp Formation) and provide a robust chronostratigraphy for paleoecologic evaluation of the interleaved paleosols. This paper evaluates the chronologic record in the context of the radiometric, magnetostratigraphic and lithostratigraphic controls. Previous inconsistencies relating primarily to K/Ar evidence were reason for the initiation of an integrated study which includes ⁴⁰Ar/³⁹Ar dating, palaeomagnetic and stratigraphic evidence. The newly determined ⁴⁰Ar/³⁹Ar-ages (Lepetit, 2010) are in agreement with Ar/Ar and U/Pb data meanwhile published by Pauquette and Le Pennec (2012) and Aydar et al. (2012). The ⁴⁰Ar/³⁹Ar-ages restrict the end of the Ürgüp Formation to the late Miocene. The paleosol sequence enclosed by the ignimbrites is thus restricted to the late Miocene, the most intense formation of pedogene calcretes correlating with the Messinian Salinity Crisis.     

New Evidence for The Role of The North Sea — Caspian Pattern on The Temperature and Precipitation Regimes in Continental Central Turkey

Monthly mean temperatures and monthly precipitation totals at six stations from theCappadocian sub‐region in the continental Central Anatolia region of Turkey were analysed in order to detect the response of the variability in the Cappadocian climate to the variability of the North Sea ‐ Caspian Pattern Index (NCPI). Most of this region is classified as semi‐arid according to various climate classifications. Time series of the NCPI for the period 1958–1998, enabled each month from October toApril to be classified as belonging to the negative phase NCP(?), positive phase NCP(+) or neutral conditions. Monthly temperature and precipitation series for each station were analysed separately for both phases. Temperatures during NCP(?) were found to be considerably higher than during NCP(+). These results confirm previous results regarding the role of the NCP in controlling the temperature regime in that region. No significant differences were found in precipitation totals between the two phases, but major differences were identified in their spatial structure.     

Mineralogical and petrological features of the Cemilköy ignimbrite,Cappadocia, Turkey

The Cemilköy ignimbrite is one of the voluminous ignimbrite deposits in Cappadocia. The Cemilköy ignimbrite contains pumice and lithic clasts of volcanic and ophiolitic origin in an ash matrix. The unwelded Cemilköy ignimbrite is distinguished from other deposits in Cappadocia by flattened pumices, elongate vesicles and a slaty fabric. The mineral assemblage of the Cemilköy ignimbrite is plagioclase, biotite, quartz and oxides (magnetite and Ti-magnetite) and the matrix is glassy. Eutaxitic texture is dominant and all pumice clasts have a vitrophyric-porphyritic texture. The same textural properties were observed throughout the spatial distribution of Cemilköy ignimbrite. Microprobe studies reveal that plagioclase compositions range from albite through oligoclase-andesine. Estimated plagioclase-liquid temperatures (T) and pressures (P) are varying between 806 and 847?°C and 4.2–7.1 (kbar), and the H₂O content of the melt is estimated to have been 5?wt.% from the pumice clasts. Based on geochemical data, the Cemilköy ignimbrite is rhyolitic and calc-alkaline in character, and all pumice clasts are enriched in LIL and LRE elements relative to HFS elements. Negative Nb, Ta and Ti anomalies, ratios of Ba/Nb >28 (56–77), Ba/Ta ?450 (590–700) and Th/Yb vs. Ta/Yb are consistent with a subduction-related origin. According to the geochemical and mineralogical-petrographical data, the Cemilköy ignimbrite originated from partial melting of a mantle source which was enriched during previous subduction processes with variable degrees of assimilation fractional crystallization (AFC) through time and Cemilköy ignimbrite erupted from a crustal magma chamber at shallow to intermediate depth.     

Hidden calderas evidenced by multisource geophysical data; example of Cappadocian Calderas, Central Anatolia

The Cappadocian volcanic field in central Anatolia (Turkey) is characterised by a sequence of 10 Neogene ignimbrites. The associated calderas have been partly dismantled and buried by subsequent tectonic and sedimentary processes and, therefore, cannot be readily recognized in the field. Recent progress in the understanding of the stratigraphic correlations and flow patterns has identified two main probable source areas for the ignimbrites. Detailed study of these areas, based on gravity surveys, remote sensing data (SPOT and ERS1 images) and digital elevation models (DEM), has provided evidence for two major caldera complexes and their relationship to old stratovolcanoes and Neogene tectonics. The older Nevsehir–Acigöl caldera complex, located between the towns of Acigöl, Nevsehir and Cardak, is inferred to be the source of the Kavak and Zelve ignimbrites. The Nevsehir–Acigöl caldera complex is defined mainly by a −35 mGal circular gravimetry anomaly about 15 km in diameter. The boundaries of this, now buried, caldera complex are shown by high gradients on the Bouguer gravity anomaly map. The younger Derinkuyu caldera complex, located between the Erdas stratovolcano and the Ciftlik basin, is inferred to be the source of the Sarimaden, Cemilköy, Gördeles and Kizilkaya ignimbrites. It is well-defined by a rectangular (35×23 km) gravity low (−30 mGal) with a positive high (+20 mGal) in the center. Gravity, remote sensing data and the DEM provide evidence that the Erdas stratovolcano, on the northern margin of the Derinkuyu caldera complex, represents the remnants of a large stratovolcano partly cut by one or more caldera collapses. The positive anomaly within the Derinkuyu caldera complex is centered on the 15-km-wide Sahin Kalesi volcanic massif. Field evidence and structural features inferred from the DEM and remote sensing data strongly suggest that this massif is a resurgent doming associated with the Gördeles ignimbrite eruption. High-resolution ERS1, SPOT and DEM images reveal that the transtensive regime, active at least since the Miocene, influenced the location of eruptive centers and caldera complexes in Cappadocia. The two caldera complexes are located in transtensive grabens. The subsidence of these grabens, continuing after the caldera collapse events, most likely resulted in the burying of the calderas and could explain the difficulties in identifying them in the field.     

Interpretation of the Gravity and Magnetic Anomalies of the Cappadocia Region,Central Turkey

The Cappadocia region, located in Central Turkey, is characterized by widespread lava flows and volcanoclastic deposits dating from Miocene to Quaternary. Gravity and aeromagnetic anomalies of the region appear to present similar high and low amplitude regions, although the aeromagnetic anomalies exhibit a rather complex pattern which is thought to be caused by remanent magnetization. The low-pass filtered aeromagnetic map shows a deep-seated magnetic anomaly which may be linked to the widespread volcanic activity at the surface. The pseudogravity transformation of the upward continued anomaly has been constructed. The pseudogravity anomaly demonstrates some form of clockwise rotation. This anomaly was modelled by means of a three-dimensional method. The top and bottom of the body are at 6.3km and 11km (including the flight height) from the ground surface, respectively. This deep body is ellipsoidal and extends along an E-W direction, which is in line with the regional stress direction deduced from GPS measurements. A new mobilistic dynamo-tectonic system appears to explain the body’s E-W elongation. The modelled body may be the source for the inferred geothermal energy of the region. Magnetic measurements were carried out on oriented rock samples collected from outcrops of ignimbrites and basalts, providing directions and intensities of remanent magnetization, susceptibilities and Koeningsberger (Q) ratios. Standard deviations of remanent directions of the Natural Remanent Magnetization (NRM) display a wide scatter implying unreliability of the surface data. Reduction to pole (RTP) transformation of magnetic anomalies was successful with the induced magnetization angle despite the complex pattern of magnetic anomalies.