Eastern Greater Caucasus Research Articles

Strong acceleration of glacier area loss in the Greater Caucasus between 2000 and 2020

Abstract. An updated glacier inventory is important for understanding glacier behaviour given the accelerating glacier retreat observed around the world. Here, we present data from a new glacier inventory for two points in time (2000, 2020) covering the entire Greater Caucasus (Georgia, Russia, and Azerbaijan). Satellite imagery (Landsat, Sentinel, SPOT) was used to conduct a remote-sensing survey of glacier change. The 30 m resolution Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM; 17 November 2011) was used to determine aspect, slope, and elevations, for all glaciers. Glacier margins were mapped manually and reveal that in 2000 the mountain range contained 2186 glaciers with a total glacier area of 1381.5 ± 58.2 km2. By 2020, the area had decreased to 1060.9 ± 33.6 km2 a reduction of 23.2 ± 3.8 % (320.6 ± 45.9 km2) or −1.16 % yr−1 over the last 20 years in the Greater Caucasus. Of the 2223 glaciers, 14 have an area > 10 km2, resulting in the 221.9 km2 or 20.9 % of total glacier area in 2020. The Bezengi Glacier with an area of 39.4 ± 0.9 km2 was the largest glacier mapped in the 2020 database. Glaciers between 1.0 and 5.0 km2 accounted for 478.1 km2 or 34.6 % in total area in 2000, while they accounted for 354.0 km2 or 33.4 % in total area in 2020. The rates of area shrinkage and mean elevation vary between the northern and southern and between the western, central, and eastern Greater Caucasus. Area shrinkage is significantly stronger in the eastern Greater Caucasus (−1.82 % yr−1), where most glaciers are very small. The observed increased summer temperatures and decreased winter precipitation along with increased Saharan dust deposition might be responsible for the predominantly negative mass balances of Djankuat and Garabashi glaciers with long-term measurements. Both glacier inventories are available from the Global Land Ice Measurements from Space (GLIMS) database and can be used for future studies.

Analysis of Regional Changes in Geodetic Mass Balance for All Caucasus Glaciers over the Past Two Decades

Glaciers and snow in the Caucasus are major sources of runoff for populated places in many parts of this mountain region. These glaciers have shown a continuous area decrease; however, the magnitude of mass balance changes at the regional scale need to be further investigated. Here, we analyzed regional changes in surface elevation (or thickness) and geodetic mass balance for 1861 glaciers (1186.1 ± 53.3 km2) between 2000 and 2019 from recently published dataset and outlines of the Caucasus glacier inventory. We used a debris-covered glacier dataset to compare the changes between debris-free and debris-covered glaciers. We also used 30 m resolution ASTER GDEM (2011) to determine topographic details, such as aspect, slope, and elevation distribution of glaciers. Results indicate that the mean rate of glacier mass loss has accelerated from 0.42 ± 0.61 m of water equivalent per year (m w.e. a−1) over 2000–2010, to 0.64 ± 0.66 m w.e. a−1 over 2010–2019. This was 0.53 ± 0.38 m w.e. a−1 in 2000–2019. Mass loss rates differ between the western, central, and eastern Greater Caucasus, indicating the highest mean annual mass loss in the western section (0.65 ± 0.43 m w.e. a−1) in 2000–2019 and much lower in the central (0.48 ± 0.35 m w.e. a−1) and eastern (0.38 ± 0.37 m w.e. a−1) sections. No difference was found between the northern and southern slopes over the last twenty years corresponding 0.53 ± 0.38 m w.e. a−1. The observed decrease in mean annual geodetic mass balance is higher on debris-covered glaciers (0.66 ± 0.17 m w.e. a−1) than those on debris-free glaciers (0.49 ± 0.15 m w.e. a−1) between 2000 and 2019. Thickness change values in 2010–2019 were 1.5 times more negative (0.75 ± 0.70 m a−1) than those in 2000–2010 (0.50 ± 0.67 m a−1) in the entire region, suggesting an acceleration of ice thinning starting in 2010. A significant positive trend of May-September air temperatures at two selected meteorological stations (Terskol and Mestia) along with a negative trend of October-April precipitation might be responsible for the negative mass balances and thinning for all Caucasus glaciers over the study period. These results provide insight into the change processes of regional glaciers, which is key information to improve glaciological and hydrological projections in the Caucasus region.

Stress–Strain State of the Earth’s Crust in the Central Caucasus

The Caucasus is a region of continental collision between Eurasia and Arabia and one of the Earth’s most seismically active and rapidly deformed continental regions. The wide range of deformation processes occurring in this relatively limited region makes the Caucasus as a whole and its central parts in particular a unique test area, the study of which can improve our understanding of the complexities of the stress–strain state, as well as the associated seismicity. During the instrumental period of observations, many strong earthquakes have been recorded here, e.g., the August 4, 1974 Bezhta earthquake (Mb = 5.4), the 1978 earthquake with a magnitude of 5.7, the February 23, 1981 Gavaz earthquake (Mb = 5), the October 12, 1992 Barisakho earthquake (Mb = 6.1), and the July 5, 2012 Zaqatala (Mb = 5.7). We have constructed the mechanisms of strong earthquakes and compared the results with the tectonic conditions of the studied region. Based on a morphostructural analysis of the modern relief of the central and eastern Greater Caucasus, a diagram of its morphostructural blocks has been compiled. The average earthquake mechanisms were constructed for the distinguished blocks, the prevailing types of slip in earthquake sources in each selected block were identified, and the fault kinematics were reconstructed. The solution was based on generally accepted tectonophysical theoretical views, with the wide application of modern structural–geomorphological methods, modern GIS technologies, and morphological analysis of the modern relief of this region. The modern tectonic stress field was reconstructed based on seismological data on earthquakes recorded during the entire instrumental period (1971–2019).

Structure and Density of Sedimentary Basins in the Southern Part of the East-European Platform and Surrounding Area

Modern satellite gravity missions and ground gravimetry provide operational data models that can be used in various studies in geology, tectonics, and climatology, etc. In the present study, sedimentary basins in the southern part of the East European Platform and adjoining areas including the Caucasus are studied by employing the approach based on decompensative gravity anomalies. The new model of sediments, implying their thickness and density, demonstrates several important features of the sedimentary cover, which were not or differently imaged by previous studies. We found a significant redistribution of the low-dense sediments in the Black Sea. Another principal feature is the increased thickness of relatively low-dense sediments in the Eastern Greater Caucasus. The deepest part of the South Caspian basin is shifted to the north, close to the Apsheron Trough. In its present position, it is almost joined with the Terek–Caspian depression, which depth is also increased. The thickness of sediments is significantly decreased in the eastern Pre-Caspian basin. Therefore, the new sedimentary cover model gives a more detailed description of its thickness and density, reveals new features and helps in better understanding of the evolution of the basins, providing a background for further detailed studies of the region.

Supra-glacial debris cover changes in the Greater Caucasus from 1986 to 2014

Abstract. Knowledge of supra-glacial debris cover and its changes remain incomplete in the Greater Caucasus, in spite of recent glacier studies. Here we present data of supra-glacial debris cover for 659 glaciers across the Greater Caucasus based on Landsat and SPOT images from the years 1986, 2000 and 2014. We combined semi-automated methods for mapping the clean ice with manual digitization of debris-covered glacier parts and calculated supra-glacial debris-covered area as the residual between these two maps. The accuracy of the results was assessed by using high-resolution Google Earth imagery and GPS data for selected glaciers. From 1986 to 2014, the total glacier area decreased from 691.5±29.0 to 590.0±25.8 km2 (15.8±4.1 %, or ∼0.52 % yr−1), while the clean-ice area reduced from 643.2±25.9 to 511.0±20.9 km2 (20.1±4.0 %, or ∼0.73 % yr−1). In contrast supra-glacial debris cover increased from 7.0±6.4 %, or 48.3±3.1 km2, in 1986 to 13.4±6.2 % (∼0.22 % yr−1), or 79.0±4.9 km2, in 2014. Debris-free glaciers exhibited higher area and length reductions than debris-covered glaciers. The distribution of the supra-glacial debris cover differs between the northern and southern and between the western, central and eastern Greater Caucasus. The observed increase in supra-glacial debris cover is significantly stronger on the northern slopes. Overall, we have observed up-glacier average migration of supra-glacial debris cover from about 3015 to 3130 m a.s.l. (metres above sea level) during the investigated period.

Recent hard evidence for the occurrence of the Leopard, Panthera pardus (Mammalia: Felidae), in the Eastern Greater Caucasus

The Eastern Greater Caucasus, which extends from the upper watershed of the Terek River in the east and covers parts of the Republics of Dagestan, Chechnya and Ingushetia (Russian Federation) as we...

Drainage network reveals patterns and history of active deformation in the eastern Greater Caucasus

The Greater Caucasus Mountains are a young (∼5 m.y. old) orogen within the Arabia-Eurasia collision zone that contains the highest peaks in Europe and has an unusual topographic form for a doubly vergent orogen. In the east-central part (45°E–49°E), the range is nearly symmetric in terms of prowedge and retrowedge widths and the drainage divide is much closer to the southern margin of the range (prowedge side) than it is to the northern margin (retrowedge side). Moreover, the divide does not coincide with the topographic crest, but rather the crest is both shifted northward by as much as 40 km and traversed by several large north-flowing rivers. Both the topographic crest and drainage divide appear to coincide with zones of active rock uplift, because they are characterized by bands of high local relief and normalized channel steepness values (>300). This uplift pattern could result from a synchronous initiation of the two uplift zones or propagation of deformation either northward or southward. The two propagating scenarios differ fundamentally in their predictions for the relative ages of topographic features; northward propagation predicts that the topographic crest is younger than the drainage divide, and the southward scenario predicts the converse. Because available geologic and topographic data are consistent with both propagation directions, we use a landscape evolution model to test all three scenarios. Model results indicate that the current topography and drainage network is best explained by a northward propagation of deformation from the south flank into the interior of the east-central Greater Caucasus. Such propagation implies recent out-of-sequence deformation within the Greater Caucasus due to reactivation or development of new structures within the core of the orogen. It remains unclear if such deformation is a transient response to an accretion cycle or stems from a fundamental change in the structural architecture of the orogen.

Upper mantleSwave velocity structure of the East Anatolian-Caucasus region

Geodynamic processes occurring in the upper mantle such as slab break off and lithosphere delamination often result in high rates of lithospheric deformation and rapid tectonic uplift of large areas. The continent-continent collision zone between Arabia and Eurasia has been widely studied in this context, but several different viable geodynamic models exist to explain the uplift and deformation of the Anatolian Plateau and the Caucasus Mountains. We have imaged the uppermost mantle shear wave velocity structure of the East Anatolian-Caucasus region using surface wave tomography to better understand the regional tectonic activity since the onset of the collision between the Arabian and Eurasian Plates. Furthermore, we used our tomographic models to better understand the processes, which are responsible for the formation of the 2 km high plateau and the widespread volcanism in eastern Turkey, as well as reactivation of deformation and deep seismicity in the eastern Greater Caucasus. Our model of regional upper mantle shear wave velocity structure supports subduction of the northern and southern branches of Neo-Tethys lithosphere between Eurasia and Gondwana and suggests a possible underthrusting of the Kura Basin lithosphere beneath the Greater Caucasus.

The Opportunity Costs of Conserving Pasture Resources for Mobile Pastoralists in the Greater Caucasus

Ecological damage caused by unadjusted and raised stocking rates are persistent problems in grazed mountain areas in developing countries, including in post-Soviet Asia. An assessment of this degradation is difficult due to site heterogeneity and insufficient knowledge about the grazing systems. We present an integrated appraisal of the potential stocking rates of sites based on physical site properties. We combine these ecological and agrarian analyses with the economic calculation of opportunity costs in scenarios. We apply this approach to a high mountain region in the eastern Greater Caucasus in Azerbaijan, which provides valuable ecosystem services and is heavily used as summer pasture by mobile pastoralists. Hence, an impact assessment of reducing the legal prescriptions of stocking rates or the calculation of payments for ecosystem services is possible. Our results show that stocking rates on many pastures are spatially unadjusted and destocking measures need to be implemented in order to preserve ecosystem services. We also discuss different distribution possibilities of the opportunity costs.

Subsidence and uplift mechanisms within the South Caspian Basin: insights from the onshore and offshore Azerbaijan region

Abstract A combination of fieldwork, basin analysis and modelling techniques has been used to try and understand the role, as well as the timing, of the subsidence–uplift mechanisms that have affected the Azerbaijan region of the South Caspian Basin (SCB) from Mesozoic to Recent. Key outcrops have been studied in the eastern Greater Caucasus, and the region has been divided into several major tectonic zones that are diagnostic of different former sedimentary realms representing a complete traverse from a passive margin setting to slope and distal basin environments. Subsequent deformation has caused folds and thrusts that generally trend from NW–SE to WNW–ESE. Offshore data has been analysed to provide insights into the regional structural and stratigraphic evolution of the SCB to the east of Azerbaijan. Several structural trends and subsidence patterns have been identified within the study area. In addition, burial history modelling suggests that there are at least three main components of subsidence, including a relatively short-lived basin-wide event at 6 Ma that is characterized by a rapid increase in the rate of subsidence. Numerical modelling that includes structural, thermal, isostatic and surface processes has been applied to the SCB. Models that reconcile the observed amount of fault-controlled deformation with the magnitude of overall thinning of the crust generate a comparable amount of subsidence to that observed in the basin. In addition, model results support the tectonic scenario that SCB crust has a density that is compatible with an oceanic composition and is being under-thrust beneath the central Caspian region.

The Mesozoic-Cenozoic tectonic evolution of the Greater Caucasus

Abstract The Greater Caucasus (GC) fold-and-thrust belt lies on the southern deformed edge of the Scythian Platform (SP) and results from the Cenozoic structural inversion of a deep marine Mesozoic basin in response to the northward displacement of the Transcaucasus (lying south of the GC) subsequent to the Arabia-Eurasia collision. A review of existing and newly acquired data has allowed a reconstruction of the GC history through the Mesozoic and Cenozoic eras. In Permo(?)-Triassic times, rifting developed along at least the northern part of the belt. Structural inversion of the basin occurred during the Late Triassic corresponding to the Eo-Cimmerian orogeny, documented SE of the GC and probably linked to the accretion of what are now Iranian terranes along the continental margin. Renewed development of extensional basin formation in the area of the present-day GC began in Sinemurian-Pliensbachian times with rift activity encompassing the Mid-Jurassic. Rifting led to extreme thinning of the underlying continental crust by the Aale-nian and concomitant extrusion of mid-ocean ridge basalt lavas. A Bathonian unconformity is observed on both sides of the basin and may either correspond to the end of active rifting and the onset of post-rift basin development or be the record of collision further south along the former Mesozoic active margin. The post-rift phase began with deposition of Late Jurassic platform-type sediments onto the margins and a flysch-like unit in its deeper part, which has transgressed the basin during the Cretaceous and Early Cenozoic. An initial phase of shortening occurred in the Late Eocene under a NE-SW compressional stress regime. A second shortening event that began in the Mid-Miocene (Sarmatian), accompanied by significant uplift of the belt, continues at present. It is related to the final collision of Arabia with Eurasia and led to the development of the present-day south-vergent GC fold-and-thrust belt. Some north-vergent retro-thrusts are present in the western GC and a few more in the eastern GC, where a fan-shaped belt can be observed. The mechanisms responsible for the large-scale structure of the belt remain a matter of debate because the deep crustal structure of the GC is not well known. Some (mainly Russian) geoscientists have argued that the GC is an inverted basin squeezed between deep (near)-vertical faults representing the boundaries between the GC and the SP to the north and the GC and the Transcaucasus to the south. Another model, supported in part by the distribution of earthquake hypocentres, proposes the existence of south-vergent thrusts flattening at depth, along which the Transcaucasus plunges beneath the GC and the SP. In this model, a thick-skinned mode of deformation prevailed in the central part of the GC whereas the western and eastern parts display the attributes of thin-skinned fold-and-thrust belts, although, in general, the two styles of deformation coexist along the belt. The present-day high elevation observed only in the central part of the belt would have resulted from the delamination of a lithospheric root.