The reduction of glaciers of Mulkhura River basin over the last century is revised in the paper. Mulkhura River basin is located on the southern slope of the central Caucasus from the Mount Bashili (4148 m) to the Mount Gistola (4860 m) and it is the main center of the contemporary glaciations in the Enguri River basin. The percentage reduction of areas of compound valley glaciers with the relation of air temperature and atmospheric precipitation is given in this paper. Also the paper considered the dynamics of the Tviberi and Tsaneriglaciers, which were the Georgia’s largest glaciers at the end of the 19th century. We used the catalog of the glaciers of the southern slope of the Caucasus compiled in 1911 by a well-known researcher of the Caucasus K. Podozerskiy, which was drawn up on the basis of the 19th century maps. In order to identify the area and number of the glaciers of the 60s of the 20th century, we used the work of R. Gobejishvili—the Georgian glaciologist of the 20th-21st centuries, composed on the basis of 1:50,000 scale topographic maps of 1960. The data of 2014 have been obtained by the Landsat aerial images of L8 OLI/TIRS (Operational Land Imager and Thermal Infrared Sensor) taken in August 2014. In the mentioned study, except of the old topographic maps and aerial images, we used the climate information especially air temperature and precipitation data of the Mestia weather station.
The glaciers are indivisible part of the environment and are a good indicator of the current change of climate. Researches of glaciers became very important especially in the last period, when climate change was observed in every mountainous region of the world. Especially important is studying of mountain glaciers as they are important natural resources and they response to climate change. The glacier melting is observed in every mountainous region after the finishing of max phase of the Little Ace Age (LIA). This process continues even today.
Mountain glaciers are a relatively reliable indicator of climate change, and their recent decline across the world has been linked to global warming [
One of the main glaciated areas of the Eurasia is the Great Caucasus Range, which stretches for about 1300 km from the north-west to the south east. It is located between the Black Sea and the Caspian Sea and represents the natural border between Georgia and Russia. The current area of glaciation is ~1100 km2.
Great influence on the climate of the Caucasus have the cyclones shifted from the southwest and west of the Atlantic and the Mediterranean Seas and the branch of Asian anticyclone, which extends in the region from the north and north-west. Cyclonic processes are formed in the warm period of the year, while the anticyclonic―in the cold period. Because of this the high peaks of the Caucasus are under the influence of these processes throughout the year, which provides their feeding by precipitation.
High Caucasus range is favorable for the existence of glaciers in Georgia. There are places in certain sections of the range, where its height exceeds 3000 - 3500 meters, by foreseen of the relief and climatic conditions, where the accumulation of solid atmospheric precipitation fallen in the cold period occurs during many years [
Mulkhura River basin is located on the southern slope of the central Caucasus from the Mount Bashili (4148 m) to the Mount Gistola (4860 m) (
During this research we used the catalogue and maps of glaciers compiled by K. Podozerskiy in 1911. The data by K. Podozerskiy are obtained just from the maps of 1880-1890, which were compiled by the plain table surveying method in 1880-1890 [
Because many glaciers lie in remote mountainous regions, remote sensing methods have often been employed in performing glacier surveys, beginning with aerial photography [
Then composite band function was used and with the help of ArcGis images were fixed with the sequence of the 7-5-3. As a result of the use of this method, we have estimated the variability of Mulkhura River basin glaciers area of 1911-1960-2014 years, as well as its ice tongue length and altitudinal variation during these years.
It is important the existence of climate elements especially air temperature and precipitation data to study the dynamics of glaciers [
By the data of 1911 there were 11 glaciers in the Mulkhura River basin with the area of ~100.0 km2 [
Share of only six glaciers in the total area of the glaciers of the Mulkhura River basin is 76.8%, their areas are as follows: southern Tsaneri―12.6 km2, northern Tsaneri―11.5 km2, Kvitlodi―9.8 km2, Nageba―4.5 km2, Asmashi―4.5 km2 and Seri―4.2 km2, which shows that the basic background for glaciations are made by these glaciers.
The rest of the 36 glaciers are relatively small in size; they are located on the slopes of the major glaciers and end within the altitude of 2650 - 3500 meters. The ice tongues of the valley glaciers come down to a lower altitude, to 2140 - 2480 m above sea level.
According to morphological types the valley glaciers form the basic background for glaciation in the Mulkhura River basin; they occupy 83.0% of the total area of the glaciers of the basin (
As for the exposition, the first place by the number and area occupy the glaciers of the overall southern exposition; their share is 45.2% in the total number and 46.1% in the total area of the glaciers (
Tviberi glacier is located in the river basin with the same name (the Tviberi River is a mouth of the Mulkhura River). It is located on the southern slope of the Caucasus. In spite of this the peaks located there, are not distinguished by the high altitude. The highest peak is of 4250 m and is lower than the peaks located next to it by 600 - 800 meters. Morphological conditions of the relief play an important role in the forming of the powerful glaciations in the basin together with the climatic conditions. The Tviberi River basin is surrounded by the quite high ranges. Glacial forms are deeply sat in the relief, built by the crystal rocks and create the favorable conditions
for accumulation of snow-icy cover. From the beginning of the 19th century to the second half of the 20th century the Tviberi River basin’s glaciers were combined and they formed the compound-valley glacier. Their joint tongue was flowing down to the 2030 m above sea level (
From the year of 1810 the glaciers of the Caucasus are retreating. In the topographical map of 19th century the Tviberi glacier is presented as a united system (
In 1960 the Tviberi glacier tongue was ended at a height of 2140 m. The surface of its tongue was covered by the weathered material of ~1.0 m thick, which greatly reduced the surface ablation. A clean surface of the glacier was melting realtively greatly in the area of the joint tongue than the surface covered by the weathered material. Because of that the clean section of the glacier was located ~10 - 15 meters lower. The area of the Tviberi glacier was 24.7 km2 in 1960 [
Decoding of the 19th-20th centuries topographical maps and aerial images of 2014 showed that due to retreat the compound-valley glacier of Tviberi was divided into the following valley types of glaciers: Seri, Asmashi, Toti, Iriti, Lichati, Laskhedari and Dzinali. The glacier tongues are ~1.0 km away from each other. The Asmashi glacier is the largest in area and length; its tongue ends at a height of 2540 m. The sides of the ice-tongue surface is covered by the ~0.5 - 1.0 m thick weathered material and the ~200 m wide clean ice flow is intruded among them in the form of a wedge. Its surface is lower than the sides by ~5 - 10 m.
Similar geomorphological conditions has the Dzinali glacier tongue. The tongues of the rest of the glaciers are poorly covered by the boulder materials. All of the glaciers develop the 100 - 300 high icefalls on flowing from the vast firn valley and form the sharply expressed step in the relief. Because of this the glacier is divided into the two parts. The upper step is a feeding area and the lower one is a melting area. The small size cirque glaciers were separated from some of the valley types of glaciers.
From the 80s of the 19th century till 2014 the Tviberi glacier tongue retreated by ~4.1 km. Such a sharp change of the tongue can be observed with the help of the old and contemporary images as well (
Kvitlodi glacier was connected to the Tviberi glacier tongue untill the first part of the 19th century. By the data of 1960 Kvitlodi was already separated from Tviberi and was ended at a distance of ~700 - 800 m at a height of 2290 m (
Tsaneri glacier with the Nageba glacier was the second glacier in Georgia by its size after the Tviberi glacier in the 80s of the 19th century and its area was 48.9 km2 (
the Lekhziri glacier. The mentioned glacier now is presented in the form of two glaciers (northern Tsaneri and southern Tsaneri), which descend from the firn valleys that are independent from each other (
Southern Tsaneri is the second largest glacier in Georgia with the area of 12.6 km2. Glacier surface cracks are weakly developed. The ice tongue surface is rich in ablation forms (wells, glacier tables, sunbcups, grooves made by melted water, etc.). The glacier tongue ends at an altitutde of 2525 m above sea level. The well expressed lateral stade moraines stretch along to its both sides (
Georgia’s third largest glacier is the northern Tsaneri with the area of 11.5 km2. It is a valley glacier and is of south-western exposition. The last part of the ice tongue is hanged over the ledge and it ends at an altitude of 3020 meters above sea level (
Nageba glacier is a valley glacier of north-western exposition. The glacier firn starts from the Tetnuldi Peak at a height of 4858 m and is surrounded by the Lakchkhilda and Kvarashi ranges. The glacier tongue creates the icefall with the cracks of different direction after flowing out from the firn. By the data of 2014 the glacier area is 4.5 km2 and its tongue ends at a height of 2800 meters.
Well-expressed lateral stade moraines stretch along to the both sides of the glacier, which join the stade moraine of Fernau of the Tsaneri glacier. This fact indicates that the glaciers were combined and represented one glacier during the last stade glaciation. There are several short stade moraines into the stade moraines on the slopes and at the base of the valley. Reduction of the glacier is best seen when comparing the old and new images (
To investigate the dynamics of glaciers it is important to analyze the climatological information, mainly the air temperature and precipitation data for the same period. Nowadays the Mestia meteorological station is the only current station and is located at 1440 m above sea level [
As our research period comprises approximately the last one century, we divide it into two periods 1906-1960 and 1961-2013. As we have mentioned above, the Mestia multi-year mean air temperature made +5.9˚C. In the same period the temperature trend is a positive (
One of the necessary conditions for the feeding of the Caucasus glaciers is the intensity of solid precipitation, which most often comes in December-January months in the south Caucasus. We have developed the Mestia meteorological station’s precipitation data of the period of 1961-2010, which showed that in the mentioned period the annual sum of the precipitation increases, and relatively, the overall trend is also positive (
But if we take only the winter months of December and January, here we can see that the trend is stable in case of January and December and precipitation sum obviously decreases; accordingly, the trend is negative (
Of course, we cannot state solely that the reduction of the Mulkhura River basin’s contemporary glacial areas is related only to the reduction of the December precipitation, but we can say that during the last half century along with the temperature increase the mentioned fact is also causes the reduction of the glaciers.
The study had concluded that during the last century the area of the glaciers in the Mulkhura River basin decreased by 34%, while their number increased by 281%. In the mentioned period such largest increase of the glaciers was not observed among the other river basins on the southern slope of the Caucasus. This situation was stipulated by the fact that by the end of the 19th century and in the early 20th century the area of the glaciers of the Mulkhura River basin made 17% of the total area of the glaciers of Georgia and the Mulkhura basin was the main center of glaciations at that time. In this basin were located two largest compound-valley types of glaciers of Georgia―Tviberi and Tsaneri (together with Nageba) glaciers. These are the glaciers due to degradation of which the relatively small size of simple valley and even smaller cirque type of glaciers emerge.
As for the atmospheric precipitation and air temperature, we had identified that the mean annual air temperature trend was positive in the years of 1906-2013. And the mean multi-year air temperature of separate period of 1961-2013 was more by 0.1˚C than the same parameter of the period of 1906-1960. Therefore, it made +6.0˚C. In addition, in the last half century, against the background of the overall increase in precipitation in the region the reduction of the December-January (especially in December) rainfall was observed, which had a negative impact on the glaciers feeding regime.
We are grateful to the Shota Rustaveli Georgian National Science Foundation for the financing our research. We would like to express our heartfelt thanks to the Hydro Meteorological Department of the National Agency of the Environment for providing the meteorological data.