There have been numerous studies of glaciers in the Greater Caucasus, but
none that have generated a modern glacier database across the whole mountain
range. Here, we present an updated and expanded glacier inventory at three
time periods (1960, 1986, 2014) covering the entire Greater Caucasus.
Large-scale topographic maps and satellite imagery (Corona, Landsat 5, Landsat 8
and ASTER) were used to conduct a remote-sensing survey of glacier change, and
the 30 m resolution Advanced Spaceborne Thermal Emission and Reflection Radiometer
Global Digital Elevation Model (ASTER GDEM; 17 November 2011) was used to determine the aspect,
slope and height distribution of glaciers. Glacier margins were mapped
manually and reveal that in 1960 the mountains contained 2349 glaciers with
a total glacier surface area of 1674.9
Glacier inventories provide the basis for further studies on mass balance and volume change, which are relevant to local- to regional-scale hydrological studies (Huss, 2012; Fischer et al., 2015) and to global calculation of sea level change (Gardner et al., 2013; Radic and Hock, 2014). In addition, glacier inventories are invaluable data sets for revealing the characteristics of glacier distribution and for upscaling measurements from selected locations to entire mountain ranges (Nagai et al., 2016).
In a high mountain system such as the Greater Caucasus, glaciers are an important source of water for agricultural production, and runoff supplies several hydroelectric power stations. Most rivers originate in the mountains, and the melting of glaciers/snow is an important component of the inputs in terms of water supply and for recreational opportunities (Tielidze, 2017). However, glacier hazards are relatively common in this region, leading to major loss of life. On 20 September 2002, for example, Kolka Glacier (North Ossetia) initiated a catastrophic ice-debris flow killing over 100 people (Evans et al., 2009), and on 17 May 2014 Devdoraki Glacier (Georgia) caused a rock–ice avalanche and glacial mudflow killing nine people (Tielidze, 2017). The Greater Caucasus glaciers also have economic importance as a major tourist attraction, e.g. Svaneti, Racha and Kazbegi regions in Georgia, with thousands of visitors each year (Georgian National Tourism Administration, 2017).
The Global Land Ice Measurements from Space (GLIMS) database (9 February 2017) for the Greater Caucasus identified in
excess of 1295 glaciers with a combined area of 1111.8 km
Thus, the objectives of this paper are to construct an updated glacier inventory for the Greater Caucasus region based on manual delineation of glaciers from multi-temporal satellite images and especially to fill the gap in the eastern Greater Caucasus.
The Caucasus mountains consist of two separate mountain systems: the Greater
Caucasus (the higher and more extensive part) extends for
The Greater Caucasus can be divided into western, central and eastern sections based on morphology divided by the mountains Elbrus (5642 m) and Kazbegi (5047 m) (Maruashvili, 1981) (Fig. 1). At the same time, the terms northern and southern Caucasus are frequently used to refer to the corresponding macroslopes of the Greater Caucasus Range (Solomina et al., 2016).
Glacier retreat started from the Little Ice Age (LIA) maximum positions in the northern Caucasus from the late 1840s, with minor re-advances in the 1860s–1880s and re-advances or steady states in the 20th century (1910s, 1920s and 1970s–1980s) (Solomina, et al., 2016).
In the Caucasus, supra-glacial debris cover has a smaller extent than in many glacierized regions, especially Asia (Stokes et al., 2007; Shahgedanova et al., 2014). Direct field monitoring reveals evident debris expansion for some glaciers (e.g. Djankuat) from 2 to 13 % between 1968 and 2010 (Popovnin et al., 2015). Glacier retreat appears to be associated with expansion of supra-glacial debris cover and ice-contact/proglacial lakes, which may increase the likelihood of glacier-related hazards and debris flows (Stokes et al., 2007). Debris cover is more common in the north than in the south (Lambrecht et al., 2011; Tielidze et al., 2017).
The study of glaciers in the Caucasus began in the first quarter of the 18th
century, in the works of Georgian scientist Vakhushti Bagrationi (Tielidze,
2016); subsequently there were many early expeditions and glacier photographs
covering the time period 1875–1906 (Solomina et al., 2016). Studies focused
on glacier mapping began when Podozerskiy (1911) published the first
inventory of the Greater Caucasus glaciers, based on large-scale military
topographical maps (
The next inventory of the Caucasus glaciers (Catalog of Glaciers of the USSR,
1967–1978) assessed glacier parameters from
Gobejishvili (1995) documented further statistical information about the
glaciers of Georgia based on the same 1960s topographic maps, reporting there
were 786 glaciers with a total area of 563.7 km
Khromova et al. (2009, 2014) used manually digitized results to estimate
changes of more than 1200 glaciers in the Caucasus in two periods:
1911–1957 and 1957–2000. They found that glacier area decreased from 1911 to 1957 by
24.7 % (0.52 % yr
Lur'e and Panov (2014) examined northern Caucasus glacier variation for
1895–2011, finding glacier area decreased by 849 km
The most recent glacier inventory, based on old topographic maps (1911/1960)
and modern satellite imagery (Landsat/ASTER, 2014) was published by
Tielidze (2016) but compiled only for Georgian Caucasus glaciers, which
reduced from 613.6
Other recent published works about the Greater Caucasus have mainly examined changes
in glacier area and length for individual river basins or separate sections.
Stokes et al. (2006, 2007) determined that 94 % of 113 selected glaciers
in the central Greater Caucasus retreated between 1985 and 2000; the largest glaciers
(> 10 km
In this article, we present the percentage and quantitative changes in the number and area of glaciers for the whole Greater Caucasus in the years 1960, 1986 and 2014, including analyses of various glacier attributes (aspect, slope) and location.
We utilize increasingly accessible global satellite imagery (Wulder et al.,
2012, 2016; Pope et al., 2014) to investigate glacier area and number change
in the Greater Caucasus in the periods
1960–1986, 1986–2014 and 1960–2014. Changes in glacier extent
in the Greater Caucasus between 1986 and 2014 were determined through
analysis of images from the Landsat 5 Thematic Mapper (TM), Landsat 8 Operational
Land Imager (OLI) and Advanced Spaceborne Thermal Emission and Reflection
Radiometer (ASTER) (Table 1). Georeferenced images were downloaded using the
EarthExplorer (
We used the Landsat 8 panchromatic band, along with a colour composite scene for each acquisition date, combining shortwave infrared, near infrared and red for Landsat, and near-infrared, red and green for ASTER images. These false-colour composite images can accurately show many glacier termini where meltwater streams are displayed in bright blue and contrast with the snout, which casts an obvious shadow (Stokes at al., 2006). This contrast remains apparent even with significant glacier retreat.
All images were acquired at the end of the ablation season, ranging from 2 August to 9 September, when glaciers were mostly free of seasonal snow under cloud-free conditions, but with some glacier margins obscured by shadows from rock faces and glacier cirque walls. In total, six Landsat 5 (TM) scenes were used for 1985–1987, with seven Landsat 8 (OLI) scenes for 2013–2016 and two ASTER scenes used for 2014 (Fig. 1c, d; Table 1). The latter were used primarily to complete coverage from isolated cloud cover in the Landsat scenes.
Large-scale topographic maps (88 sheets,
The 30 m resolution ASTER Global Digital Elevation Model (GDEM, 17 November 2011) was used to
determine the aspect, slope and height distribution of glaciers, downloaded
from NASA LP DAAC Collections (
We detected the glacier length by measurement of changes in the central flow line (Paul and Svoboda, 2009). This method uses the maximum length along the central flow line in different years, input that is required for glacier inventories.
List of satellite images scenes used in this study.
We have determined uncertainty with two independent methods (buffer and
multiple digitization). We used a buffer method similar to Granshaw and
Fountain (2006) and Bolch et al. (2010) and adopted by Tielidze (2016). The
uncertainty term for the 1960 extents is based on a buffer incorporating the
root-mean-square error (RMSE
Uncertainty is introduced by the resolution of the satellite image in terms
of what can be seen and by the contrast between the glacier and adjacent
terrain (Stokes et al., 2013). For debris-free glacier ice that is not
obscured by clouds, DeBeer and Sharp (2007) suggested that line placement
uncertainty is unlikely to be larger than the resolution of the imagery, i.e.
For 1986 and 2014 imagery we digitized the outlines of both debris-covered and
debris-free ice and tested a number of well-known semi-automated techniques
(band ratio TM3 / TM5 and OLI4 / OLI6, ratio thresholds range
Generally, for debris-free glaciers, automated delineation using the spectral ratio is more consistent and reproducible than manual delineation. These techniques are relatively useful for large sample sizes and/or large glaciers where manual delineation would be time-consuming (e.g. central Greater Caucasus), but their value can be limited by areas of glacier with supra-glacial debris (e.g. western and eastern Greater Caucasus) (Paul et al., 2013).
Following Paul et al. (2013) to determine the precision of the digitizing, we manually digitized 15 differently sized glaciers independently five times in the western, central and eastern Greater Caucasus to estimate 1986 and 2014 glacier area error. For debris-covered glaciers (Fig. 2a), the normalized standard deviation (NSD – based on delineations by multiple digitalization divided by the mean glacier area for all outlines) was 6.9 %, and the difference between the manually and automatically derived area was 13.41 %. For debris-free glaciers (Fig. 2b, c) the NSD was 5.7 %, and the difference between the manually and automatically derived area was 4.9 %.
To estimate 1960s glacier area error, we digitized multiple (3) times three
different size glaciers (< 2, 2–5,
> 5 km
Importantly, debris cover is not continuous on the snouts of many glaciers in
the Greater Caucasus and most glaciers of Mt. Elbrus (Shahgedanova et al.,
2014; Tielidze et al., 2017), but there are some glaciers covered by heavy
debris. One of the most debris-covered we digitized in the Caucasus is
Shkhelda Glacier (8.28
The total ice area loss between 1960 and 1986 was 192.8
Glaciers in the northern Greater Caucasus lost 131.0
On the southern macroslope, glacier area decreased by
61.8
Overall, the differences between the two macroslopes were small. The greater
loss was observed on the southern slope, where glaciers lost
33.0
The eastern Greater Caucasus section (Aragvi; Tergi (Terek) headwaters; Sunja right
(southeast) tributaries – Sulak, Samur, Agrichai and Kusarchai) experienced
the highest relative glacier area loss, where the total ice area loss between
1960 and 2014 was 53.3
Glacier mean elevation for the northern macroslope changed from 3458 to 3477 to 3506 m a.s.l. in 1960, 1986 and 2014 respectively, and minimum elevation changed from 1939 to 1964 to 1997 m a.s.l. For the southern macroslope, mean elevation changed from 3246 to 3278 to 3320 m a.s.l. and minimum from 1875 to 1908 to 1960 m a.s.l. in the same time period. Detailed glacier parameter changes according to different slopes and sections are shown in Table 3.
Glaciers located on Mt. Elbrus lost 9.9
The Greater Caucasus glacier number and area change according to the different slopes and sections in 1960–1986, 1986–2014 and 1960–2014.
Greater Caucasus glacier area decrease by slopes, sections and mountain massifs in 1960–1986, 1986–2014 and 1960–2014.
Among the large glaciers (> 10 km
Topographic parameters for glaciers in 1960, 1986 and 2014.
Unlike the Elbrus, the size of the change varied dramatically from glacier to
glacier on the Kazbegi-Jimara massif. The total ice area loss
between 1960 and 1986 was 6.1
Among glaciers with an area of 2–5 km
The greatest area is occupied by glaciers in the size class 1.0–5.0 km
Cumulative glacier area and number values for seven size classes in the Greater Caucasus in 1960, 1986 and 2014.
Area change for the seven glacier size classes in the
Proportion of glacier aspect by
Greater Caucasus, mean slope vs. glacier area for northern and southern macroslopes.
During the 1986–2014 period the number of smallest glaciers
(0.01–0.05 km
Glacier area reduction varies between the individual sections of the Greater
Caucasus, with the highest increase in the number of glaciers in the smallest
category (< 0.05 km
Most of the glacier area in the Greater Caucasus occurs between 3000 and
4000 m a.s.l. (857.6 km
Glaciers with north, northeast and northwest aspects are the most extensive
in the Greater Caucasus, covering 286.0
Glaciers with south aspects located on the northern slope are the most elevated in the Greater Caucasus. For the southern slope, southwest aspects are more elevated; for the entire mountain range, southeast aspects are more elevated (Fig. 8c).
The slopes with 10–15
Glacier area comparison for seven glacier classes in the Greater Caucasus according to the RGI (5), GLIMS and new Caucasus Glacier Inventory (CGI).
We chose 30 glaciers in four size classes (< 1,
1–5, 5–10, > 10 km
Of the 30 glaciers measured, 29 retreated between 1986 and 2014. Thirteen
glaciers showed less change in 1986–2014 than in 1960–1986, and one
glacier (Mizhirgi) advanced. These results correlate well with detailed field
measurement of the snout position of Chalaati Glacier (Gobejishvili, 1995;
Gobejishvili et al., 2012) and are in agreement with sporadic field
measurement and anecdotal evidence from other glaciers (e.g. field
investigation confirms that Mizhirgi Glacier advanced between 1985 and 2000).
The overall advance of Mizhirgi Glacier between 1985 and 2000 was around
110
Overall, the largest glaciers (> 10 km
According to this current inventory, Bezingi Glacier represents the
largest single glacier (37.47
Considering some errors in the 1911 catalogue (Tielidze, 2016), we calculate
that glacier area decreased from 1967.4 km
Our results also showed that eastern Greater Caucasus glaciers are shrinking faster than those in the western and central areas; the smaller size of glaciers there may be the reason for this phenomenon. The Elbrus glacier area rate of loss is lower than in the Greater Caucasus main watershed range due to the higher elevation and larger accumulation areas.
One of the important steps in utilizing our glacier inventory data is to
understand spatial patterns in glacier characteristics across the region. Our
study area displays region-wide consistency in glacier characteristics –
notably glacier area, elevation and topography – across the five subregions
based on the
Comparisons between glacier size and surface area fluctuations suggest that
smaller glaciers, though losing the least surface area, actually lost a
greater proportion of their total area. Approximately 28.37 %
(0.52 % yr
Unlike the small glaciers, the largest glaciers (> 10 km
Glacier slope may also play a significant role in determining glacier area change (Table 3); i.e. the steeper the glacier, the larger the area loss observed in our study. The same tendency was observed in the Himalaya (Salerno et al., 2008; Racoviteanu et al., 2015).
We note that direct comparison of such numbers can be critical for various reasons, such as diverse sample size or size class distribution of the investigated glaciers, different subregional to local climate conditions, various length and onset of observation periods etc.
The GLIMS glacier database (9 February 2017 version) contained a number of deficiencies which have been remedied after this inventory; for example these river basins did not contain any glacier outlines: Belaya, Malaya Laba and Mzimba in the western Greater Caucasus; Khobistskali in the central Greater Caucasus; and Aragvi, Assa, Arghuni, Sharo Argun, Andiyskoye Koysu, Avarskoye Koysu, Samur, Agrichai and Kusarchai in the eastern Greater Caucasus. These constitute more than one-half of the territory for the whole Greater Caucasus where modern glaciers are present (Fig. 10a). The GLIMS outlines also involve inconsistent registration, which appears to be associated with the use of ASTER imagery (Fig. 10b) (Khromova, 2009).
The RGI 5.0 version database similarly contains errors, especially in the
central Greater Caucasus section. For example in the Samegrelo, Lechkhumi and
Shoda-Kedela subranges, where the RGI database contains 39 nominal glaciers
(circles representing areas) with a total area of 40.2 km
Overall, glacier area difference was 165.1 km
We present a glacier change analysis including multi-temporal data sets
covering the entire Greater Caucasus for the first time. Manual digitization
from 1960s large-scale (
The main errors occur from data quality. Errors in the 1960s maps included mapped snow patches (especially for small cirque type glaciers) and uncertain glacier extents, which could be verified using available Corona 1964 satellite imagery (Fig. 2d–e). Other sources of error for aerial imagery include seasonal snow, shadows and debris cover, which can impede glacier mapping. Using GPS field data, debris cover error can be resolved for some glaciers; while incorrect identification of seasonal snow generally affects small glaciers more than larger complexes, these do not make up a large percentage of the total area.
The main study findings can be summarized as follows:
The Greater Caucasus region experienced glacier area loss at an average
annual rate of 0.44 % yr Glacier number and area changes indicate that glaciers in the eastern
Greater Caucasus have decreased (0.98 % yr Glaciers of the Elbrus and Kazbegi-Jimara massifs lost a smaller
proportion of their area between 1960 and 2014 than glaciers located in
the main watershed range: 0.27 and 0.39 % yr
The inventory presented here will further enable focus on assessing changes in glaciers, debris cover, mass balance, total volume and hydrological modelling.
The data described in this article are available for public download at
The Greater Caucasus Glacier Inventory includes the number and area change in 1960–1986, 1986–2014 and 1960–2014 by individual river basins and countries (Tables 1–2); Elbrus and Kazbegi-Jimara massif glacier number and area change in 1960–1986, 1986–2014 and 1960–2014 (Tables 3–4; Figs. 1–2); cumulative glacier area and number values for seven size classes in 1960, 1986 and 2014 for the northern, southern, western, central and eastern Greater Caucasus (Table 5; Figs. 3–12); area change for the seven glacier size classes in the western, central and eastern sections and the entire Greater Caucasus in 1960–1986, 1986–2014 and 1960–2014 (Table 6); and characteristics of glaciers used for measuring length change (Table 7).
The supplement related to this article is available online at:
The authors declare that they have no conflict of interest.
We gratefully acknowledge the financial support from the Shota Rustaveli Georgian National Science Foundation “State science grants for outgoing research internship of young scientists 2016” project – the Greater Caucasus Glacier Inventory (IG/3/1/16). We also gratefully acknowledge the financial support from the International Educational Center of Georgia “Professional Development and Retraining Program 2017–2018”. Special thanks to the editor, Chris R. Stokes, and two reviewers, Frank Paul and Maria Shahgedanova, for useful suggestions and detailed comments which clearly enhanced the quality of the paper. Edited by: Chris R. Stokes Reviewed by: Maria Shahgedanova and Frank Paul