Fluctuations of Kashkatash Glacier
during the last four centuries
(Elbrus Area, Nothern Caucasus, Russia)
and Olga Solomina
Institute of Geography Russian Academy of Science
Like most mountain glaciers those in the Caucasus are currently retreating, although this process is rather poorly documented in this area. We focused our study on the retreat of a typical valley glacier Kashkatash (43,18 N, 42,7 E; area - 2,5 km2; length - 4,6 km, front elevation - 2600 m), located in the Elbrus Area. We compared the oldest high quality photograph of the glacier forefields, taken by H. Burmester (1913) in 1911 (fig.1) with the aerial photographs of 1957, 1965, 1987, map of scale 1:25 000 based on the data of 1950s, satellite images (Corona of 1971, ASTER of 2005, EROS+ASTER of 2006) and oblique photographs taken in 1990s-2000s (fig.2). We estimated the linear glacier retreat and the age of numerous stadial moraines over the last centuries basing on geomorphic, tree-ring and lichenometric data and discussed our results in the context of previous sparse glacier fluctuation reconstructions in this region (Serebryanny et al., 1989; Solomina, 1999, Zolotarev, 2008). For this purpose we first georeferenced and digitized the map of Kashkatash glacier tongue and forefields, created DEM and made orthorectification of the aerial photographs (using the DEM). The accuracy of our georeferencing is limited by GPS capacity (15 meters). Lichonometry was quite successfully used to date moraines in the central Caucasus since 1980s (Serebryanny et al., 1989) due to quite regular growth rate of Rhizocarpon geographicum (sensu lato) anda number of reference points controlling the growth curve for the last millennium. We used traditional lichenometric approach measuring the maximum diameters of these lichens on the whole surface of each moraine and using the mean of five largest diameters as the predictor of the age of moraines. More than 100 samples of pine (cores and disks) collected in summers 2008, 2009 and cross-dated against the regional pine ring-width chronology were used to estimate the minimum age of moraines and the rate of wood colonization of the glacier forefields. We identified several end moraines at Kashkatash glacier within the distance of 900 meters from the front position of the glacier in 2005. The minimum age of the outer moraine is at least 450 years according to the tree-ring data. This moraine is adjacent to one of the most prominent end moraine deposited in the middle of the 18th century. This date is based on the age of the oldest tree (AD1803) plus five years correction for the height of the sampling, plus approximately 50 years of excesis – time required for colonization estimated by the modern aerial photographs in Baksan valley. The position of the moraine of the middle 19th century shows that the glacier was approximately 80 meters shorter than a century before. We identified the moraine of the 19th century at the photograph of 1911 as well as 3 to 4 younger moraine ridges. At this photograph all of them look very fresh and they are totally lacking any vegetation (fig.2). If we take into account the modern rate of moraine colonization the freshness of moraine surfaces indicates that all these advances of Kashkatash glacier occurred between 1850s and 1911. This conclusion agrees well with the Bolshoy Azau glacier advances occurred in 1876, 1880-1881, 1884, 1890 and described by the first travelers (Bogatikov et al., 2004). These dates also agree well with our tree-ring data. In the late 19th to the early 20th centuries the retreat of the glacier was most dramatic (approximately 400 meters). However Kashkatash glacier was almost stable between 1911 and 1957, and it retreated from these positions by 100 meters by 2005. The comparison of aerial photograph and space images also shows that up to the middle of 20th century only very sparse vegetation occupied glacier forefield. Dramatic changes happened in the last 50 years while the whole surface of the sandur and young moraines is covered now by a dense pine wood. The increased rate of glacier retreat and plant colonization of the forefields agrees well with the global warming trends in the second half of 20th century.
Photo by Burmester (1911) Photo by Bushueva (2009)