Glacier variations since the Little Ice Age are still poorly studied on the southern slope of the Greater Caucasus. Addressing this, new research studies the behaviour of the Chalaati Glacier from its maximum extent during the Little Ice Age.

For the first time in the history of glaciological studies of the Georgian Caucasus, researchers applied the cosmogenic surface exposure dating technique Beryllium-10 (a radioactive isotope 10Be) in order to study the change of the Chalaati glacier since the Little Ice Age (13th to 19th Century). Surface exposure dating is a collection of geochronological techniques for estimating the length of time that a rock has been exposed at or near the Earth's surface. The age of moraines was also determined by tree-ring analysis (dendrochronology technique).

In addition, lichenometry was used as a supplementary tool to determine the relative ages of glacial landforms. Lichenometry is a geomorphic method of geochronologic dating that uses lichen growth to determine the age of exposed rock, based on a presumed specific rate of increase in radial size over time. Furthermore, large-scale topographical maps (1887, 1960) were used along with satellite imagery – Corona, Landsat 5 TM, and Sentinel 2B. Repeated photographs were used to identify the glacier extent in the late XIX century.

Based on the 10Be ages from the oldest lateral moraine of the Chalaati Glacier, the researchers discovered that the onset of the Little Ice Age occurred ~730 years ago (CE ~1250–1330), while the dendrochronology and lichenometry measurements show that the Chalaati Glacier reached its secondary maximum extent again about 210 years ago (CE ~1810). From that time through 2018, the glacier area decreased by about 34 percent, while its length retreated by ~2280 m.

"Chalaati is one of the most frequently visited glaciers in Georgia due to its close location to the road, gentle valley inclination, and low position of the terminus. Today this valley is used for the construction of hydropower. Water and debris from Chalaati Glacier will be filling this reservoir, the rate of which is highly depends on the future state of Glacier, making this study especially relevant," says lead author Levan Tielidze.

Reference: Tielidze L.G., Solomina O.N., Jomelli V., Dolgova E.A., Bushueva I.S., Mikhalenko V.N., Brauche R., ASTER T. 'Change of Chalaati Glacier (Georgian Caucasus) since the Little Ice Age based on dendrochronological and Beryllium‑10 data.'Ice and Snow. 2020;60(3):453-470.

Image: Levan Tielidze.

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