Age of moraines of the Bolshoy Azau Glacier in the upper course of the Baksan River valley according to dendrochronological data

Abstract

Basing on tree­ring analysis of more than 150pines growing in the Azau clearing, the minimum age of the deposits created by the Greater Azau Glacier was identified. Historical evidence, cartographic data, remote sensing materials, as well as the results of lichenometric studies and radiocarbon dating of buried soils were used as additional sources of information. We determined limits of the area covered by the glacier tongue at the end of the 19th century. It was also shown that the highest and most pronounced lateral moraine, conventionally called the «17th century moraine», was formed earlier than the end of the 15th century. Judging from the size of the maximum lichens of Rhizocarpon geographicum (120–130mm) on its surface, the age of the moraine, determined by the dendrochronological method was found to be underestimated. It may be several centuries older than the end of the 16th century. We re­examined a pine trunk buried in the sediments at the bottom of the valley which was discovered in the 1960s. Previously it was dated by radiocarbon (140±75BP[1], the calibrated date– 1650–1960 CE). According to the new data, the most probable tree­ring dates of the buried tree are 1759–1883CE, however, the second most likely dates are 1826–1950CE. Unfortunately, low statistical estimates do not allow us to confirm the reliability of the dates. The paper also discusses the controversial issue of the position of the moraine of 1849CE, which was described by H.Abich[2]. The annex to the article contains a translation of a fragment of this important paper related to the Greater Azau Glacier. Suppressions of pine growth from the moraines of the Greater Azau in the 1640s, 1710s, 1800s, 1840s, and 1860sCE are synchronous with the advances of the Bosson, Mer de Glace and Grindelwald glaciers in the Alps[3].