Dynamics of lakes on Fedchenko Glacier from 2016 to 2021

The aim of this work is to investigate dynamics of lakes on Fedchenko glacier on Pamir mountains, as the area growth of lakes causes faster filtration, lower surface albedo and as consequence raises speed of the glacier and intensity of melting. Lowest part of this glacier has continuous debris cover, low velocities and nearly horizontal surface, which increases the likelihood of lakes in each season. This paper provides insight into the dynamics of the total area of lakes on the last 11.5 km of Fedchenko during 2016–2021, and provides a comparison of the area within and between each season at three altitudinal levels. Lake outlines are identified by combining two indexes – Normalised Difference Water Index and Modified Soil-Adjusted Vegetation Index – which were range-cut in range to separate water from other surfaces on the glacier. The changes in the patterns of seasonal lakes dynamics can be due to various reasons, so temperature and precipitation data are used to analyze the changes in supraglacial lake regime. Result shows that lakes occupy a small percentage of the total area – about 2% for the whole period, with a minimum of 0.7% in 2016 and a maximum of 2.2% in 2020. However, there are significant changes in the dynamics of the lakes, with the amplitude of area doubling from 0.15 km² to 0.3 km² over the period 2016–2021, with an increase in the absolute seasonal maximum value by 0.2 km². The regime also changes rapidly over the six years, from normal with an area peak only in late May in 2016–2018 to more chaotic regime with several peaks, usually two, in May and July, in 2019–2021. An important role in the analysis is played by two largest lakes on Fedchenko Glacier – moraine–dammed lake at the highest altitude range (3300–3600 m a.s.l.) and proglacial lake at the lowest altitude range (2900–3100 m a.s.l.) – which mainly have opposite dynamics comparing to small supraglacial lakes. They are continuously filling up until the end of ablation season, but the result shows that their relative area growth is less than growth of new smaller lakes over a period of six years. The rapid area growth and more chaotic dynamics of supraglacial lakes can indicate specific influence of climate changes on glaciers.