Historical analysis of glacier surges and ice-dammed lake outburst floods in the Kumdan group, Karakoram

Glacier surges and associated ice-dammed lake outburst floods pose significant hazards in the Karakoram, where fragmented historical records show unclear trends in surge behaviour and flood frequency. Therefore, this study integrates historical archives, remote sensing data, digital elevation models (DEMs), surface velocity time series (ITS_LIVE), and ground observations to analyse the surge dynamics and associated glacial lake outburst flood (GLOF) history of the Kumdan group glaciers (Chong Kumdan, Kichik Kumdan, and Aktash). Historical records cross-verified with original sources and imagery confirm 16 GLOFs since 1835, predominantly from Chong Kumdan and Kichik Kumdan, with none from Aktash, despite its surges. Chong Kumdan exhibits long active phases (7–10 years) and an ∼77-year surge cycle for its primary tributary ‘a’, with asynchronous surges in its tributary ‘b’ and the main trunk. It generated the most devastating floods, including significant events in 1835, 1926, and 1929, but the last GLOF occurred in 1934. The recent surge (2001–2010) caused the terminus to advance ∼100 m short of the Shyok River, which was therefore not dammed. Kichik Kumdan shows shorter active phases (∼2 years) with cycle lengths decreasing from 33 years (1833–1866) to 27 years (1970–1997). Its last significant GLOF occurred in 1903, with post-1970s surges failing to form stable ice dams. Aktash shows periodic surges but no GLOFs occurred due to effective subglacial drainage that prevents river blockages. We observe a decline in surge-induced GLOFs because of climate warming, which reduces mass accumulation, shortens surge cycles, and weakens ice dams. DEM analyses show recent thickening in reservoir zones of Chong Kumdan (∼22 m) and Kichik Kumdan (∼20 m) from 2015 to 2022, indicating potential future surges. These findings provide crucial insights for policymakers and local communities in managing glacier-related hazards for improved risk assessment and mitigation strategies.