The Karakoram mountain range is prone to natural disasters such as glacial surging and glacial lake outburst flood (GLOF) events. In this study, we aimed to document and reconstruct the sequence of events caused by glacial debris flows that dammed the Immit River in the Hindu Kush Karakoram Range on 17 July 2018. We used satellite remote sensing and field data to conduct the analyses. The order of the events in the disaster chain were determined as follows: glacial meltwater from the G2 glacier (ID: G074052E36491N) transported ice and debris that dammed the meltwater at the snout of the G1 glacier (ID: G074103E36480N), then the debris flow dammed the Immit River and caused Lake Badswat to expand. We surveyed the extent of these events using remote sensing imagery. We analyzed the glaciers' responses to this event chain and found that the glacial debris flow induced G1 to exhibit accelerating ice flow in parts of the region from 25 July 2018 to 4 August 2018. According to the records from reanalysis data and data from the automatic weather station located 75 km from Lake Badswat, the occurrence of this disaster chain was related to high temperatures recorded after 15 July 2018. The chains of events caused by glacially related disasters makes such hazards more complex and dangerous. Therefore, this study is useful not only for understanding the formation of glacial disaster chains, but also for framing mitigation plans to reduce the risks for vulnerable downstream/upstream residents.

Lakes and permafrost on Qinghai-Tibet Plateau (QTP) are both important indicators of climate change. Previous literatures have shown the usefulness of optical remote sensing in lake expansion monitoring and the effectiveness of synthetic aperture radar (SAR) interferometry (InSAR) in retrieving permafrost deformation on QTP. However, none of them incorporated both optical remote sensing and InSAR to investigate an event that may exhibit causal links between lake outburst and permafrost degradation. This study integrated both the Google Earth Engine (GEE) analysis on optical images and the small baseline subset (SBAS) processing on SAR datasets to evaluate the potential impact of a lake outburst event on permafrost degradation. The outburst of Zonag Lake (headwater lake) that occurred on 14 September 2011 was focused, and its consequential influence on the permafrost degradation surrounding Salt Lake (tailwater lake) was investigated. The GEE processing on Landsat and HJ-1 imageries allowed an efficient monitoring of the Salt Lake expansion over past 20 years. In addition, the SBAS-InSAR analysis on temporal Envisat and Sentinel-1 datasets further discovered the accelerated permafrost degradation surrounding Salt Lake after 2014. The results provide an evidence that on QTP the outburst of a headwater lake may significantly accelerate the permafrost degradation surrounding the tailwater lake. Such degradation may be attributed to the thermal alteration of the permafrost thawing-freezing cycle and the melting ground ice, along with the subsequent changes on hydrological connectivity and soil permeability. With the continuous trend of the permafrost degradation surrounding Salt Lake, potential risks may be further exposed to the regional environment and infrastructures such as the Qinghai-Tibet railway and highway, thus deserving a particular attention in the near future. The novelties of this study are: 1) technically, the preliminary attempt to integrate the GEE and InSAR techniques for a joint analysis of lake expansion and permafrost degradation, and 2) scientifically, the finding that lake outburst may accelerate permafrost degradation on QTP.

Glacial lake outburst flood (GLOF) is one of the major natural disasters in the Qinghai-Tibetan Plateau (QTP). On 25 June 2020, the outburst of the Jiwenco Glacial Lake (JGL) in the upper reaches of Nidu river in Jiari County of the QTP reached the downstream Niwu Township on 26 June, causing damage to many bridges, roads, houses, and other infrastructure, and disrupting telecommunications for several days. Based on radar and optical image data, the evolution of the JGL before and after the outburst was analyzed. The results showed that the area and storage capacity of the JGL were 0.58 square kilometers and 0.071 cubic kilometers, respectively, before the outburst (29 May), and only 0.26 square kilometers and 0.017 cubic kilometers remained after the outburst (27 July). The outburst reservoir capacity was as high as 5.4 million cubic meters. The main cause of the JGL outburst was the heavy precipitation process before outburst and the ice/snow/landslides entering the lake was the direct inducement. The outburst flood/debris flow disaster also led to many sections of the river and buildings in Niwu Township at high risk. Therefore, it is urgent to pay more attention to glacial lake outburst floods and other low-probability disasters, and early real-time engineering measures should be taken to minimize their potential impacts.