Abstract. Glacial lake outburst floods (GLOFs) have become more frequent and attracted more and more attention under conditions of global warming. However, there are few observations of the reasons for outbursts and their processes because of their unexpected occurrence and their inaccessible location in high-elevation areas. The GLOF of the Guangxieco Lake, which is the only outburst lake below an elevation of 4000 m in Tibet, provides a case study for discussing the reasons for outbursts. This paper reconstructs the process in detail using geomorphological evidence, interviews of the local inhabitants, archive material and satellite images. It was found that: (1) There were three main reasons for the GLOF in 1988: intense pre-precipitation and persistent high temperatures before the outburst, ice avalanche by rapid movement of the Gongzo Glacier and low self-stability of the end-moraine dam by perennial piping. (2) The GLOF with the peak discharge of 1270 m3 s-1 was evolved along the Midui Valley following sediment-laden flow–non-viscous debris flow–viscous debris flow–non-viscous debris flow–sediment-laden flood. Eventually the sediment-laden floods blocked the Palongzangbu River. (3) Comparing the conditions for the outburst in 1988 and at present, the possibility of a future outburst is thought to be small unless the glacier moves rapidly again.
Glacier lake outburst floods of the Guangxieco Lake in 1988 in Tibet, China