What 190 years of glacial lake outburst flood data tells us about the Hindu Kush Himalayas

An analysis of the International Centre for Integrated Mountain Development’s (ICIMOD) latest data on glacial lake outburst floods (GLOF) since 1833 has suggested that over 70 per cent of the 700 GLOF outbreaks have happened in the past 50 years. 

The year 1980 saw the highest number of GLOF events, 15, followed by 2015 (13). The years 1973, 1974, 2002 and 2010 all experienced 10 GLOF events. 

But, according to ICIMOD, “the overall increase in GLOFs is mainly due to better observations and reporting, but the overall damage to infrastructure from these events has likely increased in the recent past”. 

A GLOF outburst, according to ICIMOD, “is sudden release of water from a lake fed by glacier melt that has formed at the side, in front, within, beneath, or on the surface of a glacier”. 

The report, Glacial lake outburst floods in High Mountain Asia documented in regional effort, also quantified the number of lives lost — over 7,000 have died due to GLOF outbursts since 1833 across the Hindu Kush Himalayan region. 

Over half of the GLOF outbursts (54 per cent) were triggered due to mass movements like avalanches, rock falls and landslides while another 18 per cent were due to extreme rainfall events, it highlighted. 

“This points to a need for better forecasting of precipitation at altitude as well as mapping of an increasingly unstable cryosphere,” the report said.

Cryosphere, according to the National Oceanic and Atmospheric Administration, is the frozen water or ice water of the earth system.

GLOFs also tend to have a domino impact. According to the analysis, while eight GLOF events occurred in China, their impacts were felt in neighbouring countries like Nepal. 

The report also cautioned how “without a major step up in both monitoring, mitigation and early warning for all, it is likely we will see more major examples of GLOFs such as South Lhonak.”

According to ICIMOD, the GLOF outburst in the South Lhonak lake in Sikkim on the intervening night of October 3-4, 2023 was responsible for 102 deaths.

Earlier, Down to Earth reported how researchers had earlier warned about the outburst in the South Lhonak lake. 

According to the researchers, glacial retreat over the years has led to significant growth in the area around the South Lhonak lake. This increase had led to heightened chances of a GLOF in the region.