Glacial Lake Outburst Flood (GLOF) is the sudden surge of water from a lake fed by a glacial melt. It may form in front, beneath, or even on the surface of a glacier. Experts believe that the devastating October 2023 flash floods in Sikkim was caused by a GLOF.

It was the overflow from the South Lhonak glacial lake in north Sikkim on October 4 that unleashed violent floods washing away highways, bridges, a dam and human settlements downstream. Close to 50 persons died in the disaster.

GLOFs are not a recent phenomenon. But, according to the International Centre for Integrated Mountain Development (ICIMOD), the frequency and risks from glacial melts have increased because of global warming and climate change. As the earth warms, new glacial lakes form, existing ones expand and merge with other water bodies causing flash floods like the one witnessed in Sikkim.

Uttarakhand, Sikkim, and Himachal Pradesh in the Himalayan region run the risk of being severely impacted by GLOF events.

According to a 2018 report on the status of glacial lakes in the Hindu Khush Mountain ranges by the ICIMOD there are more than 25,000 glacial lakes spread across the region which encompasses central and south Asia.

Two recent GLOF related incidents in the Himalayan region included the flash floods in the holy town of Kedarnath in 2013 and the catastrophic floods in February 2021 in Chamoli district of Uttarakhand.

Experts are agreed that given the risk of GLOF events, it is imperative that construction and development activity in the seismologically sensitive Himalayan region be planned carefully to minimise damage to the environment and human life.