Glacial Lake Burst Behind Uttarakhand Floods? A Look At Previous Instances

Five people have died and at least 50 are missing after flash floods hit Uttarakhand's Uttarkashi on Tuesday. The disaster struck Dharali village, a popular tourist spot near Gangotri, sweeping away homes, hotels, and restaurants in a sudden deluge. 

Chief Minister Pushkar Singh Dhami confirmed on Wednesday that 190 people have been rescued. Evacuation plans are being drawn up for pilgrims stranded in Gangotri Dham via Nelong Valley.

Initially attributed to a cloudburst, experts are now investigating the possibility of a glacial lake outburst flood (GLOF).

This occurs when excessive water accumulates in a lake formed by melting glaciers, and the natural dam holding it back suddenly fails, triggering a dangerous flood. Such bursts can be caused by heavy rainfall, landslides, avalanches, earthquakes, or rapid glacier melt.

This is not the first such incident.

South Lhonak Lake, Sikkim (2023)

Over 90 people died on October 4, 2023, when South Lhonak Lake in Sikkim burst after heavy rainfall and a landslide sent debris crashing into the glacial lake. The outburst unleashed a powerful flood that destroyed the Teesta III hydroelectric dam and swept through towns downstream. The disaster left hundreds missing or displaced. Authorities previously flagged the lake as highly vulnerable due to its rapid expansion from glacial melt.

Chamoli, Uttarakhand (2021)

On February 7, 2021, a massive flash flood tore through the Rishiganga and Dhauliganga valleys in Chamoli district. Initially believed to be caused by a GLOF, later analysis confirmed the event was triggered by a rock and ice avalanche from a hanging glacier near Nanda Devi. The collapse released a deluge of debris and water, devastating two hydro projects and killing more than 200 people. 

Chorabari Lake (Gandhi Sarovar), Kedarnath (2013)

The 2013 Kedarnath tragedy was triggered in part by the bursting of Chorabari Lake. An avalanche caused the moraine-dammed lake to rupture, releasing an estimated 262 million litres of water. This sudden outburst, combined with intense rainfall, led to devastating floods that killed nearly 6,000 people. The town of Kedarnath and the surrounding areas were virtually wiped out.

Ladakh, Other Himalayan Regions (2010-16)

Between 2010 and 2016, several glacial lake and landslide-dammed lake outbursts were recorded in Ladakh and neighbouring Himalayan regions.

In 2010, a cloudburst in Leh triggered flash floods in Nidder.

In 2013, GLOFs were recorded in Kargil, followed by outbursts in Gya (2014), Phugtal (2015), and Achinathang (2016).

India's vulnerability to GLOFs is not new. Historical records dating back to the 19th and 20th centuries reveal dozens of such events, especially in Ladakh's Shyok and Nubra valleys. The 1893 formation and 1894 breach of Gohna Tal in Uttarakhand also remains a textbook case of a landslide-dammed lake disaster.