A recent study published in the journal Science has linked the catastrophic 2023 Glacial Lake Outburst Flood (GLOF) in Sikkim to the combined effects of glacial melt, permafrost thaw, lake expansion and extreme terrain instability driven by climate change. The disaster originated from the breach of the South Lhonak glacial lake, one of the fastest-growing and most hazardous glacial lakes in Sikkim, leading to massive downstream flooding in India and Bangladesh.The event highlights the growing vulnerability of the Himalayan cryosphere, the risks associated with unregulated infrastructure development in fragile mountain ecosystems, and the urgent need for scientific monitoring and disaster preparedness.
On the night of 3 October 2023, a lateral moraine — a ridge of frozen rock and debris beside the South Lhonak glacier — collapsed into the glacial lake.This collapse triggered:
The floodwaters travelled rapidly downstream and reached Chungthang village around 68 km away within two hours, destroying the 1,200 MW Teesta-III Hydropower Project and damaging several downstream dams.The event was classified as a Glacial Lake Outburst Flood (GLOF), which refers to the sudden release of water from a glacial lake.
A Glacial Lake Outburst Flood (GLOF) occurs when water stored in a glacial lake is suddenly released due to the failure of natural barriers such as:
GLOFs are highly destructive because they carry:
The Himalayan region is increasingly vulnerable to GLOFs due to rapid glacier retreat caused by climate change.
The study identifies permafrost thaw as the principal long-term destabilising factor.Permafrost refers to permanently frozen ground found in high mountain and polar regions. Rising temperatures caused:
The study estimates warming impacts extending nearly 100 metres below the ground surface.This gradual weakening made the slope vulnerable to collapse.
The study also found that the South Lhonak lake expanded nearly 12 times between 1975 and 2023.The expansion occurred due to continuous meltwater inflow from the glacier above the lake.Key findings include:
| Parameter | Findings |
|---|---|
| Lake Expansion Period | 1975–2023 |
| Expansion Rate | 0.32 km² per year |
| Overall Growth | Nearly 12-fold |
| Glacier Trend | Negative mass balance (shrinking glacier) |
The study links this directly to rising regional temperatures.
The paper highlights that average regional temperatures have been increasing by 0.08°C per decade since the 1950s.Climate change contributed through:
The study concludes that climate change significantly increased the sensitivity of the Himalayan environment to cascading hazards.
Although long-term climatic changes created unstable conditions, the immediate trigger was intense rainfall during 3–4 October 2023.Rainfall caused:
The study notes that while rainfall was typical for the season, the terrain had already become extremely fragile.
The disaster triggered multiple secondary hazards across the Teesta basin.
| Impact | Details |
|---|---|
| Lives Lost | 55 people |
| Buildings Damaged | 25,900 |
| Bridges Damaged | 31 major bridges |
| Agricultural Land Flooded | 276 km² |
| Secondary Landslides | 45 |
| Sediment Eroded | 270 million cubic metres |
The flood impacts extended beyond Sikkim into:
Eventually, floodwaters discharged into the Brahmaputra River system.
The study warns about the rapid expansion of hydropower projects in fragile Himalayan regions.The Teesta basin reportedly hosts one of the highest concentrations of hydropower projects in the Himalayas.
The paper notes that more than 650 hydropower projects are planned or under construction across high-mountain Asia.
The study stresses the need for integrated disaster risk reduction strategies.
The paper also emphasises the importance of balancing climate adaptation with institutional accountability.
The Sikkim GLOF is significant for India because it highlights:
The issue is important for topics related to:
| Feature | Details |
|---|---|
| Location | North Sikkim |
| Type | Glacial lake |
| Status Mentioned | One of the largest and fastest-growing glacial lakes in Sikkim |
| Growth | Expanded nearly 12 times between 1975 and 2023 |
| Feature | Details |
|---|---|
| Meaning | Sudden release of water from a glacial lake |
| Causes | Moraine failure, glacier melt, avalanches, landslides |
| Major Risks | Floods, landslides, sediment transport, infrastructure destruction |
| Feature | Details |
|---|---|
| Capacity | 1,200 MW |
| River Basin | Teesta River |
| Impact | Destroyed during 2023 GLOF |
| Institution | Details |
|---|---|
| Indian Institute of Technology Bhubaneswar | Institution associated with study lead author |
| University of Graz | Institution of geoscientist quoted in article |
| International Centre for Integrated Mountain Development (ICIMOD) | Regional mountain research organisation mentioned |
| Feature | Details |
|---|---|
| Published In | Science |
| Focus | Drivers and impacts of 2023 Sikkim GLOF |
| Main Theme | Climate change, glacier melt, permafrost thaw and cascading hazards |
Updated – 30 January 2025 ; 07:31 PMNews Source:Carbon Brief