Three years after South Lhonak disaster, what has Sikkim learnt?

You may not have heard of Rimbi, a scenic stop in west Sikkim. A few days ago, a massive landslide damaged homes and government buildings, forcing families to safer locations. Thankfully, no loss of life has been reported.

But look at that landscape. Where exactly is safe in Sikkim?

Rimbi was not a glacial lake outburst flood. That is precisely the point. This is my home state, and it hurts to say this: in 2026, no district is completely safe. No road is guaranteed to remain open.

These hazards are everybody’s problem. There is no part of the state where we can pretend that extreme weather and geological hazards belong to somebody else’s life.

Three years ago, on October 4, 2023, South Lhonak glacial lake in North Sikkim burst. Water, ice, rock and debris tore down the Teesta basin, destroying bridges, roads, homes, livelihoods and the Chungthang hydropower project.

Close to 200 people lost their lives, hundreds were injured, and damage ran into billions of rupees.

Three years later, the question is not simply how much Sikkim has recovered. What did we actually learn? Because recovering from a disaster and learning from one are two different things. Rebuilding what we lost matters. But the decisions behind that rebuilding matter just as much.

Recovery means rebuilding a bridge. Learning means questioning its location. Recovery means repairing a road. 

Learning means understanding the slope above it. Recovery means installing a warning system. Learning means ensuring people receive the warning and know where to go. It means asking whether the bridge belongs in the same place, whether the road remains exposed, and whether an alarm can actually lead people to safety.

Scientists had studied South Lhonak for years. It was among the region’s largest and fastest-growing glacial lakes.

A 2021 study had modelled a potential outburst, warning that lake growth could increase the danger from avalanche impacts, exposing downstream settlements and infrastructure, including Chungthang.

Recent research indicates that a landslide deposited huge volumes of debris into the lake while glacier ice was lost through calving. These events contributed to the moraine’s collapse and generated the flood wave. It was a chain of events, and understanding that chain matters when we prepare for what comes next.

Another study found substantial lake expansion between 2016 and 2023, alongside a longer-term warming trend in the surrounding landscape.

Climate change is already changing Sikkim’s glaciers, snow, ice and mountain waters, interacting with landslides, avalanches, extreme rainfall and fragile slopes.

It is central to growing Himalayan risk. But it alone cannot explain every disaster’s scale. The other part is what we build, where we build it and whether we act on warnings.

The destruction of Teesta Stage III exposed that vulnerability. After the disaster, the Central Water Commission decided to review design floods for dams vulnerable to GLOFs, including whether spillways could handle extreme floods combined with glacial lake outbursts.

A disaster can be natural. But vulnerability is often built by humans.

Remember Chamoli in Uttarakhand in 2021. Rock and glacier ice collapsed from Ronti Peak, becoming a devastating debris flow through the Ronti Gad, Rishiganga and Dhauliganga valleys.

More than 200 people were killed or remained missing. Two hydropower projects were severely damaged.

Scientists later found evidence of deformation and fractures before the collapse, raising questions about monitoring and construction in fragile terrain.

Then came Dharali, Uttarakhand, in August 2025. Its immediate trigger remains under scientific investigation. But the destruction was familiar: water, mud, rock and debris overwhelming homes and infrastructure.

ISRO’s satellite analysis documented the destruction and highlighted Himalayan settlements’ increasing vulnerability. A 2026 study argued that “cloudburst” alone was inadequate: intense rainfall, saturated and unstable slopes, and a landslide contribution were involved.

And in August this year, a glacier collapse across the Nepal–China border sent ice, rock, mud and water through Himalayan valleys. Hundreds died; thousands were reported missing in the aftermath.

Settlements and border infrastructure were devastated. Continuing landslides and rising water complicated rescue operations.

The terrifying detail? It happened in under eight minutes. Even an advanced warning system would not have worked.

Glaciers, rivers and climate change do not recognise borders. Nepal’s Prime Minister recently called for cooperation with India and China on Himalayan climate resilience, satellite data, glacial lake monitoring and early-warning systems.

That was a practical warning. The Himalaya is one connected system. Sikkim is part of it. What happens across a border should concern us because the questions are familiar: what are we monitoring, what are we building, and how quickly can we act?

So, have we learnt from South Lhonak? Yes. But perhaps not enough.

Sikkim has expanded scientific monitoring and detailed assessments of high-risk glacial lakes. Earlier this year, it received an indigenous monitoring and risk-assessment technology suite developed by C-DAC and MeitY

In August, a multidisciplinary expedition assessed high-risk lakes in Mangan district. In September, the state government reviewed GLOF preparedness: early warnings, hydrological monitoring, flood forecasting, hazard mapping, mitigation and evacuation.

These steps deserve recognition. But are we preparing only for the disaster we have already experienced?

The next disaster could be a GLOF, a landslide, an avalanche or extreme rainfall. It could be several happening together. That is why preparedness must extend beyond the kind of disaster we remember most clearly. The next emergency may test a completely different part of our defences.

We cannot simply count warning systems. We must ask whether they work.

Can a warning reach a village at night? Will the mobile network work, and will people understand the message? Have they practised evacuating? Are routes and designated shelters safe? Does the district administration know which buildings can serve as shelters? What happens if the road to them disappears?

We have already seen infrastructure fail precisely when people need it most.

And how much infrastructure can the Himalaya safely carry? Roads cut into unstable slopes, construction beside rivers, hydropower projects across fragile basins: where are the limits? When scientists identify a hazard, who has the authority to say “stop”?

A warning is useful only if somebody is willing to act on it. A report cannot save a village by sitting in an office. A satellite image cannot evacuate a family. A sensor cannot make decisions.

Governments and planners must act. Citizens must demand that they do. Otherwise, we risk collecting more information without changing the decisions that leave people exposed. Scientific knowledge must reach the people who can act on it.

The greatest danger is spending years preparing for another South Lhonak while ignoring the other ways Sikkim can be devastated.

Rimbi, Chamoli, Dharali and the Nepal–China disaster had different triggers. But they share a warning: the Himalaya is changing, and the margin for error is shrinking.

Sikkim cannot prevent every landslide, avalanche or extreme rainfall event. We cannot reverse climate change from Gangtok. But we can decide how much additional risk we create, whether development respects the mountains’ limits, and whether scientific warnings matter before disaster strikes.

We can plan villages, roads, hospitals, schools and hydropower projects for the Himalaya that exists today.

Three years after South Lhonak, that is the real test: whether Sikkim has changed because of it.

Another disaster will come. We do not know where, when or in what form. No district, road or village is permanently safe. There is no room for complacency.

Climate change is already here. Will we keep building as though it isn’t? Or learn to live with the mountains we have—before they remind us, once again, who is really in control?

Also Read: EastMojo Exclusive: Confusion over PAP is ruining foreigners’ trips to Mizoram