What caused the 'shocking' landslide that destroyed a Himalayan village?

CBC

3 days ago

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It was a shocking scene captured on video: a torrent of water, mud and rock slamming into the Himalayan village of Dharali with such a force that it knocked buildings from their foundations and buried homes up to their rooftops in an instant.
In a video that circulated on social media and that CBC News has verified, you can see residents in the northeastern Indian state of Uttarakhand attempting to flee as the torrent came crashing down from the mountains on Tuesday.
An estimated 360 million cubic metres of debris barrelled into the village in a matter of seconds.
By the end of the week, dozens of people were still missing, while officials confirmed at least six deaths.
It's monsoon season in India, but experts are investigating whether a phenomenon known as a cloudburst — a sudden and intense rainfall in a small location — caused the disaster or if it was brought on by a glacial lake breach.
While officials in India face backlash over development regulations that might have made the situation worse, scientists say human-caused climate change exacerbates the potential for further catastrophic events like this.
It was "shocking and gut wrenching" to see what happened in Dharali, climate scientist Raghu Murtugudde told CBC News in an interview from Mumbai.
He says India has some of the highest mountains in the world, but the communities that have been "living there peacefully" for decades are now more vulnerable to disasters because of climate change.
Here's what we know about what happened in Dharali and the factors that might have led to the catastrophe.
Where is Dharali?
Dharali is located more than 350 kilometres northeast of India's capital New Delhi.
It's situated 2,600 metres above sea level, along the Bhagirathi River, on the Himalayan mountain slopes of northeastern Uttarakhand state.
It was home to fewer than 1,000 people before the disaster.
It is a domestic tourist spot and pit-stop for Hindu pilgrims climbing to the temple town of Gangotri and, according to Indian Express, Dharali and other nearby communities were holding a religious festival this week.
Many homes, hotels and other buildings were constructed on either side of another river that flows seven kilometres down from the end of a glacier, at an elevation of 6,700 metres, to empty into the Bhagirathi.
In recent years, other places in Uttarakhand have experienced similar — but even deadlier — disasters. As many as 6,000 people died in June 2013 when extreme rainfall caused floods, landslides and a glacial lake breach near the mountain town of Kedarnath.
Then in February 2021, almost 200 people died in a nearby district when part of a glacier broke off, causing an avalanche of ice, rock and water that triggered floods along the river valleys below.
Was it a cloudburst — and what exactly is that?
Early reports on the disaster suggested a cloudburst may have occurred in the area.
That's when warm, moist air from a lower elevation is forced up the mountain slopes where it mixes with cooler air and creates a huge storm cloud.
Moisture droplets in the cloud expand, and new droplets form as strong upward air currents prevent the droplets from falling.
When the cloud can no longer contain the water, it bursts, rapidly releasing a massive amount of rain — at least 100 millimetres per hour over a 20 to 30 square kilometre area below — often causing flash floods and landslides.
Some meteorologists say the amount of rain that fell in Dharali and elsewhere in Uttarakhand that day was not nearly enough to suggest a cloudburst.
But there weren't cloudburst monitors in that area and the rainfall might have been greater at higher elevations, said Murtugudde, who is a visiting faculty member at the Indian Institute of Technology Kanpur and professor emeritus at the University of Maryland.
"So, we don't have the data as of yet and we may not have it anytime soon," he said.
Cloudburst or not, Murtugudde says, the weather pattern that brought heavy rain to the region could have been a factor in the Dharali disaster.
He says the Indian subcontinent's monsoon season is fuelled by warm air from the Arabian sea. But climate change has contributed to rising temperatures in the Middle East and the Mediterranean region that are "pulling" hotter air further north and "pumping" more moisture into the Himalayan foothills.
Not only does this bring more rainfall, he says, it also contributes to glaciers melting and the further creation of glacial lakes.
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Did a glacial lake collapse?
Another potential cause of the flash flood and landslide in Dharali what's known as a glacial lake outburst flood.
"Huge glacial lake outburst floods that are a combination of ice, sediment, rocks that can have quite disastrous impacts not only on infrastructure but loss of life," said Rodrigo Narro Pérez, an assistant professor at McMaster University's School of Earth, Environment and Society.
Glacial lakes, he explains, are held by natural dams, known as moraines, that can be comprised of ice as well as loose sediment and rocks.
He says there can be different factors that cause that natural dam to fail and unleash all of the meltwater.
In some cases pressure from rainfall breaks the moraine, or the force of a large mass, like an avalanche or landslide, could shatter the damn.
In Dharali, he says, it may have even been a combination of both.
Narro Pérez says the Himalayas are at increased risk of this happening. There are 7,500 glacial lakes in the Indian Himalayas, and the overall volume of them has been increasing — 50 per cent in 30 years, according to a 2020 study.
But he says there are only monitoring systems for 190 that are considered high risk, leaving little possibility for early warning and the potential to save lives.
He points to another disaster in Switzerland, in May, where a rock slide from a glacier buried 90 per cent of the village of Blatten.
The difference, he says, is that there was an early warning system in place and officials had evacuated the village days earlier. Only one life was lost.
"But it is a numbers game," he said. "In the last couple of years, we're seeing the number of glacier lakes exponentially increase — not only in terms of the number, but also in the volume."
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How much of a factor is climate change?
There are many variables that led to what happened in Dharali, says Prasoon Singh, a fellow at the The Energy Resources Institute's Earth Science and Climate Change Division based in New Delhi.
He told Reuters that human-caused impacts, such as deforestation and land management, may have also been a factor in this disaster.
Others have criticized the local government for lax construction regulations and allowing development along the river bed.
But regardless, Singh says, such disasters are increasing in frequency and intensity, and "that can be attributed directly to changing climatic conditions."
And even if there had been effective warning systems and measures in place, the "risk is never zero" and it's only getting worse with climate change, says Murtugudde.
Adaptation may be a local concern, he says, but mitigating global warming requires international cooperation.
"Rich and poor doesn't matter anymore ... global warming is not creating any winners," he said.
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