What we know about deadly Nepal-Tibet floods

Devastating landslides and flash floods on the Nepal-Tibet border have caused widespread damage and left hundreds dead or missing.

At least 547 people have been killed and 977 people remain unaccounted for two days after floodwaters tore through the border region, sweeping away homes and roads, local officials have said.

Rescue workers say they now face a critical moment to reach remaining survivors as fears mount of further flooding in the disaster’s aftermath.

Here is what we know so far.

Initial reports of an earthquake on the Nepal-Tibet border led many to believe that a tremor had caused a landslide, which in turn caused the devastating floods early on Wednesday.

However, the US Geological Survey (USGS) later confirmed that the disaster was caused by a “glacial collapse”, which is when a glacier or part of a glacier disintegrates.

The impact of the collapsed glacier hitting the bottom of a valley was so powerful that it registered a magnitude of 5.2, according to the agency, causing “subsequent catastrophic impacts downstream”.

Powerful floodwaters and debris travelled some 62 miles (100km) downstream from the Trishuli and Bhote Koshi Rivers, the USGS said, careering through towns popular with mountaineering tourists and pilgrims in northern Nepal.

Footage showed a wall of mud and rock sweeping away buildings, roads and vehicles, as people fled the fast-moving wave of material in the Nuwakot region.

In one video, a towering wall of water and mud was seen rushing down a gorge along the Trishuli River and enveloping the Rasuwagadhi Border checkpoint, a multi-storey building on the Nepalese side of the border.

Gyirong Port, over the border, was also hit. A number of deaths were reported in Tibetan villages.

Scientists are trying to piece together the exact order of events as rescue efforts continue. Mike Searle, professor of Earth sciences at Oxford University, said the glacier could have collapsed “hours or days” before the flooding hit Nepal and Tibet.

He told the BBC: “I think the sheer wave of debris suggests there was a landslide first, the water built up, (which) dammed the river, and then it burst in one huge great flood.”

The International Centre for Integrated Mountain Development (ICIDMOD) has warned secondary flooding could occur in the coming days as a result of debris that washed into the river systems.

The ICIDMOD said they were assessing whether the Trishuli River had been temporarily blocked in narrow sections. If this is the case, it is at risk of forming a landslide dam and a second flood.

Separately, China has warned there is a “high risk” that a lake which formed after the landslide may burst its banks, causing a new flood downstream.

State media reported that rescue operations were briefly suspended on Friday after the lake, which has formed at the confluence of the Chhochen Khola and Purepu Tsangpo rivers, overflowed – before water levels dropped slightly. Heavy rain is forecast over the next few days.

The number of people killed or missing is still becoming clear.

At least 547 people had died as of Friday, according to Nepali police, while the country’s disaster agency said 977 people were still missing.

The government has released a list of more than 500 foreign nationals who have been out of contact since the floods hit, including 33 UK nationals. The missing also include 44 members of the Nepali army and 28 police officers, disaster officials have said.

Meanwhile, five people have died in Tibet and 558 are missing, China’s state broadcaster CCTV reported on Friday.

It is not clear if any of the missing in the Nepali and Chinese figures have been counted twice.

China’s Premier Li Qiang arrived in Gyirong on Thursday to supervise rescue and relief operations – the main crossing point for tourists and traffic between China and Nepal.

Brigadier General Rajaram Basnet, a spokesman for Nepal’s army, told the BBC that rain and unpredictable weather in the area were making rescue operations increasingly challenging.

Tourists from all over the world come to Nepal for its mountains and sacred sites. Reports of those missing include the following:

Smaller numbers of travellers from South Korea, South Africa, Portugal, the Netherlands and New Zealand are also among the missing.

Nepal’s Prime Minister Balendra Shah said “the entire nation has been left shocked and deeply distressed” and that officials would coordinate with China on the response.

China’s President Xi Jinping urged an “all-out” search and promised stronger monitoring and early warning systems to prevent secondary impacts.

In neighbouring India, Prime Minister Narendra Modi said his government was “prepared to provide Nepal with all possible types of humanitarian assistance”.

UN Secretary General António Guterres says he is “saddened by the severe flooding”, adding that UN teams and partners are mobilising supplies and personnel in Nepal to support the government-led response.

The US has promised $500,000 (£367,982) in aid which will be used to cover emergency shelter, water, sanitation and other relief items for communities affected by the floods.

Prime Minister Andy Burnham said the UK has offered £5m to help the Nepalese government and will do “everything we can” to support British nationals in Nepal.

Climate change is known to be driving faster glacier melt in the Hindu Kush Himalaya region.

Geologist Daniel Shugar – one of the first experts to suggest Wednesday’s flash flooding could have been caused by glacial activity – said glacial thinning caused by global warming could increase the risk of landslides.

But it is still too early to link the event to climate change definitively, Shugar, who is based at the University of Calgary in Canada, told the BBC.

Simon Cook, a geoscientist at the University of Dundee, said however that climate change “could have an impact”.

He said his team believed they had identified where the collapse had occurred. He told the BBC that the lower part of a glacier in Nepal near the Langtang Lirung peak – approximately 15km (9 miles) west of the site of the floods – had collapsed.

Cook estimated that the glacier collapsed in a north-westerly direction and then travelled westwards downstream.

He told the BBC “permafrost is partially holding some mountainsides together, this permafrost is warming and thawing and degrading so you are going to get more landslides”.