The Akerneset mountain in western Norway, covered in green moss and shrubs, has been slowly splintering for decades, its eastern flank losing up to 10 centimetres (3.9 inches) a year, and gradually sliding into the Sunnylvsfjord below.
"The entire mountainside is loose and it's moving, and it could create quite a large collapse," explained geologist Lars Harald Blikra, standing beside a fissure he has been monitoring for some 20 years in his job at the Norwegian Water Resources and Energy Directorate.
Falling masses of rock, breaking off in one big chunk or several pieces over time, will "go into the fjord, creating large tsunamis", he said, his orange safety helmet fixed firmly to his head.
"It can happen in two or three years or it can happen in 50 years. We don't know."
According to a 2016 risk assessment by Norway's Directorate for Civil Protection, 54 million cubic metres (1,907 cubic feet) of rock could detach, producing waves dozens of metres high that could, in just minutes, wash over some 10 villages bordering the fjord.
While the scenario inspired the Norwegian disaster movie "Bolgen" ("The Wave"), this is absolutely "real life", Blikra said.
In 1934, a landslide just a few kilometres away caused a deadly tsunami, with waves of up to 64 metres. It claimed the lives of 40 people.
"We are not here for fun," stressed Blikra.
"There is a large probability that we could have a large event which could create a major threat to society."
- Waves of 80 metres? -
Nestled at the inner end of the fjord, the villages of Hellesylt and Geiranger are at greatest risk.
According to worst-case scenarios, these tourist hotspots could be submerged by waves of 70 to 80 metres.
Olav Arne Merok, a resident in his 70s who has lived his entire life in Geiranger, would be among those affected.
"Here, we're at around 30-40 metres (altitude). Obviously, if the wave is 90 metres high, we'll be under water," he said, erupting in hearty laughter.
"But we can't live in constant fear thinking about it. Otherwise you stop living," he explained from the spacious deck outside his house.
On the quai where the many cruise ships dock in summer, Geir Gjorva, a 69-year-old shipping agent, was also unruffled.
"Nobody knows how big (the wave) will be, if it will be like this, this or even this," he said, lifting his arm to show different heights.
"It could arrive slowly ... or quickly. No-one knows."
"It's not something we talk about on a daily basis," he added.
"Everybody knows the warning system and (emergency) measures work well."
- 'Nightmarish scenario' -
Because of the lurking danger, Akerneset is one of the most monitored mountains in the world.
A battery of GPS and topographic instruments on the surface and sensors deep inside its entrails measure its every movement in order to sound the alarm if necessary.
According to geologists, the mountainside will not plunge into the fjord without warning.
The main break is expected to be preceded by signs that should provide enough time to evacuate people from the area.
"Evacuating thousands of people from a small area because of the risk of a landslide is a nightmarish scenario for a mayor," admitted Einar Arve Nordang, the newly elected mayor of Stranda, the municipality encompassing the villages of Hellesylt and Geiranger.
But "we are ready", he insisted.
All the emergency plans are set, each authority knows what to do when the time comes and the population is regularly kept abreast of developments.
Whenever it happens, "we have several ways of communicating", explained Nordang.
"We can use an SMS geolocalisation service, internet, Facebook, TikTok...".
Atop Akerneset, experts are meanwhile mulling ways to delay the inevitable.
One possibility would be to drain the mountain of its water, which acts both as a lubricant and a pressuriser.
But that would be complex and costly, as all equipment would have to be transported by helicopter.
Sverre Magnus Havig, a senior director at the Water Resources and Energy Directorate, said such an operation could "significantly" delay the mountain's collapse.
"Instead of the risk that this will happen in the next hundred or two hundred years, this will maybe happen in the next 1,000 years".
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