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Earthquakes in Greenland are rare. At least, they’re supposed to be. But a few weeks ago, a 4.1 “quake” struck Nuugaatsiaq, a tiny island off Greenland’s west coast, triggering a massive tsunami that smashed homes, leaving at least four people dead.

One brave but panicked Greenlander recorded that 17 June incident .

But what residents – and seismic equipment – initially labelled a quake may be nothing of the sort.

“Everyone was fooled by the collapse of a mountain,” says , a Swiss glaciologist who has been studying Greenland’s glaciers since 1995. “The tsunami wasn’t triggered by an earthquake.”

Luethi believes the culprit was a landslide at nearby Karrat fjord. And as the falling mountain hit the ocean, it created enough seismic noise to dupe sensors and generate the waves that inundated Nuugaatsiaq.

It’s a recognised pattern. In 2002, discovered that landslides can fool seismometers and initiate tsunamis. , a landslide triggered a tsunami that levelled the uninhabited mining town of Qullissat.

“Ice cannot hold a mountain together if the ice flows,” adds Luethi. “Melting and freezing cycles mean rocks are getting destroyed. There’s so much unstable rock in Greenland and they have no earthquakes to shake it down.”

That’s why there’s such a powder keg brewing, Luethi says. The landslide in Nuugaatsiaq 1000 metres in length and 300 metres wide. And while the ensuing tsunami was disastrous, it’s shifting focus from the real problem: this wasn’t a one-off. This region is full of craggy fjords undergoing temporal shift. Meaning more so-called quakes – and accompanying tsunamis – seem imminent.

“All of these fjords are very steep,” says of the University of Alaska Fairbanks. “If you have loose materials cemented together with melting ice, there’s potential for more of these tsunamis.”

Truffer, a physicist who uses ground-based radar to measure the movement of glaciers, thinks this is linked to temperature rise. Now he believes the adjacent mountains are also at risk of eroding and causing another tsunami.

Locals aren’t taking any chances. The remaining population of Nuugaatsiaq as have many nearby communities.

What determines the severity of these tsunamis? It depends on where these events occur, and the size of the calved off rock, ice or iceberg involved.

“Basically, the deeper the water, the faster the wave,” points out , a New York University professor who studies ice-ocean interaction, and has tracked Greenland tsunamis that have travelled as fast as planes. “Five hundred miles per hour. It’s shocking, but there’s a fair amount of evidence that this happens from time to time.”

So was this a landslide triggered by an earthquake, or a seismic event traced to a landslide? The Geological Survey of Denmark and Greenland are also working to determine the cause. However, Luethi and Truffer, who between them have nearly 50 years’ experience studying this ice say the evidence is compelling. A growing contingent of

“If Greenland continues to warm will there be more incidents like this?” Truffer wonders before detailing his next step. “Just next to the landslide, there’s a smaller area that’s looking very unstable. It looks like it’s warming and creeping down the mountain and breaking up. That’s the one we’re worried about now. The destructive power of these things is phenomenal.”