The right half of the highlighted area shows the scarred hillside in Greenland's Karrat Fiord after a landslide fell about a kilometre in June causing a tsunami that peaked at 90 metres.

A massive landslide is thought to be the cause of a 90-metre tsunami that wrecked towns along the Greenland coast in June, washing away at least four people and several houses.

The tsunami was initially thought to have been caused by a magnitude 4.1 earthquake, but seismologists now think the landslide was the cause of the seismic signal.

The landslide fell 1000 metres from the steep sides of Greenland's Karrat Fiord into the water below.

HERMANN FRITZ A closer look shows the area of the landslide on the right, while on the left of the picture is the area where a landslide has started to separate from the hillside.

Scientists think global warming could make such events increasingly common in cold, glacial regions where slopes of rock and ice become unstable.

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HERMANN FRITZ A house smashed up by part of an iceberg that broke off a glacier during the Greenland landslide. It is thought the house floated off its foundations when the tsunami hit, then dropped onto the ice.

At Karrat Fiord, wide cracks in the hillside 1000 metres above the water have raised concerns of another massive landslide. Because of the hazard three villages remain evacuated.

A research team that visited the scene in July found a large volume of rock had plunged, probably spontaneously, from one of the steep sides of the fiord, shattering chunks of a glacier as it fell 1000 metres to the water, Nature.com reported.

That pushed water levels up by more than 90 metres along the coastline on the same side of the fiord as the slide. Although the tsunami dissipated quickly as it crossed the deep 6km-wide fiord, it still sent water 50m up on the hillside opposite.

CHRIS LARSEN Spruce trees shaved off a peninsula with Taan Fiord, Alaska, as a result of a landslide-generated tsunami in October 2015.

The research team included Professor Hermann Fritz of Georgia Tech in the US. The wave would have been travelling about the length of a football field every second, he said. It would probably have taken only about five minutes to get to a village about 30km away.

Researchers wanted to understand why four people were swept out to sea, while other residents were able to avoid the danger and record video of the tsunami coming ashore.

"The combination of a small earthquake from the plunge of the landslide, the sound, and unusual iceberg motion in the fiord prompted a spontaneous self-evacuation," Fritz said.

He compared the event to the famous 1958 tsunami in Lituya Bay, Alaska where a major quake, possibly with a magnitude as big as 8.3, triggered a landslide that caused water to rise by 500m above the normal tide level. That is the highest runup in recorded history.

Preliminary estimates suggested the Greenland landslide had at least as much volume as the Lituya Bay rockslide, and maybe more, but it plunged into deeper water and a much larger fiord system, Fritz said.

Another similar event was a landslide-generated tsunami in Taan Fiord in Icy Bay, Alaska in October 2015, which is thought to have had a peak runup of about 190m. That event happened after a period of heavy rain was followed by a mountainside collapsing into the sea near Tyndall Glacier, spilling an estimated 180 million tonnes of rock in 60 seconds.