00:00Researchers say they've solved the mystery of the origins of the seismic signal that shook the Earth for nine days last September.
00:07They've pinned it down to a massive landslide which caused a tsunami in a remote fjord in Greenland.
00:13The risk of these Arctic landslides is increasing because of climate change, according to scientists, as Victoria Gill reports.
00:23A land continuously carved and moulded by vast glaciers.
00:27But in one fjord in the east of Greenland, a seismic event has transformed the landscape here forever.
00:33We're seeing here a simulation of how this seismic signal travelled around the world.
00:38When we run this, we'll start to see this wave.
00:42This animation shows the signal that baffled scientists for nine days in September of last year.
00:48The dots are seismic monitors around the world, picking up vibrations from something happening in Greenland.
00:55At the same time that scientists were puzzling over that, a team working in Greenland received a report of a large tsunami in the east of the country.
01:04These photographs show what caused it, a huge landslide into this fjord.
01:09Look at the mountaintop in this image taken before the event.
01:13And look at it afterwards. The top of the mountain is gone, collapsed into the fjord, taking part of the glacier with it.
01:20The scientists analysed the depth and shape of this narrow, 200km long fjord.
01:25And that revealed why the tsunami the landslide caused reverberated around the world for so long.
01:31The wave was essentially trapped.
01:33The energy of that wave just can't escape.
01:35So that wave has to just keep bouncing back and forth, sloshing back and forth in the fjord.
01:40It just can't go anywhere.
01:42Never before has such a long duration, large scale movement of water, over nine days in this case, been observed.
01:49Remote as it is, this is a location that cruise ships do visit.
01:53Fortunately, no vessels were in the area when the landslide happened.
01:56But scientists say the risk of these events is increasing with climate change.
02:01This glacier was holding up the mountain.
02:03Over decades it melted and thinned, and eventually millions of cubic metres of rock simply collapsed.
02:09It's a destructive side effect of climate change that was felt around the world.
