Rockslides and tsunamis are new climate threat. Peat fuels wildfires in Greenland.

In cold, glacial regions, rocks and ice are held together on steep rock sides. Rising temperatures could make these slopes unstable and these events more common due to rising temperatures from climate change. 

Warm temperatures have been implicated in causing mountain boulders to expand, which can lead to landslides and generate massive tsunamis in fjords. The phenomenon has been reported at Switzerland’s Matterhorn as well.

The journal Nature reports on the Greenland rockslide and tsunami that killed 4.

The landslide occurred on the evening of 17 June, in the barren Karrat Fjord on the west coast of Greenland. It caused a sudden surge of seawater that wreaked havoc in the fishing village of Nuugaatsiaq, located on an island within the fjord about 20 kilometres away (see ‘Greenland tsunami’). The wave washed away eleven houses, and four people are presumed dead.

The slide was so large that it generated a seismic signal suggestive of a magnitude-4.1 earthquake, confounding initial efforts to identify its cause, says Trine Dahl-Jensen, a seismologist at the Geological Survey of Denmark and Greenland. But more careful examination indicated no significant tectonic activity just before the landslide.

A research team that visited the site earlier this month found that a large volume of rock had plunged — probably spontaneously — from one of the steep sides of the fjord into the water 1,000 metres below, and shattered chunks of a glacier. That disturbance pushed water levels up by more than 90 metres along the coastline on the same side as the slide. And although the tsunami dissipated quickly as it crossed the deep, six-kilometre-wide fjord, it still had enough energy to send water 50 metres up the hillside opposite. The team also measured an increase in water levels of about 10 metres on shorelines 30 kilometres away.

“Landslide-generated tsunamis are much more locally limited than tsunamis produced by sea quakes, but they can be massively tall and devastating in the vicinity,” says Hermann Fritz, an environmental engineer at the Georgia Institute of Technology in Atlanta who led the research team.

New Scientist reports that the freezing and thawing of ice is creating unstable rock throughout Greenland.

“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 was reportedly 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 Martin Truffer 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 has been evacuated, 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 David Holland, 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.”

The AGU shared a spectacular video showing a rockslide on the flanks of the Geiranger Fjord in Norway.

There are a couple of interesting elements to this rockslide.  The first is the timing – yet again we see a major rockslide occurring in the spring, again without an obvious trigger in terms of a seismic event or heavy rainfall.  This is not unusual, and of course it may be associated with now and ice melt as temperatures rise after the winter.

Second, the video shows the mobility of a small proportion of the blocks that have detached in the Geiranger Fjord event.  Take a look at this still from the video:

Note the splashes a considerably ahead of the main landslide dust cloud, which presumably mark the impact on the water of individual blocks.  Only a small proportion of the blocks travel this far, but they are a nice illustration of the extreme end of the mobility distribution.

Major rockslides are of course nothing new in Norway, and not far from this site is the Akernes landslide, which is considered to be a significant hazard that is closely monitored.