This is part of an earlier article published in Swedish about a not so immediate threat, but it came to mind after the latest reports of record breaking temperatures.
We don’t have many earthquakes in Scandinavia. But a big crack in the hills of the Lapland region bear witness of the enormous forces that once shook the barren landscape. 9000 years ago a quake ripped the bedrock apart. Tensions in the earth’s crust created a ten-meter high fault 150 kilometres in length. The resulting formation is called Pärvie by the Sami, the word for a breaking wave – a wave of stone that runs through the northern countryside.
Modern geologists estimate the quake that created this rift to a force eight on the Richter scale. That is quite impressive considering that the northern mountains of Sweden are far away from any seismically active zones.
The earthquake was the result of the ice melting at the end of the latest ice age. The rapid climate change freed the earth’s crust from the pressure of billions of tons of ice. The melting glaciers flowed away in grand, wide rapids. Forces that had lain dormant for millennia were set free, and the earth bounced back as the burden eased.
Similar giant quakes could hit us again – after the next future ice age. And we have already begun to prepare for that event.
The final repository for the Swedish nuclear waste is being built in Forsmark, 150 km north of Stockholm. The repository must be able to last for at least one hundred thousand years, a time period when ice caps are expected to come and go, with subsequent strong tremors in the ground. So the repository must be made to survive these so-called post-glacial earthquakes without radioactive leakage.
There is no doubt that major changes in glaciers and ice sheets can create movements in the earth’s crust.
The ice age that ended around 10 000 years ago did not only affect the Swedish North. It also coincides with a period of strong volcanic activity in Iceland, when the pressure on the underground magma eased. And there are traces of large earthquakes associated with the melting of the ice at several locations in North America.
But how sensitive is the Earth’s crust? Can you really say that the relatively moderate climate change that we are seeing now could lead to more earthquakes and volcanic eruptions?
– One must remember that the stress in the crust is always caused by the movement of tectonic plates, says one of Sweden’s leading seismologists, Reynir Bödvarsson at Uppsala University. And those movements are driven by the heat from the earth’s interior. What the ice or water masses can do is move the incidents in time, he says.
Reynir Bödvarsson does not exclude that the stability created by such a thick sheet of ice can make the earth’s crust to store extra energy over time in the form of tensions and make stronger quakes when the pressure disappears. But there will not be more of them.
In southern Alaska one of the Pacific Northern continental plates presses against the coastline. It makes the area around the southern Bering Strait to an area prone to earthquakes. It is also one of the arctic regions on Earth where the climate is changing the fastest. Over the last one hundred years, several glaciers in the area have disappeared and others have lost hundreds of meters in thickness. Two scientists from NASA and the US Geological Survey in 2004 used the GPS data to calculate if this melting of the glaciers was connected to the earthquake with magnitude 7.2 which occurred in 1979. Their conclusion was that the reduced pressure on the plates may well have triggered the quake.
The British volcanologist Bill McGuire at London’s University College has for years warned that even small variations in water levels or ice covers can trigger large reactions from a slumbering earth.
In a study he has shown that the weather phenomenon El Nino has an effect on seismic activity off Easter Island in the Pacific. Differences of some millimetres in the sea level can cause very big variations in the pressure on the sea floor in the deeper areas, which in its turn increases or decreases the friction as the tectonic plates are sliding back and forth.
We know also that volcanoes can be affected by changes in the weather. The low pressures of the North Atlantic winter make the level of the seawaters rise. The higher pressure from the masses of water puts an upward pressure on the magma under volcanoes located along the coast. This is a measurable phenomenon along the coast of Iceland, for example.
– It does, but it is largely on the margin, said Reynir Bödvarsson in Uppsala. The outbreaks would come anyway, but they are affected over time. Bödvarsson is, by the way, Icelander by birth.
So the question remains. Just how sensitive are the seismic forces to climate change? The answer is that we cannot know. Yet.
Big changes can have very serious consequences. Small variations might be significant if they occur in particularly critical areas.
Bill McGuire, the man who looked at the plates by Easter Island, fears that even small amounts of water in the wrong place could trigger a disaster.
1963 the newly constructed Vajont dam in northeastern Italy was filled with water. Today, several geologists believe that it was the pressure of the water that triggered the smaller quakes that made the adjacent hill of Monte Toc to tumble into the dam. The collapse created a two hundred and fifty meter high tidal wave that killed two thousand people.
In India, four years later 180 people died in an earthquake that followed the construction of a dam in Maharashtra state.
Redistributions of large masses can thus sometimes get local seismic effects, and a few centimetres of sea level rise in the ocean may represent a load of several billion tons over a fairly large area.
The place on earth where the largest redistribution of ice and water masses is expected in the foreseeable future is Greenland. Right now between 150 and 300 billion tons of ice per year is disappearing from the island, depending on how and where you measure it. And the rate of melting is accelerating.
The change is most rapid in the low-lying coastal areas.
Nobody knows today how this redistribution of huge masses affects the forces that are bound in the earth’s crust. The melting leads to rising sea levels, and flooding of the coasts. This may lead to landslides, which trigger even more landslides or earthquakes along the continental shelves around the North Atlantic.
– One cannot dismiss the risk that ice melting could trigger major quakes in Greenland, said Reynir Bödvarsson. But they can also be absent. There is no regularity in this, he says.
So how dangerous can it get?
Eight thousand years ago a gigantic landslide under the sea off the coast of Norway created a tsunami that rolled westward across the North Sea. You can still see the traces of the twenty-five meter high waves that drenched the eastern seaboards of Scotland and the Faroe Islands. It was probably a disaster for the Mesolithic peoples living along the coast then.
It is not known what triggered the underwater collapse, but a probable cause was the release of large clathrates of methane that lay under the sea floor.
The huge landslide occurred after a rapid rise in sea levels after the ice cap disappeared from Scandinavia. Is there any risk for a similar event in the future, but this time on the other side of the North Atlantic, the east coast of Greenland, and directed towards Norway? A tsunami induced by climate change.
– It bears thinking about, said Reynir Bödvarsson. You cannot exclude it, but it is no obvious result. There are, as I said, no regularity in these events.
Ok, this might be considered scare mongering. There are more threatening consequences of the ongoing climate change.