Warming speeds 'world's slowest moving landslides'

By Matt McGrath
Environment correspondent, BBC News

  • Published
AlaskaImage source, UAF
Image caption,
Alaska's famous Dalton Highway runs through the valley of the slow moving landslides

Rising global temperatures are helping to speed up slow moving landslides across Alaska.

Researchers told BBC News that the geological features, known as frozen debris lobes, are now threatening a major highway.

The warming climate is said to have hastened some of the rocky fingers to a heady speed of five metres a year.

Engineers believe that either moving the roadway or freezing the ground may be effective solutions.

Image source, UAF
Image caption,
This frozen debris lobe is very close to the edge of the highway

These teardrop shaped, slow moving bodies of material are made up of soil, rock, water, ice and trees.

Researchers for many years believed these features to be rock glaciers - but scientists in Alaska believe that the masses they've observed are different and distinct. They call them frozen debris lobes.

The lobes are often covered in trees and vegetation and according to those who have studied them, they don't have an icy core. They say that thanks to a combination of pressure and temperature, the water at the centre stays liquid.

The lobes are gathering speed, according to those who have studied them. In size they can be 100m wide, 20m high and up to 1km in length.

"They are coming downhill, the closest is only 40 metres away from the toe of the embankment of the highway," said Dr Margaret Darrow from the University of Alaska, Fairbanks.

"You can figure out that moving at 5m a year, how many years it's going to take!"

According to a research paper published in 2012 by Dr Darrow, the rate of movement of the lobe closest to the highway was just over 1cm a day between 1955 and 2008. However measurements in 2012 showed a speed of 2.5cm per day.

The scientists say there are over 23 such lobes within 2km uphill of the Dalton Highway, one of the most important roads in Alaska.

It links Fairbanks in the centre of the state to the Arctic shore on the north coast. The critically important Trans-Alaskan oil pipeline sits right beside it.

Dr Darrow says that she believes rising temperatures in the region are responsible for the increase in speed. She says that there is an internal flow within the lobe that she attributes to unfrozen water within the soil, that allows it to slide along at increasing speed.

Image source, UAF
Image caption,
Dr Margaret Darrow gets close to the toe of the lobe which is toppling trees in its way

"When the temperatures are warmer, it moves faster," she told BBC News.

"I would project that if temperatures warm it will move faster, and there's a relationship between temperatures and precipitation. I would assume that with rising temperatures we will see more rainfall and if that is the case they will move faster."

Climate researchers say that Alaska has warmed by double the rate of the rest of the United States over the past 50 years.

Plans have now been drawn up to move a section of the Dalton highway in 2017 in order to avoid a collision with the ever encroaching lobe.

Image source, UAF
Image caption,
Alaska's highways department is set to move a section of roadway under greatest threat from the landslide

Some have proposed blowing up the part nearest the road, but the scientists think this would make matters worse. A better solution, they believe, is to freeze the ground around the lobe.

"There's one feature that is really threatening the road within 10 years, but cooling if done right should work - if theoretical physics works as we think it does," said Dr Ronald Daanen, with the Alaska Department of Natural Resources, who was the first researcher to identify the features back in 2007.

"It needs to happen from underneath so you'd need to do some directional drilling."

There are still some sceptics within the scientific community who question the true nature of these geological features - and show some reluctance to classify the lobes as distinct phenomena.

"Some people really still want to to call these features rock glaciers," said Dr Daanen.

"Europeans like to hang on to terms that they know."

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