Itkillik River eats into the thawing riverbank at an average rate of 19 metres per year.
According to estimates, Alaska's thawing permafrost soils cost the USA several 100 million dollars every decade – primarily because airports, roads, pipelines and set-tlements require relocation as a result of sinking ground and eroding river banks.
An international team of researchers has now measured riverbank erosion rates, which exceed all previous records, along the Itkillik River in Alaska's north. In a stretch of land where the ground contains a particularly large quantity of ice the Itkillik River eats into the river bank at 19 metres per year, the researchers report in a study recently published in the journal Geomorphology.
'These results demonstrate that permafrost thawing is not exclusively a slow process, but that its consequences can be felt immediately', says permafrost researcher Dr Jens Strauss from the Pots-dam research unit of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI).
Together with colleagues from the USA, Canada and Russia he investigated the Itkillik River at a loca-tion where the river cuts through a plateau, and the subsurface of which consists to 80 percent of pure ice and to 20 percent of frozen sediment.
'This ground ice is between 13,000 and more than 50,000 years old, extends column-like to depths of more than 40 metres and in the past stabilised the riverbank zone', says Jens Strauss.
However, as the scientists' research work, which extended over several years, demonstrated, these stabilisation mechanisms fail if two factors coincide: (1) the river carries flowing water over an ex-tended period; (2) the riverbank consists of a steep cliff, the front of which faces south and therefore is exposed to a lot of direct sunlight.
Jens Strauss: 'There are two reasons for the fast and, especially, enduring, decay of this cliff. On the one hand the river water is warmer than the permafrost, thaws it and immediately transports the falling material away. This transport away is particularly fast if there is a very large amount of ice in the ground.'
And on the other hand the cliff is thawed by the sunlight. 'Although the mean annual temperature in this region is minus twelve degrees Celsius, in the summer sunlight it becomes so warm that lumps of ice and mud flow down the slope', reports the study's lead author Mikhail Kanevskiy from the Uni-versity of Alaska Fairbanks.
In all, in the 2007 to 2011 period, the approximately 700 metre long and 35 metre high cliff retreated up to 100 metres. A land area of approximately 31,000 square metres was lost in this time. This cor-responds to the size of around 4.3 football fields. Converted to a mass of ice and soil, the Itkillik River carried away 70,000 tonnes of material per year – including 880 tonnes of organic material (organic carbon), previously stored in the permafrost soil.
In addition, in August 2007 the scientists witnessed how, in only a few days, up to 100 metre long and 13 metre deep fissures formed in the plateau and an 800 square metre block collapsed into the river. 'Such failures follow a defined pattern. First, the river begins to thaw the cliff and scours an overhang at the base. From here, fissures form in the soil following the large ice columns. The block then disconnects from the cliff, piece by piece, and collapses', explains Jens Strauss.
Luckily, the section of the river with the high erosion rates lies in a very sparsely populated area, so that neither villages nor important structures such as roads or buildings are endangered. However, the magnitude of the riverbank erosion gives Jens Strauss food for thought: 'The rate at which a riverbank retreats in permafrost regions depends on the ice content of the soil and other geograph-ical factors. In view of the increasing mean temperatures in the Arctic, our Itkillik River example clearly demonstrates the speed at which erosion can take place.'
The objective now is to apply this newly gained knowledge when planning new settlements, power routes and transport links, for example. 'What's more, the erosion impairs water quality in the rivers. A fact that can become a problem for all those communities that produce their potable water by treating river water', says Jens Strauss.
Notes for Editors:
The study was published with the following title in the journal Geomorphology:
• Mikhail Kanevskiy, Yuri Shur, Jens Strauss, Torre Jorgenson, Daniel Fortier, Eva Stephani, Alexan-der Vasiliev: Patterns and rates of riverbank erosion involving ice-rich permafrost (yedoma) in northern Alaska, Geomorphology, doi:10.1016/j.geomorph.2015.10.023 (http://www.sciencedirect.com/science/article/pii/S0169555X15301872 )
Printable photographs can be found in the online version of this press release at: http://www.awi.de/nc/en/about-us/service/press.html
Your scientific contact at the Alfred Wegener Institute in Potsdam is Dr Jens Strauss, phone +49 (0)331 288-2173 (e-mail: Jens.Strauss(at)awi.de).
Your contact in the Communications and Media Department is Sina Löschke, phone +49 (0)471 4831-2008 (e-mail: medien(at)awi.de).
The Alfred Wegener Institute researches in the Arctic, the Antarctic and oceans in the central and high latitudes. It coordinates polar research in Germany and provides important infrastructure such as the research icebreaker Polarstern and stations in the Arctic and Antarctic for the international science community. The Alfred Wegener Institute is one of the 18 research centres belonging to the Helmholtz Association, which is Germany's largest scientific organisation.
Ralf Röchert | idw - Informationsdienst Wissenschaft
Global study of world's beaches shows threat to protected areas
19.07.2018 | NASA/Goddard Space Flight Center
NSF-supported researchers to present new results on hurricanes and other extreme events
19.07.2018 | National Science Foundation
A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.
The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
20.07.2018 | Power and Electrical Engineering
20.07.2018 | Information Technology
20.07.2018 | Materials Sciences