Coastal erosion

The Atlantis of the Arctic

The clock is ticking for Muostakh Island: another 100, 140, maybe even 200 years, then the small isle off the coast of Siberia will disappear from the map. Then, where today 15-metre-tall bluffs of ice-rich, frozen ground still defy the currents of the Lena River and the waves of the Laptev Sea, there will be nothing left. The cause: coastal erosion. Every year, Muostakh loses up to 20 metres of its coast – which makes it an ideal site for researchers at the Alfred Wegener Institute to investigate how rising temperatures and the retreat of arctic sea ice are increasingly eating away at coasts in the High North.

“We had just turned the camera off, when about 2 metres from where we were standing an overhang suddenly broke off and fell to the sea 20 metres below,” recalls Dr Thomas Opel, a geographer at the Alfred Wegener Institute. This took place in the summer of 2012, when a team from the television network Rundfunk Berlin Brandenburg (rbb) accompanied a team of AWI researchers during their work on the Siberian permafrost island.

The banana-shaped island is located near the eastern Lena Delta. In the summer of 2012 it was still roughly 7.5 kilometres long and measured 500 metres at its widest point. Muostakh largely consists of an extremely ice-rich core covered by a thin layer of soil: an arctic outpost and one of the places where climate change is making the coast collapse so rapidly that scientists can observe the changes as if under a microscope. “We were so angry with ourselves for not just leaving the camera on a bit longer. It would have made for a very impressive scene,” says Opel.

Nevertheless, the missed opportunity was the least of their worries that day: when you’re standing atop the bluffs, it’s very hard to tell which ledges are likely to crumble and which ones are safe. Aside from the missed shot, the greatest loss the AWI team had that day was a marking rod, which Opel’s colleague Frank Günther had installed as a point of reference for measuring the coastal erosion a year earlier. “I emailed Frank later that day to let him know his marking rod had been lost. It’s extremely rare that we can say the exact day and even the hour when part of the coast will collapse,” adds Opel.

Facing losses with increasing speed


Over the past 60 years, Muostakh has lost more than half a kilometre of its north-south expanse, and with it nearly a quarter of its total surface area. And this is likely to worsen: if we consider the island as a whole, between 2010 and 2013 the entire coast receded nearly twice as quickly as in previous years. Since 2010 major sections of the coast have lost an average of 3.4 metres per year – as opposed to 1.8 metres per year in the past.

“We examined extremely high-resolution aerial and satellite images taken between 1951 and 2013, then compared them with the summer temperatures and the areas of open water off the coast,” explains AWI geographer Dr Frank Günther. By doing so, the permafrost researchers realised that there was a close connection between the average summer temperature and the erosion rate. According to Günther, “If the average summer temperature rises by one degree Celsius, it accelerates the erosion by 1.2 metres per year."

And Muostakh isn’t just losing surface area, but volume, too – more than 30 percent since the 1950s. “More than 80 percent of the island’s subsurface is made of ice, which formed over several millennia. As air temperatures rise, the seasonal thaw layer on the surface goes deeper and thaws the underlying ice, causing the island’s surface to collapse back upon itself,” relates Günther. 


Two forces against one island

The researchers discovered that there are two different processes affecting the small island in the Laptev Sea and causing its ice cliffs to crumble. As Günther explains, “First of all, the permafrost on the cliffs is completely bare, which means it’s basically defenceless when it comes to rising air temperatures. So it’s thawing faster here, and as a result, the land mass continues to recede.” Secondly, the waters of the sea and the Lena River are gnawing away at Muostakh’s frozen subsurface. “In the past, a thick layer of sea ice protected the coasts from erosion practically year-round. But in the past three years alone, the number of ice-free days per year has risen considerably – an average of two weeks more than 20 years ago,” says Dr Paul Overduin, an AWI specialist for submarine permafrost, which Muostakh is surrounded by.

The two additional ice-free weeks and rising air temperatures also pose another threat for the island: until a few years ago, the thawing process and periods of open water came at different times of year: the ground thawed throughout the summer before slowly beginning to refreeze in late August, while the sea ice cover only receded in the late summer months and returned in the early autumn. Today these processes are increasingly overlapping. “That’s bad news for Muostakh, because taken together, the two processes are far more powerful than they are separately. And they’re extremely effective when it comes to accelerating the island’s erosion,” explains Frank Günther.

Muostakh – A symbol for the Arctic coast?

This development presents the AWI researchers with a new question: Does this relation also apply for other islands in the Laptev Sea, or perhaps even for much of the arctic coast? “We’ve already observed a rise in erosion rates in other sections of coastline. But Muostakh is like our own private laboratory: not only can we observe on a small scale how coastal erosion is progressing, we can also more closely investigate the processes involved. The only ‘problem’ is that the processes we see on the island are so impressive, they can sometimes tempt us to jump to conclusions,” says AWI geochemist Dr Hanno Meyer.

“In the past, many research efforts focused on the island’s northern cape. But our aerial and satellite images show that the erosion rates there – a long-term average of 11, currently 17 and at times as much as 39 metres per year – are extremely high and far above average for the rest of the island. If we look at Muostakh Island as a whole, the processes are similar to those in other coastal areas of Siberia,” adds Frank Günther.

Accordingly, the rapidly disappearing island is to some extent representative of a coastline spanning thousands of kilometres, as well as numerous other small islands, all of which are increasingly becoming unstable and receding in the face of wind, waves and warmer summers. Year after year, they are losing part of their land mass to the arctic sea ice. And yet: most of the islands and peninsulas will survive for another few centuries.

(Kristina Bär)