Yakutsk: Robust permafrost capital

By BBC News Online's Lucy Walker

As Yakutsk, the world's largest permafrost city, sits marooned in a sea of flood water, questions are being asked about whether the worst spring floods in years will irreparably damage the city's infrastructure.

Every building in the city of 200,000 people - from apartments to factories, the university and hospital - is constructed on a frame of stilt-like piles, most made of wood.

Surging floodwater has already all but destroyed the town of Lensk, 840km upstream.

The 27,000 residents of Lensk have been evacuated and Emergency Situations Minister Sergei Shoigu was quoted by the Itar-Tass news agency as saying that the town should be rebuilt elsewhere.

Bombers are being used to blast the ice about 30km north of Yakutsk in attempt to release the floodwater threatening the city.

Time to move?

Robert Headland at the Scott Polar Research Institute in Cambridge told BBC News Online the buildings should weather the flooding well.

"The design of these buildings is generally sound and well suited to the region," he says. "Wood is an excellent choice of material for these piles.

"It's abundant and a good insulator, much better than metal which would conduct heat to the permafrost layer, and in these conditions the rate of decay is very, very slow."

Thousands have been evacuated

At the start of building, the wooden piles are hammered into the permafrost and quickly freeze into place.

The ground above may warm by several degrees, but even with the level of flooding we are seeing this year, it is not enough to melt the permafrost beneath, Mr Headland says.

He says the biggest risk to these buildings is from the floodwater itself, which is carrying huge lumps of ice, trees, and bits of buildings and roads that have been washed away.

Reversal of fortune

Until the last ice age 12,000 years ago the River Lena, like others in the region, flowed south from the Arctic Circle into Lake Baikal and the Caspian Sea.

But the geographical shifts that followed have left the Lena flowing northwards, from its origins to the west of Lake Baikal 4,400km to the Laptev Sea.

Yakutsk is suffering the worst floods in a century

The river bed spans about 15km in its middle reaches, growing to a 25km-wide delta at its mouth.

The region is used to flooding. Each year spring meltwater builds up upstream, blocked at the river's frozen mouth.

This year, after the harshest winter for half a century, there is just more water to shift.

With temperatures below freezing for an average of seven months of the year, residents of Yakutsk are used to harsh conditions.

Founded as a fortress in 1632, the city expanded during the Soviet era, fuelled by rich reserves of gold and diamonds.

Many Russians traditionally believed vodka kept them warm, but now central heating and triple glazing keep most of the city at a manageable temperature.

In summer the area becomes a mosquito-infested swamp.

But the river, with its seasonal traffic of snow scooters or vast ships, remains the vital transport link in a city that has no railway and is cut off each spring and autumn as the river melts and then freezes.