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August 5, 2012 12:42 pm
Mount Fuji locals worry after Fukushima
By Mure Dickie in Fujinomiya, Japan

Like many Japanese, Tomoko Tokiwa has a deep affection for Mount Fuji, the beautiful conical volcano that is one of the nation’s most celebrated symbols.
But the nursery worker says the five decades she has lived on Fuji’s lower slopes have been accompanied by fear of a fiery eruption.

“I was born and brought up on the base of Mount Fuji. I love it, but it’s also a bit frightening,” she says.

Ms Tokiwa is not the only one who worries. The earthquake and tsunami that ravaged Japan’s north-east coast last year acted as a harsh reminder of the potential for natural disasters in one of the world’s most seismically active archipelagos.
Since previous earthquakes have been linked to increased volcanic activity, some residents near Fuji, which lies 100km west of Tokyo, wondered if the March 2011 tremor might act as a trigger. Speculation spiked four days later when a magnitude 6.4 earthquake rocked the area.

“A lot of people were anxious that the earthquakes might have an influence on Mount Fuji,” says Yutaka Suzuki, a manager at a land ministry office that monitors the mountain from its lower slope.

Visitors to the office’s website, which includes live images of the mountain, doubled in the days after the quakes, Mr Suzuki says.

A Fuji eruption could have far reaching consequences. When the mountain last spewed fire in 1707, it buried nearby areas in more than 2m of ash and covered what is now Tokyo in a blanket around 4cm deep. The government estimates that an eruption of a similar scale today could cause Y2.5tn ($32bn) of economic damage.

It is also impossible to rule out larger eruptions that could bring economic activity in the capital to a halt for an extended period and threaten its transport links with central and western Japan, crippling manufacturing supply chains.

Air links might also be disrupted. In 2010, an ash cloud from Iceland’s Eyjafjallajökull volcano closed more than 75 per cent of European airspace for a week, affecting more than 100,000 flights and 10m passengers.

The good news is that fears of immediate danger appear unwarranted as seismic activity in the Fuji area has subsided. A 20m-long crack that appeared halfway up the volcano last year was deemed to be a normal side effect of the tremors.

Japan can also take comfort in the fact that Fuji is being closely monitored with seismologists watching for tremors that might signal magma movement. A network of stations with global position system devices is also watching its waistline with a precision unmatched by even the most fanatical human weight watcher.

By measuring the distance between points on either side of the mountain, the GPS monitors should be able to detect any bulging of the volcano that might indicate rising magma – even if the movement amounts to only a few centimetres over tens of kilometres.
Tetsuro Imakiire, research co-ordinator at the Geospatial Information Authority, which compiles data from the GPS stations, says the system offered a useful reminder that Fuji is still live when it recorded a 2cm “inflation” of the mountain in the year before last March – though the movement since appears to have stopped.

The range of technologies being used to monitor Fuji mean there should be at least some warning before any eruption, Mr Imakiire says. In June, the governments of three prefectures in the Fuji area created a panel to study evacuation plans.

Experts say there would likely be at least a few weeks of warning signs before a major Fuji eruption. But Motoo Ukawa, professor at the department of geosystem sciences at Nihon University, warns that there is still so much scientific uncertainty surrounding volcanoes that nothing should be taken for granted.

There is also no way of knowing whether the main threat from an eruption would come from ash clouds, lava, or pyroclastic torrents, which are fast, dangerous torrents of superheated gas and rock.

“Local authorities [need] to think properly about how to carry out evacuations,” says Mr Ukawa. “It won’t be possible to come up with full preparations, but we should do what we can and then gradually improve things year by year.”