When the sleeping giants wake

Thu, Aug 16, 2012, 01:00

Iceland’s 2010 volcanic eruption was merely an economic disaster; future eruptions may have more dire effects, which is why Irish scientists are trying to improve the accuracy of predictions

NEW ZEALAND’S Mount Tongariro blew its top last week, belching out enough ash to close roads and disrupt regional air travel. Yet who could have predicted the eruption, given that the volcano had been quiescent for the past 115 years?

European air traffic experienced much wider disruption in 2010 when Iceland’s Eyjafjallajökull underwent a major eruption lasting weeks. It, too, had been quiet for 90 years before it sprang to life.

Volcanologists have long sought to better predict the erratic behaviour of volcanoes. And Irish scientists this month travelled to Iceland in pursuit of this goal. Two of them hiked thousands of feet up the Hekla volcano, placing motion sensors close to its summit before returning home last weekend.

The scientists aim to figure out what is happening beneath a volcano and so improve the accuracy of forecasts. The sensors will record any earthquakes over the next two months.

“We are interested in the specific precursory signals that are sometimes seen before an eruption,” Christopher Bean, professor of geophysics at University College Dublin, explains. He was accompanied by his colleague Dr Aoife Braiden, with logistical support from the Icelandic Met Office.

Hekla, one of Europe’s most active volcanoes, is a likely candidate for Iceland’s next eruption. It has erupted dozens of times since the 12th century and its ash falls turn up in many Irish bogs.

Before an eruption, molten rock moves upwards and this can be detected in ground vibrations. Bean’s sensors – seismometers – measure these tremors and he uses computer models to work out whether they are due to magma, or gas movement or the volcano edifice itself creaking.

Bean compares it to a cardiograph: looking at individual wiggles and diagnosing what’s happening. “We want to understand what those signals are telling us,” he says. Precise predictions are not easy, however. “Even though you record the signals, it is like the straw that breaks the camel’s back.” The pressure caused by gas escaping from magma kilometres below the surface can have a large influence on eruptions.

The volcanic ash cloud from the 2010 Eyjafjallajökull eruption caused the cancellation of 100,000 flights, inflicted €4 billion in economic damage and, at its peak, closed 80 per cent of European airports. Iceland has about 30 active volcanos and there is evidence that they affected Ireland’s climate in past centuries (see panel). A handful of these volcanos remain under close scrutiny.

In May 2011, the volcano Grímsvötn erupted with far greater intensity than Eyjafjallajökull had. Wind direction and the short duration of the eruption meant fewer flight cancellations, even if it forced US president Obama to cut his visit short. It is not seen as an imminent threat.

Hekla, on the other hand, has been inflating and “seems ready for its next eruption”, according to Icelandic volcanologist Prof Pall Einarsson, who views it as most likely to go next.

Icelandic monitoring instruments can help Ireland respond to the threat of an imminent eruption. Dr Brian McConnell of the Geological Survey of Ireland observed data from the 2010 eruption in real time over the internet.

“One of the main signs that a volcano is about to erupt is a rapid increase in the number of earthquakes,” he says.

From his office in Beggars Bush, Dublin, McConnell noted a sudden increase in earthquakes moving up the volcano on May 4th. “I was able to predict that this was a new batch of magma arriving at the base of the volcano and that would probably mean the eruption would be reinvigorated.”

Eyjafjallajökull had initially erupted in March, with a lava flow from its side and minor ash fall. The eruption and ash plume that caused flight chaos began mid-April. Its explosiveness increased when rising new magma met an older body of magma within the volcano, McConnell explains. The magma burst through 200 to 300 metres of ice, the combination of magma and melted water boosting the explosion, propelling fine-grained ash 9km into the sky. It was hard, silica-rich and glassy and put aircraft at risk from abrasion on windows and body and damage to jet engines.

McConnell acknowledges there was a lot of learning by doing during 2010, but says we are better prepared for such an event now. UCD is a partner in an EU funded project, FutureVolc, which seeks to improve monitoring of Icelandic volcanoes.

Preparation is sensible. Eyjafjallajökull has a troublesome larger sister called Katla. “It is covered by a glacier and can be very explosive,” says McConnell, adding that it is only a matter of time before Katla erupts.

“Katla is the difficult child in the family,” Einarsson says. It is constantly active, with between 10 and 20 small earthquakes recorded every day. “This constant activity makes it special because the volcanoes are normally quiet between eruptions. So we are guessing a lot.”

Bean’s group in UCD has its own mobile seismic network, which they have deployed on Mount Etna, continental Europe’s most active volcano. However, Europe’s biggest threat by far is Vesuvius, says Bean. “It is a sleeping beast. It is doing nothing at the moment, but it could wake up over a very short period of time and be extremely dangerous.”

The site of nearby Pompeii is a reminder of its potential, and greater Naples these days is home to three million people. Italy has an evacuation plan in place for a Vesuvius eruption, but a timely and correct prediction will be critical.

This is why research by the UCD scientists and others is so essential. Better numerical models could save lives.

Volcanoes, severe winters and showers of blood

An extensive trawl of medieval Irish records links severe winters and strange tales with volcanic eruptions.

Dr Francis Ludlow, now at Harvard, looked at Irish chronicles from AD 400 to 1600 for his PhD thesis at Trinity College Dublin. The entries in annals are tabloid-type headlines, usually recording disastrous events. Ludlow says there are several hundred weather entries, giving Ireland a uniquely well-endowed set of records compared to elsewhere in Europe.

There were 70 believable entries describing severe cold during these 1200 years, says Ludlow. He also looked at spikes of sulphuric acid in Greenland ice cores, which record volcanic eruptions. Ludlow found a strong statistical link between large volcanic eruptions and subsequent reports indicating a severe winter. In all, 38 out of 48 volcanic events matched one or more descriptions of acute cold weather or harvest failure.

Some apparently fanciful entries in the annals, such as three records of showers of blood, precisely coincided with years of major eruptions. Rain tainted with volcanic ash could explain these records.

“Early medieval showers of blood seem to have some sort of volcanic origin, and probably from Iceland,” says Ludlow. The early annals and chronicles were recorded by monastic scribes and the Bible represented a reference framework for unusual events.

A record from 939 of the sun turning blood red has been interpreted by scholars as a phenomenon possibly caused by volcanic ash. Ludlow said this was followed by annals noting severe weather two years later in 941, when Norsemen were reported raiding across frozen lakes and streams.

There has been renewed interest in the potential impact of volcanic eruptions on a regional or global climate, notes Dr Gill Plunkett, palaeoecologist at Queen’s University Belfast. The most explosive eruptions have gained most attention as possible triggers. “But it may well be – where Iceland is concerned – that it’s the longer, more effusive eruptions that emit huge quantities of aerosols that should be looked at,” she says.

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