Looking for His glorious appearing! Titus 2:13

The red-hot fountains of molten lava, glowing like wildfire, are nothing short of spectacular. Yet they could be ominous portents of things to come. 

For the second time in four nail-biting years, seismologists in the land of fire and ice, Iceland, are bracing for a monumental volcanic eruption that, once again, threatens to disrupt European air traffic.

Back in 2010, the Eyjafjallajokull volcano, which melted through 200 metres of glacier, sent more than 200 million cubic metres of fine ash billowing almost 10 kilometres into the sky. As a result, several European countries were forced to ground or re-route thousands of flights for several days.

Graphic: Jamie Brown

This time the threat of an eruption – potentially even more powerful than the one in 2010 – is posed by Bardarbunga, the biggest of Iceland's 30 or so volcanic systems. Located roughly at the country's centre, the volcano's 10-kilometre caldera lies several hundred metres beneath Vatnajokull, Europe's largest glacier by volume.

Scientists are taking the latest rumblings seriously: roughly 8000 years ago, after all, the volcanic leviathan let rip with the largest eruption of the past 10,000 years.

"It is very difficult to predict exactly what will happen with an eruption," says Monash University vulcanologist Professor Ray Cas, who is president of the International Association for Volcanology and Chemistry of the Earth. 

Lava flows from Bardarbunga volcano

"Some just fizzle out after relatively minor activity, while others develop into major eruptions," Cas says.

To gauge the likelihood and extent of an eruption, scientists gather all manner of information, including earthquake patterns, ground movements and the complex chemistry of gases. 

"In this case, the eruption could just stop, or if the molten magma migrates under the glacial ice cap, a sub-glacial eruption could begin – with the potential to become very explosive," he says. "This is because of the super-heating melt-water at the base of the glacier."

Lively: Smoke plumes from the Grimsvotn volcano, under the Vatnajokull glacier. But the next threat is posed by Bardarbunga lying several hundred metres beneath Vatnajokull.

Radiating from Bardarbunga's crater is a fracture in the crust that trends towards the north-east, says another Monash earth scientist, Dr Patrick Hayman.

Initially, he says, magma moved from a depth of up to 15 kilometres below the crater, to the tip of this fracture – then pushed and shoved its way further north-eastwards.

"Many of the earthquakes recorded in recent weeks have been related to this movement of magma," Hayman notes. "The first eruption, last month, occurred about 5 kilometres north-east of the glacier's edge, forming what is known as a fissure eruption – a long, narrow crack from which magma erupts."

Because of the connection between the fracture and the volcano, the concern has been that magma will rise beneath the glacier between the fissure and the volcanic crater. "So there is a real possibility of a showdown between the magma and ice," Hayman warns.

Flood danger

A recent inspection flight over the glacier found two depressions up to 35 metres deep, caused by the melting and collapse of removed ice. 

"Of course, one of the concerns is melting of large volumes of ice and the rapid release of this melt-water forming a flood," says Hayman.

There is often the potential for explosive eruptions when magma and water interact. "The hot magma, when it comes in contact with water, can instantly chill, contract and fracture into small particles of volcanic glass that we call ash – our term for a particle of less than two millimetres," Hayman says. "However, these interactions don't always lead to explosive activity; often they only produce steam."

Geoscientists have monitored magma in two ways. First, the volume of erupted magma has been calculated and, second, high-precision GPS monitors tracked the extent to which the ground had been deformed.

"They found that changes in ground deformation – in other words, how much volume has been lost – correlate closely with the quantity of magma erupted on the surface," Hayman says. "So far, there doesn't seem to be any build-up of magma at depth." 

Seismic puzzle

All volcanoes are the surface expression of magma "plumbing" systems that sit deep in the crust. In the case of Eyjafjallajökull, and now Bardarbunga, magma originating from the Earth's mantle gets stored in chambers within the crust. 

Pressure builds as more magma enters the system, resulting in earthquakes and fracturing of the crust. Eventually, the pressure becomes too great and magma is erupted.

Most volcanoes are confined to zones along boundaries between crustal plates and are closely associated with earthquakes. Earthquakes, meanwhile, often occur at around the same time – even thousands of kilometres apart.

This is one of the puzzles of seismology. Overturning a once widely held belief among seismologists that earthquakes in different areas are independent, studies in the US and Kazakhstan have shown increases in tectonic activity hundreds of kilometres from epicentres of large earthquakes. Geophysicists believe this is due to changes in parts of the crust resulting from earthquakes.

Earthquakes and volcanoes are not periodic – they occur in irregular cycles. What's more, they do not relate to tides or seasons – or anything else for that matter. And yet large earthquakes often come in clusters lasting for days or weeks.

In recent weeks, thousands of earthquakes – some greater than five on the Richter scale – have occurred in the vicinity of Iceland's Bardarbunga. These earthquake swarms, as they are known, tell vulcanologists about the way magma is moving in the crust. 

Earthquakes that are relatively close to one another may be related, Hayman says: "In fact, large earthquakes can trigger other quakes. This has been well documented with the earthquake associated with the Boxing Day tsunamis."

All of the earth's huge crustal plates are linked, adds Cas, and stress that builds in one can sometimes be transmitted to an adjacent plate. 

Predictive power

Some Russian and Chinese seismologists believe they can predict the occurrence of some earthquakes and volcanic eruptions. 

The Chinese, in fact, claim to have predicted almost half of all earthquakes of seven or more on the Richter scale since 1978. Using the level of water in wells to make their predictions, they realised that levels rise or fall according to whether water is being absorbed by, or streaming out, of aquifers.

This, in turn, depends on motions within the earth. In keeping with the eastern notion of cyclicity and the interplay between opposites, the Chinese have found periodic changes in seismic activity in western China. One area might be active for, say, 150 years or so while another is dormant; the dormant area then becomes active for the next 150 years, and so on.

Russian seismologists, meanwhile, have searched to identify seismic patterns that might help them predict the time, area and size of a quake. Their computer models, based on statistical analyses, occasionally raise false alarms, while some earthquakes go unpredicted.

Western experts remain largely sceptical of these efforts. "I'm not aware of any technique that allows the exact timing and location of major earthquakes to be predicted," Professor Cas says. Once earthquakes become frequent in a particular region, it may be that they are followed by a major event, he suggests.

"With volcanoes, precursor signals such as increased volcanic earthquakes, ground displacements and changes in the rates of gas release or gas composition can be used to indicate that an eruption is possible," he says. 

Precise forecasting, Cas notes, is rarely possible more than a few hours in advance: "But sometimes eruptions begin with little or no warning."

On relatively short timescales of days or hours, scientists rely on a raft of techniques to predict volcanic activity. "For the current Icelandic eruption, for example, the magma about 10 kilometres down was tracked as it moved north-east over a number of days and came closer to the surface," Hayman says. "By this point we knew an eruption was very likely."

Quakes: how they work

The immensely powerful earth-moving forces that shape the continents are as active today as they were 4.5 billion years ago, when our planet was in the throes of being formed.

Beneath the Earth's relatively thin, rigid crust lies a mantle of solid crystalline rock. At a depth of more than 100 kilometres or so, the rock is so hot that it's malleable and squishy and can flow like plasticine.

Over aeons, the covering crust fragmented into colossal brittle sections called plates. There are seven main ones and several smaller chips off the old blocks, all moving and shoving against each other as they slide across the hot, soft mantle – not unlike boats being heaved across a sandy beach.

The plates are continuously colliding and being forced under one another, a process called subduction. Occasionally, they fracture, causing earthquakes and volcanoes. 

Their effects can be felt soon afterwards from hundreds of kilometres away, because the elastic waves produced by an earthquake travel at between four and 10 kilometres a second.

Volcanoes come in three varieties: active (likely to explode again), dormant (no activity for many years) and extinct (no sign of activity for ages).

Something like 1900 of the Earth's volcanoes are currently active. So which are the major ones to watch?

There's evidence, experts say, for the accumulation of vast quantities of magma beneath Yellowstone National Park and Mount St Helens in the US, for example. 

Eruptions on the scale envisaged would have potentially devastating consequences, based on the effects of the last super-volcanic eruption of Toba in Indonesia, about 73,000 years ago.

Some geoscientists say a truly monstrous volcano might bring about the end of life, as we know it.