AFTER WHAT HAS been a quiet 2015, Etna saw one of its first paroxysms of the year. Over the last few weeks, the Voragina crater on Etna has been restless, with low level Strombolian activity that was mainly confined to the crater. However, last night, the Voragine crater unleashed a lava fountainthat reached 1 kilometer (~3,200 feet) over the volcano with an accompanying ash plume that topped 3 kilometers (~9,800 feet). Even with all that intensity of eruption, the paroxysm was over in only 50 minutes.
This was Etna’s first significant eruption since May 2015, when the activity was centered at the New Southeast Crater, but the Voragine Crater had been sputtering lava occasionally since the start of the year.
This past Saturday there was an unexpected eruption of Japan’s Ontake volcano. Below is a video of some first hand footage of the eruption. As usual, Erik Klemetti writing for Eruptions blog at Wired.com has the 411 on the eruption and why no one saw it coming.
Based on what I’ve read and seen (and this is speculation on my part), this eruption may have been a steam-driven explosion known as a “phreatic” eruption. The Japanese Meteorological Agency suggested that even compared to a smaller eruption in 2007, this explosion had almost no warning. This occurs when water seeps into the cracks in the crater area of a volcano and gets hot enough to flash to steam. This rapid boiling causes fracturing of the rock and explosively ejects material out of the crater as the pressure inside the crater or conduit goes up exponentially.
Klemetti reminds readers that there is no way to predict most volcanic eruptions, and thus not to blame volcanologists or the hikers for being there. Below are Klemetti’s tips for hikers who are planning a volcano hike, more detail at Eruptions blog:
How do you prepare yourself if you’re hiking in volcanic terranes? Here are a few tips:
Get to know your volcano.
Be doubly prepared.
Let people know where you are.
Understand the risk.
Mount Ontake, a volcano straddling Nagano and Gifu prefectures, erupted around 11:53 a.m. Saturday, leaving several hikers injured and stranded in mountain trails.
The Earth seems to have been smoking a lot recently. Volcanoes are currently erupting in Iceland, Hawaii, Indonesia and Mexico. Others, in the Philippines and Papua New Guinea, erupted recently but seem to have calmed down. Many of these have threatened homes and forced evacuations. But among their less-endangered spectators, these eruptions may have raised a question: Is there such a thing as a season for volcanic eruptions?
Surprisingly, this may be a possibility. While volcanoes may not have “seasons” as we know them, scientists have started to discern intriguing patterns in their activity.
Eruptions caused by a shortened day
The four seasons are caused by the Earth’s axis of rotation tilting towards and away from the sun. But our planet undergoes another, less well-known change, which affects it in a more subtle way. Perhaps even volcanically.
Due to factors like the gravitational pull of the sun and moon, the speed at which the Earth rotates constantly changes. Accordingly the length of a day actually varies from year to year. The difference is only in the order of milliseconds. But new research suggests that this seemingly small perturbation could bring about significant changes on our planet – or more accurately, within it.
In February 2014, a study in the journal Terra Nova showed that, since the early 19th century, changes in the Earth’s rotation rate tended to be followed by increases in global volcanic activity. It found that, between 1830 and 2013, the longest period for which a reliable record was available, relatively large changes in rotation rate were immediately followed by an increase in the number of large volcanic eruptions. And, more than merely being correlated, the authors believe that the rotation changes might actually have triggered these large eruptions.
Altering the spin of a planet, even by a small amount, requires a huge amount of energy. It has been estimated that changes in the Earth’s rotation rate dissipate around 120,000 petajoules of energy each year – enough to power the United States for the same length of time. This energy is transferred into the Earth’s atmosphere and subsurface. And it is this second consequence that the Terra Nova authors believe could affect volcanoes.
The vast quantities of energy delivered to the subsurface by rotation changes are likely to perturb its stress field. And, since the magma which feeds volcanic eruptions resides in the Earth’s crust, stress variations there may make it easier for the liquid rock to rise to the surface, and thereby increase the rate of volcanic eruptions.
The Terra Nova study is far from conclusive. Nevertheless, the idea that minute changes to the Earth’s spin could affect volcanic motions deep within the planet is an intriguing one.
But there’s another natural phenomenon which has a much stronger claim to affect volcanic activity – one which might be just as surprising: climate change.
Eruptions caused by climate change
In recent decades, it has become apparent that the consequences of planetary ice loss might not end with rising sea levels. Evidence has been building that in the past, periods of severe loss of glaciers were followed by a significant spike in volcanic activity.
Around 19,000 years ago, glaciation was at a peak. Much of Europe and North America was under ice. Then the climate warmed, and the glaciers began to recede. The effect on the planet was generally quite favourable for humankind. But, since the mid-1970s, a number of studies have suggested that, as the ice vanished, volcanic eruptions became much more frequent. A 2009 study, for example, concluded that between 12,000 and 7,000 years ago, the global level of volcanic activity rose by up to six times. Around the same period the rate of volcanic activity in Iceland soared to at least 30 times today’s level.
There is supporting evidence from continental Europe, North America and Antarctica that volcanic activity also increased after earlier deglaciation cycles. Bizarrely, then, volcanic activity seems – at least sometimes – to rise and fall with ice levels. But why? Again, this strange effect might be down to stress.
Eruptions cause by the melting of ice
Ice sheets are heavy. Each year, Antarctica’s loses around 40 billion tonnes. They are so heavy, in fact, that as they grow, they cause the Earth’s crust to bend – like a plank of wood when placed under weight. The corollary of this is that, when an ice sheet melts, and its mass is removed, the crust springs back. This upward flexing can lead to a drop in stress in the underlying rocks, which, the theory goes, makes it easier for magma to reach the surface and feed volcanic eruptions.
The link between climate change and volcanism is still poorly understood. Many volcanoes do not seem to have been affected by it. Nor is it a particularly pressing concern today, even though we face an ice-free future. It can take thousands of years after the glaciers melt for volcanic activity to rise.
Yet while it may not be an immediate hazard, this strange effect is a reminder that our planet can respond to change in unforeseen ways. Contrary to their brutish reputation, volcanoes are helping scientists understand just how sensitive our planet can be.
Robin Wylie does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.
The Bárðarbunga (or Bardarbunga) volcano has erupted, evoking memories of the 2010 Icelandic ash cloud that caused chaos across European and North American air routes. Dave McGarvie, a volcanologist at The Open University who has been in Iceland studying the latest eruption explains what’s going on.
What has been happening?
The ice-covered Bárðarbunga volcano has a magma chamber beneath it, and measurements indicate that magma from this chamber has been escaping into a vertical underground crack which has migrated some 40 km north-east away from the chamber. We call this a dyke intrusion. Escape of magma from the chamber has removed support from the chamber roof which has collapsed to trigger the largest earthquakes in the area. At the far north-east tip of the dyke intrusion it managed to find a route to the surface on August 29 to produce a small eruption at the Holuhraun lava field that lasted only a few hours.
After a pause a larger eruption started in the same place on August 31, which continues at the time of writing. Both of these eruptions occurred along an ancient fissure that had erupted in 1797. So it looks like the magma in the new dyke intrusion met the old and cold 1797 dyke intrusion and followed this easy pathway to the surface. Had this not happened the new dyke intrusion might have kept moving to the north-east.
What is the situation right now?
At the moment a vigorous eruption is taking place along a crack – about 1.5 km long – from which lava is fountaining. This is called a fissure eruption and these are common in Iceland. The lava fountains reach up to 70m high, and on collapsing they coalesce to form lava flows that are streaming away from the erupting fissure that currently covers an area of 10.8 square kilometres. An eruption plume of steam and volcanic gases has reached 6km into the atmosphere, but there is no ash.
The good news for Iceland is that despite Bárðarbunga being covered with ice, both eruptions took place in the an ice-free area which means that no ice is being melted and therefore there is no danger from flooding. And the good news for international air travel is that small fissure eruptions like these produce lots of lava but little or no ash, so any airspace closure is only local.
Is this a dangerous eruption?
Not really. Near the eruption and downwind there will be a hazard from gases escaping from the eruption if they are in high enough concentrations – mostly sulphur dioxide and possibly also some fluorine and chlorine. Scientists working in certain areas have to wear gas masks. Although the lava is slow moving it is best to stay a few hundred metres away. Staying away from the strike of the erupting fissure is also a good idea in case it becomes longer.
The Icelandic scientists working in the area are familiar with this type of eruption and know the hazards and how to minimise the risks. But at present there are no plans to allow any one else into the area.
What happens next?
One big uncertainty is whether new magma is entering the system or not, and if so how much, and where, and at what rate. For example, if more magma is entering the system than is being erupted, then the dyke intrusion may start moving again or an eruption may happen elsewhere such as under the Bárðarbunga volcano itself, or the dyke intrusion may surface under the nearby glacier. Both of these would involve much melting of ice and would trigger floods (as magma can melt up to 14 times its own volume of ice).
Another uncertainty is that we don’t yet know whether this is an isolated event or whether it is the start of a prolonged episode involving multiple events of seismic unrest and magma movement. If it is the latter, then we have some idea of what to expect as there was a well-studied episode between 1975-84 at a volcano called Krafla in north Iceland. During this episode there were 21 events of seismic unrest, some of which were accompanied by dyke intrusions moving out from the magma chamber, a few of which broke to the surface and formed eruptions just like the present Holuhraun eruption.
We also don’t know whether the drainage of magma from the chamber beneath the Bárðarbunga volcano is going to trigger an eruption there. There is a lot of ice at this volcano because it contains a crater, or caldera, some 10km in diameter that is about 700m deep and filled with ice. So even a modest eruption here would generate a lot of meltwater.
What is the best-case scenario?
That the dyke intrusion stalls in the crust and cools, and the eruption at its tip ceases.
What is the worst-case scenario?
Unfortunately there is more than one. The first is that an eruption might start at the Bárðarbunga volcano itself, and there is a remote possibility that this could be a large explosive eruption producing an ash cloud. Fortunately because of the ash cloud produced during the Grímsvötn eruption of 2011 we have a fair idea of what this might look like and how best to minimise disruption to air travel. A reassuring fact is that lessons learned and changes made as a result of the Eyjafjallajökull 2010 eruption meant that despite erupting twice as much ash, disruption due to the Grímsvötn 2011 ash cloud was much less.
The second is that the dyke intrusion continues to the north-east and triggers an eruption at the Askja volcano. Askja last erupted in 1961, but its most notorious eruption was in 1875 when an explosive rhyolite eruption produced an ash cloud that spread over northern Europe. Rhyolite is a “sticky” magma type that fragments more easily into ash, hence has a higher potential to produce ash clouds that cause disruption to air travel.
However, we are unlikely to have a repeat of the 1875 eruption because there is probably not much rhyolite magma left, plus there is now a deep crater lake covering the 1875 eruption site. There remains the possibility that some ash could be produced if a dyke intrusion mixed with the remaining rhyolite magma and triggered an explosive eruption.
Have lessons been learned?
The Bárðarbunga volcano didn’t get to be the second largest mountain in Iceland by sitting around doing nothing for centuries, so an eruption was inevitable, and recent signs of unrest were building towards this eruption. But as we have so little high-quality data from past eruptions to inform what might happen in the future, it is necessary to observe and gather high-quality data to learn what we can as fast as we can. This is what Icelandic scientists are excellent at doing.
I am aware that there is a lot of anxiety because the disruption caused by the Eyjafjallajökull 2010 eruption is still fresh in everyone’s minds. However, even if we had an exact repeat of this eruption tomorrow only a fraction of the flights would be cancelled. The decision makers have learned and moved on.
Dave McGarvie does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.
Quick post today, but RUV is reporting that three small explosions occurred in the area just north of Vatnajökull. The nature of the explosions are unknown at this point, but from the rough translation of the article in Icelandic, they sound an awful lot like a phreatic explosion — that is, explosions driven by steam. If magma is directly involved, they would then become phreatomagmatic. In both cases, it could be a case where intruding basalt is interacting with saturated sediment at the edges of the Vatnajökull.