Simon Redfern

A team of scientists from the UK, the US, Australia and New Zealand have modelled the fate of a huge floating raft of volcanic rocks that formed in 2012 during a submarine eruption of a Pacific volcano.

Described in this month’s edition of Nature Communications, they show how satellite images of the floating-rock raft’s passage across the Pacific can be used to test models of ocean circulation. Their results could be used to forecast the dispersal of future pumice (volcanic rock) islands, and protect shipping from the hazards they pose.

The eruptions of the Icelandic volcano, Eyjafjallajökull, in 2010 brought the hazards associated with volcanic ash sharply into focus. Air routes across northern Europe were disrupted, leaving many passengers stranded and far from home for days on end.

Ocean hazard

But hazards of floating islands of pumice spewed into the ocean from erupting volcanoes are less well-known.

One such island grew from an explosion of the Havre volcano in the South Pacific, between Tonga and New Zealand, in July 2012. The volcano threw out a cubic kilometre of molten magma, which suddenly froze to form bubble-filled pumice.

It is the bubbles trapped in pumice that make it so light – half the density of water – so the rock floats on water. Like natural flotsam, pebble to boulder-sized lumps of pumice clump together. This can create huge floating rafts in the seas around erupting volcanoes, and they can be tens of centimetres thick but thousands of kilometres in length.

Records of the use of pumice exist since the time of the Romans and Ancient Greeks. Its rough texture made them effective abrasives to remove dead skin from calluses and corns.

However, today, such floating pumice can pose a hazard for shipping. Hulls can be damaged by abrasion from the hard but light pumice, and when it approaches land these pumice rafts can block harbours and disrupt navigation.

Havre’s pumice island affected an area of ocean twice as big as both islands of New Zealand put together, floating atop the sea. Boats entering the volcanic debris reported engine problems, as the rock and dust clogged their water cooling intakes.

Threat to ocean life

It is not just the effects on shipping that have been a worry. The rafts of pumice stones block the sunlight from reaching plankton in the seas beneath. These plankton form the base of food chain when they convert sunlight to food through photosynthesis, and can be severely affected by floating pumice.

Floating rocks can also act as ferries for exotic invading species, such as shellfish and other organisms that make them their floating home. Indeed, it has been speculated that pumice islands like these were the first home that early life on Earth could have clung to and sprung from.

The study, led by Martin Jutzeler at the National Oceanography Centre in Southampton, UK, shows how the rafts eventually break up into ribbons of rock that can cover a wide area. The simulation techniques that the team has developed will allow the progress of future volcanic rafts to be predicted, and warnings issued to shipping, in the same way as volcanic ash clouds can be forecast for aircraft approaching stratospheric eruptions.

This article was originally published on The Conversation.
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Thank goodness Mount Sinabung isn’t a supervolcano. Binsar Bakkara/AP

Devastating supervolcanoes can erupt simply due to changes that happen in their giant magma chambers as they slowly cool, according to a new study. This finding marks the first time researchers have been able to explain the mechanism behind the eruptions of the largest volcanoes on Earth.

Geologists have identified the roots of a number of ancient and possible future supervolcanoes across the globe. No supervolcano has yet exploded in human history, but the rock record demonstrates how devastating any eruption would be to today’s civilisation. Perhaps most famous is the Yellowstone supervolcano in Wyoming, which has erupted three times in the past two million years (the last eruption occurred 600,000 years ago).

These giant volcanic time bombs seem to explode once every few hundred thousand years, and when they do they throw huge volumes of erupted ash into the sky. At Yellowstone, the eruption that happened two million years ago ejected more than 2000km³ of material – enough to cover Greater London in a mile thick layer of ash.

It is estimated that a super-eruption like that would drive a global temperature drop of 10˚C for more than a decade. Such a dramatic change in global climate is difficult to comprehend. Aside from the instant local devastation, there would be global impacts such as crops failing, followed by large famines.

Despite their potential threat, comparable to a large asteroid impact, the mechanisms and origins of super-eruptions have remained obscure. Modestly sized volcanoes operate on different time-scales and magnitudes, and their eruptions appear to be triggered by pulses of molten rock, magma, which increase the pressure on underground magma chambers that feed their vents.

Two papers recently published in the journal Nature Geoscience try to solve the mystery of how super volcanoes are formed and how they erupt.

Using experiments and computer modelling scientists have discovered what drives a super-eruption. They find that, over time, the underground magma becomes increasingly more buoyant. It is like a beach ball held down beneath the waves until it is released, when it shoots into the air, forced up by the dense water around it.

In the first paper, a team led by Wim Malfait and Carmen Sanchez-Valle of ETH Zurich the Zurich team used a synchrotron, an instrument that can generate intense X-rays, to measure the density, temperature and pressure of molten rock held in a magma chamber several kilometres below the surface. They mimickeed deep Earth conditions in the lab at the European Synchrotron Radiation Facility, which allows probing of substances held at temperatures up to 1,700˚C and the pressure of 36,000 atmospheres.

An artist’s impression showing the magma chamber of a supervolcano with partially molten magma at the top. The pressure from its buoyancy is sufficient to punch through 10km or more of the Earth’s crust above it. ESRF/Nigel Hawtin

To feed a supervolcano you need a huge magma chamber. The Zurich team’s results show that as the magma chamber cools it begins to solidify and crystals grow in it that are denser than the magma, which then fall to the base of the chamber. In contrast, the remaining molten rock in the chamber gets progressively less dense, and, if there is enough of it, their measurements showed that the magma eventually becomes light enough that it forces its way through more than 10km of Earth’s overlying crust.

Co-author Carmen Sanchez-Valle, also at ETH Zurich, said: “Our research has shown that the pressure is actually large enough for the Earth’s crust to break. As it rises to the surface, the magma will expand violently, which is a well known origin of a volcanic explosion”.

The second paper by Luca Caricchi and colleagues at the University of Bristol, describes computer simulations of the same processes, finding that the buoyancy of melt in maturing magma chambers is also key to these huge events.

Supervolcanoes require a steady accumulation of molten rock that remains hot enough that it does not completely solidify. It is then simply a matter of time. Malfait’s data show that eventually buoyancy alone is sufficient to trigger these rare, but massive, geological catastrophes.

The eruption of massive supervolcanoes seems to be an inevitable part of their “life cycle”. Just as a star may eventually become a supernova, so a huge magma chamber can eventually become a massive eruption. This contrasts with the way that more familiar smaller volcanoes erupt, where blasts follow directly from rapid injections of magma, or from earthquakes that might trigger them, or even from pressure release on melting of overlying glaciers, as seen in Iceland recently.

This article was originally published at The Conversation.
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Volcanic Mount Sinbung in Sumatra, Indonesia, has sprung to life in a series of massive eruptions over the last few days. The volcano had lain dormant for more than 400 years before a few minor eruptions three years ago. But this week more than 5,000 people have been evacuated from nearby towns and villages as Sinbung makes her presence felt.

As Sinabung puts on her show of power, in the Mediterranean the volcano Etna has also been active this week. But the view of Etna’s summit is far more gentle, as extraordinary smoke rings have been puffed into the Sicilian sky, as if the volcano is sitting back and relaxing for a while. Photographer Tom Pfeiffer managed to capture the scene with a series of fantastic shots.

The Indonesian volcano, however, erupted an ash cloud more than four miles into the air. A super-heated avalanche of lava, ash and rock raced down its flanks at terrifying speeds on Monday. There are reports of a stream of red hot lava extending a kilometre or so from the vent.

Sinabung’s activity is fed by the slow tectonic descent of rocks forming the floor of the Indian ocean, drawn down and northward into Earth’s mantle beneath Indonesia. This geological feature is called the “Sunda Arc” and it is home to some of the largest volcanic eruptions ever seen.

The 1815 eruption of Mount Tambara, above the Sunda Arc, remains the largest recorded volcano ever. But it is topped by the super-eruption of Toba, also in Sumatra, which scientists place at 70,000 years ago as the largest in human history. The eruption of Indonesian Krakatoa was smaller than both, yet was heard 3,000 miles away and caused widespread devastation and more than 35,000 deaths.

Indonesia, the world’s fourth most populous nation, sits atop a geological powder keg. This week’s eruption of Sinabung serves as a reminder.

This article was originally published at The Conversation.
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