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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.
Read the original article.

Synchrotron X-ray CT scans reveal the structure of plankton shells. Credit: O Branson, University of Cambridge

Climate changes from millions of years ago are recorded at daily rates in ancient sea shells, new research shows. A synchrotron X-ray microscope has revealed growth bands in plankton shells that show how shell chemistry records the sea temperature.

The results could allow scientists to chart short timescale changes in ocean temperatures hundreds of millions of years ago. Plankton shells show features like tree rings, but representing daily growth bands, recording historical climate.

It’s important to understand current climate change in the light of how climate has varied in the geological past. One way to do this, for the last few thousand years, is to analyse ice from the poles. The planet’s temperature and atmosphere are recorded by bubbles of ancient air trapped in polar ice cores. The oldest Antarctic ice core records date back to around 800,000 years ago.

Our results just published in the journal Earth and Planetary Sciences Letters reveal how ancient climate change, pushing back hundreds of millions of years ago into deep time, is recorded in the shells of oceanic plankton.

As microbial plankton grow in ocean waters, their shells, made of the mineral calcite, trap trace amounts of chemical impurities, maybe only a few atoms in a million getting replaced by impurity atoms. Scientists have noticed that plankton growing in warmer waters contain more impurities, but it has not been clear how and why this “proxy” for temperature works.

When the plankton die, they fall to the muddy ocean floor, and can be recovered today from that muddy ocean floor sediments, which preserve the shells as they are buried. The amount of impurity, measured in fossil plankton shells, provides a record of past ocean temperature, dating back more than 100 million years ago.

Now, alongside co-workers from the Department of Earth Sciences at the University of Cambridge, we have measured traces of magnesium in the shells of plankton using an X-ray microscope in Berkeley, California, at the “Advanced Light Source” synchrotron – a huge electron accelerator that generates X-rays to study matter in minuscule detail.

Magnesium bands in the foram shell demonstrate incorporation into the mineral structure. Credit” O Branson, University of Cambridge

The powerful X-ray microscope has revealed narrow nanoscale bands in the plankton shell where the amount of magnesium is very slightly higher, at length scales as small as one hundredth that of a human hair. They are growth bands, rather like tree rings, but in plankton the bands occur daily or so, rather than yearly.

These growth bands in plankton show the day by day variations in magnesium in the shell at a 30 nanometre length scale. For slow-growing plankton it opens the way to seeing seasonal variations in ocean temperatures or plankton growth in samples dating back hundreds of millions of years.

The X-ray data show that the trace magnesium sits inside the crystalline mineral structure of the plankton shell. That’s important because it validates previous assumptions about using magnesium contents as a measure of past ocean temperature.

The chemical environment of the trace elements in the plankton shell, revealed in the new measurements, shows that the magnesium sits in calcite crystal replacing calcium, rather than in microbial membranes in their impurities in the shell. This helps explain why temperature affects the chemistry of plankton shells – warmer waters favour increased magnesium in calcite.

Our group are now using the UK’s “Diamond Light Source” synchrotron X-ray facility to measure how plankton shells grow and whether they change at all in the ocean floor sediments. Their latest results could allow scientists to establish climate variability in Earth’s far distant past, as well as providing new routes to measure ocean acidification and salinity in past oceans.

Hear me talk more on this here: From ABC Radio National “The Science Show”