Secrets of Patagonia's rare and violent volcanoes

Volcanic eruptions are some of the most powerful and unpredictable natural phenomena on Earth. Investigating one of the world's rarest and most explosive types of eruption in Patagonia could help save lives across the globe, explains Hugh Tuffen

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More about the author

Dr Hugh Tuffen is a volcanologist, Royal Society University Research Fellow and reader in the Lancaster Environment Centre at Lancaster University, UK.

He is fascinated by the power and beauty of volcanoes, and committed to help better understand their behaviour to assist the many millions threatened by volcanic activity.

When I was contacted by the Patagonia: Earth's Secret Paradise production team in 2014 to assist with filming the region’s volcanoes, I jumped at the chance to leave the Lancastrian winter and take a film crew to the spectacular volcano Cordón Caulle, the site of a huge eruption in 2011, and a stunning location that fascinates me.

This was an unusual and important eruption, being only the second time that rhyolite – a particularly thick and explosive kind of magma – had erupted on Earth in the last 50 years.

Remarkably, the previous eruption was also in Patagonia, further south at volcán Chaitén in 2008.

Rhyolite eruptions are poorly understood as they are so rarely seen, but they can be exceptionally large and violent. A vast eruption of similar magma at Toba, Sumatra, only 70,000 years ago, plunged Earth into a volcanic winter that lasted for several years, which some argue drove humans close to extinction.

As well as belching towering, destructive plumes of ash, rhyolite eruptions are famed for creating lava flows made of obsidian – the mysterious black volcanic glass that has fascinated everyone from early tool-makers to Minecraft fans.

At first the power of the eruption – equal to one Hiroshima-sized nuclear bomb every ten seconds – was difficult to fathom

The Cordón Caulle eruption began on June 4th 2011, following days of ever-increasing earthquakes and gas emissions. The ash plume swiftly reached 15km (9.3 miles) in height and was carried by the wind towards Argentina.

Meanwhile, melting of snow by hot ash generated swift-moving, hot mudflows that poured down the volcano flanks. Fortunately, thousands had been evacuated from the vicinity of the volcano, and there were no fatalities.

At first the power of the eruption – equal to one Hiroshima-sized nuclear bomb every ten seconds – was difficult to fathom. Usually, such powerful eruptions end swiftly, within days, but Cordón Caulle continued to pump out ash for almost a year, causing great hardship for the local population. During this time thick, black lava also slowly oozed out of the crater – an obsidian flow.

I first witnessed the extraordinary natural forces at work at Cordón Caulle in early 2012 when I joined an expedition to observe the continuing, albeit less intense eruption, collect samples of ash and lava, and shoot a short film. We hiked through eerily silent, ash-choked rainforest until the distant rumbling intensified and we could watch metre-sized chunks of lava being blasted from the vent at dizzying speeds of 100 metres per second.

The obsidian flow, as thick as a ten-storey building, creaked and groaned as it inexorably inched forward; a glacier of volcanic glass. Steam and sulphurous volcanic gases streamed out of deep cracks that riddled the ash-blanketed ground.

Now that the eruption has finished, I am drawn back to Cordón Caulle each year. As the ground cools and gas emissions diminish, we can search a little more closely for clues about the eruption, and why the ash plume was so long-lived. Clues are hidden inside the vent itself, an area of fractured lava half the size of a football pitch that was the source of such a colossal volume of ash, pumice and lava.

Fractures provided pathways for pressurised gas to escape from the volcano, but these became clogged by tiny particles of ash that stuck to them, creating a miniature world of drifted dunes until they blocked the fractures entirely. Our working hypothesis is that the ash was rushing out of the vents at such speed that it became electrically charged, and this charging helped it to stick to the fracture surfaces, driving the blockages. Consequently, the blocked valves were opened again and again by trapped gas, in many months of near-continuous explosions that gave the ash plume remarkable persistence.

Patagonian volcanoes are providing unique new insights into hazardous eruptions, including a type of magma responsible for some of the Earth’s largest volcanic events, and the striking footage of the recent eruptions at Villarrica and Calbuco vividly demonstrates their power.


That no lives have been lost to eruptions in Patagonia for many years is testament to the supremely efficient response of the Chilean authorities and scientists. I hope that many more secrets about volcanic activity will be revealed by studying the volcanoes in this beautiful and remote corner of the world.

'Patagonia: Earth’s Secret Paradise' begins in the UK on BBC Two, Friday 25 September at 21:00 BST.