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Keen readers may have gleaned from an earlier post linking volcanic activity and language diversity in Southeast Asia my interest in Indonesia’s volcanoes.

If you asked what, to me, is the key difference between Indonesia and Australia I would say that Indonesia is alive. I mean that in a number of ways I won’t go into here save for one; in Indonesia, the land itself is alive. I remember being captivated the first time I flew over a Javanese volcano and thinking it was among the most awesome sights I had ever seen. In a way I still struggle to describe, it awoke feelings of being at the distant edge of the planet and, at the same time, a recognition of the primeval world of my very distant human ancestors.

As the below graphic makes clear, Indonesia’s land mass is inseparable from volcanic activity, being built on some of the most geologically active foundations on earth with constant land mass loss and regeneration. Their destructive capabilities, balanced with the resulting incredibly fertile soil that turn supports Indonesia’s huge population, gives Indonesian volcanoes literally the power of life and death over large swathes of the population.

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Not all volcanoes are equally potent of course. Some, in the global or even Indonesian context, appear little more than local irritants that provide endearingly photogenic backdrops attracting tourists.

In contrast there are Indonesian volcanoes presenting much, much larger threats. Almost certainly the most famous was Krakatoa in the Sunda Strait just to the west of Java.

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Krakatoa’s eruption (depicted above and below) in 1883 killed countless thousands, literally sent shockwaves around the world, potentially reshaped Indonesia’s affinity for Islam and was almost certainly the loudest noise in recorded human history.

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What is particularly sobering about Krakatoa in the annals of Indonesian volcanoes is that, on balance, the eruption wasn’t even that significant. Earlier that century, in 1815, Tambora (to the east of Java and depicted below) erupted and put Krakatoa into perspective, killing over ten thousand local people immediately and over 100,000 through subsequent famine. Today Krakatoa remains a household name, but memories of Tambora are fading fast.

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(Above) Tambora caldera (crater) in 2009 from 350 km above. Image credit: NASA Earth Observatory, available at http://eoimages.gsfc.nasa.gov/images/imagerecords/39000/39412/ISS020-E-06563_lrg.jpg

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(Above) Tambora crater rim in 2008. Image credit: Flickr by paulzpicz at http://flickr.com/photos/23477176@N03/2596759611

If the world survived Tambora then Indonesia’s volcanoes will remain largely Indonesia’s problem, right? Looking at the below graph, overlaying actively volcanoes on population centres it will indeed be a problem sooner or later for a major Indonesian population centre.

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And yet this is where it gets truly scary. I suspect that while a lot of people have heard of Krakatoa, and a smaller number have heard of Tambora, few have heard of Rinjani. A guide to the comparative size of the eruptions can be seen below.

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(Above) Mountains that change the world Image credit: After Tambora, The Economist, http://www.economist.com/news/briefing/21647958-two-hundred-years-ago-most-powerful-eruption-modern-history-made-itself-felt-around

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(Above) Sunrise on Rinjani Image credit: Massew64, Wikimeda Commons, https://commons.wikimedia.org/wiki/File:Rinjani_Volcano,_Lombok.JPG

And yet, compared with Rinjani, knowledge of Toba in Sumatra is even further limited. The size of Toba volcano is in a different league again, making Toba a supervolcano with just a few global rivals (based on the volume of volcanic material forced into the air from its most recent explosion) including Yellowstone (in the United States, which last erupted 600,00 years ago) and Taupo/Oruanui (in New Zealand).

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The lake formed in the caldera (crater) of the Toba eruption is some 35km wide and 100km long, a scale not evident in the satellite picture above but more apparent in the picture below.

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Toba, around 1.2 million years old, erupted around 840,000, 700,000 and 74,000 years ago, but the last one was possibly the largest on earth in at least the last 2.5 million years. Along with Taupo/Oruanui, which last erupted some 25,000 years ago, Toba is the only supervolcanic eruption since modern humans began emerging in the last couple of hundred thousand years. Just how explosive was the Toba eruption? Well, in ejecting some 2500-3000 cubic kilometres of volcanic material the eruption was in the vicinity of five times the size of Taupo/Oruanui, 20 times the size of Tambora and an incredible 200 times the size of Krakatoa.

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There is a strong argument that when Toba (seen from the sky in the above picture) last erupted it was the closest humans have come to being pushed to extinction by a single event. I have no geological or statistical expertise to suggest when, but at some point in the future Toba, the greatest supervolcano on earth, will return to life and its eruption, in a world with a far greater human population and interconnectedness, may cause physical, geographical and economic destruction as the world has never before experienced.

For so much of life as we now know it, Sumatra may be where the world ends.

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