The Top-10 most Dangerous Volcanic Systems – Introducing the MDE-concept


A city doomed to destruction as the nearby volcano suffers a catastrophic eruption. First blasted by the shock wave, then enveloped by 800 centigrade hot pyroclastic flows as well as pummelled by a rain of rocks as large as hills to be eventually swallowed up as the volcanic edifice collapses into the magma chamber, the inhabitants had no chance at all except those who heeded the warnings issued by the Volcanological Institute. Where the city once stood is now a deep circular depression filled by the ocean. (Composite image by Prunelle)

There are reports in local Sumatran newspapers that Toba has a bout of indigestion. Low level volcanic type earthquakes have occurred and in the village of Purasa there is gas and steam coming out of the ground. It is important to remember that Toba currently is in a phase of reconstruction and that it is highly unlikely that a large eruption will happen. Toba’s main mode of operations is currently resurgent doming and construction of margin stratovolcanoes along the ring fault of the YTT-caldera.


The Sipoholon Hot Springs on the western shore of Lake Toba are part of a great number of active thermal areas located along Toba’s western caldera ring fracture and also along the western edge of Samosir Island, the resurgent dome. (

If an eruption occurs it would probably be between VEI-1 and VEI-4. The last eruption occurred a few hundred years ago when the Tandukbenua volcano was formed on the NW-rim of the caldera. The current activity is taking place at the resurgent dome of Samosir Island inside the caldera itself and is a normal part of the resurgence and rebuilding of an upper magma reservoir, it may cause a small to medium sized eruption.

Once again, nope it will not destroy the world… But I fear an eruption of nonsense won’t be long in coming. Which reminds me. After yet another eruption of Yellowstone Angst a week ago, I had an interesting discussion with Henrik about us doing a series of articles on the most dangerous volcanoes. Not the Decade Volcano list! We both agree that was done out of expediency, Henrik did an article on it a year ago or so saying pretty much that. It’s in the archives.


A beautiful resort that is not on the current Decade Volcano programme. But will it make our list? (Uncredited image on Ristorante il Rudere website)

Anyway, there’s an ogre in each and everyone of us and after throwing the ball around for a while, we agreed on a set of criteria for our list of the ten most dangerous volcanic systems at the moment. First of all, the system must be one capable of a truly devastating eruption within the next 10 – 100 years. We’re not discussing a hypothetical VEI 8 eruption that could happen some 50,000 years or more from now, but one that could happen tomorrow geologically speaking.

Our second criterion and the most important one is that if the volcanic system has a full-scale major eruption, a million lives or more could be at risk from primary, secondary and tertiary effects of such an eruption. We call this MDE – Million Death Expectancy. That’s right, volcanic systems capable of having eruptions in the foreseeable future that could kill a million people or more.


This little baby did not make the list in spite of being able to meet our MDE-criterion under certain specific conditions. NASA MODIS image of the 2011 VEI 4 Grímsvötn eruption. But what this volcano did in some 24 hours, one of our candidates recently did in a couple of hours.

It didn’t take long for us to come up with the ten in our opinion most dangerous volcanic systems on the planet and agree upon the order even if we did decide to exclude Grímsvötn in the end, a volcano with a clear capability of meeting the MDE criterion. Of the 16 original Decade Volcanoes, only one or two made it to our list and I’m sorry to say, Etna is not amongst them. I expect that a certain vulcanologist working for the INGV might have something to say about that. If he wants to, he’s more than welcome to argue his case in the comments section – or even better; in a Guest Post once we have concluded our series.

Starting Friday (barring further noteworthy eruptions happening), I will kick of with number 10 on our list after which we will publish our list in ascending order over the following weeks. Henrik will help me to write at least some of the articles which we hope will be enjoyable reading even if the subject is gruesome and downright ghoulish.

Carl & Henrik

PS. Mutterings from a shared utility room some 550 km from here inform me that we had better have a part two that looks at the current Decade list and why we feel it is inadequate. I expect Carl will enlighten us once the household chores are done. / Prunelle

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