This week in Geoscience, we’re looking at earthquakes and volcanoes, and some of their major hazards (and I mean major hazards).
The #VolcanoCup: The Winner
I’m sorry to see the end of Twitter’s Volcano Cup, but we have a winner and it’s worth having a look at why. Krakatoa took on the mighty Taupo Volcanic Field in New Zealand and ran out a resounding winner with 59% of the vote.
Last week I gave you my reasons for voting for Krakatoa, and here are just some of the others given on Twitter.
“Totally destroyed the Dutch trade empire. Gotta love the attempt at hazard mitigation by telegraph too”
“a living laboratory for the study of island revegatation”
“The loudest eruption ever witnessed and it destroyed 3 islands.”
It’s worth having a quick look at what, and where, this great beast of Indonesia is. First up, I want to correct a geographical howler that Hollywood ought to be ashamed of. Possibly the one thing that a lot of people know about the volcano comes from the name of the film, Krakatoa, East of Java. It’s actually west of Java. (I haven’t seen the film so can’t speak of its scientific accuracy, but if it can’t get its location right, I don’t hold out much hope.)
The volcano is the result of the subduction of the Indo-Australian plate beneath the Sunda plate: melting rock rises to form the volcanoes for which Indonesia is notorious. If you want accurate information about it, there are plenty of resources, but the one I turn to is the Global Volcanism Program, a database maintained by the Smithsonian Institution/National Museum of Natural History. Its listings on Krakatoa give detailed information on its geology and activity and are worth a browse.
Probably the most interesting fact is that Krakatoa remains active. The database lists 55 confirmed eruptions (there will have been many more which aren’t recorded). When the island blew itself and its neighbours apart in 1883, that wasn’t the end. It kept erupting and a new volcano, known as Anak Krakatoa, began building among the devastation. It’s now over 800 metres high and has erupted over 40 times since the 1883 eruption.
The Volcano Explosivity Index and the Next Volcanic Eruption
The Earth, and its population, is at the mercy of cataclysmic volcanic eruptions. This week, an article in Nature reported on research which highlights the need for us to be prepared for the disastrous impacts of large volcanic eruptions. By ‘large’ they meant events which rated 7 on the Volcanic Explosivity Index, which is (roughly) the equivalent to the magnitude scale used for earthquakes.
The VEI scale measures volume of material erupted and, like its earthquake equivalent, is logarithmic. In other words, an eruption with a VEI of 7 will produce ten times the material produced by a VEI 6, though some may produce it in a short time, catastrophically, and others over a matter of years, with different impacts.
To put this into context, of the 8,765 eruptions on the GVP database for which a figure is given for explosivity, just eight have a VEI of 7. Of course, this comes hedged with caveats, because the database doesn’t include some major supervolcanic eruptions (such as Yellowstone) where the data just isn’t available — and, as the graphic shows, Yellowstone would have come in at a mind-blowing VEI 8.
But it’s instructive nonetheless. Only three VEI 7 eruptions have occurred in the past 2000 years — at Toba, in Indonesia, in 1815; Rinjani, also Indonesia, in 1257 and Changbaishan, in eastern China, in 942. For the record Krakatoa and the most recent large eruption, Pinatubo in 1991, came in at VEI 6, while other notorious eruptions, including Mount St Helen’s and Vesuvius, came in a level lower.
On thing we can be sure of is that, eventually, such an eruption is going to occur and, if we have to be ready for it.
The Damage from 2017’s Earthquakes
It’s always difficult to assess what makes one earthquake more damaging than another. Does one life lost make an event more serious than hundred of people injured or thousands made homeless? How should the long terms effects be measured against the shorter term ones?
In essence this is a subjective judgement and not one that I’d like to try, so I was interested to see that someone has actually taken on that task. The website earthquake.com has produced an Earthquake Impact Database which includes various factors (such as deaths, injuries, homes destroyed, tsunami height and so on) and produced a figure for damage.
The page is heavily copyrighted and I fully respect that, so I’m wary of quoting too much information from it, though you can look at it yourself. That said, I think I’m safe to tell you that the most damaging earthquake of 2017 is deemed to be the M8.1 which struck Mexico in September (there’s a caveat in here, in that not all of the values are readable in my browser).
The database is a fascinating resource if for no other reason than it brings together the impacts of the world’s major earthquake in a single place. And although the year’s most damaging tremor was also the largest, the database clearly indicates that magnitude alone isn’t necessarily what defines a damaging seismic event.
The Earthquake Cup
The Volcano Cup may be over, but the Earthquake Cup is in full swing. So far, the bigger beasts have got through — the 1994 Boxing Day earthquake; the San Francisco earthquake of 1906 — along with some of the smaller but more significant or deadly ones of recent years — the central Italy series from 2009-2017 and Haiti in 2010.
It’ll be interesting to see how the voting falls out. In the Volcano Cup, it seemed that size mattered. It’ll be interesting to see if the same happens in the Earthquake Cup, or whether the votes recognise that the significance of an event is, as the Earthquake Impact Database mentioned above so clearly shows, about much more than who shouts the loudest.