A guest post from Holly Ferrie, Geosciences student with the Open University.
If you’ve been keeping track of the science press in the last few months, you may have noticed a dramatic headline popping up in a number of places. ‘Life at threat from supervolcano in 200 million years!’ ‘The supervolcano forming under the Pacific that could wipe out life!’ ‘Extinction level supervolcano!’ This is the result of some fab research into mantle plumes by Professor Michael Thorne et al, an unfortunate press statement issued by the University of Utah, and an epic amount of hyperbole by the news outlets that latched on to it.
The big deal was that Thorne had found evidence of piles of magma interacting at the core-mantle boundary (about 2900km deep) in such a way that might, possibly, produce a megaplume one day. Within days this was blown out of proportion with Strombolian force, and the story became that in 200 million years time, one of two things was going to happen; either a supervolcano would destroy all life on the planet, or a flood basalt would. Doubtless these things will happen again countless times in the Earth’s future, but destroying all life? That’s incredibly unlikely.
As expected, supervolcanoes were the stars of the show, but while I was glad to see the word ‘Ontong-Java’ in papers like the Daily Mail, flood basalts got just a passing mention. To worsen the blow to a flood basalt geek like me, every paper I read made it seem as though flood basalts were over in just one single eruption, and that the outpourings of lava were without a doubt the most dangerous thing about them. No mention of the fact it’s effusive and more like Hawaii on speed mode, no mention of the real duration (it’s in the order of millions of years), no mention of ash or wider environmental effects (although to its credit the Mail did mention ocean anoxia, or loss of oxygen).
So I’m going to give a quick primer on what would really happen in a flood basalt eruption. First off, if the Pacific has not completely subducted by the time this supposed plume arrives at the surface, it will erupt underwater, creating something called a Large Igneous Province (a LIP). After a delay of up to a million years, ocean anoxia would kick in from all the released chemicals, killing marine life. We would of course notice the rising sea level in coastal areas as lava takes up space in ocean basins, displacing water onto continental shelves!
I sought the advice of Professor Paul Wignall – a well-renowned researcher of the Permian mass extinction – to confirm how much of a danger a continental flood basalt would pose.
Prof. Wignall told me that first we would notice rapid cooling. Fire fountains from these eruptions can reach kilometres high, injecting sulfur dioxide into the stratosphere where it reflects sunlight away and cools the planet. Further down in the atmosphere, sulfur dioxide would cause acid rain. In human terms, this would be like Iceland’s Laki eruption of 1773 all over again, but on a global scale; livestock would die, people would get breathing problems, structures would become corroded – and in the modern age, most flights would be grounded.
Now here’s where it becomes a proper song of ice and fire, because once the cooling is over, we would find that the volcano has spewed enough carbon dioxide and water vapour into the air to warm the planet up considerably. Over the millions of years that a flood event lasts, this temperature change could rack up into the tens of degrees – more than enough to pose a serious hazard to species that cannot adapt as easily as humans. We would recover quickly from the first eruption, but subsequent eruptions would wear us down, largely because they wouldn’t give plant biomass enough time to recover – and ultimately everything depends on that.
Finally, Prof. Wignall said it was quite realistic for extinctions to start occurring over a human lifetime should a flood basalt province start forming. So, as it turns out, flood basalts have wider and longer lasting environmental implications than supervolcanoes – they are dangerous things, and infinitely more fascinating. Instead of the hyped-up sexy science of supervolcanoes, perhaps it’s flood basalts that should be demanding more of our attention?