Recorder history documents numerous volcanic eruptions as devastating, such as the eruption of Mount Vesuvius in 79 AD, the eruption of Krakatau in Indonesia in 1883, or that of Eyjafjellajökull in 2010. And although these outbreaks had caused immense damage, they are not at the top of the expert scale. An international research team has discovered in ice cores that volcanic eruptions had taken place during the last ice age that far eclipse those described so far.
A total of 1,850 volcanic eruptions over the past 60,000 years were detected in ice cores from Antarctica and Greenland by the research team led by PhD student Jiamei Lin and Assistant Professor Anders Svensson of the Niels Bohr Institute at the University of Copenhagen. They found that 85 of these had global impacts, and 25 of these massive eruptions were more powerful than any volcanic eruptions known to date. “Eyjafjellajökull, which paralysed European air traffic in 2010, pales in comparison to the eruptions we identified further back in time,” Anders Svensson explains. “Many of these were larger than any eruption over the last 2,500 years.” The work, which also involved researchers from the University of Bern’s Oeschger Center for Climate Change Research, was published in the latest issue of the journal Climate of the past.
The strength of a volcanic eruption is indicated by the Volcanic Explosivity Index VEI, which has a scale of 1 to 8. The strongest eruption known to date was that of Tambora on the island of Sumbawa in Indonesia on April 10, 1815. This eruption, which had ejected between 160 and 213 cubic kilometers of material into the atmosphere and had cost the lives of more than 70,000 people, is given a magnitude 7 on the VEI scale. The effects of this eruption caused global temperatures to drop by 0.4 – 0.7°C, so that a year later the summer failed completely globally, resulting in crop failure and famine. It took years for the global system to recover. Other known eruptions considered catastrophic were even lower, for example the eruption of Mount Vesuvius in 79 AD with a magnitude 5, Krakatoa in 1883 a 6 on the scale.
New analysis of sulfur residues in ice cores from Antarctica and Greenland and cross-referencing with other data allowed the team to determine the strength and age of the eruptions. This created the most accurate 60,000 year timeline to date. Symbol image: Dorte Dahl-Jensen
However, the outbreaks researchers have now discovered far eclipse even those disasters. Thanks to a new analysis of sulfur residues in the different layers of six ice cores from Antarctica and Greenland and a synchronization of the respective layers for age determination, Jiamei Lin and her colleagues succeeded in establishing the strength of the eruptions and a timeline of about 60,000 years. They found evidence of 1,113 outbreaks in Greenland cores and 737 in those from Antarctica. The strength of the eruptions was so great in 85 eruptions that they had led to deposits at both polar regions. Analysis of sulfuric acid residues showed that 69 eruptions had emitted more sulfur into the atmosphere than the Tambora eruption. This likely resulted in the decline in global temperatures over several years.
The authors of the study were also able to determine the frequency of the outbreaks. “Tthe frequency of volcanic eruptions is rather constant and comparable to that of recent times. During the deglacial period (16–9 ka b2k), however, there is a notable increase in the frequency of volcanic events recorded in Greenland and an obvious increase in the fraction of very large eruptions” they write in their paper. “We don’t know if they (magnitude 8 eruptions, ed.) will happen in a few hundred years or a few thousand years,” Anders Svensson comments. “Tambora sized eruptions appears to erupt once or twice every thousand years, so the wait for that may be shorter.” The team considers the information content for climate models to be much more important. “Vulcanism can supply us with answers as to how much temperature changes when Earths atmospheric radiation budget changes, whether due to CO2 or a blanket of sulphur particles”, Svensson adds. “So, when we have estimated the effects of large volcanic eruptions on climate, we will be able to use the result to improve climate models.”
Featured image: Mount Cleveland eruption in Alaska. (C) ISS Crew Earth Observations experiment
Dr Michael Wenger, PolarJournal
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