In 1104, after 250 years of slumber, it covered half the entire country in ash and volcanic bombs. In 1693, a violent, seven-month-long eruption produced more than 216 million cubic meters (7.63 billion cubic feet) of volcanic debris per hour, some of which made it across the sea to Norway.
Hekla’s largest historical eruption occurred in 1766, which lasted until 1768 and featured terrifying, extensive, prolonged lava flows, gigantic lava bombs the size of desks, and sudden flooding thanks to the rapid melting of the ice caps.
Herein, though, lies the problem with Einarsson’s analysis. As pointed out by Erik Klemetti at Wired, the time between Hekla’s eruptions is quite inconsistent, and the regularity in the last few decades is only looking at a very short segment of the volcano’s timeline, which stretches back at least 7,000 years.
Since the 1104 event, there have been 24 eruptions of varying intensity, meaning that there is one roughly every 38 years. So it’s possible another Hekla eruption won’t happen at this rate until the year 2038.
It seems that Hekla doesn’t play by the rules. There was a 41-year gap between the powerful 1766 event and a smaller eruption in 1725, which implies that a gap of several decades can result in a catastrophic eruption. However, after a violent eruption in 1158, there was a 48-year gap before the next eruption in 1206, which turned out to be rather puny by comparison.
The next eruption, however powerful, will likely produce prolonged and persistent ash clouds, just like Eyjafjallajokull did in 2010 (pictured here). J. Helgason/Shutterstock
Along with the fact that volcanologists have very little pressure data on the volcano, which Einarsson is using to make his conclusions, the only conclusion that can realistically be made is that the chance of a major Hekla eruption is about as likely as there not being one at all in the next year or so.
Or, as Klemetti puts it: “Volcanoes care not for your puny human schedules.”