The ice-covered Grímsvötn volcano on Iceland produced an unusually giant and highly effective eruption in 2011, sending ash 20km into the environment, inflicting the cancellation of about 900 passenger flights. As compared, the a lot smaller 2010 eruption of Eyjafjallajökull led to the cancellation of about 100,000 flights.

Understandably, any point out of one other explosive eruption from an Icelandic volcano will elevate issues within the air journey trade, which is at present reeling from the COVID-19 pandemic. However there are clear indicators that the Grímsvötn volcano is on the brink of erupt once more. Consequently, the authorities have lately raised the menace stage for this volcano.

Grímsvötn is a peculiar volcano, because it lies virtually wholly beneath ice, and the one completely seen half is an outdated ridge on its south aspect which varieties the sting of a big crater (a caldera). And it’s alongside the bottom of this ridge, below the ice, that almost all current eruptions have occurred.

One other peculiarity is that the warmth output from the volcano is awfully excessive (2000-4000MW), and this melts the overlying ice and produces a hidden subglacial lake of meltwater. That is as much as 100 metres deep and has ice as much as about 260 metres thick floating on it. Contemporary ice is regularly flowing into the caldera, the place it melts, and so the water stage simply retains rising and rising.

The roughly 1.5km huge gap melted within the ice by the 2011 eruption.

Dave McGarvie, Creator supplied

This meltwater can escape all of a sudden, and after travelling southwards beneath the ice for about 45km it emerges on the ice margin as a flood, which up to now has washed away roads and bridges. Thankfully, the passage of meltwater beneath the ice to its outlet will be tracked, and so roads are closed in good time to keep away from travellers getting caught within the flood and killed.

One more essential peculiarity of Grímsvötn is that it may have a hair-trigger response to stress. This occurs when the meltwater lake drains – elimination of the water from throughout the highest of the volcano quickly reduces the stress. This will set off an eruption – it’s like lifting the lid off a stress cooker. This has occurred many occasions at Grímsvötn.

Grímsvötn is Iceland’s most steadily erupting volcano, and over the previous 800 years some 65 eruptions are recognized with some certainty. The time gaps between eruptions are variable – and, for instance, previous to the bigger 2011 eruption there have been smaller eruptions in 2004, 1998 and 1983 with gaps of between 4 and 15 years. Crucially, and with the following eruption in thoughts, Grímsvötn seems to have a sample of rare bigger eruptions that happen each 150-200 years (for instance 2011, 1873, 1619), with smaller and extra frequent eruptions occurring roughly as soon as a decade in between.

Indicators of exercise

A excessive frequency of eruptions at a volcano permits scientists to detect patterns that result in eruptions (precursors). And if these are repeated every time a volcano erupts then it turns into attainable for scientists to be extra assured that an eruption is more likely to occur within the close to future. It’s, nonetheless, seldom attainable to be exact concerning the precise day.

Previous ridge of Grímsvötn.

Dave McGarvie, Creator supplied

Icelandic scientists have been fastidiously monitoring Grímsvötn since its 2011 eruption, and have seen varied alerts that recommend the volcano is on the brink of erupt. For instance, the volcano has been inflating as new magma strikes into the plumbing system beneath it (consider burying a balloon within the sand after which inflating it). Growing thermal exercise has been melting extra ice and there has additionally been a current enhance in earthquake exercise.

So what occurs subsequent? Once more, based mostly on the sample noticed at previous eruptions, an intense swarm of earthquakes lasting a number of hours (one to 10 hours) will sign that magma is shifting in the direction of the floor and that an eruption is imminent. In instances the place the hidden subglacial lake drains and triggers the eruption, the earthquakes happen after the lake has drained and simply earlier than the eruption.

The smaller Grímsvötn eruptions expend a number of power once they work together with water and ice on the floor. Which means the ensuing ash will get moist and sticky and so falls from the sky comparatively shortly. Ash clouds subsequently solely journey a number of tens of kilometres from the eruption web site. This can be a good state of affairs for Icelanders and likewise for air journey, because it prevents the formation of considerable ash clouds that would drift round and shut off airspace.

However will or not it’s a small eruption? If Grímsvötn’s previous sample of occasional giant eruptions with extra quite a few smaller eruptions occurring in between continues into the longer term, then the following eruption needs to be a small one (given there was a big one in 2011). And the phrase “ought to” is essential right here – Iceland’s volcanoes are complicated pure methods and patterns usually are not at all times adopted faithfully.

Dave McGarvie doesn’t work for, seek the advice of, personal shares in or obtain funding from any firm or organisation that will profit from this text, and has disclosed no related affiliations past their educational appointment.