The ice-protected Grímsvötn volcano on Iceland created an unusually massive and effective eruption in 2011, sending ash 20 kilometres into the ambiance, resulting in the cancellation of about 900 passenger flights. In comparison, the a lot smaller sized 2010 eruption of Eyjafjallajökull led to the cancellation of about 100,000 flights.
Understandably, any point out of a different explosive eruption from an Icelandic volcano will elevate issues in the air journey marketplace, which is presently reeling from the COVID-19 pandemic.
But there are crystal clear signs that the Grímsvötn volcano is obtaining completely ready to erupt again. As a end result, the authorities have just lately elevated the danger amount for this volcano.
Grímsvötn is a peculiar volcano, as it lies nearly wholly beneath ice, and the only forever obvious part is an old ridge on its south side which forms the edge of a massive crater (a caldera). And it is together the foundation of this ridge, beneath the ice, that most modern eruptions have transpired.
Another peculiarity is that the heat output from the volcano is extraordinarily higher (2000-4000 MW), and this melts the overlying ice and provides a hidden subglacial lake of meltwater. This is up to 100 metres (328 toes) deep and has ice up to about 260 metres (850 toes) thick floating on it. Fresh new ice is regularly flowing into the caldera, exactly where it melts, and so the water amount just keeps increasing and increasing.
This meltwater can escape suddenly, and following travelling southwards beneath the ice for about 45 kilometres it emerges at the ice margin as a flood, which in the past has washed absent roads and bridges. The good thing is, the passage of meltwater beneath the ice to its outlet can be tracked, and so roads are shut in fantastic time to steer clear of travellers obtaining caught in the flood and killed.
Still a different crucial peculiarity of Grímsvötn is that it can have a hair-trigger reaction to force. This transpires when the meltwater lake drains – removal of the water from across the top of the volcano speedily decreases the force.
This can trigger an eruption – it’s like lifting the lid off a force cooker. This has transpired many times at Grímsvötn.
Grímsvötn is Iceland’s most regularly erupting volcano, and over the past 800 a long time some 65 eruptions are acknowledged with some certainty. The time gaps between eruptions are variable – and, for instance, prior to the more substantial 2011 eruption there have been smaller sized eruptions in 2004, 1998 and 1983 with gaps of between 4 and 15 a long time.
Crucially, and with the following eruption in brain, Grímsvötn appears to have a pattern of infrequent more substantial eruptions that manifest just about every 150-200 a long time (for instance 2011, 1873, 1619), with smaller sized and additional recurrent eruptions transpiring about once a decade in between.
Indications of action
A higher frequency of eruptions at a volcano permits researchers to detect patterns that lead to eruptions (precursors). And if these are repeated every time a volcano erupts then it gets achievable for researchers to be additional self-assured that an eruption is probable to happen in the in the vicinity of long term.
It is, nonetheless, rarely achievable to be specific about the specific working day.
Icelandic researchers have been meticulously monitoring Grímsvötn due to the fact its 2011 eruption, and have seen several alerts that recommend the volcano is obtaining completely ready to erupt.
For instance, the volcano has been inflating as new magma moves into the plumbing program beneath it (imagine of burying a balloon in the sand and then inflating it). Increasing thermal action has been melting additional ice and there has also been a modern maximize in earthquake action.
So what transpires following? Again, primarily based on the pattern noticed at past eruptions, an intensive swarm of earthquakes lasting a handful of hrs (one particular to 10 hrs) will signal that magma is transferring in direction of the surface and that an eruption is imminent. In scenarios exactly where the hidden subglacial lake drains and triggers the eruption, the earthquakes manifest following the lake has drained and just prior to the eruption.
The smaller sized Grímsvötn eruptions expend a large amount of strength when they interact with water and ice at the surface. That indicates the ensuing ash gets moist and sticky and so falls from the sky rather quickly.
Ash clouds hence only journey a handful of tens of kilometres from the eruption internet site. This is a fantastic scenario for Icelanders and also for air journey, as it prevents the formation of sizeable ash clouds that could drift close to and near off airspace.
But will it be a smaller eruption? If Grímsvötn’s past pattern of occasional massive eruptions with additional a lot of smaller sized eruptions transpiring in between proceeds into the long term, then the following eruption ought to be a smaller one particular (given there was a massive one particular in 2011). And the word “ought to” is crucial here – Iceland’s volcanoes are advanced organic methods and patterns are not usually followed faithfully.
Dave McGarvie, Volcanologist, Lancaster University.
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