Iceland's Most Active Volcano Looks Like It's Getting Ready to Erupt Again

sciencealert.com ^ | 9 OCTOBER 2020 | DAVE MCGARVIE,

[BenLurkin]

Grímsvötn volcano on Iceland produced an unusually large and powerful eruption in 2011, sending ash 20 kilometres into the atmosphere, causing the cancellation of about 900 passenger flights. In comparison, the much smaller 2010 eruption of Eyjafjallajökull led to the cancellation of about 100,000 flights.

Grímsvötn is a peculiar volcano, as it lies almost wholly beneath ice, and the only permanently visible part is an old ridge on its south side which forms the edge of a large crater (a caldera). And it is along the base of this ridge, under the ice, that most recent eruptions have occurred.

Another peculiarity is that the heat output from the volcano is extraordinarily high (2000-4000 MW), and this melts the overlying ice and produces a hidden subglacial lake of meltwater. This is up to 100 metres (328 feet) deep and has ice up to about 260 metres (850 feet) thick floating on it. Fresh ice is continually flowing into the caldera, where it melts, and so the water level just keeps rising and rising.

This meltwater can escape suddenly, and after travelling southwards beneath the ice for about 45 kilometres it emerges at the ice margin as a flood, which in the past has washed away roads and bridges. Fortunately, the passage of meltwater beneath the ice to its outlet can be tracked, and so roads are closed in good time to avoid travellers getting caught in the flood and killed.

Yet another important peculiarity of Grímsvötn is that it can have a hair-trigger response to pressure. This happens when the meltwater lake drains – removal of the water from across the top of the volcano rapidly reduces the pressure.

This can trigger an eruption – it's like lifting the lid off a pressure cooker. This has happened many times at Grímsvötn.

[xp38]

To say nothing of the carbon alert!