The Icelandic volcano Hekla is said to be on the brink of erupting for the first time in 16 years.
The volcano, located in the south of the country, has erupted approximately once every 10 years between 1970 and 2000, but has been quiet since then and geologists say that could mean trouble. When the eruption comes, it could be a major one.
“Hekla is a dangerous volcano,” University of Iceland Geophysics Professor Páll Einarsson said.
“We could be looking at a major disaster when the next eruption begins if we are not careful.
“This is a risky moment which we need to take seriously.
“Hekla is ready – at any moment,” he said.
The earliest recorded eruption of Hekla took place in 1104 and since then there have been between 20 and 30 major eruptions, with the mountain sometimes remaining active for periods of up to six years.
But they are extremely varied and difficult to predict.
Some are very short – a week to 10 days – whereas the 1947 eruption, which started 29 March 1947, ended in April 1948.
The most recent eruption was on 26 February 2000.
Hekla is a stratovolcano – of the same type as Vesuvius, Krakatoa, Mount Saint Helens and Mount Pinatubo. However, unlike them, it also has some distinctly Icelandic features including a long crater row, or fissure.
This volcanic ridge is 1,491 metres at its highest and about 40 kilometres long, with the most active part of the ridge, a fissure about 5.5 kilometres long named Heklugjá, considered to be the volcano Hekla proper.
This fissure opens along its entire length during major eruptions and is fed by a magma reservoir estimated to have a top four kilometres below the surface. The tephra (the rock that makes up a pyroclastic flow) produced by its eruptions is high in fluorine, which is poisonous to animals.
This is an unusual form of stratovolcano and is related to Iceland’s specific geology.
Stratovolcanoes, also known as composite volcanoes, are usually conical and built up by many layers (strata) of hardened lava, tephra, pumice, and volcanic ash. The lava flowing from them typically cools and hardens before spreading far.
In Iceland, volcanic vents are typically long fissures that open up parallel to the rift zones where the Eurasian and the North American Plate lithospheric plates are diverging – a system that is part of the Mid-Atlantic Ridge.
Hekla lies in the area near the rift where the south Iceland seismic zone and eastern volcanic zone meet.
The volcano’s frequent large eruptions have covered much of Iceland with tephra and these layers can be used to date eruptions of Iceland’s other volcanoes.
Around 10% of the tephra created in Iceland in the last 1,000 years has come from Hekla, amounting to five cubic kilometres.
The volcano has produced one of the largest volumes of lava of any in the world in the last millennium, around eight cubic kilometres.
Hekla is 50 kilometres away from Eyjafjallajökull, another active volcano which caused chaos when it erupted in 2010, sending a massive plume of volcanic ash into the atmosphere.
The fallout saw air traffic grounded across Europe.