Iceland's ice cap has been melting rapidly in response to climate change. Vatnajökull, Iceland's largest ice cap, with an area of about 8000 km2, has lost 10% of its mass. In response to the ice loss the area around the ice cap has risen up to 25mm per year. This depressurization will increase magma production and volcanic activity.
"Our work suggests that eventually there will be either somewhat larger eruptions or more frequent eruptions in Iceland in coming decades," said Freysteinn Sigmundsson, a vulcanologist at the University of Iceland.
"Global warming melts ice and this can influence magmatic systems," he told Reuters. The end of the Ice Age 10,000 years ago coincided with a surge in volcanic activity in Iceland, apparently because huge ice caps thinned and the land rose
At the end of the last ice age volcanism increased in Iceland and many volcanoes around the world in response to glacial melting. Ice loss reduced the reduced pressure over the upper mantle magma source. Pressure reduction causes an increase in the fraction of mantle melt for most volcanoes without a change in temperature because most magma is less dense than the solid rock it is in equilibrium with.
While the present eruption in Iceland is probably not related to ice melting because it is under a small icecap with a relatively insignificant mass loss, the mass loss of Iceland's largest ice cap is causing a significant increase in magma production. At ridges, such as the mid-Atlantic ridge that Iceland is centered on, the hot mantle wells up under the ridge. When the upwelling mantle rises close enough to the surface, the rock begins to melt due to depressurization. Under Iceland some of the upper mantle is a mixture of melt and rock. Because partially melted rock produces more melt at constant temperature when pressure is decreased, ice cap melting causes increased magma production by a process called decompression melting.
Vulcanologists have calculated the increased fraction of magma produced in response to the melting of Iceland's largest ice cap.
Because magma at the mid-Atlantic ridge where Iceland is centered, is generated by decompression melting, the uplift and depressurization is increasing the production of magma in Iceland.
The modeling indicates that a substantial volume of new magma, ~0.014 km3/yr, is produced under Vatnajökull in response to current ice thinning. Ice retreat also induces significant stress changes in the elastic crust that may contribute to high seismicity, unusual focal mechanisms, and unusual magma movements in NW-Vatnajökull.
A relatively simple calculation shows that magma production rates over the whole of Iceland will be increased by about 10%. The relative production percentage increase under individual ice caps will be much higher.
Our model indicates that recent retreat of Vatnajökull can cause increased mantle melting at a rate of about 0.014 km3/yr. The steady-state melting rate under Iceland can be inferred from the fact that the melt extracted at the plate boundary forms the crust. In order to generate ~30 km thick crust over the 300-km north-south length of Iceland spreading at 1.9 cm/year, a magma generation of ~0.17 km3/yr is required. Thus our inferred magma volume increase of 0.014 km3/yr corresponds to ~10% increase in magma production. This percentage would be larger if the melt generated by glacial retreat would be compared to the melting under Vatnajökull only, but not the whole of Iceland.
We appear to be going into part of a natural cycle of increasing volcanic activity in Iceland augmented by the effects of climate change. Increased Icelandic volcanism could have serious effects on Europe and North America. Icelandic volcanic eruptions can be far more destructive than the present event which is disrupting air travel in Europe. The 1783 Laki eruption caused a major famine in Iceland, deaths from toxic gas and extreme weather in Europe, and a bitterly cold winter in North America.
An estimated 120 million tons of sulfur dioxide were emitted, approximately equivalent to three times the total annual European industrial output in 2006, and also equivalent to a Mount Pinatubo-1991 eruption every three days. This outpouring of sulfur dioxide during unusual weather conditions caused a thick haze to spread across western Europe, resulting in many thousands of deaths throughout 1783 and the winter of 1784.
The summer of 1783 was the hottest on record and a rare high pressure zone over Iceland caused the winds to blow to the south-east. The poisonous cloud drifted to Bergen in Norway, then spread to Prague in the Province of Bohemia by 17 June, Berlin by 18 June, Paris by 20 June, Le Havre by 22 June, and to Great Britain by 23 June. The fog was so thick that boats stayed in port, unable to navigate, and the sun was described as "blood coloured".
Inhaling sulfur dioxide gas causes victims to choke as their internal soft tissue swells. The local death rate in Chartres was up by 5% during August and September, with over 40 dead. In Great Britain, the records show that the additional deaths were outdoor workers, and perhaps 2-3 times above the normal rate in Bedfordshire, Lincolnshire and the east coast. It has been estimated that 23,000 British people died from the poisoning in August and September.
The haze also heated up, causing severe thunderstorms with hailstones that were reported to have killed cattle, until it dissipated in the autumn. This disruption then led to a most severe winter in 1784, in which Gilbert White at Selborne in Hampshire reported 28 days of continuous frost. The extreme winter is estimated to have caused 8,000 additional deaths in the UK. In the spring thaw, Germany and Central Europe then reported severe flood damage.