Introduction

Iceland has a high concentration of active volcanoes due to unique geological conditions. The island has about 130 volcanic mountains, of which 18 have erupted since the settlement of Iceland in 874 AD. Over the past 500 years, Iceland's volcanoes have erupted a third of the total global lava output. Although the Laki eruption in 1783 had the largest eruption of lava in the last 500 years, the Eldgjá eruption of 934 AD and other Holocene eruptions were even larger. Another relevant eruption is the Katla 1918 Eruption.

Geologists explain this high concentration of volcanic activity as being due to a combination of the island's position on the Mid-Atlantic Ridge and a volcanic hotspot underneath the island. The island sits astride the boundary between the Eurasian and North American Plates, and most volcanic activity is concentrated along the plate boundary, which runs across the island from the south-west to the north-east of the island. Some volcanic activity occurs offshore, especially off the southern coast. This includes wholly submerged submarine volcanoes and even newly formed volcanic islands such as Surtsey and Jólnir.

Source: http://en.wikipedia.org/wiki/Volcanism_of_Iceland

The most recent volcanic eruption in Iceland was that of Eyjafjallajökull, which started on April 14, 2010. The Eyjafjallajökull eruption closely followed an eruption in Fimmvörðuháls, which had erupted on March 20, temporarily quiesced by April 12, and then erupted with a large ash plume (due to magma coming out under ice) on April 15th2010.
The most violent and destructive eruptions in the last 1000 years are listed below.

Following table lists the most active volcanos on Iceland in the last 1000 years. Please note that due to the great number of eruptions on Iceland the list is not complete but only includes the most powerfull and active volcanos of the last 1000 years.

    Source: http://www.volcanodiscovery.com/en/iceland.html
    Source: http://en.wikipedia.org/wiki/Volcanism_of_Iceland
    Source: http://iceland.vefur.is/iceland_nature/Volcanoes_in_Iceland

Eyjafjalla

The volcano has erupted relatively frequently (aprox. every 200 years ) since the last glacial period. The stratovolcano, whose vents follow an east-west trend, is composed of basalt to andesite lavas. Most of its historical eruptions have been explosive. However, fissure vents occur on both (mainly the west) sides of the volcano.

The volcano, which has a crater 3–4 kilometres in diameter, erupted in 920, 1612 and again from 1821 to 1823 when it caused a glacial lake outburst flood. It erupted twice in 2010—on 20 March and 14 April. The March event forced a brief evacuation of around 500 local people, but the April eruption was ten to twenty times more powerful and caused massive disruption to air traffic across Northern Europe.

Eyjafjalla Eruptions: 920, 1612, 1821, 2010

1821-23 Eruption

Some damage was caused by a minor eruption in 1821. Notably, the ash released from the eruption contained a large fraction of fluoride, which in high doses may harm the bone structure of cattle, horses, sheep and humans. The eruption also caused some small and medium glacier runs and flooding in nearby rivers. The eruptive phase started on 19 and 20 December 1821 by a series of explosive eruptions and continued over the next several days. The sources describe heavy ash fall in the area around the volcano, especially to the south and west. After that event the eruption continued on a more subdued level until June 1822.

From the end of June till the beginning of August 1822, another series of explosive eruptions followed. The eruption columns were shot to considerable heights, with ashfall all over the country. The period from August to December 1822 seemed quieter, but farmers attributed the death of cattle and sheep in the Eyjafjörður area to poisoning from this eruption.

The ash of Eyjafjallajökull’s 1821 eruptions is to be found all over the south of Iceland. It is dark grey in colour, small-grained and intermediate rock containing about 68–70% silicon dioxide.

In the spring of 1823, the nearby volcano Katla under the glacier Mýrdalsjökull erupted and at the same time steam columns were seen on the summit of Eyjafjallajökull.

    Source: http://en.wikipedia.org/wiki/Eyjafjallaj%C3%B6kull
    Source: http://www2.norvol.hi.is/page/ies_Eyjafjallajokull_eruption
 

Katla

The volcano Katla is subglacial and has a reputation as one of the most dangerous volcanoes of Iceland. Its peak reaches 1493 m in height and the extension of the glacier Mýrdalsjökull which lies over it reaches 595 km². Katla erupted very powerfully in 1918 but there is evidence of smaller eruptions after that. Icelandic volcanologists are expecting another eruption in next few years so the Myrdalsjokull glacier and the Katla caldera are monitored quite closely.

Katla is among the most frequently erupting volcanoes in Iceland, averaging about two eruptions each century. The volcanic massive is partly covered by the glacier Mýrdalsjökull which fills a caldera depression and covers the eruptive vents. In spite of the basaltic composition of the products (transalcalic FeTi basalts) the eruptions are explosive due to the subaquatic mode of extrusion. The eruptions are accompanied by enormous laharic  floods (A lahar is a type of mudflow or landslide composed of pyroclastic material and water that flows down from a volcano) which have formed a vast sandur plain which are widely distributed in Holocene while ocean sediments and ash particles in the Greenland ice core indicate strong activity over much longer time periods. A remarkable feature of this volcanism is the uniform composition of its products with time.

The last eruption in Katla occurred in 1918. The Southern coast was extended by 5 km by the laharic flood deposits. The present volcanic repose is among the longest known in historic times, but monitoring of ground deformation and seismicity does not reveal any signs of reawakening. Seismic unrest does occur from time to time and a precautionary measure the traffic across the sandur plain is then halted on both sides of the plain.

    Source: http://en.wikipedia.org/wiki/Katla
    Source: http://www.earthice.hi.is/page/ies_katla1918
 

Eyjafjalla and Katla

Over the past 1100 years, Eyjafjallajökull has erupted four times: in 920, in 1612, between 1821 and 1823, and in 2010. Each of the first three of these incidents preceded an eruption in the nearby subglacial volcano, Katla. Katla—a much more active volcano known for its powerful subglacial eruptions and its large magma chamber, much larger than that of the Eyjafjallajökull volcano system–has not shown any unusual activity, such as expansion of the crust or seismic activity, in 2010, although geologists have been concerned about its general instability since 1999. Some geophysicists in Iceland support the notion that the recent volcanic eruption at Eyjafjallajökull may trigger a second eruption at Katla, one which would cause major flooding due to melting of glacial ice.

 Páll Einarsson (palli@raunvis.hi.is)

    Source: http://en.wikipedia.org/wiki/Eyjafjallaj%C3%B6kull
    Source: http://www2.norvol.hi.is/page/ies_Eyjafjallajokull_eruption    

Laki

Laki or Lakagígar (Craters of Laki) is a volcanic fissure situated in the south of Iceland, not far from the canyon of Eldgjá and the small town Kirkjubæjarklaustur, in Skaftafell National Park.

Laki is part of a volcanic system, centering on the Grímsvötn volcano and including the Thórdarhyrna volcano.  It lies between the glaciers of Mýrdalsjökull and Vatnajökull, in an area of fissures which run in a south-west to north-east direction.

The system erupted over an 8 month period during 1783-1784 from the Laki fissure and the adjoining Grímsvötn volcano, pouring out an estimated 14 km3 of basalt lava and clouds of poisonous hydrofluoric acid/sulfur-dioxide compounds that killed over 50% of Iceland's livestock population, leading to famine which killed approximately 25% of the population.

The eruption continued until 7 February 1784, but most of the lava was erupted in the first five months. Grímsvötn volcano, from which the Laki fissure extends, was also erupting at the time from 1783 until 1785. The outpouring of gases, including an estimated 8 million tons of hydrogen fluoride and estimated 120 million tons of sulfur dioxide, gave rise to what has since become known as the "Laki haze" across Europe.

    Source: http://www.guardian.co.uk/world/2010/apr/15/iceland-volcano-weather-french-revolution
    Source: http://news.bbc.co.uk/2/hi/uk_news/magazine/8624791.stm
    Source: http://en.wikipedia.org/wiki/Laki
 

Volcanic Risk Reduction Strategies

The distribution of European air-traffic due to the Eyjafjalla eruption in spring 2010 caused great economic loss and immobility. The consequences of a stronger and longer eruption on Iceland, similar to the Laki 1783 eruption, could not only affect air-traffic more severely but also agriculture and public health throughout Europe.

The GRF Davos has been brought upon WeatherTec, a product of Swiss company meteosystems who claims to be able to "rain clouds out" , thus bring volcanic ashes to the ground. The proposed technology is shortly introduced below. GRF Davos did not asses theoretical and practical feasibility.

• WeatherTec creates a local electrical disturbance by charging atmospheric aerosols with corona generated negative ions.
• Disturbance is created from the ground by an emitter system.
• Technical due diligence carried out by Max Plank Institute for Meteorology and Biogeochemistry. No objections to feasibility are brought up. Many applications are possible including: generate/enhance rainfall, remove excess vapours from the atmosphere (positive CO2 feedback), create snow to store water and reflect sunlight, dissipate fog/smog)
• Testing has not been carried out and is required. Global effect of local usage is not clarified yet. Potential health threats of emissions are also not clarified yet.