I have just finished reading 'Island on Fire' by Witze and Kanipe. This fascinating new book is mainly about the 1783 eruption of the Laki chain of Icelandic volcanoes. Many people in Europe remember the Eyjafjallajokull eruption in 2010 because it sent out a plume of dust particles that disrupted air traffic over Europe. There was a fear that the dust particles would get into jet engines and cause planes to crash.
The Laki eruption was far more deadly, not because of the force of the eruption or its dust emissions, but because it sent out a massive cloud of toxic fluorine, chlorine and sulphur dioxide [as much sulphur dioxide as 12,000 coal fired power stations emit in a year] that spread over much of Europe and probably killed tens of thousands of people by affecting health and crops. Its emissions may even have affected the flow of the Nile and caused famines in Egypt.
In 1783 communications were poor and science primitive so the cause of Europe's distress was not understood. Divine displeasure was thought more likely than a volcano in Iceland. It is only recently that scientists have began to understand what happened [and become alarmed by their findings].
The public may not be aware of the risks of Laki type events but the UK Government is worried. The Cabinet Office publishes a National Risk Register which covers the main threats to the UK [a copy of the 2013 edition can be downloaded from here].
The Register identifies four main risks.
1. An influenza epidemic.
3. Catastrophic terrorist attacks [although the government adds that mass impact terrorist events are “unlikely”].
4. Volcanic eruptions.
The 2010 eruption of the Eyjafjallajökull volcano in Iceland showed some of the consequences that a volcanic eruption far away can have on the UK. The NRR assessment is that there are two main kinds of risk from volcanic eruptions. The first is an ash-emitting eruption, similar to Eyjafjallajökull. This kind of eruption is economically dangerous because of the possible disruption of transport.
The second, which is slightly less likely than an ash-emitting eruption but which could have widespread impacts on health, agriculture and transport, is an effusive-style eruption in Iceland on the scale of Laki. This second type could kill many humans and animals and is now one of the highest priority risks.
The Laki eruption from the Grimsvötn volcano in Iceland is the best understood large magnitude eruption of this type. In 1783–84 Grimsvötn erupted along a 27km-long fissure system (Laki). Significant levels of sulphur dioxide, chlorine and fluorine were released over a number of months, causing visible pollution across the UK and Northern Europe which is thought to have resulted in mass crop failure and thousands of excess deaths. At least 20% of the population of Iceland succumbed to famine and disease. Records suggest that mortality in England in the summer of 1783 was 10–20% above average and there are similar historical accounts of increased mortality rates and/ or respiratory disorders in France, the Netherlands, Italy and Sweden.
Incidentally, Icelandic volcanoes are particularly dangerous. Not only because there are a lot of them, but also because it is easier for their output to get into the stratosphere and travel over large areas. At the equator the boundary between the troposphere and the stratosphere is 18 kilometres above ground. At the poles it is only 8 kilometres up.
Witze, A. and Kanipe, J., 2014. An island on fire: the extraordinary story of Laki.