The eruption of Eyjafjallajökull volcano in 2010 demonstrated just how disruptive Icelandic volcanoes can be. The effects were all the more remarkable since, in volcanological terms, the 2010 activity was relatively trivial in terms of magnitude or intensity. Imagine then scaling up the 2010 episode by several hundred times. This begins to help in understanding the severe consequences of the Laki eruption, which began in June 1783, also in southern Iceland. This had a magnitude, Me, of about 6.6. It is the largest-known lava-flow eruption in the past millennium – nothing close to it has been witnessed in recorded history – and it led to the deaths of around a quarter of the Icelandic population. It also precipitated an environmental crisis in Europe. Tens of thousands of people perished in England and France, possibly as a repercussion of the eruption.

In this chapter, we examine the nature of these phenomena. One of the most important issues is to explain the loss of life. Some have argued for even greater socio-political reverberations, claiming that the eruption's climatic aftermath helped to fuel the uprising that culminated in the French Revolution. Does this claim hold up to scrutiny?