Iceland is the land-based expression of the Mid-Atlantic Ridge and is one of the most volcanically active regions of the world. Volcanic eruptions on Iceland are a source of geological hazard to humans and the environment due to the release of ash, gases and lava. The composition of the material released is determined by the chemical composition of the surrounding bedrock and the magma upwelling from the Earth’s crust. The effects of historical eruptions on Iceland have been locally devastating and of global impact. The eruption of Lakagígar in 1783-1784 is known to have been the largest eruption in historical time, and is responsible for the death of ~22 % of theIcelandic population. Skeletal fluorosis is a disease that is sometimes observed following large volcanic eruptions. Volcanic ash can travel great distances in the upper atmosphere and spread over vast areas far away from the erupting volcano. Volcanic ash can change incomposition in the atmosphere, and bring about climate-changing effects. Most notably in recent times, violent ash eruptions can also cause problems to the aviation industry, when ash enters and damages airplane engines. Iceland has many active volcanoes and needs to ensure plans for future eruptions are in place. One such measure is an evacuation plan that protects people living close to an active volcano, such as the most lively on Iceland: Hekla, Katla and Eyjafjallajökull.