The ash cloud resulting from the 2010 eruption of Eyjafjöll caused severe disruption to air travel across Europe but as a geological event, it is not unprecedented. Analysis of peat and lake sediments from northern Europe has revealed the presence of microscopic layers of Icelandic volcanic ash (tephra). These sedimentary records, together with historical records of Holocene ash falls, demonstrate that Icelandic volcanoes have generated substantial ash clouds that reached northern Europe many times. Here we present the first comprehensive compilation of sedimentary and historical records of ash-fall events in northern Europe, spanning the last 7000 years. Within this period ten tephra layers have been identified in the Faroe Islands, 14 in Great Britain, 11 in Germany, 38 in Scandinavia and 33 in Ireland. Seven ash fall events have been historically documented prior to the Eyjafjöll 2010 event. Ash fall events appear to be more frequent in the last 1500 years, but it is unclear whether this reflects a true increase in eruption frequency or dispersal, or is an artefact of the records themselves or the way they have been generated. In the last 1,000 years, volcanic ash clouds reached Northern Europe with a mean return interval of 53 ± 8 years (the range of return intervals is between 6 and 112 years). Modelling using the ash records for the last millennium indicates that for any 10 year period there is a 17% probability of tephra fallout event in Northern Europe. These values must be considered as conservative estimates due to the nature of tephra capture and preservation in the sedimentary record.
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