LAUSR

Abstract Far-travelled volcanic ash (fine-grained tephra) clouds pose economic and societal risks largely through their potential impact on the aviation industry. A long view of ash clouds extending over northwest Europe assembled from the study and geochemical characterisation of cryptotephra (i.e. tephra invisible to the naked eye) in sedimentary records can help inform the understanding of the frequency of such events, and the nature of eruptions that generate them. Here we review the records of cryptotephra deposition in northwest Europe during the Mid- to Late Holocene (the last eight millennia) to gain insights into the sources of volcanic ash reaching this region. We consider almost 500 published and unpublished datasets for cryptotephras recorded in sedimentary sequences ranging from Ireland to Latvia and, on the basis of their major element geochemical composition, we identify 90 unique ash horizons and their likely provenance. The majority (72%) of the cryptotephras derive from Icelandic eruptions, but a large proportion (24%) originates from other volcanic regions, including Alaska, the Cascades, Kamchatka, Mexico, the Azores and possibly the Mediterranean. Although moderate magnitude eruptions in Iceland may potentially disperse ash clouds over Europe, it appears that only large magnitude events in more distant regions have generally had this capacity and then only when suitable meteorological conditions prevailed. Nevertheless, the cryptotephra records demonstrate that ash clouds from most volcanic regions capable of producing large explosive eruptions in the northern mid- to high latitudes, particularly those to the west of Europe, as well as in tropical North America, have the potential to extend to northwest Europe. Volcanic ash forecasts for this region need therefore to take into account possible risks posed not only by Icelandic eruptions, but also by any large magnitude eruptions in North America or the North Pacific area.