One of the largest Holocene eruptions in Iceland was the Hekla 3 ( or H3 ) eruption circa 1000 BC , which threw about 7.3 km3 of volcanic rock into the atmosphere , placing its Volcanic Explosivity Index ( VEI ) at 5 . This would have cooled temperatures in the northern parts of the globe for a few years afterwards . Traces of this eruption have been identified in Scottish peat bogs , and in Ireland a study of tree rings dating from this period has shown negligible tree ring growth for a decade
Hekla 3
Hekla 3 eruption
Hekla