The Hekla 3 eruption (H-3) c. 1000 BC is considered the most severe eruption of Hekla during the Holocene. It threw about 7.3 cubic kilometres (1.8 cu mi) of volcanic rock into the atmosphere, placing its Volcanic Explosivity Index (VEI) at 5. This would have caused a volcanic winter, cooling temperatures in the Northern Hemisphere for several years afterwards.