Laki or Lakagígar (Craters of Laki) is a volcanic fissure situated in the south of Iceland, not far from the canyon of Eldgjá and the small village Kirkjubæjarklaustur, in South-East Iceland. Lakagígar is the correct name as the Laki mountain itself did not erupt, but fissures opened up on each side of it. Lakagígar is part of a volcanic system, centering on the Grímsvötn volcano and including the Þórðarhyrna volcano. It lies between the glaciers of Mýrdalsjökull and Vatnajökull, in an area of fissures which run in a south-west to north-east direction.
The system erupted over an 8 month period during 1783-1784 from the Laki fissure and the adjoining Grímsvötn volcano, pouring out an estimated 14 km3 (3.4 cu mi) of basalt lava and clouds of poisonous hydrofluoric acid/ Sulphur Dioxide compounds that killed over 50% of Iceland's livestock population, leading to famine which killed approximately 25% of the population.
The Laki eruption and its aftermath has been estimated to have killed over six million people globally, making it the deadliest volcanic eruption in historical times. The drop in temperatures, due to the sulphuric dioxide gases spewed into the northern hemisphere, caused crop failures in Europe, droughts in India, and Japan's worst famine.