The Lakagigar 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/sulfur-dioxide compounds that killed over 50% of Iceland's livestock population, leading to famine which killed approximately 25% of the population. Laki created two vast lava fields with a total area of 565 km², and the total volume of tephra emitted was estimated to have been 12,3 km³. The consequences were enormous.
The Lakagigar eruption has been estimated to have killed over two million people globally, making it the deadliest volcanic eruption in the history of mankind. The drop in temperatures, due to the sulfuric dioxide gases spewed into the northern hemisphere, caused crop failures in Europe, droughts in India, and Japan experienced its worst famine.
On 8 June 1783, a fissure with 130 craters opened with phreatomagmatic explosions because of the underground water interacting with the rising basalt magma. Over a few days the eruptions became less explosive, Strombolian, and later Hawaiian in character, with high rates of lava effusion. This event is rated as VEI 6 on the Volcanic Explosivity Index, but the eight month emission of sulfuric aerosols resulted in one of the most important climatic and socially repercussive events of the last millennium. The eruption continued until 7 February 1784, but most of the lava was erupted in the first five months. Grímsvötn volcano, from which the Laki fissure extends, was also erupting at the time from 1783 until 1785.
Artistic portrayal of Lakagigar eruption of 1783