Laki eruption of 1783–1784

The Laki event, also called the Skaftáreldar in Icelandic accounts, began in June 1783 along a fissure system in south-central Iceland associated with the Grímsvötn volcanic system. It was not a single brief explosion: fissure vents produced repeated eruptive activity and extensive basaltic lava flows over several months, with activity continuing into early 1784. Geological and atmospheric studies estimate that the eruption released very large quantities of sulfur dioxide, which can form sulfate aerosols in the atmosphere.

In Iceland, volcanic gases and acid deposition damaged vegetation and crops, while fluorine-contaminated pasture harmed livestock. The resulting famine and disease contributed to a severe demographic crisis. An atmospheric haze was reported beyond Iceland, including in Europe; historical accounts describe respiratory and eye irritation. The event demonstrates how a long-lived fissure eruption can affect people far from its vents through gases and aerosols, not only through lava and ash.

Sulfur dioxide can be converted into sulfate aerosols that reflect some incoming sunlight, producing a cooling influence. The years following Laki included cooling and other climate anomalies, but attributing each seasonal extreme to the eruption is difficult. A climate-model study found that the unusually warm European summer of 1783 was better explained by atmospheric blocking than by the eruption, while volcanic forcing contributed to cooling and may have affected later winter and spring circulation. The findings caution against treating a striking weather event as a simple direct consequence of a volcanic eruption.

Laki is a major example used to study the atmospheric effects of high-latitude volcanic eruptions. It shows that a large, sustained basaltic fissure eruption can release gases over a long period and create regional air-quality hazards as well as climate-relevant aerosols. Reconstructions combine geological evidence, historical observations, ice-core records and climate simulations; the precise size and timing of particular effects depend on the evidence and method used.