Abstract

In mid-June 1783, a peculiar haze descended upon Europe. It quickly became apparent that this was no ordinary fog: It was dry rather than wet, lasted for months, and turned the sun and moon bloodred. Day by day, the haze grew increasingly dense. By the last week of June, the concentrations of its pollutant properties seemingly reached their peak: Contemporaries in parts of England, the Low Countries, and the German Territories reportedly tasted sulphur in the fog with every drawn breath. There were complaints of sore eyes and throats, breathing difficulties, and asthmatic attacks. Then, seemingly overnight, an apparent frost swept through towns, villages, and farms, destroying the vegetation in its path.

These events inspired many to speculate about their cause. Unbeknown to mainland Europeans at the time, a 27-kilometer-long fissure volcano had sprung to life in the remote Icelandic highlands. The Laki fissure produced the largest lava volume of any volcanic eruption in the last millennium. In Iceland, volcanic ejecta poisoned the fields, meadows, and ponds, which caused malnutrition, hunger, and disease in the human population. The jet stream then carried the ejecta to Europe, where it was a catalyst for many a fierce debate. In the spirit of the Enlightenment, naturalists used reason and experimentation in an attempt to lift the fog of ignorance.

News about this volcanic eruption only reached Europe after the fog had vanished. As a result, the real origin of this corrosive fog remained a mystery for over a century.