Effects in North Africa of the 934–940 CE Eldgjá and 1783–1784 CE Laki eruptions (Iceland) revealed by previously unrecognized written sources

In historic times, two catastrophic fissure eruptions originated in the Eastern Volcanic Zone of Iceland, known as Eldgjá eruption (934–940 CE) and Laki eruption (1783–1784 CE). Eldgjá produced 19.7 km3 of lava flows and 1.3 km3 of tephra; Laki emitted 14.7 km3 of lavas and 0.4 km3 of tephra. They released 232 and 122 megatons of SO2 into the atmosphere, respectively. Abundant historic descriptions of the effects of the Laki eruption indicate that the SO2 release produced a sulphuric aerosol that spread across the northern hemisphere with devastating impacts on the population and the environment, especially in Europe. In this study, we present two new written sources that enable the effects of the Eldgjá and Laki eruptions to be fixed to an exact date and place of occurrence in North Africa. These are a medieval North African chronicle known as Rawḍ al-Qirṭās, written in 1326 CE and describing events in Morocco, and a chronicle of events in the island of Djerba (southern Tunisia), written by Muhammad b. Yusef al-Musabi in 1792–1793 CE. These previously unrecognized sources describe in detail the fading of sunlight coupled with the persistent presence of a thick fog made up of fine particles carried over from long distances. The chronicles report events in Morocco in the time period October 938–October 939 CE, and in Tunisia in the year 1783 CE. These data can be interpreted as the first detailed evidence of the consequences of the Eldgjá and Laki eruptions in North Africa. They also can be helpful in dating and determining the area of influence of the eruptions; this may be useful for several applications, such as the numerical simulation of these events, or hazard planning in case of possible future similar eruptions from the same Icelandic area.