DID CHIMBORAZO VOLCANO CAUSE THE LATE ANTIQUE LITTLE ICE AGE OR OTHER CLIMATE CHANGES AT A REGIONAL TO GLOBAL SCALE?

The Late Antique Little Ice Age (LALIA) was a period of significant climate-induced historical change in the Late Roman and Early Islamic Mediterranean between 536 and 660 AD. LALIA is thought to have started with the Justinianic plague (541-549 AD) that caused a high death toll in the population of the Western and Eastern Roman Empires. Despite the significance of LALIA, the trigger of the event is still up for debate. The general consensus is that the likely cause of the LALIA is volcanic activity, though the specific volcanoes have yet to be identified. My research aims to determine whether Chimborazo, an ice-capped stratovolcano located near Riobamba, Ecuador, and one of the largest volcanoes on the American continent, is the culprit.

As Chimborazo is located near the equator (01°28′09″S 78°49′03″W), a potentially large-scale explosive eruption may produce large amounts of ash that can be dispersed in the atmosphere in both the northern and southern hemispheres. A few studies using radiocarbon dating and tephrochronology have estimated half a dozen eruptions throughout the Holocene including the most recent eruption believed to have occurred 1,500 years ago. Chimborazo may be a viable suspect as one of the triggers of LALIA, but the complete eruptive history has yet to be determined.

Recent field missions conducted in April 2022 and July 2023 revealed new explosive episodes throughout the Holocene history of Chimborazo. Specimens of paleosols found between layers of pumices, lapilli, and ash were inspected using 14C radiocarbon AMS analysis at the Center for Applied Isotope Studies of the University of Georgia. Dating analysis revealed three events: 6,550±30 years BP, 5,670±35 years BP, and 1,860±30 years BP. The most recent event occurred around 160 AD, which coincides with an unidentified eruption event of similar age recorded in the ice cores retrieved from both Greenland and West Antarctica. To corroborate these geochronological data, we are currently reconstructing the source parameters that may have produced an eruption of VEI (Volcanic Explosivity Index) > 5 (> 10 km³ of erupted magma); this involves using petrographic and geochemical analyses of the collected volcanic tephra in combination with empirical tephra distribution from tephra thickness measured in the field.