Volcanic activity in the Garrotxa region ended only 8,300 years ago

A research team recently carried out an important study on the palaeoclimatic evolution, volcanic activity and its socio-ecological impact in the Volcanic Field of La Garrotxa. The results of the palaeoenvironmental study have been published in the prestigious journals The Holocene and Scientific Reports. The Universitat Autònoma de Barcelona, the University of Burgos, the IPHES-CERCA, the IDAEA-CSIC, the University of Valencia and the University of Montpellier participated in the study.

The study, carried out on a 14-metre deep borehole in La Vall d'en Bas, has revealed very interesting and unprecedented data on the palaeoclimatic and palaeoenvironmental evolution of the Volcanic Field of La Garrotxa, and researchers discovered that its volcanic activity lasted until only 8,300 years ago (until now it was thought that volcanism ceased around 13,000 years ago), which constitutes the most recent volcanism in the whole of the Iberian Peninsula.

"It was possible to document eruptions almost 5,000 years more recently than those previously recorded in the area, which were considered the most recent on the Iberian Peninsula, and it was possible to characterise in detail for the first time both the social and environmental impact of these eruptions," explains Maria Saña, a researcher in the UAB Department of Prehistory and one of the main authors of the study.

This volcanic activity caused several lava flows to block the Fluvià river valley near Olot and a large lake was formed on the plain known today as Pla de les Preses. The sediments deposited in this ancient lake surrounded by volcanoes, which include numerous layers of volcanic ash and lapilli, have been studied by different specialists through the analysis of sedimentary, palaeoclimatic and biological indicators such as chronostratigraphy, sedimentology, pollen, ostracods, lacustrine algae and diatoms. All this has made it possible to reconstruct the palaeoclimatic evolution of the last 13,000 years in the north-east of the Iberian Peninsula, the volcanism of La Garrotxa and the impact of these eruptions on the plant and lake ecosystems and on the Mesolithic human populations of the area.

The sedimentary sequence of the studied borehole records local and regional signals related to the geomorphological, palaeoclimatological and volcanic dynamics of the volcanic field of La Garrotxa. The geological and biological indicators analysed, the aquatic organisms, the pollen record, the sedimentology and the geochemistry mainly report local hydrological variations, which have been related to the main climatic trends of the Holocene and late Pleistocene, including several abrupt climatic changes that offer clues about the processes that could be triggered in the context of current global warming.

In the area closest to the volcanic activity area (up to 50 km) and during volcanic eruption events, different processes such as lava flows, deposition of volcanic materials, ash fallout, emanation of gases and aerosols and pyroclastic flows, and earthquakes affected flora and fauna (bioresources), as well as air and water quality, and constituted a hazard for human populations.

"One of the objectives of the research was to evaluate the dynamics of Neolithisation in various areas of the eastern Pre-Pyrenees, including La Garrotxa and, specifically, also in La Vall d'en Bas and the Llierca valley, the area where contemporary Mesolithic occupations have been documented during episodes of volcanism," says Maria Saña. In this sense, and from the study of nearby archaeological sites, it is observed that the nearest hunter-gatherer populations left the area temporarily during periods of high volcanic activity, and then returned in times of calm, demonstrating a high capacity for reorganisation and adaptation. "The abandonment of the volcanic zone may have lasted hundreds of years," Saña explains.
 
The results published show, in great detail, the palaeoenvironmental evolution of the north-east of the Iberian Peninsula and the socio-ecological impact of the volcanism that occurred in La Garrotxa. They also highlight the interest in developing interdisciplinary palaeoecological research, which analyses all the processes involved in the landscape transformations caused by volcanism and allows for a correct understanding and knowledge of its effects.
 
Original articles:
 
Iriarte, E., Revelles, J., Finsinger, W., Mesquita-Joanes, F., Rodrigo, M.A., Burjachs, F., Expósito, I., Marti-Molist, J., Planagumà, Ll., Alcalde, G., Saña, M. (2023). Youngest Iberian Holocene volcanic eruptions and paleoenvironmental evolution of a barrier-paleolake in the Garrotxa Volcanic Field (NE Spain). The Holocene. https://journals.sagepub.com/doi/10.1177/09596836231169989
 
Revelles, J., Marti-Molist, J., Burjachs, F., Finsinger, W., Iriarte, E., Mesquita-Joanes, F., Pla-Rabes, S., Rodrigo, M.A., Alcalde, G., Saña, M. (2023). Socio-ecological impact of monogenetic volcanism in the La Garrotxa Volcanic Field (NE Iberia). Scientific Reports. https://www.nature.com/articles/