A team of researchers from different national and international centers, IPHES-CERCA, Universitat Rovira i Virgili, University of Burgos, IDAEA-CSIC, Universitat Autònoma de Barcelona, University of Valencia and the University of Montpellier, carried out a paleoenvironmental study on paleoclimatic evolution, volcanic activity and its socio-ecological impact in the Volcanic Field La Garrotxa (Girona). The results were published in The Holocene and Scientific Reports.
Drilling works at a depth of 14 meters in Vall d’en Bas (Girona) revealed unprecedented data on the paleoclimatic and paleoenvironmental evolution of the La Garrotxa Volcanic Field (GVF, Girona).
The researchers found that its volcanic activity lasted until just 8,300 years ago (until now it was thought that volcanism had ceased around 13,000 years ago), this being the most recent volcanism in the entire Iberian Peninsula.
The sediments deposited in the ancient lake surrounded by volcanoes, which include numerous layers of volcanic ash and lapilli, have been studied by different specialists.
This volcanic activity caused several volcanic flows to block the Fluvià river valley near Olot and a large lake formed in the plain that is now known as Pla de les Preses.
The project dates this eruption using the carbon 14 method with organic matter present in the soil that was covered by the lava flow.
The sediments that were deposited in this ancient lake surrounded by volcanoes, which include numerous layers of volcanic ash and lapilli, have been studied by different specialists, analyzing different sedimentary, paleoclimatic and biological indicators such as chronostratigraphy, sedimentology, pollen, ostracods, lake algae, diatoms, etc.
All this allowed us to reconstruct the paleoclimatic evolution of the last 13,000 years in the northeast 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.
Location of the Pla de les Preses borehole in the Vall d’en Bas valley (Girona). The digital elevation map shows volcanic lava flows corresponding to eruptions over the past 20 years. The photograph shows the location of the Pla de les Preses survey, the Croscat volcano (in the background) and the town of Olot. / IPHES
The sedimentary sequence of the studied survey records local and regional signals related to the geomorphological, paleoclimatological and volcanic dynamics of the La Garrotxa volcanic field.
The analyzed geological and biological indicators, aquatic organisms, pollen record, sedimentology and geochemistry mainly report local hydrological variations, which have been related to the main climate trends of the Holocene and Late Pleistocene, including several abrupt climate changes that offer clues about the processes that could triggered in the context of current global warming.
Volcanic eruption events affected flora and fauna, as well as air and water quality, and posed a danger to human populations
In the area closest to the zone of volcanic activity (up to 50 km) and during volcanic eruption events, several processes such as lava flows, deposit of volcanic materials, ash rain, emanation of gases, aerosols, pyroclastic flows and earthquakes affected the flora and fauna (bioresources), as well as air and water quality, and constituted a danger to human populations.
In this sense, and from the study of nearby archaeological sites, it is observed that the closest hunter-gatherer populations left the area temporarily during periods of high volcanic activity, to return later in times of calm, demonstrating a high capacity for reorganization and adaptation. .
Remains of charophyte algae present in the lake sediments studied. Oospores of these macroalgae covered by calcium carbonate (gyrogonites). / María A. Rodrigo (University of Valencia)
The published works show, in great detail, the paleoenvironmental evolution of the northeast of the Iberian Peninsula and the socioecological impact of the volcanism that occurred in La Garrotxa.
In addition, they show an interest in developing interdisciplinary paleoecological research that analyzes all the processes involved in the transformations of the landscape caused by volcanism and allows for a correct understanding and knowledge of its repercussions.
Iriarte, E., et al. Younger volcanic eruptions from the Iberian Holocene and paleoenvironmental evolution of a barrier paleolake in the Campo Volcanico de Garrotxa (NE Spain). Holocene (2023)
Revelles, J., et al. Socio-ecological impact of monogenetic volcanism in the La Garrotxa Volcanic Field (NE Iberia). Scientific Reports (2023)