La Garrotxa: Researchers Pinpoint Youngest Volcanic Area In Spain

Brett Smith for – Your Universe Online

Although volcanic scientists are able to approximate the age of lava flows, determining the exact timing of each of a volcano´s eruptions has proved difficult in the past.

A joint research team from the Universitat Autònoma de Barcelona, University of Girona, the Catalan Institute of Human Paleoecology and Social Evolution (IPHES) and other organizations has looked to establish a chronology of eruptions in the volcanic region of La Garrotxa, which contains forty volcanic cones and twenty lava flows. It is considered to be the best conserved volcanic region in the Iberian Peninsula.

In an article in the journal Acta Geologica, the team published the first results of their research surrounding Croscat Volcano, one of the more recently active formations. This volcano is the highest and youngest volcano in the entire Iberian Peninsula, reaching a height of 620 ft. A study published in a 2011 edition of the Journal of Volcanology and Geothermal Research revealed that the Santa Margarida Volcano and the Croscat were the product of the same eruption event and likely shared the same magma flow.

Using radioactive carbon dating methods, the team attempted to analyze organic matter that was on the soil surface just prior to the time of the eruption. They also looked to determine the environmental conditions at the time of eruption.

“The general idea is based on the hypothesis that if scientists could date the palaeosoil found right below the lava clay ejected by the volcano, they would have the dating of the moment before the eruption,” said Maria Sana, a researcher at the UAB Department of Prehistory.

To collect these samples, scientists drilled the clay layer in the area of Pla del Torn, located a few meters to the northeast of the volcanic cone. The two samples that were tested, between 39 and 49 feet deep, were located at the base of the clay layer and the top of the palaeosoil.

Samples from the surface of this pre-eruption level were then analyzed for pollen content, a technique used to get a glimpse of the vegetation of the area at the time prior to the eruption of Croscat. The samples were also dated using 14C techniques on the organic material found within the samples.

Using soil analysis methods developed by IPHES, the report revealed that based on the presence of Mediterranean grasses, particularly asteraceae and artemis, the landscape of the Garrotxa was wide open at the time of eruption, with well-defined meadows or steppes.

Evidence of oaks indicated a temperate environment, a sign of temperate climates that followed the Last Ice Age. Additionally, the presence of riverside trees (elm, alder and willow) and aquatic plants (bulrush, cattails, alisma) points to an increase in rainfall throughout the region.

The carbon dating has shown that the age of the top of the palaeosoil is approximately between 13,270 and 13,040 years ago, giving a date range for the volcano´s last eruption. During this time, the inhabitants of the peninsula were beginning to leave the sanctuaries of caves as they continued their hunter-gatherer lifestyle.

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