Complex interaction between Strombolian and phreatomagmatic eruptions in the Quaternary monogenetic volcanism of the Catalan Volcanic Zone (NE of Spain)

The Catalan Volcanic Zone (CVZ), at the NE of the Iberian peninsula, is one of the Quaternary alkaline volcanic provinces of the European rifts system. The CVZ has been active during the last 12 Ma. Despite the fact that this volcanism is significant in extension and volume, and that eruptions have also occurred in Holocene times, it is mostly unknown compared to the contemporaneous alkaline volcanism in other parts of Western and Central Europe. Volcanism younger than 0.5 Ma is mostly concentrated in an area of about 100 km ² located between the main cities of Olot and Girona. This basaltic volcanic field comprises more than 50 monogenetic cones including scoria cones, lava flows, tuff rings, and maars. Magmatic eruptions range from Hawaiian to violent Strombolian. Phreatomagmatism is also common and has contributed to the construction of more than a half of these volcanic edifices, frequently associated with the Strombolian activity but also independently, giving rise to a large variety of eruptive sequences. We describe the main characteristics of this volcanism and analyse in particular the successions of deposits that form some of these volcanoes and discuss the potential causes of such a wide diversity of eruptive sequences. We find that the main cause of such complex eruptive behaviour resides in the stratigraphic, structural and hydrogeological characteristics of the substrate above which the volcanoes were emplaced, rather than on the compositional characteristics of the erupting magma, as they do not show significant variations among the different volcanoes studied.