Phreatomagmatic volcanism in complex hydrogeological environments: La Crosa de Sant Dalmai maar (Catalan Volcanic Zone, NE Spain)

The volcano of La Crosa de Sant Dalmai is a roughly circular asymmetrical maar that forms part of the Catalan Volcanic Zone(Girona Province, NE Spain). The edifi ce is an example of a maar-diatreme volcano constructed on a mixed basement of hard Paleozoic granites and schists and soft Pliocene and Quaternary deposits. The heterogeneities and differences in these rocks' hy draulic properties and fracturing patterns infl uencedthe way in which the magma-water interaction took place during the eruption and, consequently, the style of the eruption and the resulting deposits. The eruption of La Crosa de Sant Dalmai consisted of four consecutive eruptive phases characterized by alternating phreatomagmatic and magmatic fragmentation. The eruptive sequence and the variety of deposits-mainly fallout with subordinate surges-generated by this singleeruption are a stark contrast to the compositional monotony of the magma, which thus highlights the role played by the geological and hydrological characteristics of the substrate in determining the eruptive style and associated hazards in this type of volcanism. © 2014 Geological Society of America.This study was partially funded by the grant CROSAND and the European Commission (FT7 Theme: ENV.2011.1.3.3-1; grant 282759:“VUELCO”).Peer Reviewe