Reconstructing an eroded scoria cone : the Miocene Soonica Hill volcano (Lower Silesia, SW Poland)

The basaltic rocks of Sośnica Hill near Targowica (Fore-Sudetic Block) belong to the Cenozoic Central European Volcanic Province. The volcanic succession at Sośnica is over 40 m thick and comprises pyroclastic fall deposits (mainly tuff breccias), subvolcanic intrusions (plug, dykes and other intrusive sheets) and aa-type lavas. Field relationships and structural data enable a detailed reconstruction of the vent location, morphology and eruptive history of the original volcano. Initial Hawaiian to Strombolian-type explosive eruptions produced a pyroclastic cone. Subsequently subvolcanic intrusions and lavas were emplaced. The lavas were fed from the central vent of the volcano, breached the cone and flowed southwards. Later eruptions resumed at a new vent on the western slopes of themain cone. The final volcanic edifice-a breached Strombolian scoria cone with a lava flow and a parasitic cone-was 500-1000 m in diameter at the base and 90-180mhigh. The preserved SWsector of this volcano, where the pyroclastic deposits were protected from erosion by the surrounding plugs and lavas, corresponds to ca. 1/2 of the height and 1/8 of the volume of the original volcano. Compared with many other remnants of Cenozoic volcanic centres in Lower Silesia, this volcano is exceptionally well preserved and exposed.