This geosite is open for the public.
Básti diatrema (diatrema): On the western edge of the village of Óbást, in the wall of the field road, is the excavation of the remains of a maar-type volcanic horn (diatreme). Given the location of the lava blanket of nearby Pogányvár, the currently excavated diatreme is approx. It was 300 meters below the surface. In the lower part of the excavation there is a megabrica with large blocks of sandstone and rhyodacite tuff. The blocks reach a diameter of 5 m. Presumably, they were caused by the collapse of the wall of the diarrhea (Konečný et al. 2004). Upwards, there are lapillary tuffs with decayed blocks, fine-grained tuffitic layers, followed by lapillary tuffs with basalt debris. Because basalt lava is absent, the age of the diarrhea cannot be determined radiometrically.