Lower Silesia; Tertiary; basalts; chemical composition; serpentinization; iddingsitization; uralitization; carbonatization

The karst of northern Lithuania is developed in gypsiferous layers of the Pasvalys and Nemunelis beds of the Tatula Formation of the Upper Devonian (Frasnian) stage. The new sinkholes formed during the last ten years in around Birzai and Pasvalys indicate recent karst activity. 84 recent sinkholes appeared around the villages of Karajimiskis, Mantagailiskis in the Birzai district from 1995 to 1999. The three biggest sinkholes occur in Pasvalys. Karst processes and phenomena are particularly dangerous in urban areas. The sudden appearance of sinkholes and ground subsidence have often caused building damage. New sinkholes indicate a very sensitive engineering geological environment.