KARST IN BULGARIA
(by V. Popov, 2002)
23% of the territory of Bulgaria, with more than 6000 karst caves (Developed in carbonate rocks)
KARST IN EUROPE (in carbonate rocks)
(http://web.env.auckland.ac.nz/our_research/karst)
about 22% of the continent's territory
KARST IN THE WORLD (in carbonate rocks)
(Ford & Williams, 2007)
13.2% of the land on the continent (except Antarctica and Greenland)