When gases in the underground force their way out, an interesting phenomena appears. In their way, gases mix water and soil to form mud and create little eruptions. In time, craters are formed, sometime with a classic shape of a dwarf volcano. In other cases the craters are just some pits of mud. The soil around is not fertile and gets the unusual aspect of a Lunar or Martian surface. The crude found in small quantities can also give a gray-blue color.
The Romanian mud volcanoes from Berca (Buzau) are accessible by car from the national road that ties Buzau to Nehoiu. As opposed to the dry area of the reservation, the area around is a beautiful green area with hills and winding road.
Similar phenomena exist in the world in Island (Hverir), United States (Yellowstone National Park, Wyoming and Lassen, California), Costa Rica, (Rincon), New Zealand (Waiotapu), Azerbaijan (Baku).