Wikipedia picture of the day on September 14, 2017: The Berca Mud Volcanoes are a geological and botanical reservation located close to Berca in Buzău County, Romania. The phenomenon is caused due to gases that erupt from 3,000 metres (9,800 ft) deep towards the surface, through the underground layers of clay and water, they push up underground salty water and mud, so that they overflow through the mouths of the volcanoes, while the gas emerges as bubbles. When the mud arrives at the surface, it dries off, changing the landscape in ways like you can see here.