Stone Forest (Pobiti Kamani)

West of Varna in Bulgaria, natural stone columns, the tallest 6 to 10 meters high, rise from the sand in groups along a belt more than 8 kilometers long. The Russian officer Viktor Teplyakov took them for ruins in the 1820s, but they are the hardened sands of a sea floor about 50 million years old. How the sand turned to stone is still open: De Boever and colleagues trace the columns to methane seeping up through it, Nachev and colleagues to small mounds built by microbes and algae.