Note: Single-source report; awaiting corroboration.
Azerbaijan is home to at least 220 mud volcanoes, with some estimates reaching about 350, making it one of the densest concentrations on Earth. These features are common in sedimentary basins where hydrocarbons like oil and methane become trapped beneath sedimentary rocks under high pressure, causing eruptions of cold slurries instead of molten lava.
Many mud volcanoes cluster near Baku and Qobustan on the Absheron Peninsula. Here, geological structures provide pathways for methane-rich mud to surface, forming conical structures ranging from 20 to 400 meters tall and 100 to 4,500 meters wide.
Along Azerbaijan's Caspian Sea coast, including underwater, there are at least 140 mud volcanoes. Some islands in the Baku archipelago have formed through volcanic activity. Xərə Zirə Adası, known for eruptions in 1961 and 1995, still has two active vents. Duvannı Island erupted in 2006 and remains active.
These islands often display tadpole shapes, with sediment 'tails' created by erosion and redeposition from currents and wave action. The tails likely form on islands' lee sides, where erosive forces are weakest. Other tadpole-shaped islands with similar features are found further south, including Səngi Muğan Adası, noted for violent eruptions.