The Evolution of a Ghost Island (Kumani Bank/Island) in the Southwestern Caspian Sea

The paper presents results of satellite monitoring of the evolution of a ghost island (Kumani Bank/Island) located in the southwestern part of the Caspian Sea. The monitoring was carried out from 1993 to 2025 and was based on data from multispectral sensors of the optical range—the MSI (Multispectral Instrument) of the Sentinel-2A and -2B satellites and scanning radiometers TM (Thematic Mapper) of the Landsat-5 satellite, ETM+ (Enhanced Thematic Mapper Plus) of the Landsat-7 satellite, OLI (Operational Land Imager) and OLI-2 of Landsat-8 and -9—as well as data from the C-SAR synthetic aperture radar of the Sentinel-1A and -1B satellites. We used satellite data with a high spatial resolution of 10–30 m which allowed us to detect the time of appearance and disappearance of the island on the sea surface, as well as reveal its exact dimensions. Since 1861, the island has periodically appeared as a result of mud volcano activity, existed for several months and then disappeared, washed away by currents. Using satellite data, we considered the main stages of changes in underwater mud volcanism in the Kumani Bank area over more than 30 years: relatively long periods of quiet gryphon activity and then a sporadic activation with a massive release of a gas–water–mud mixture—a paroxysmal phase of the eruption accompanied by the spread of clearly expressed tongue-shaped plumes from the bank/island. We found that there are no signs in the Kumani Bank area of seabed oil seepages, since no oil films are observed at the water surface in the sea area around it, unlike the water area lying to the south and characterized by a constant discharge of oil fluids at the bottom. In the paper, we discuss various mechanisms for the appearance and disappearance of the island on the sea surface, including changes in the level of the Caspian Sea.