Transformation of an Underwater Bank into the Kumani Island in the Southwestern Part of the Caspian Sea

The article presents the results of satellite monitoring of the evolution of the Kumani Bank/Island located in the southwestern part of the Caspian Sea from 1993 to 2025. The monitoring was carried out based on data from multispectral sensors of the optical range - MSI (Multispectral Instrument) of the Sentinel-2A, -2B satellites, scanning radiometers TM (Thematic Mapper) of the Landsat 5 satellite, ETM+ (Enhanced Thematic Mapper) of the Landsat 7 satellite, OLI and OLI-2 (Operational Land Imager) of the Landsat 8, 9, as well as data from the synthetic aperture radar (SAR) C-SAR of the Sentinel-1A, -1B satellites. The satellite data used have a high spatial resolution of 10–30 m, which made it possible to establish the time of appearance and disappearance of the island from the sea surface, as well as its exact dimensions. Since 1861, the island has periodically appeared due to mud volcano activity. It has existed for several months and disappeared, as a result of denudation by currents. The main stages of changes in underwater mud volcanism in the Kumani Bank area over more than thirty years are considered using satellite data. Relatively long periods of quiet gryphon activity and 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 on the water surface. It was found that in the Kumani Bank area, there are no signs of oil seepage onto the bottom surface since no oil film is observed on the water surface in the sea area around it, unlike the water area lying to the south, which is characterised by a constant discharge of oil fluids on the bottom. Various mechanisms for the appearance and disappearance of an island on the sea surface are discussed, including changes in the level of the Caspian Sea.