The continued rising mode, since about 1978, in the level of the Caspian Sea cannot be ascribed to a change in the hydrologic balance that is governed solely by runoff, precipitation, and evaporation. Such a change fails to explain some of the chemical links (K/Cl, Rb/Cl, Ca/Cl, Sr/Cl, and K/Rb) between Kara Bogaz and Caspian Sea waters. A more realistic model must include a tectono-hydrodynamic factor that allows for subsurface addition of saline water to Caspian Sea and Kara Bogaz waters. The subsurface water component could be akin to the coastal thermal springs in the area, but must dissolve some evaporite deposits in the subsurface before addition to the waters of the inland sea. A budget calculation gives an estimate of 2% to 9% subterranean addition of saline water to the seawater. Such an addition could cause a rise in the level of the Caspian Sea from 63 to as much as 225 cm within the past 20 yr.

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