インド東海岸におけるラグーンの地形とその発達

抄録・要旨

The few available remote sensing studies on the lagoons along the east coast of India have indicated significant geomorphic features in and around these coastal wetland ecosystems. Lake Chilka, the largest coastal lagoon in India, exhibits rocky erosional features such as headlands, sea cliffs, sea stacks, etc., along its landward margin, suggesting it to be an open coast Probably during the late Pleistocene. The 8 km wide beach ridge/barrier spit belt that separates Lake Chilka from the open sea appears to have formed after the Holocene transgression. Lake Kolleru which is sandwiched between the Krishna and Godavari deltas, though being much inland and fresh water lake at Present, was in fact a coastal lagoon, presumably formed along the coast during the Holocene transgression. Lake Pulicat, the second largest lagoon, on the other hand, appears to have formed very recently, apparently after the development of the third strandline along the east coast whose age is surmised as 1,500 years B.P. The existence of a number of islands in these lagoons which appear to be the detached portions of the earlier formed beach ridges including those of the third strandline series (the youngest) suggests either the subsidence due to tectonic activity, or sediment compaction, or a slight sea level rise in the recent Past. Detailed morpho-stratigraphic studies are necessary for a proper understanding of the evolution of the lagoons along the east coast of India.