Rishiri Island, located in the northern end of Japanese Islands, is an independent volcanic island and famous for the submarine groundwater discharges. From a viewpoint of hydrology, the island is quite asymmetry. Many surface water (springs, rivers and lakes) exists on the eastern side of the island, whereas little surface water on its western side. This difference is thought to be caused by the geologic asymmetry of the basement rocks.
Major elements in the samples of precipitation, surface water, groundwater and submarine spring water were analyzed to make clear the groundwater flow system of the island. Sea water transported by wind was mixed with the rain water. The inland water was blended with the rain water and the dissolved ions from the rocks. The surface water was strongly affected by the salty rain water and sea salt particles directly transported by wind. Submarine spring water is considered to be composed of almost fresh-and-pure groundwater.
