Rurinuma (Goshikinuma Pond Group)
Rurinuma (Lapis Lazuli Pond) is one of the Goshikinuma ponds, a colorful cluster of around 30 shallow ponds and marshes formed when Mt. Bandai erupted in 1888 and triggered a landslide that blocked a nearby river.
Rurinuma is a blue, green, and milky white pond. Experts believe this unusual color may come from the high levels of calcium and sulphate ions in the water. Drepanocladus fluitans moss growing in a rare mat formation on the pond floor may also affect the color. Like Bentennuma and Aonuma, this pond is fed by water from the highly acidic Copper Pond, a crater lake located high on the northern slope of Mt. Bandai. As a result, there is little plankton growth or aquatic life.