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Rishiri Rebun Sarobetsu NP, Hokkaido
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Minamihama Wetland fills a volcanic maar—a broad explosion crater. Its surrounding crater wall rises only about 10–15 m, and Menuushoro Pond at the wetland’s southern edge averages about 80 cm deep.
Minamihama lies just about 5 m above sea level, yet it is a Sphagnum-rich high moor—one of Japan’s northernmost. “High” describes the raised, rain-fed bog, not its altitude.
Peat cores show the wetland’s history reaches back about 5,500 years. Sphagnum bog formed in its center around 4,100 years ago, and Sakhalin spruce began spreading into the wetland about 1,340 years ago, possibly as the surface dried.
Spring brings bogbean flowers; summer brings irises. Look closer among the Sphagnum, too: sundews grow here, adding a carnivorous plant to this small wetland’s unusual cast.
Minamihama has been a Rishirifuji Town Natural Monument since 1979. The designation recognizes its characteristic wetland plant communities, including cotton grass and other bog plants.
