The Sawasaki community, located at the westernmost tip of Sado Island, harvests a kind of seaweed called Iwanori on the coast from December to March. In 1802, a large earthquake off the shore of Ogi uplifted the coast from the seabed by about 1 m, creating a wide, flat, and uplifted wave-cut platform. The flat terrain created by the earthquake is ideal for collecting seaweed, and the wave-cut platform developed along the coast created the perfect environment for fields of seaweed to grow. The official name for iwanori is “Uppuruinori”. It is called Iwanori (lit. “rock nori”) because it thrives on the coastal rocks.

Iwanori collected from rocky areas and seaweed fields has a stronger aroma and flavor than ordinary cultivated seaweed, with a chewy texture. Most of the seaweed is shipped as dried products, but it is also sold in stores from January to March on Sado Island.