Pumice cloud drifting north along Japan’s coastline

Pumice, spewed into the ocean from a distant underwater volcano has clogged the cooling water intakes of ships and killed farmed fish around the Japanese island of Okinawa. The drifting stones earlier reached southern Kyushu, and have now been spotted farther north, off Shikoku.

On 1 November, Japan's Coast Guard announced its planes had spotted pumice stones at two locations near Shikoku Island’s Kochi Prefecture: 146 kilometers off Cape Ashizuri on 30 October in the west of the prefecture, and 207 kilometers off Cape Muroto in the east on 31 October. They also reported that the rafts of stones were observed at locations all around Okinawa Island and in the sea along the Ryukyu chain to the southeast of Okinawa on 31 October, and drifting near the Maejima Islands on 2 November.

The stones are from an August eruption of the Fukutoku-Okanoba undersea volcano near South Iwo Jima, in Japan’s Ogasawara Island chain in the Pacific Ocean. They have drifted toward Japan and have now entered the Kuroshio Current, which runs all the way up Japan’s west coast to Hokkaido.

The stones have affected 11 ports on Okinawa and 19 in Kagoshima Prefecture, keeping about 750 fishing boats in port. Forty fishing boats have been damaged, some with disabled engines. Ferry services have been temporarily disrupted. Indian mackerel being farmed off Okinawa mistook the stones for feed, consumed them, and died.

Floating booms, such as those used for oil-spill cleanup, have been used to prevent more pumice from entering ports. At a port in the village of Kunigami on Okinawa Island, a power shovel is removing about 10 metric tons of pumice a day, but where to ultimately put the accumulated stones is yet undecided.

The Coast Guard has advised vessels to detour around the floating rafts, though this may not always be possible, as the stones are floating in areas measuring dozens of square kilometers. The Coast Guard has also advised vessel-owners check the strainer of seawater cooling systems on vessels regularly for early detection of clogging. One of the Coast Guard’s own patrol vessels was stranded at sea when the seawater strainer, used for filtering debris from seawater used for cooling the engine, filled with small pumice stones. It was towed to port in Okinawa by another patrol vessel.

Photo courtesy of WikiMedia Commons