A series of eruptions from the Titan Ridge submarine volcano, beneath the Bismarck Sea in the southwest Pacific Ocean, has produced a large volume of pumice (a light volcanic rock, produced by the rapid cooling of gas rich lava from submarine eruptions, which can float on the sea), much of which has washed up onto the shores of Manus Island, the largest of the Admiralty Islands and a province of Papua New Guinea. This has caused serious problems for the local population, as it has formed a barrier between them and the sea, too dense to push a boat through, but too quicksand-like to walk across. This in turn has prevented them from harvesting fish and other seafood, the main staples of the island, as well as forcing them to become entirely dependent on the islands limited supply of freshwater for washing and hygiene, rather than bathing in the sea. The large accumulations of pumice are also likely to have smothered local coral reef ecosystems, harming longer-term fishing prospects in the region.
Pumice forms when hot lava from submarine volcanic eruptions encounters seawater and cools rapidly, simultaneously crystalising and degassing to form a lightweight volcanic rock with many gas filled vesicles (bubbles) within it, which often floats on the sea surface. Big submarine eruptions can produce large volumes of pumice, forming rafts of pumice that cover hundreds of square kilometres, and drift on the ocean surface for months before dissipating or washing ashore.
Titan Ridge, also known as the Central Bismarck Sea Volcano, is located about 125 km to the southeast of Manus, on the northern edge of the South Bismarck Plate. It is located on the boundary between the Willaumez Transform Fault and an unnamed section of area of seafloor spreading, where the South Bismarck and Pacific plates are being pulled apart, while at the same time the Pacific Plate is moving to the west and the South Bismarck Plate to the east. Here fresh material from the upper mantle is rising up through the fault and being erupted from the volcano as volcanic material, primarily pumice caused by the rapid cooling of a liquid melt containing dissolved gasses.
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