A change in sea color Tuesday suggests submarine volcanic activity has begun about 1 km off the west coast of Miyake Island, and 2,000 residents have already evacuated to shelters on its north side.
"Volcanic activity on Mount Oyama appears to have subsided, as we believe magma activity has moved underground from the island's volcano to the ocean floor west of the island," said an official of the Coordinating Committee for the Prediction of Volcanic Eruptions, which advises the Meteorological Agency.
However, a magma eruption in shallow waters may lead to a large-scale explosion involving bursts of steam, the official warned, adding that a 40-meter-wide area of ocean west of the island has turned yellowish brown.