Tidal surge

The Japan Meteorological Agency released a report of an expert panel on the surge mechanism on Thursday.

It cites barometric waves, or changes in atmospheric pressure due to the eruption shock, as a main cause. But it says further studies are also needed on other factors that may have pushed up sea levels.

After the eruption in the South Pacific, tidal surges of a few centimeters to more than 1 meter were observed across Japan and damaged ships and fish-farming facilities.

The Japan Meteorological Agency’s study group said in a draft report compiled 15 March that the tidal surges differed from those generated by a strong offshore earthquake.

It noted that disturbances in the atmosphere were detected after the eruption of the Hunga Tonga-Hunga Ha’apai volcano around 1 pm. on 15 January.

The resulting air pressure waves reached near the Honshu main island, about 8,000 kilometers from the volcano, around 8:40 p.m., according to an analysis of images captured by Japan’s Himawari weather satellite.