Meteorological and volcanic tsunami signals generated by the Hunga Tonga-hunga Ha’apai eruption

An eruption of the Hunga Tonga-hunga Ha’apai Volcanic Eruption on 15 January 2012 caused tsunami waves, observed globally in tide gage records. In this study we investigate the origin of tsunami waves through the analysis of tide gauge records and numerical simulations in the Indo-Pacific region. The atmospheric pressure wave (Lamb wave) due the eruption was recorded in meteorological stations across Australia. The moving pressure jump was recorded as a ~6.5-hPa jump at the Norfolk Island; ~3.5 hPa at Broken Hill, NSW and Perth and was estimated to be travelling at ~340 ms–1. In the deep ocean this allows for Proudman resonance between the ocean and atmosphere generating a meteotsunami propagating westward across the Indian Ocean. Tide gauges located across the whole Indian Ocean basin recorded the meteotsunami generated by the pressure jump. There were two distinct signal on the tide gauge records. The first signal was recorded in advance of the predicted volcanic tsunami along the east coast of Australia and was due to the meteotsunami. The arrival of the second signal corresponded to tsunami wave generated by the displacement of the volcano travelling as a ‘free’ wave. These findings were confirmed by numerical simulations using an ocean circulation model that incorporated a moving atmospheric pressure jump travelling at a speed of ~ 340 ms–1. The long ocean waves were amplified due to Proudman resonance in the deep ocean, where the water was deeper than 5000 m. The model predicted of the meteotsunami corresponded well with observations.