TEMPORAL VARIATIONS OF ATMOSPHERIC PRESSURE AND WATER LEVEL DUE TO MAJOR EXPLOSIVE ERUPTION FROM HUNGA TONGA-HUNGA HA'APAI IN TONGA AT BAY MOUTH OF TANABE BAY

Abstract

 A major explosive eruption from Hunga Tonga-Hunga Ha'apai in Tonga occurred on January 15, 2022. This eruption caused tsunami, and many tsunamis were reported along the Pacific rim including the coast of Japan. This paper shows the outline of the observed results on atmospheric pressure and water level at the bay mouth of Tanabe bay, Wakayama, Japan, and the comparative findings on the characteristics of water level fluctuation measured under different conditions.

 In the observed results at the offshore observation tower at the bay mouth of Tanabe bay, atmospheric pressure fluctuation of about 2hPa was measured after around 7 hours of the eruption, and a 0.35m tsunami was measured between 0:00 a.m. and 1:00 a.m. on January 16. Water level data measured at the bay mouth of Tanabe bay contains several components with different frequencies. The dominant component is the natural period of Tanabe bay and its period is around 40 minutes. Additionally, fluctuation components from 10 to 20 minutes are included during the peak of water level variation. The fluctuation components from 10 to 20 minutes are also observed in water level data measured by offshore buoy after the eruption in Tonga. On the other hand, the fluctuation components from 10 to 20 minutes are not found in water level data of tsunami due to distant earthquake in 2015. This result means that water level fluctuation components from 10 to 20 minutes is a characteristic component of tsunami excited by atmospheric pressure variation due to the eruption in Tonga 2022.