The major eruption that occurred on 15 January 2022 on Hunga Tonga Hunga Ha’apai (HTHH) in Tonga generated powerful acoustic waves that propagated through the atmosphere all over the world. Although the eruption energy was soon estimated from the acoustic waves and the ash cloud, its ranking on the Volcanic Explosivity Index (VEI) is still debated. Here, we show the erupted magma volume can be calculated from the significant resonance of the remote seismoacoustic waves recorded in Taiwan. A resonant frequency (f) of ∼0.0117 Hz persisted for >25 min was clearly recorded by both a dense broadband seismic array and also several infrasonic stations in Taiwan. If the volcanic cavity produced by the erupting magma is considered a classic Helmholtz resonator, then the f constrains the possible volume of the erupted magma to 0.215±0.015  km3⁠. We may conclude that the major eruption on HTHH rated a 4 on the VEI scale. In addition to neutralization between low content of the sulfur dioxide and a huge amount of water, it is potentially too small to cause any significant climate change in 2022.

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