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Tsunamis generated by eruptive column collapse: an experimental approach

Céline Vaerewyck1, Raphaël Paris1, Olivier Roche1

Abstract

During shallow underwater or island volcanic explosive eruptions, rising plumes composed of gas and suspended magma fragments can reach altitudes up to 40--50 km (e.g., Krakatau 1883, Hunga Tonga--Hunga Ha'apai 2022). When the eruptive column collapses, the granular material falling into the water at high velocity becomes a potential tsunami source. To investigate this poorly-documented mechanism of tsunami generation, we conducted laboratory experiments by releasing monodisperse glass beads (66±10 µm in diameter) vertically from a hopper into a 7 m-long water-filled channel. We tested a range of water depths of 20-25 cm and fall heights of 65-115 cm, using particle mass of 2-35 kg. We recorded wave dynamics using shadowgraphy with LED panels and two high-speed cameras (250 fps), and quantified through image analysis the leading wave amplitude (up to 5 cm), speed (1.3 - 1.6 m/s), and wavelength (1.5 - 4.5 m). We also identified three successive wave types: rim waves, collapse waves, and uplift waves. Our results show that initial wave speed and amplitude at 1.4 m from the impact zone increase with particle mass, flow rate, and volume fraction, and reach a maximum value determined by the limited water depth before it decreases. The wave behavior corresponds to an intermediate-depth regime, differing from the shallow water assumption. Our results demonstrate that eruptive column collapse into water can generate tsunamis. This issue needs to be further investigated in the context of volcanic hazards.