A HIGH-RESOLUTION TSUNAMI SQUARES SIMULATION OF THE 2022 HUNGA-TONGA HUNGA-HA'APAI TSUNAMI

On Jan. 15^th, 2022, the Hunga Tonga-Hunga Ha'apai (HTHH) submarine volcano erupted, triggering shockwaves and meteotsunami noticed as far away as the Caribbean. HTHH contends for the fiercest volcanic explosion in more than a century. Tsunami spawned by the eruption caused catastrophic local destruction. We present a Tonga-wide simulation of these waves using the Tsunami Squares method.

Field surveys show that all houses on Mango Isl. were raised, with similar near-complete devastation on Nomuka, and the western coast of the main island of Tongatapu. “Earwitness” accounts report at least five loud artillery-like blasts. Smaller Blasts 1 and 2 echoed shortly before 4:00 UTC, followed by increasingly strong Blast 3 at 4:06 UTC, Blast 4 at 4:18 UTC, and Blast 5 at 4:33 UTC. Blasts 4 and 5 broke windows in downtown Nuku‘alofa, 65 km south of HTHH and knocked over people on the coasts of Tongtapu and Ha’apai. Accepting that overpressure >0.15 PSI breaks window glass, we propose that the explosive yields from Blasts 4 and 5 were at least 10 megatons, but foreseeably >20 MT.

Our TS simulation is based on a model deduced from atomic tests and is calibrated by the Nuku’alofa tide gauge, pre/post eruption satellite imagery and field run-up surveys. The gauge provides the most definitive record of blast timings, but its ~1 m reported wave height is underestimated due to the gauge’s sheltered location within a harbor. We assembled Maxar and Planet imagery 3 months prior to and 2 weeks after the eruption. We estimated wave run-up heights from the time-separated imagery around all the Tongan islands. Elevations of areas stripped of vegetation were defined as minimum wave run-up heights. This provides extensive coverage, although topography is uncertain. Thirdly, tsunami field runup surveys were collected using differentially corrected GPS equipment with flow-height markers measured at 63 sites on Tongatapu and 17 sites in Ha’apai islands.

Simulations from just Blasts 3 (1/4 MT) and 4 (10 MT) toss waves >20 m onto Tongatapu and 2-15 m onto the Ha’apai and Vava’u island groups. Simulated wave heights agree well with run-ups extracted from satellite and field data. Our results emphasize complex wave-topography interplay across the Tongan archipelago. “Wave Wrap-Around”, “Wave Capture”, and “Wave Breaking” are clearly documented in our simulation.