Hunga-Tonga Games: Unravelling the Timing and Size of the Biggest
Volcanic Explosion in 30 Years
Abstract
We attempt to construct a timeline of The Hunga Tonga – Hunga Ha’apai
eruption on 15 January 2022 through analyses of seismic, barometric,
infrasonic, lightning, and satellite data. Satellite imagery at 04:00
UTC showed no ash in the air, but by 04:10 UTC, a plume had risen to 18
km. Over the next 20 minutes, the plume rose to 58 km. USGS determined
that Mw5.8 volcanic earthquake of unknown mechanism had occurred at
04:14:45. Gravity waves were observed in satellite imagery, and
barometric and infrasound stations around the world recorded ultra-low
frequency pressure variations of more than 100 Pa, inducing
ground-coupled airwaves around the globe, and meteo-tsunamis in the
Caribbean Sea and Mediterranean Sea. Tsunami waves were recorded in
coastal areas around the Pacific Ocean. From record sections, we
determined speeds of 3.9 km/s and 299 m/s for the initial seismic and
infrasound signals respectively, converging to an eruption onset time of
~0402 UTC ± 1 minute. The global pressure pulse has a
speed of ~314 ± 3 m/s, consistent with theoretical
models for Lamb waves (Bretherton, 1969), suggesting an origin time of
~0415 ± 2 minutes (consistent with the Mw5.8 volcanic
earthquake, and sharp increases in lightning flash rates), and peaking
around ~0429 ± 2 minutes. We suggest that Surtseyan
volcanic activity commenced at ~04:02, building to a
sub-Plinian eruption ~7 minutes later, before a
phreato-Plinian eruption commenced at ~04:14. The peak
Lamb wave amplitude at the closest station (757 km from HTHH) was 780
Pa. Assuming geometrical spreading like 1/√r (where r is the
source-receiver distance), we estimate a lower bound of
~23 kPa for reduced pressure by extrapolation back to 1
km. Adding a near field term that decays like 1/r, we estimate an upper
bound of 170 kPa for reduced pressure. Comparison of these values with
those from other eruptions (McNutt et al. in this session) suggests the
15 January HTHH eruption was in the VEI 5-6 range.