The 15 January 2022 climactic eruption of Hunga volcano, Tonga, produced an explosion in the atmosphere of a size that has not been documented in the modern geophysical record. The event generated a broad range of atmospheric waves observed globally by various ground-based and spaceborne instrumentation networks. Most prominent is the surface-guided Lamb wave (
≲
0.01 Hz), which we observed propagating for four (+three antipodal) passages around the Earth over six days. Based on Lamb wave amplitudes, the climactic Hunga explosion was comparable in size to that of the 1883 Krakatau eruption. The Hunga eruption produced remarkable globally-detected infrasound (0.01–20 Hz), long-range (~10,000 km) audible sound, and ionospheric perturbations. Seismometers worldwide recorded pure seismic and air-to-ground coupled waves. Air-to-sea coupling likely contributed to fast-arriving tsunamis. We highlight exceptional observations of the atmospheric waves.
The lowermost section of a Vulcanian or Plinian volcanic eruption column may be thought of as a momentum‐driven, turbulent, free‐shear jet flow. We propose that large‐amplitude and long‐duration infrasonic (<20 Hz) signals recorded at ranges of tens of kilometers during powerful eruptions at Mount St. Helens, USA, and Tungurahua, Ecuador, represent a low frequency form of jet noise. A preliminary test of this hypothesis is made by comparing the observed infrasonic spectra to the empirically‐derived similarity spectra for pure‐air jets. Although the spectral shapes are in approximate agreement, the observed volcanic signals have additional complexities not present in the pure‐air laboratory data. These features may result from multiphase flow containing solid particles and liquid droplets, very high temperatures, and perhaps complex crater morphology. However, the overall similarity between the volcanic signals and jet noise indicates that broadband infrasound measurements at volcanoes may provide a quantitative link to eruption jet dynamics, and would aid substantially in the remote assessment of volcanic hazard.
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