
Though its underwater origin muted some of the fireworks, the 15 January 2022 eruption of the Hunga Tonga–Hunga Ha‘apai volcano near the island of Tonga in the South Pacific Ocean was one of the most powerful eruptions in recent history. Seismic, infrasound, and satellite imaging data suggest that the volcano released more than the 10 EJ that Mount Pinatubo did in 1991 and that it produced the tallest eruption plume, reaching some 55 km, in the satellite era. Now Corwin Wright of the University of Bath in the UK and an international team have demonstrated that the atmospheric effects of the eruption were just as impressive.
The researchers compiled data from several satellites and ground-based stations to track the eruption’s influence from surface to space. The observations reveal that as the visible plume raced upward immediately following the eruption, scores of powerful atmospheric waves also spread in all directions. Lamb waves, which propagate along Earth’s surface, reached speeds of about 320 m/s, comparable to those of the waves generated by the infamous Krakatoa eruption of 1883. Satellite imaging (one example in the animation below) captures those initial waves circling the globe at least three times and getting distorted by geographic features, such as the Andes mountain range.

Farther aloft, gravity waves (not to be confused with gravitational waves) were triggered by the resistance of gravity and buoyancy to the air pushed vertically during the eruption (see the article by Erdal Yiğit and Alexander Medvedev, Physics Today, June 2019, page 40). Satellite data revealed the waves moving throughout the troposphere and stratosphere at nearly their theoretical maximum speeds based on wavelength. To explore even higher altitudes, the researchers analyzed the time delays in navigation satellite signals to track the propagation of waves speeding at up to 667 m/s in the highly charged ionosphere.
Although the sheer energy of the eruption was instrumental in the ensuing atmospheric maelstrom, Wright and colleagues also highlight the volcano’s surroundings. The eruption occurred in a relatively shallow underwater basin, which means that the seawater did little to blunt the blast, the researchers say. Instead, the water was “flash-boiled” and, as part of the visible plume, “propelled into the stratosphere,” where it released an enormous amount of latent heat upon condensing. That explains the detection of both the initial atmospheric waves and a constant stream of lower-amplitude waves that continued to propagate from above the volcano’s location for hours, fueled presumably by the continued condensation of seawater in the plume.
Overall, the Hunga Tonga eruption disrupted the global atmosphere like no other event, natural or human induced, in recent history. By studying that unprecedented shock to the system, researchers hope to better understand the subtler disturbances that regularly course through the atmosphere. (C. J. Wright et al., Nature, in press, doi:10.1038/s41586-022-05012-5.)