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.

Acoustic waveform inversions can provide estimates of volume flow rate and erupted mass, enhancing the ability to estimate volcanic emissions. Previous studies have generally assumed a simple acoustic source (monopole); however, more complex and accurate source reconstructions are possible with a combination of equivalent sources (multipole). We deployed a high‐density acoustic network around Yasur volcano, Vanuatu, including acoustic sensors on a tethered aerostat that was moved every ∼15–60 min. Using this unique data set we invert for the acoustic multipole source mechanism using a grid search approach for 80 events to examine volume flow rates and dipole strengths. Our method utilizes finite‐difference time‐domain modeling to obtain the full 3‐D Green's functions that account for topography. Inversion results are compared using a monopole‐only, multipole (monopole and dipole), simulations that do not include topography, and those that use a subset of sensors. We find that the monopole source is a good approximation when topography is considered. However, initial compression amplitude is not fully captured by a monopole source so source directionality cannot be ruled out. The monopole solution is stable regardless of whether a monopole‐only or multipole inversion is performed. Inversions for the dipole components produce estimates consistent with observed source directionality, though these inversions are somewhat unstable given station configurations of typical deployments. Our results suggest that infrasound waveform inversion shows promise for realistic quantitative source estimates, but additional work is necessary to fully explore inversion stability, uncertainty, and robustness.

Abstract:The March 2016 eruption of Pavlof Volcano, Alaska produced ash plumes that canceled over 100 flights in North America. The eruption produced strong tremor recorded by seismic and remote low-frequency acoustic (infrasound) stations, including the EarthScope Transportable Array. The relationship between the tremor amplitudes and plume height changes considerably between the waxing and waning portions of the eruption. Similar hysteresis has been observed between seismic river noise and discharge during storms, suggesting flow and erosional processes in both rivers and volcanoes can produce irreversible structural changes detectable in geophysical data. We propose that the time-varying relationship at Pavlof arose from changes in the tremor source related to volcanic vent erosion. This relationship may improve estimates of volcanic emissions and characterization of eruption size and intensity. One Sentence Summary:The relationship between volcanic tremor and plume height changes during the waxing and waning portions of the eruption. Main Text:There are a number of well-documented challenges in monitoring volcanic eruptions and their associated hazards (e.g. 1, 2). Observatories typically rely on local seismic networks and satellites to make critical decisions about eruption size and intensity. However, seismic networks can be sparse and difficult to maintain, particularly at remote volcanoes like those in the Aleutian Islands. Satellites often have limited spatial and temporal resolution and may be inhibited by cloud cover. Other remote geophysical methods, such as infrasound (low frequency acoustic) arrays, can provide unique and detailed information on eruption processes (e.g. 3), but may also be part of a sparse network and have limited signal-to-noise ratio (SNR) and latency due to the propagation distance. It is therefore a priority to integrate multiple observations to assess the eruptive hazards during crisis response. However, we currently lack the ability to quantitatively link seismo-acoustic observations to the intensity of ash emissions.Seismic and infrasonic volcanic tremor is the continuous vibration of the ground and air, respectively, from a volcano. The origin of volcanic tremor is a subject of active research, with attempts to understand its relation to fluid transport in the solid earth and atmosphere (e.g. 3, 4). Volcanic tremor during a sustained eruption is termed eruption tremor. Models of seismic eruption tremor include a downward vertical force on the Earth in response to volcanic jet thrust (5), erosion of the volcanic conduit and vent (6), and chaotic wagging of a magma column (7). Infrasonic tremor during eruptions has been compared to the noise from high velocity, turbulent jet flows (8) and longer period oscillations are modeled as the result of the emplacement and oscillation of the plume (9).However, these models do not explain all features of eruption tremor, and do not currently provide accurate estimates of critical eruption source parameters, such as mass flux and plume h...