What causes the fast ash removal after the 2022 Hunga eruption?

Water vapor and sea salt emission as well as aerosol dynamics accelerate particle growth & removal in the 2022 Hunga plume

The record-breaking eruption of the Hunga submarine volcano in January 2022 injected an unprecedented 150 Tg of water vapor into the stratosphere (Millan et al., 2022), with plume heights reaching up to 58 km (Carr et al., 2022). This led to an exceptional hydration of the stratosphere (~ 10% increase in stratospheric water vapor budget), also accelerating SO2 oxidation to H2SO4 and sulfate aerosol formation (Zhu et al., 2022). Another intriguing aspect of this eruption was the unexpectedly rapid removal of volcanic ash: despite the eruption's magnitude, only small amounts of fine ash were detected and have been removed within one to two days (Legras et al., 2022). The mechanisms behind this fast ash removal remain unclear.

In order to address these diverse, yet interconnected complexities, researchers at IMKTRO, KIT perform numerical simulations with the ICOsahedral Nonhydrostatic model with Aerosols and Reactive Tracers (ICON-ART). They investigate the interplay of injected water vapor and different species in ash aging, growth and subsequent removal via the following pathways (Figure 1):

Fig. 1: Aerosol processes in volcanic plumes
  1. accelerated oxidation of SO2 and sulfate formation followed by condensation/coagulation with ash 
  2. coagulation with sea salt and enhanced uptake of water owing to the highly hygroscopic nature of sea salt
  3. wet aggregation of particles during the plume rise
  4. activation of particles to large hydrometeors (cloud droplets, rain, ice, snow)

The first pathway is evaluated in the study by Bruckert et al. (in review). They showed that ash aging is stronger due to faster SO2 oxidation and sulfate production in the presence of injected water vapor (Figure 2). Additionally, by comparing observed and modeled SO2 and sulfate masses, they demonstrated that the actual SO2 emissions were approximately three times higher than the initial estimate of 0.4 Tg. Accounting for water vapor emissions and their role in atmospheric chemistry is essential to accurately reproduce the observed SO2 and sulfate masses. Although the model reproduces well the development of SO2 and sulfate aerosols, the emissions and growth by aerosol dynamics considered in this study alone cannot explain the rapid ash removal, as was seen in satellite images.

These results served as the foundation for an ongoing work which investigates the remaining three pathways. For this purpose, Chopra et al. (in prep.) performed experiments with ICON-ART, where they emitted sea salt along with ash, SO2 and water vapor. Preliminary results show an even stronger aging of ash in presence of water vapor and sea salt than in Bruckert et al. (in review), hence, an enhanced growth of particles. This also emphasizes the importance of including sea salts emission along with ash and SO2 in modelling studies and the subsequent effects on aerosol dynamical processes.

Fig. 2: SO2 mass (a), sulfate mass (b), and ash mass (solid lines and left axis, c) and fraction of aged aerosols (dashed lines and right axis, c) for an experiment with (black lines) and without (orange lines) water vapor consideration in chemistry in the first week following the eruption.

 

Authors: Simran Chopra and Julia Bruckert

Workinggroup: Aerosol and Reactive Tracer Modelling

References:

Bruckert, J., Chopra, S., Siddans, R., Wedler, C., and Hoshyaripour, G. A.: Aerosol dynamic processes in the Hunga plume in January 2022: Does water vapor accelerate aerosol aging?, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2024-4062, 2025.

Carr, J. L., Horváth, Á., Wu, D. L., & Friberg, M. D. (2022). Stereo plume height and motion retrievals for the record-setting Hunga Tonga-Hunga Ha'apai eruption of 15 January 2022. Geophysical Research Letters, 49, e2022GL098131. https://doi.org/10.1029/2022GL098131

Legras, B., Duchamp, C., Sellitto, P., Podglajen, A., Carboni, E., Siddans, R., Grooß, J.-U., Khaykin, S., and Ploeger, F.: The evolution and dynamics of the Hunga Tonga–Hunga Ha'apai sulfate aerosol plume in the stratosphere, Atmos. Chem. Phys., 22, 14957–14970, https://doi.org/10.5194/acp-22-14957-2022, 2022

Millán, L., Santee, M. L., Lambert, A., Livesey, N. J., Werner, F., Schwartz, M. J., et al. (2022). The Hunga Tonga-Hunga Ha'apai Hydration of the Stratosphere. Geophysical Research Letters, 49, e2022GL099381. https://doi.org/10.1029/2022GL099381

Proud, S. R., Prata, A. T., and Schmauß, S. (2022). The January 2022 eruption of Hunga Tonga-Hunga Ha’apai volcano reached the mesosphere. Science, 378(6619):554–557.

Zhu, Y., Bardeen, C.G., Tilmes, S. et al. Perturbations in stratospheric aerosol evolution due to the water-rich plume of the 2022 Hunga-Tonga eruption. Commun Earth Environ 3, 248 (2022). https://doi.org/10.1038/s43247-022-00580-w