Volcanology - Review of Recent Eruptions

Discuss advances that have been made in understanding volcanic processes through studies of eruptions that took place over the past decade.

Fiona Fang, Trinity Hall, 1909 words

Over the past decade, densely instrumented eruptions have enabled volcanic processes to be analysed through time-resolved, multi-parameter observations across multiple spatial and temporal scales. These events have advanced understanding by placing stronger quantitative constraints on magma transport, degassing, structural failure, and plume–atmosphere coupling, while also clarifying the limits of eruption forecasting. This essay first examines open-vent basaltic systems, where exceptionally well-instrumented eruptions such as Kīlauea (2018) demonstrate system-scale coupling between magma transport and structural collapse, and where advances in geochemical and geophysical monitoring enhance interpretations while exposing the limits of signal-based forecasting (Sigmundsson et al., 2022). It then considers the triggers for explosive eruptions in inefficient degassing systems, with a particular focus on eruption transitions (La Soufrière, 2020–21) and water-driven phreatomagmatic processes (Taal, 2020 and Whakaari (White Island), 2019), where rapid changes in permeability and pressure reorganise eruptive behaviour on short timescales yet remain difficult to anticipate. Finally, it assesses advances in understanding eruption plumes, where advance in satellite observations reveal mechanisms such as radiative self-lofting and large-scale stratospheric hydration from recent eruptions of Raikoke (2019) and Hunga Tonga–Hunga Haʻapai (2022), linking volcanic activity directly to atmospheric circulation and radiative forcing. Together, these eruptions demonstrate that the major progress of the past decade lies in placing stronger quantitative constraints on coupled volcanic processes from conduit to surface to atmosphere.

Recent advances in understanding open-vent basaltic volcanoes stem from the ability to resolve system-scale dynamical coupling between magma transport, reservoir pressure, and structural failure, most clearly demonstrated by the 2018 eruption of Kīlauea. Kīlauea is a persistently active basaltic shield volcano on Hawaiʻi, characterised by an open-vent system and a long-lived summit–rift plumbing network that has historically supported sustained effusive eruptions. In 2018, this normally stable configuration was disrupted through a cascade of coupled magmatic and tectonic processes. Long-term pressurisation within the summit–rift plumbing was followed by collapse of the Puʻu ʻŌʻō vent on 30 April, which redirected magma laterally downdrift and initiated intrusion into the Lower East Rift Zone (LERZ, Neal et al 2019, Patrick et al 2020). Fissures opened on 3 May, establishing a highly efficient distal outlet that drained the summit reservoir, while the Mw 6.9 south-flank earthquake on 4 May further modified the regional stress fields (Neal et al 2019). As tracked by lava-lake level change and summit deformation, magma withdrawal, though small relative to total storage, triggered a rapid reservoir pressure drop by 17 MPa, driving the system from elastic subsidence into fault-bounded caldera collapse beginning on 16 May (Anderson et al 2019). Thereafter, sustained high-rate LERZ effusion (with lava rates >100 m³ s⁻¹, Neal et al 2019) drove summit reservoir depressurisation, which triggered episodic caldera collapse (Patrick et al 2020), with each collapse modulating the discharge in turn, demonstrating that open-vent basaltic systems can reorganise abruptly once plumbing connectivity and system state cross critical thresholds (Patrick et al., 2020). These advances in understanding volcanic processes as a coupled system are underpinned by long-term observatory science combined with dense, real-time, multi-parameter monitoring (e.g. GNSS, UAS, infrasound) (Neal, 2019).

Other recent eruptions further illustrate both the growing potential and the inherent limitations of modern monitoring in resolving open-vent eruption dynamics. For example, in the 2021 Tajogaite eruption at La Palma, Ubide et al. (2023) shows how advances in geochemical workflow can turn petrology into time-resolved monitoring of magma supply. They analyzed volcanic matrix from dated samples across the full 85-day eruption period, combining high-resolution trace elements with ⁸⁷Sr/⁸⁶Sr to fingerprint changes in melt composition. Their time series resolves discrete magma inputs: early products show a more radiogenic Sr signature (≈0.70313), followed by a mixing trend and then a split into less radiogenic compositions (≈0.70304), interpreted as injections of compositionally distinct basanite batches. These petrological signals align with other independent monitoring signals, including increased Very-Long Period (VLP) and a sharp SO₂ peak (25,000 Tm on 2 Nov, fivefold above late-October values), supporting the inference that fresh magma reached the shallow system even when effusion-rate indicators did not show an obvious step change. Overall, this case illustrates advances in analytical and monitoring techniques refine interpretations of magma system dynamics. However, it is worth noticing that even dense, high-quality monitoring can be misleading if precursor behaviour is interpreted without sufficient understanding of the underlying physical controls. For example, Increased rates of deformation and seismicity are well-established precursors to volcanic eruptions, and their interpretation forms the basis for eruption warnings worldwide. However, the Fagradalsfjall eruption on 19 March 2021 challenged this as it was preceded by declining seismicity and deformation immediately before eruption onset, which can be explained by the release of tectonic stress during dike emplacement (Sigmundsson et al., 2022). This further highlights that improved monitoring techniques alone does not guarantee improved forecasting, unless observed signals are analyzed within a context-dependent, process-based framework.

In inefficient degassing systems, one of the key advances concerns eruption transition dynamics, which remain among the most complex and difficult volcanic processes to anticipate. The recent La Soufrière (St Vincent) eruption (2020-2021) featured a clear shift from prolonged effusive lava dome growth to sustained explosive activity, reflecting a fundamental change in conduit and magma system behaviour. Observations show that dome and explosive products are petrologically similar, with no clear evidence for major mafic recharge, indicating that the transition was not driven by a change in magma composition but by reorganisation within an already crystal-rich, vertically extensive plumbing system (Weber et al 2023). High resolution remote sensing using SAR backscatter data (Dualeh et al 2023) reveals a short-lived but pronounced acceleration in dome extrusion rate (from 1.8 to 17.5 m³ s⁻¹ in the final 2 days before explosivity) coincident with increases in seismic tremor and SO₂ emissions, supporting interpretation of the transition as a rapid shift in magma transport and degassing state that enabled pressurisation and fragmentation. However, aside from the short-lived acceleration in extrusion rate in the final 2 days before explosive onset, the preceding three months of dome growth at La Soufrière were characterised by low levels of unrest and weak conventional precursors, underscoring the persistent difficulty of identifying the timing of effusive–explosive transitions. This challenge was addressed operationally through a structured expert-elicitation framework that evaluated multiple plausible scenarios, leading to an escalation to Red Alert on 8 April (~18 hours before explosive activity onset on 9 April) and the precautionary evacuation of ~16,000 people, with no reported fatalities (Joseph et al. 2022).

Recent progress in understanding inefficient degassing systems also comes from phreatomagmatic and hydrothermal eruptions, where rapid water–magma interactions can trigger explosive activity with limited magmatic warning. On 12 January 2020, Taal began with magma ascending beneath a water-filled crater lake. As hot magma approached the surface, heat transfer into lake water drove rapid vaporisation. The volumetric expansion from liquid water to steam increased pressure within the shallow conduit and enhanced fragmentation efficiency, producing a sustained ash column that reached 16–17 km altitude. Multi-sensor analyses combining seismo-acoustic data, lightning detection networks, and satellite observations resolved discrete eruptive phases and indicate that a large proportion of the ~42 million m³ crater lake was vaporised within the first 12 hours. As the available surface water diminished, eruptive behaviour evolved, reflecting the changing balance between magma discharge and external water supply (Perttu et al., 2023). On the other hand, the 9 December 2019 eruption of Whakaari followed a different pathway. Seismic analyses show progressive sealing of a shallow hydrothermal system, allowing pressure to accumulate beneath a low-permeability cap (Ardid et al., 2022). Failure of this cap released pressurised steam and gas, generating an explosion without clear evidence of fresh magma intrusion. Satellite SO₂ retrievals show only a brief increase in flux (40 minutes before onset), consistent with rapid depressurisation immediately prior to failure (Burton et al., 2021). These observations therefore indicate that shallow permeability changes and fluid overpressure alone can drive explosive activity.

Last but not least, recent advances in satellite remote sensing allow eruption plumes to be tracked, quantified, and physically interpreted throughout the troposphere and stratosphere, as illustrated by the eruptions of Raikoke (2019) and Hunga Tonga–Hunga Haʻapai (2022). Raikoke is a small, remote stratovolcano in the central Kuril Islands that erupted explosively on 21–22 June 2019 in a short-lived but intense VEI 4 event, rapidly transitioning from initial explosions to sustained sub-Plinian activity after nearly a century of quiescence. A striking advance from this eruption is the observation that a coherent portion of the plume became trapped within a stratospheric anticyclone – a rotating, low-mixing air mass characterised by anticyclonic circulation – and subsequently rose diabatically over weeks. This behaviour is explained by radiative self-lofting, whereby ash and absorbing aerosols heat through solar radiation absorption, increasing the buoyancy of the plume relative to the surrounding stratosphere and driving continued ascent. The anticyclonic circulation further suppresses entrainment and dilution by background air, allowing the plume to remain dynamically coherent. As documented by Khaykin et al. (2022), the anticyclone contained ~24% of the total SO₂ mass emitted by Raikoke and ascended to ~27 km altitude, persisting for more than three months and circumnavigating the globe three times.

Another major advance in the study of volcanic plumes arises from the eruption of Hunga Tonga–Hunga Haʻapai. This shallow submarine-to-subaerial volcano in the Tonga–Kermadec arc produced an exceptionally powerful VEI 5–6 eruption on 15 January 2022, characterised by a violent phreatomagmatic explosion and rapid caldera-scale collapse following several weeks of escalating activity. Through rapid mass and heat injection, the eruption generated the most intense eruption cloud of the modern satellite era, marked by extreme vertical growth and umbrella spreading that launched powerful atmospheric gravity waves (Proud et al 2022). Unlike classic sulfate-dominated stratospheric eruptions, Hunga injected an unprecedented 146 ± 5 Tg of water vapour into the stratosphere (equivalent to ~10% of the global stratospheric H₂O burden), as quantified by the Microwave Limb Sounder (MLS) aboard Aura (Millán et al., 2022). Because water vapour is a strong absorber of longwave radiation, this introduced a potential positive radiative forcing, contrasting with the net cooling typically associated with sulfate aerosols (Millán et al., 2022). Elevated stratospheric H₂O further enhanced HOx chemistry and facilitated halogen activation on hydrated aerosols, producing a negative ozone response (~2–10%) in the upper stratosphere and mesosphere (Fleming et al., 2024), though the magnitude of polar ozone impacts remained strongly dependent on meteorological conditions (Wohltmann et al., 2024).

Over the past decade, densely instrumented eruptions have advanced understanding of volcanic processes by resolving behaviour across interconnected conduit, surface, and atmospheric domains. In open-vent basaltic systems, quantitative constraints on magma withdrawal and reservoir pressure have clarified how structural failure and caldera collapse are dynamically linked to magma transport. In inefficient degassing systems, recent eruptions have shown that transitions from effusive to explosive activity, as well as water- and steam-driven explosions, are governed by rapid changes in permeability and fluid overpressure that can reorganise eruptive behaviour on short timescales. At the atmospheric scale, high-resolution satellite observations have revealed that eruption plumes actively modify their environment through radiative heating, diabatic ascent, and chemical perturbation, extending volcanic influence into the stratosphere. Together, these advances reflect a shift toward interpreting volcanic activity as a threshold-sensitive, physically coupled system operating across multiple scales. While monitoring capability has expanded substantially, continued progress depends on integrating observations within robust process-based frameworks that recognise the nonlinear nature of volcanic behaviour.

##Bibliography

1. Anderson, K.R., Johanson, I.A., Patrick, M.R., Gu, M., Segall, P., Poland, M.P., Montgomery-Brown, E.K. and Miklius, A., 2019. Magma reservoir failure and the onset of caldera collapse at Kīlauea Volcano in 2018. Science, 366(6470), p.eaaz1822.

2. Ardid, A., Dempsey, D., Caudron, C. and Cronin, S., 2022. Seismic precursors to the Whakaari 2019 phreatic eruption are transferable to other eruptions and volcanoes. Nature Communications, 13(1), p.2002.

3. Burton, M., Hayer, C., Miller, C. and Christenson, B., 2021. Insights into the 9 December 2019 eruption of Whakaari/White Island from analysis of TROPOMI SO2 imagery. Science Advances, 7(25), p.eabg1218.

4. Dualeh, E.W., Ebmeier, S.K., Wright, T.J., Poland, M.P., Grandin, R., Stinton, A.J., Camejo-Harry, M., Esse, B. and Burton, M., 2023. Rapid pre-explosion increase in dome extrusion rate at La Soufrière, St. Vincent quantified from synthetic aperture radar backscatter. Earth and Planetary Science Letters, 603, p.117980.

5. Fleming, E.L., Newman, P.A., Liang, Q. and Oman, L.D., 2024. Stratospheric temperature and ozone impacts of the Hunga Tonga‐Hunga Ha’apai water vapor injection. Journal of Geophysical Research: Atmospheres, 129(1), p.e2023JD039298.

6. Joseph, E.P., Camejo-Harry, M., Christopher, T., Contreras-Arratia, R., Edwards, S., Graham, O., Johnson, M., Juman, A., Latchman, J.L., Lynch, L. and Miller, V.L., 2022. Responding to eruptive transitions during the 2020–2021 eruption of La Soufrière volcano, St. Vincent. Nature Communications, 13(1), p.4129.

7. Khaykin, S.M., De Laat, A.J., Godin-Beekmann, S., Hauchecorne, A. and Ratynski, M., 2022. Unexpected self-lofting and dynamical confinement of volcanic plumes: the Raikoke 2019 case. Scientific Reports, 12(1), p.22409.

8. Neal, C.A., Brantley, S.R., Antolik, L., Babb, J.L., Burgess, M., Calles, K., Cappos, M., Chang, J.C., Conway, S., Desmither, L. and Dotray, P., 2019. The 2018 rift eruption and summit collapse of Kīlauea Volcano. Science, 363(6425), pp.367-374.

9. Millan, L., Santee, M.L., Lambert, A., Livesey, N.J., Werner, F., Schwartz, M.J., Pumphrey, H.C., Manney, G.L., Wang, Y., Su, H. and Wu, L., 2022. The Hunga Tonga‐Hunga Ha’apai hydration of the stratosphere. Geophysical Research Letters, 49(13), p.e2022GL099381.

10. Patrick, M.R., Houghton, B.F., Anderson, K.R., Poland, M.P., Montgomery-Brown, E., Johanson, I., Thelen, W. and Elias, T., 2020. The cascading origin of the 2018 Kīlauea eruption and implications for future forecasting. Nature Communications, 11(1), p.5646.

11. Perttu, A., Assink, J., Van Eaton, A.R., Caudron, C., Vagasky, C., Krippner, J., McKee, K., De Angelis, S., Perttu, B., Taisne, B. and Lube, G., 2023. Remote characterization of the 12 January 2020 eruption of Taal Volcano, Philippines, using seismo‐acoustic, volcanic lightning, and satellite observations. Bulletin of the Seismological Society of America, 113(4), pp.1471-1492.

12. 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), pp.554-557.

13. Sigmundsson, F., Parks, M., Hooper, A., Geirsson, H., Vogfjörd, K.S., Drouin, V., Ófeigsson, B.G., Hreinsdóttir, S., Hjaltadóttir, S., Jónsdóttir, K. and Einarsson, P., 2022. Deformation and seismicity decline before the 2021 Fagradalsfjall eruption. Nature, 609(7927), pp.523-528.

14. Ubide, T., Márquez, Á., Ancochea, E., Huertas, M.J., Herrera, R., Coello-Bravo, J.J., Sanz-Mangas, D., Mulder, J., MacDonald, A. and Galindo, I., 2023. Discrete magma injections drive the 2021 La Palma eruption. Science Advances, 9(27), p.eadg4813.

15. Weber, G., Blundy, J., Barclay, J., Pyle, D.M., Cole, P., Frey, H., Manon, M., Davies, B.V. and Cashman, K., 2024. Petrology of the 2020–21 effusive to explosive eruption of La Soufrière volcano, St Vincent: insights into plumbing system architecture and magma assembly mechanism.

16. Wohltmann, I., Santee, M.L., Manney, G.L. and Millán, L.F., 2024. The chemical effect of increased water vapor from the Hunga Tonga‐Hunga Ha’apai eruption on the Antarctic ozone hole. Geophysical Research Letters, 51(4), p.e2023GL106980.