Hydrothermal Eruptions and Volcanic Processes

Hydrothermal eruptions represent a class of volcanic activity driven by the rapid vaporisation of groundwater or hydrothermal fluids rather than by fresh magma ascent. Such eruptions can occur with little or no magmatic input and are often characterised by abrupt onset, intense steam release, and the ejection of altered rock fragments and juvenile‐free tephra. These events may be triggered by pressure perturbations within shallow hydrothermal systems, seismic shaking, or thermal intrusion of magmatic fluids into permeable fracture networks. Beyond the immediate threat of ballistic ejecta and pyroclastic density currents, hydrothermal eruptions offer critical insights into subsurface fluid pathways, alteration mineral assemblages and stress evolution beneath active edifices. Volcanic processes underpinning these eruptions range from brittle failure of rock caps to dynamic crack propagation, fluid pressurisation, and the rapid expansion of superheated water. Integrating geophysical monitoring, geochemical characterisation and geodetic deformation studies has advanced our understanding of precursor signals and eruption mechanisms. Collectively, research on hydrothermal eruptions enhances hazard assessment, informs geothermal resource development and illuminates fundamental interactions between magmatic heat sources and overlying hydrothermal reservoirs.

Research from Nature Portfolio

Recent studies have applied stress‐field inversion and precise geophysical measurements to resolve the timing and mechanics of hydrothermal eruptions. A quantitative evaluation of temporal stress changes beneath a stratovolcano demonstrated that deviations in focal‐mechanism misfit angles can herald pressurisation by hydrothermal fluids, offering a potential eruption indicator. Separately, multi‐parameter monitoring of tilt, tremor and electric‐field variations at a small‐scale phreatic site revealed that shallow hydrothermal intrusions drive near‐surface groundwater flow; depletion of cold groundwater precedes explosive steam release. Together, these advances underscore the value of high‐resolution stress and electromagnetic observations for detecting subtle precursory signals within dynamic hydrothermal systems.

Hydrothermal Eruptions and Volcanic Processes publication trend

The graph below shows the total number of articles in hydrothermal eruptions and volcanic processes across all publications each year (not limited to Nature Index journals).

Technical terms

Hydrothermal eruption: An explosive event driven by rapid flashing of water or hydrothermal fluids without primary magma ejection.

Phreatic eruption: A steam‐driven explosion that fragments pre‐existing rock through the instantaneous vapourisation of water.

Pyroclastic density current: A ground‐hugging mixture of hot gases, ash and rock fragments flowing away from an eruption.

Tephra: Fragmental material produced by a volcanic eruption, including ash, lapilli and bombs, often lacking juvenile magma.

InSAR (Interferometric Synthetic Aperture Radar): A remote‐sensing technique that measures ground deformation by comparing radar images taken at different times.

Focal mechanism misfit angle: The angular deviation between observed earthquake fault‐slip vectors and the regional stress field, indicative of local stress perturbations.

Crack propagation: The growth of a fracture in rock under stress, which can form pathways for fluid migration.

Fluid pressurisation: The build‐up of pressure within a confined fluid body due to heating, gas exsolution or influx of external volatiles.

References

1. Monitoring eruption activity using temporal stress changes at Mount Ontake volcano. Nature Communications (2016).
2. Phreatic volcanic eruption preceded by observable shallow groundwater flow at Iwo-Yama, Kirishima Volcanic Complex, Japan. Communications Earth & Environment (2022).
3. Shallow Magmatic Hydrothermal Eruption in April 2018 on Ebinokogen Ioyama Volcano in Kirishima Volcano Group, Kyushu, Japan. Geosciences (2020).
4. Chronology of the 2015 eruption of Hakone volcano, Japan: geological background, mechanism of volcanic unrest and disaster mitigation measures during the crisis. Earth, Planets and Space (2018).
5. Depressurization of a hydrothermal system following the August and November 2012 Te Maari eruptions of Tongariro, New Zealand. Geophysical Research Letters (2016).