Albert’s article Volcanoes and rain explores the possible links between volcanic eruptions and subsequent periods of wet weather. But there is another side to this story: rain can, in turn, have an impact on volcanic activity, and maybe even trigger eruptions!

The possibility of rainfalls causing eruptions has actually been speculated long ago. Georg Forster, who acted as a naturalist during Cook’s second voyage to the Pacific, wrote this observation about the Yasur volcano (Vanuatu) in his travel account A Voyage Round the World, published in 1777:

“We remarked that this was the second time the explosions of the volcano had recommenced after showers of rain; and were therefore led to suspect, that the rain in some measure excites these explosions, by promoting or encreasing the fermentation of various mineral substances in the mountain.”

Of course, two observations of a phenomenon is not considered to be enough data to presume correlation, even less causation, by modern scientific standards. And the proposed mechanism appears somewhat amusing in regard of today’s knowledge. Nevertheless, Forster’s intuition may have held some truth, because rain can indeed influence volcanic activity, even if some of these purported links remain controversial. Let’s start with the more obvious ones.

Some watery hazards

Some volcanic hazards directly involve the presence of water, and I mean atmospheric water, not the water dissolved in magma as a gas phase, nor the marine or land water of phreatomagmatic eruptions. The two mains hazards that require rain are lahars and phreatic eruptions. It sounds like stating the obvious, but a study has shown that lahars are more frequent after heavy rainfalls (Farquharson & Amelung, 2022). More rain means more water can remobilise the ashes down the slopes of a volcano and generate the deadly volcanic mudflows. The same research article demonstrates a similar relationship between heavy rain and phreatic eruptions. In this type of eruption, water heated by a magmatic source suddenly flashes to steam, triggering an explosion of vapour and pulverising the rocks above—no “fresh” (juvenile) magma being emitted. Because this kind of eruption does not involve any movement of magma, it is very unpredictable, and can be deadly even in countries where volcanoes are well-monitored, such as Japan, where the phreatic eruption of Mount Ontake caused 63 victims in 2014. More rain means more water enter the porous, volcanic rocks above a magmatic source, enhancing the probability of a phreatic eruption.

Perhaps less obvious is the link between rainfall and dome collapse. Lava domes being extruded are unstable edifices, prone to crumble. A good example of this instability happened during the long-lived eruption of Soufrière Hills volcano (Montserrat), which produced dome after dome for more than 15 years (1995–2013). A study (Matthews et al., 2009) has shown a statically robust relationship between intense rain episodes and the collapse of these domes. And Soufrière Hills is not the only volcano where rain has been accused of causing dome collapse: it has also been proposed at Japanese Mount Unzen (Yamasato et al., 1998). A possible mechanism is “quench fragmentation”, where the rain provokes rapid cooling of the lava dome surface and its subsequent explosion. Another possible explantation is that water, penetrating the permeable rock of the dome, inhibits its degassing, resulting in overpressure. However, Matthews et al. recognise that “there was no rainfall-related change in deeper, volcano–tectonic activity”, meaning that this interaction remains surficial. As for the case of lahars and phreatic eruptions, rain-triggered dome collapses do not involve the magmatic system. Can rain spark a “true”, magmatic eruption?

When water forces magma out

This has been postulated by a study following the East Rift Zone eruption of Kīlauea in May 2018, which curtailed in dramatic fashion the 35-years-long eruptive cycle at Puʻu ʻŌʻō. According to this research (Farquharson & Amelung, 2020), the 2018 events where preceded by an intense rainy episode, with 2.25 meters of rain poured on the volcano during the first quarter of the year, compared to 0.90 meters on average. (These numbers always amaze me, as my city receives less than 0.6 meters annually. Clermont-Ferrand is located in the rain shadow of the Chaîne des Puys, a range of monogenetic cones, or when volcanoes prevent rain!) By means of modelling, Farquharson and Amelung argue that this colossal quantity of water has increased the pore-pressure of Kīlauea and, ultimately, triggered a dyke intrusion without a supply of magma from below. Other authors disagree though (Poland et al., 2022), and this result remains controversial.

If truth be told, this was not the first time that this hypothesis was proposed at a basaltic shield volcano. In the early 1990’s, a French team had already devised a similar idea for the Piton de la Fournaise volcano, on La Réunion island (Carbonnel et al., 1990). And their case did not rest upon one eruption, but upon dozens, giving it a more solid support. Their simple but elegant analysis consisted in splitting the eruptive record in two six-months periods: eruptions happening in November–April, when 70–75 % of the rain occur, and eruptions happening in May–October. For the record spanning from 1800 to 1987, the data yields a ratio of 1.7 times more eruptions during the wet season. For the 1956–1987 subset, for which the record is exhaustive, this ratio is even higher, at 1.85. (It would be interesting to verify if this relation holds up for the most recent period, as the volcano has erupted numerous times since 1987, as recently as February 2026—during the wet season.) This does not mean that rain is always a factor: eruptions do happen during the dry season. But they are less frequent. Again, the invoked mechanism is that the infiltration of meteoric water in the porous and fractured rocks of the edifice puts more pressure on the surficial magmatic system, forcing the magma up. A process that seems pretty intuitive once you think about it. Water adds weight to the volcano, increasing the lithostatic pressure on the reservoir—or should we rather say “litho-hydrostatic” pressure? This effect is not limited to water in its liquid form: a recent study showed a relationship between the snow-load at Ruapehu (New-Zealand) and its activity, which seems to follow a seasonal pattern (Yates et al., 2024). But let us focus on rain here.

The long-term effect of rain on volcanic systems

Contrary to basaltic volcanoes, rain might inhibit the eruption of large silicic systems at a longer timescale (Glazner, 2020). Again, the mechanism is quite intuitive. Water circulating in porous rocks transfers heat to the surface by convection, a process that is way more effective at removing heat than simple thermal conduction through a dry, rocky crust. Over long timescales, the large silicic magmatic systems located in wet regions will tend to cool off and crystallise, yielding granitic plutons, while similar systems in dry conditions will be more prone to erupt. To illustrate this, one can look at a map of the Andes presenting the location of major late Cenozoic calderas (below): most of them are located in the arid parts of the mountain range.

Rain is so powerful that it could even displace an entire volcanic range! How? Orography has an impact on climate, creating a wet windward side and a dry leeward side. On the windward side, precipitation enhance erosion. The eroded crust, more heavily fractured, offers an easier path for magma to reach the surface. New volcanoes then tend to grow on the windward side, where the process will eventually repeat itself. Over millions of years, the whole range migrate. This effect of rain has been proposed to explain the westward migration of volcanism in the Cascades and in the Southern Andes during the late Cenozoic (Muller et al., 2022). In both cases, rain from the Pacific Ocean would have promoted erosion on the West side of the mountains, in turn promoting the ascent of magma on this side and ultimately the migration of the range.

This article shows that the volcano–climate relationship in not one-sided. Yes, volcanic eruptions can exert a hold over the climate. But in turn, there can be a climatic forcing on magmatic and volcanic activity. This influence actually extends beyond that if rain: glaciation cycles also play a major role in magma production, but that is another story. Anyway, it should be no surprise that water is a powerful agent in shaping a small marble called “the Blue Planet”, including its volcanoes.

Jean-Marie Prival, February 2026

Parts of this post have previously been published in Kipuka, a French magazine which ‘revue de vulgarisation scientifique dédiée aux volcans’. (If you feel unsure about vulgarising volcanoes, it means popularising, i.e. making it accessible to the general public. VC pleads guilty: we also share this goal.)

References

Farquharson, J. I.; Amelung, F. Volcanic Hazard Exacerbated by Future Global Warming-Driven Increase in Heavy Rainfall. R. Soc. open sci. 2022, 9 (7), 220275. https://doi.org/10.1098/rsos.220275

Matthews, A. J.; Barclay, J.; Johnstone, J. E. The Fast Response of Volcano-Seismic Activity to Intense Precipitation: Triggering of Primary Volcanic Activity by Rainfall at Soufrière Hills Volcano, Montserrat. Journal of Volcanology and Geothermal Research 2009, 184 (3–4), 405–415. https://doi.org/10.1016/j.jvolgeores.2009.05.010

Farquharson, J. I.; Amelung, F. Extreme Rainfall Triggered the 2018 Rift Eruption at Kīlauea Volcano. Nature 2020, 580 (7804), 491–495. https://doi.org/10.1038/s41586-020-2172-5

Poland, M. P.; Hurwitz, S.; Kauahikaua, J. P.; Montgomery-Brown, E. K.; Anderson, K. R.; Johanson, I. A.; Patrick, M. R.; Neal, C. A. Rainfall an Unlikely Factor in Kīlauea’s 2018 Rift Eruption. Nature 2022, 602 (7895), E7–E10. https://doi.org/10.1038/s41586-021-04163-1

Carbonnel, J.-P.; Soler, E.; Hubert, P. Hypothèse sur la genèse de certaines éruptions volcaniques du Piton de la Fournaise (île de la Réunion). C. R. Acad. Sci. Paris 1990, 310 (II), 75–80

Yates, A. S.; Caudron, C.; Mordret, A.; Lesage, P.; Pinel, V.; Lecocq, T.; Miller, C. A.; Lamb, O. D.; Fournier, N. Seasonal Snow Cycles and Their Possible Influence on Seismic Velocity Changes and Eruptive Activity at Ruapehu Volcano, New Zealand. Journal of Geophysical Research: Solid Earth 2024, 129 (12), e2024JB029568. https://doi.org/10.1029/2024JB029568

Glazner, A. F. Climate and the Development of Magma Chambers. Geosciences 2020, 10 (3), 93. https://doi.org/10.3390/geosciences10030093

Muller, V. A. P.; Sternai, P.; Sue, C.; Simon-Labric, T.; Valla, P. G. Climatic Control on the Location of Continental Volcanic Arcs. Sci Rep 2022, 12 (1), 22167. https://doi.org/10.1038/s41598-022-26158-2