Earthquakes shook the east of the large island of Hawaii for weeks. Most of the tremors were more than 40 kilometers from the summit of Kilauea, and in between the earth’s crust was deformed over dozens of kilometers: Magma rose from the depths and spread underground. Then cracks in the earth tore open, lava fountains shot into the sky. The 35-year eruption of Kilauea had entered a new phase.
“This last phase of the eruption began with magma spreading underground, forming so-called passages along weak zones. We have now looked at why these magma passages were able to penetrate the rock and believe that heavy rains made this process easier.”
In the three months before, Hawaii had the highest amounts of precipitation in the past 50 years, describes Falk Amelung from the University of Miami. To be more precise: 2250 liters of water per square meter – around 900 are normal, explains the geophysicist:
“The rainwater penetrated deep into the subsoil, weakening the cohesion of the rock, which made it easier to break. This effect can play a role in the formation of earthquakes, as has long been known.”
Heavy rains caused violent eruptions of Kilauea
This effect is responsible for the earthquakes in areas where crude oil is obtained through fracking. At Kilauea, seeping rainwater is said to have increased the pore pressure in the rock to such an extent that the magma could penetrate more easily and spread underground. Heavy precipitation, according to the hypothesis of the geophysicists, should change the behavior of the volcano.
“For this to work, heavy rain really has to fall for months. Only then does the effect build up underground. A completely different question is whether the lava will eventually flow out into crevices, like at the finale of the 35-year eruption in 2018.”
Next, geophysicists looked at the eruptions since records began in 1790. The result: around 60 percent of all eruptions occurred during the rainy season. An indication that there could be something to your idea and that it is worth investigating further, judges Falk Amelung. And he is excited to see how his colleagues will receive them. Michael Manga from the University of California at Berkeley is rather skeptical.
Water intensifies the cracks in the porous volcanic rock
“I’m a lot more skeptical than the authors. In principle it’s an interesting idea. But the question is how important this process is. The pressure changes in the rock that we are talking about are really tiny. They are smaller than those, which the moon causes in them through its tidal forces. If the moon does not affect the behavior of the volcano, why should heavy rain do it? “
Michael Manga believes that rain can “move” an eruption forward by a day or two at most. Falk Amelung assesses the effect differently, sees stronger effects:
“If we have a system in which such high pressure has built up that an eruption is imminent, then a longer period of rain can trigger the eruption. And on Kilauea this works particularly well because the rock that builds it up is very porous and the water can therefore penetrate well. “
One now has to look at other, similarly structured volcanoes to see whether these effects can be reproduced there. In any case, a geological debate has started.
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