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A volcanic eruption looks like a sudden natural disaster: the crater spews lava, which covers the immediate environment with a layer of liquid rock. There are volcanic eruptions that last only a few hours, but many last for days, some even for years. The recent eruption of Kilauea, an active shield volcano on the Hawaiian island of Big Island, began in 1983. For 35 years, magma went through a series of cracks in the so-called eastern rift to the surface.
On May 3, 2018, this ditch opened up and gave way to a massive flow of lava that destroyed the southeastern part of Big Island. Geophysicists Falk Amelung and Jamie Farquharson of the University of Miami have investigated why the constantly increasing volcanic activity suddenly turned into destructive lava flows. Their study, which has just been published in Nature, assumes that unusually heavy rains earlier in the year could be the cause of the disaster.
Record rain
The rainy season in Hawaii generally begins in March. However, in 2018, these first rains of the year started earlier and broke all records. Data from NASA satellites and other measurement points were able to determine an average amount of precipitation of more than 2.25 meters, this corresponds to 2,225 liters per square meter, in the first quarter of the year. In previous years the average was 0.9 meters. According to the two geophysicists, this could have caused the groundwater level to rise sharply, which in turn increased the pressure on the rock. As a result, magma found new cracks elsewhere on the island, which have given way to pressure from inside the earth.
The study’s starting point was knowledge of the nature of the rock: volcanic rock in Hawaii is highly permeable. Rainwater can reach a few kilometers below the surface of the earth, that is, the deepest layers of the earth, where magma is stored to some extent. For the pressure in the lower layers of the earth to change, the water would have to accumulate for a few weeks. Farquharson and Amelung have now calculated whether this was the case around the Kilauea before May with a model.
Kilauea spits during the rainy season
Rain has long been known to have an impact on seismic events. Until now, however, it has been assumed that this influence only extends to the surface of the earth or the highest layers of the earth. The model of the scientists of EE. USA It shows that in the case of Kilauea this influence could have penetrated much deeper into the earth. According to his calculations, the pressure had increased sharply to a depth of one to three kilometers: before and during the eruption it increased from around one hundred pascals to one thousand pascals. The mechanical stress in the subsoil reached the highest value in 50 years.
Farquharson and Amelung conclude that this increased pressure further weakened the rock system and led to mechanical errors, ultimately making the large eruption possible. They also corroborate their thesis with historical observations and records. According to this, 60 percent of the Kilauea eruptions occurred during the rainy season, although it is much shorter than the dry season. This suggests a correlation between rainfall and volcanic activity at Kilauea throughout history.
Models only, no measurements
Geoscientist Michael Manga from Berkely University’s Department of Earth and Planetary Sciences can certainly get something from his colleagues’ theses in a Nature commentary. The fact that external processes that do not originate from the Earth’s interior can play a role in volcanic eruptions is a reminder that volcanoes are part of Earth’s dynamic system. Manga notes that these are models, not measurements. After all, when volcanoes are monitored, pressure measurements in the deepest layers of the earth are not carried out nor are hydrogeological data collected.
As is often the case in geosciences, scientists would have to use historical records, Manga writes. This is also the case with the Kilauea, which, historically, is active much more frequently in the rainiest time of the year. Manga advocates that interactions between surface, environment, climate, and climate with volcanic activity be carefully examined. Science is just beginning to understand these interactions.
