Not all volcanoes are suddenly explosive. Some constant rivers of bleak and slow lava for millennia, such as those of the Hawaiian Islands or the Galapagos.
This is what volcanologist Michael Stock of Trinity College Dublin in Ireland calls “boring” volcanoes – yet beneath their monotonous exterior, there is a bomb that Stock and his colleagues have just discovered.
By analyzing the microscopic crystals in basalt and the ejected material of two volcanoes in the Galapagos, the researchers discovered hidden magma systems that are not that simple or predictable.
Although the Wolf and Fernandina volcanoes in the Galapagos have apparently spewed the same basaltic lava throughout their existence, new findings suggest that they are located on a chemically diverse system of molten rocks, some of which have the potential to set explosive activities in motion .
Just because these volcanoes seem boring on the surface doesn̵
“This was really unexpected. We started the study wanting to know why these volcanoes were so boring and what process led the exploded lava compositions to remain constant for long periods,” says Stock.
“Instead we discovered that they are not boring at all: they hide these secret magmas underground.”
There is no reason to think that these two Galapagos volcanoes are about to change their eruptive behavior anytime soon. This kind of thing happens at a rate that even a snail can touch with one foot.
However, the study points to one way in which seemingly harmless volcanoes could potentially become eruptive in the distant future, and somehow explains how they could have done so in the distant past.
“This discovery is a turning point because it allows us to reconcile apparently divergent observations, such as the presence of explosive deposits on several Galapagos volcanoes,” says Benjamin Bernard, a volcanologist involved in monitoring Galapagos volcanoes at the Geophysical Institute.
“It also allows us to better understand the behavior of these volcanoes, which is essential for monitoring volcanoes and assessing hazards.”
While the Wolf and Fernandina volcanoes are thought to emit mostly uniform basaltic lava, which has a relatively low viscosity, the new study has found evidence for other advanced forms of magma that flow below various depths.
This diversity of magma, however, seems to be suffocated by large volumes of basaltic magma, which rises through the crust from a hot spot or plume of hot magma, under Wolf and Fernandina.
“So,” conclude the authors, “monotonous activity does not reflect simplicity or chemical homogeneity in magmatic systems”.
Instead, it could say more about where the volcano is located than the hot spot. Large volumes of basalt that plummet through the crust, the authors argue, would suffice to overwhelm other more explosive forms of magma, which tend to be rich in silica.
These basaltic magma plumes, however, are not fixed and, although they may persist for tens of millions of years, they move, albeit very slowly.
Knowing where they are going and how these small changes can affect volcanic eruptions will help us prepare better for the future, however far it may be.
Under Wolf and Fernandina, researchers found magma compositions similar to those that erupted in Mount St. Helens in 1980. On the surface, however, the lava was 90% basalt.
“Magmas are more likely to explode explosively when they have higher concentrations of silica and water,” Stock explained to Newsweek.
“Water forms gas bubbles – the same as carbon dioxide in cola – but the high silica content makes the magmas very sticky. The gas bubbles cannot escape so the pressure builds up, generating an explosive eruption. “
For now, we would do our best not to judge volcanoes only by their calm exterior.
The study was published in Nature Communications.