Much larger than craters, volcanic calderas are circular depressions carved into the Earth’s surface when a volcano’s underground magma chamber rapidly empties and collapses in on itself. Better, then, not to be around…
Over the past two million years, the Yellowstone supervolcano located in the American national park of the same name has experienced three volcanic eruptions massive enough to form such structures and thus sculpt the landscape. Suffice to say that it is monitored like milk on fire – not to mention that these major events are interspersed with less significant eruptions.
However, new research shows that the underground reservoirs of magma that fuel the supervolcano’s eruptions appear to be moving northeast from the Yellowstone caldera. According to a team led by seismologist Ninfa Bennington of the US Geological Survey, this region could therefore concentrate future volcanic activity, reports Science Alert.
Two types of tanks
To understand this research work published on January 1 in the journal Nature, you need to know that Yellowstone’s eruptions come from “rhyolitic” type reservoirs, that is to say containing magma rich in silica – making this material “the volcanic equivalent of granite, sticky, viscous and slow moving”compares the scientific news media.
Previous studies assumed that these rhyolitic reservoirs overhung deeper reservoirs. The latter, of the “basaltic” type, would contain a magma with a low silica content but rich in iron and magnesium, which would therefore not conduct electricity in the same way. Ninfa Bennington and her colleagues took advantage of this difference to probe the bowels of the volcano.
Thus, by measuring the surface variations of the magnetic and electric fields of the ground (“magnetotelluric” study) on a large scale in the Yellowstone caldera, the researchers were able to model the distribution of the reservoirs and the molten matter found there.
388 to 489 cubic kilometers of magma
Their results revealed the existence of at least seven distinct regions with high magma content, some of which feed other regions, at depths between 4 and 47 kilometers below the ground (the boundary between the Earth’s crust and the mantle). , notes Science Alert.
To the northeast, huge reservoirs of basaltic magma in the lower crust heat and maintain chambers of rhyolitic magma in the upper crust, the researchers found. The storage volume of the latter is estimated between 388 and 489 cubic kilometers – a volume “comparable” to that of previous eruptions at the origin of calderas.
If the eruptions that formed the caldera (rhyolitic) were interspersed with smaller eruptions (basaltic) inside the circle, we do not know exactly how these events occur. The authors of the study suggest that the rhyolitic magma chambers must “to cool down completely” before the basaltic magma can penetrate it.
As for determining exactly when and how these future eruptions will occur, this will require a “deeper analysis”they conclude.
