The Kīlauea volcano in Hawaii is said to be the most active volcano in the world, but we still don’t really know how it was born.
New research suggests that the original magma uterus is more than 90 kilometers below the hot spot. Although previous studies have found two shallow magma chambers below Kīlauea, they were not large enough to account for all the liquid rock emitted by this volcano.
In 2014, a larger chamber was detected, about 11 kilometers deep (i.e., 6.8 miles), with seismic waves, but now it appears that the original magma chamber is even deeper.
A new analysis of broken fragments of ancient volcanic rocks, dredged on the southeastern flank of the Big Island, suggests that Kīlauea was born from a pool of pyroclastic material about 100 kilometers deep.
Between 210,000 and 280,000 years ago, the Pacific tectonic plate shifted and a plume of magma plunged up into the sea. As the hot liquid in the pipe cooled and solidified, it formed a large “shield” that exploded through the waves about 100,000 years ago.
This is how Kīlauea arose, but the original rocks ejected from this hot spot are incredibly hard to find, buried as they lie beneath numerous layers of more recent lava. The dredged rock in the current study offers an unprecedented view of the deep and distant past of the volcano.
Previously, the Kīlauea volcano was thought to have formed through a solid rock that was partially melted by the heat of the hot spot.
The new research, however, finds no evidence to support this hypothesis. The collected rocks were found to contain a set of rare earth elements that the models suggest could only be formed in a specific way.
Instead of partially melting, it appears that the Kīlauea volcano was originally formed by fractional crystallization. This term describes the creation of crystals in deep magma pools, which subsequently do not react with residual fusion.
“We explored the formation of these samples through experimental work, which involved melting synthetic rocks at high temperatures (> 1,100 ˚C) and pressures (> 3 GPa) and using a new method to model their element concentrations. of rare earths, “he explains. the lead author, geologist Laura Miller of Monash University in Australia.
“We found that samples could only be formed by crystallization and removal (fractional crystallization) of garnet.”
Garnet is a crystal that can form when magma is subjected to high pressures and temperatures more than 90 kilometers below the Earth’s crust. The fact that their presence is necessary to explain the composition of the Kīlauea rocks suggests that the original eruption came from similar depths.
Or maybe even deeper. Experiments show that garnet can crystallize at depths of up to 150 kilometers below the earth’s crust.
The original source of the Hawaiian Islands may not be as deep, but new findings suggest that the Kīlauea plumbing is not as shallow as we thought before.
“This defies the current view that fractional crystallization is only a shallow process and suggests that the development of a deep magma chamber (> 90 km) is an important early stage in the birth of a Hawaiian volcano. “says Miller.
Other volcanoes in other parts of the world, such as Mount Vesuvius, also show crystalline formation times suggesting “deep, long-lived” magma deposits hiding beneath the surface. However, Kīlauea’s original magma chamber appears to be much deeper than most.
Why this remains a mystery at the moment.
The study was published in Nature Communications.