Kīlauea Volcano in Hawaii is said to be the most active volcano in the world, yet it’s still unclear how it originated.
New research suggests that the original magma womb lies more than 90 kilometers below the hotspot. While previous studies have found two shallow magma chambers beneath Kīlauea, they weren’t large enough to account for all the liquid rock this volcano spews out.
A larger chamber, about 11 kilometers deep (or 6.8 miles), was detected using seismic waves in 2014, and yet it now appears that the original magma chamber is even deeper. deep.
A new analysis of broken fragments of ancient volcanic rock, dredged from the southeastern flank of the Big Island, suggests that Kīlauea arose from a pool of pyroclastic material nearly 100 kilometers deep.
Between 210,000 and 280,000 years ago, the Pacific tectonic plate shifted and a plume of magma rushed upwards into the sea. As the hot liquid cooled and solidified , it formed a large “shield” that burst through the waves about 100,000 years ago.
Thus, Kīlauea was born, but the original rocks ejected from this hotspot are incredibly hard to find, buried under many layers of newer lava. The igneous rock dredged in the current study offers unprecedented insight into the volcano’s deep and distant past.
Previously, Kīlauea Volcano was thought to have been created from solid rock that partially melted due to the heat from the hotspot.
The new research, however, finds no evidence to support this hypothesis. The rocks collected were found to contain a suite of rare-earth elements that, according to models, could only form in a specific way.
Instead of partial melting, Kīlauea Volcano appears to have originally formed by fractional crystallization. This term describes the creation of crystals in deep pools of magma, which do not subsequently react with residual melting.
“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 rare earth element concentrations,” says lead author, geologist Laura Miller of Monash University in Australia.
“We found that the samples could only be formed by the 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 its presence is necessary to explain the composition of Kīlauea’s rocks suggests that the original eruption originated 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 in the Hawaiian Islands may not be that deep, but new findings suggest Kīlauea’s plumbing isn’t as shallow as we once thought.
“This challenges the current view that fractional crystallization is only a surface process and suggests that the development of a deep (>90 km) magma chamber is an important early step in the birth of a Hawaiian volcano.” , explains Miller.
Other volcanoes elsewhere in the world, such as Mount Vesuvius, also show crystal-forming times that suggest there are “long-lived” reservoirs of magma hidden beneath the surface. Yet Kīlauea’s original magma chamber appears to be much deeper than most.
Why this remains a mystery for now.
The study was published in Nature Communication.