Indonesia’s volcanoes are among the worlds most dangerous. Through chemical analysis of tiny minerals in lava from Bali and Java, researchers from Uppsala University have found new clues.
The author of the study, Frances Deegan says, “Magma is formed in the mantle and the composition of the mantle under Indonesia used to be only partly known. Having better knowledge of Earth’s mantle in this region enables us to make more reliable models for the chemical changes in magma when it breaks through the crust there, which is 20 to 30 kilometers thick, before an eruption.”
The composition of magma varies greatly from one geological area to another, and has a bearing on the kind of volcanic eruption that occurs.
Volcanism arises in subduction zones. When the sinking tectonic plate descends into the mantle, it heats up and the water it contains is released, causing the surrounding rock to start melting.
Magma reacts chemically with surrounding rock when it penetrates Earth’s crust before reaching the surface.
“Lava consists of roughly 50 percent oxygen, and Earth’s crust and mantle differ hugely in their oxygen isotope composition. So, to trace how much material the magma has assimilated from the crust after leaving the mantle, oxygen isotopes are very useful,” says Deegen.
https://phys.org/news/2021-06-knowledge-earth-mantle-indonesia-explosive.html