Crystals hint at a volcano’s ability to erupt
A thin section of volcanic rock under the microscope, showing white plagioclase crystals of varying sizes. This rock is from Cerro Tuzgle, a dormant volcano in northwestern Argentina.
(Photo credit: The University of Queensland )
Key points
- Tiny plagioclase crystals in volcanic rocks form in the final stages before eruption.
- Samples from around the Pacific Ring of Fire had the same chemical signature indicating the same processes happening inside different volcanoes.
- The crystals could indicate which volcanoes need to be closely monitored.
University of Queensland researchers have shown tiny crystals are a window to activity inside volcanoes and could provide clues to when they might erupt.
PhD candidate Daniela Parra-Encalada from the School of the Environment examined a common white crystal called ‘plagioclase’, found in rocks.
The smallest crystals from Andean volcanoes of different ages, eruptive styles and activity levels had the same chemical signature.
“Plagioclase grows in magma only a few kilometres below the surface, reacting to changes in temperature, water content and magma composition,” Ms Parra-Encalada said.
"Analysing the chemistry of individual crystals rather than whole rocks allows us to reconstruct different stages of a volcano's history and identify the processes that occurred immediately before eruption.
“The smallest, newest crystals – just the width of a human hair – were formed during the final stages of an eruption.
“Every volcanic rock sample we collected during our field trip across a 230-kilometre stretch of the Central Andes in Chile and Argentina carried evidence of the same process.”
Some of the research team in the field in the Andes Mountains. L-R Associate Professor Teresa Ubide (UQ), Professor Gideon Rosenbaum (UQ), Assistant Professor Patricia Larrea (Universidad de Zaragoza) and Daniela Parra-Encalada (UQ).
(Photo credit: The University of Queensland )
Cerro Overo crater with volcanic rocks in northern Chile.
(Photo credit: The University of Queensland )
Thin cross-sections of 28 representative rocks from 7 volcanoes and 2 more ancient super-eruptions were examined under special microscopes, and the chemical composition of plagioclase microcrysts were analysed and mapped.
Ms Parra-Encalada compared the results with research from other areas around the Pacific Ring of Fire.
“We found similar characteristics in the smallest plagioclase crystals in other datasets, suggesting that all of these volcanic eruptions were triggered by the same process,” she said.
"We used modelling to show the chemical signature of the crystals was most likely linked to very hot magma coming from deeper underground, pushing into a shallow magma reservoir.
“This destabilises the volcano plumbing system, eventually triggering the eruption.”
The team has termed the newly identified geochemical pattern the ‘plagioclase eruptibility field’ and will investigate whether it occurs in oceanic volcanoes.
Plagioclase crystal under an optical microscope using cross-polarised light with the rings showing its growth.
The same crystal showing its chemical composition mapped using X-ray fluorescence.
Study senior author Associate Professor Terese Ubide said future research could determine whether the chemical signature of plagioclase could be used to identify volcanoes that warrant closer monitoring because it may indicate they are more prone to eruption.
"We are keen to test whether this pattern holds across volcanoes in different tectonic settings", Dr Ubide said.
“Plagioclase crystals could also reveal how magma systems accumulate valuable metals such as copper and gold, potentially creating new links between volcanology and critical minerals research.”
Read the research published in Nature Communications.
Collaboration and acknowledgements
Assistant Professor Patricia Larrea of Universidad de Chile, Chile, and Unversidad de Zaragoza, Spain, and Emilce Bustos of Universidad Nacional de Salta, Argentina, are co-authors of the research.
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