2023-07-05 20:06:15
A year and a half has passed since the La Palma volcano awoke after 50 years of rest from the Cumbre Vieja volcanic edifice. From September 19 to December 13, 2021, the volcano ejected about 200 million cubic meters of volcanic material which covered an area of about 12 square kilometers.
In a study recently published in the journal Science Advanceswe try to shed light on this event through the study of its lava.
As it happened with the previous ones, the eruption of 2021 modified the landscape and topography of the islandbut the damage inflicted on the population was much greater as a result of the large population increase on the island in recent decades.
The volume of material emitted also had an influence, ten times higher than that of previous eruptions. The eruption affected 7,000 people, caused damages of more than 800 million euros and put volcanology on the consciousness of the entire country.
During its course, data from seismicity, ground deformation and gas composition to try to forecast the evolution of the volcano.
In addition, it was examined chemical composition of lava. The chemistry of the magma determines its physical properties, such as viscosity, and with it the eruptive style and the danger of the eruption.
In our study we analyzed the chemistry of the magma emitted throughout the entire eruption. We detected variations that we could relate to changes in the style of the eruption and its completion. Our results could prove useful for monitoring future volcanic events.
Viscous lava. Juan J. Coello Bravo, Author provided
Laser to study rocks
During the eruption we carried out numerous campaigns in which our team took turns to sample the lavas emitted by the different eruptive mouths. Knowing the date, location and emitting mouth of the lava flows is essential to assess the chemical variations of the magma on a scale of days, which is unusual in the study of volcanic rocks.
In addition, the sampling we perform is very difficult to repeat. Many of the samples obtained were covered by later lavas during the eruption.
Once in the laboratory, we analyze the samples with a laser-based technique. The method allowed us to isolate the chemical information coming from a specific part of the collected rocks. In this way, we were able to obtain more detailed data than with traditional analyses, which require crushing the rock samples before analyzing them.
Lava fluida.
R. Balcells, Author provided
Study the nougat without touching the almonds
Magma, or molten rock, is made up of a liquid part, a gaseous part, and a solid part. Solids are mineral crystals that form as magma cools on its way to the Earth’s surface.
When the magma rises to the surface and forms a lava flow, the gas is released, and the liquid part cools rapidly to form a rocky matrix that surrounds the crystals. This matrix is largely made up of volcanic glass. As a result, the volcanic rocks take on an aspect similar to Alicante nougat, with almonds large (mineral crystals) surrounded by almond paste (rocky matrix).
Microscopic view of the lava. Author provided
The crystals give a lot of information about what happens under the volcano before the eruption. However, when we want to analyze small variations in the chemistry of the melt during the eruption, the crystals allow us to botherbecause what interests us is the composition of the rock matrix.
Isolating the matrix of a volcanic rock in order to analyze it is not easy, because the crystals are small –usually about the size of a grain of salt, or at most like a walnut–. But that’s where the laser comes in. This high precision instrument allows us to access any point of the matrix without tap the surrounding crystals.
We use an ultraviolet laser similar to those used in myopia operations. The laser allows us to generate matrix vaporized particles that we can then analyze with a Mass spectrometer.
rocky lava. Juan J. Coello Bravo, Author provided
Not all lava is the same
Our results indicate chemical changes in the magma that fueled the eruption throughout its three months. These changes are related to variations in the type of lava, earthquakes, and the levels of sulfur dioxide emitted by the volcano.
The viscous and thick lavas at the beginning of the eruption, which moved like apisonadoras, have a different chemical composition from later lavas. The latter were faster and flowed forming rivers and lava tubes that reached the sea.
The distance reached and the dangers caused by the advance of the two types of lava are different. Therefore, rapid monitoring of possible chemical changes in the emitted magma could help to manage future volcanic emergencies.
In addition, our data seems to mark the moment when, two weeks before the end of the eruption, the magma that fed it began to cool. This indicates that the magma supply was possibly running out. In the future, similar observations could help detect the end of other volcanic eruptions.
Image taken by a drone of the eruption. Geological and Mining Institute of Spain, Author provided
Monitoring of future eruptions
We do not know when the next eruption will be in the Canary Islands. What we do know is that there will be, because the islands are of volcanic origin and are nourished by the magmas that make them grow and be as fertile as they are spectacular.
We hope that our laser analysis can help scientific monitoring and reduce the economic and, above all, human impacts of volcanic eruptions. Impacts that, unfortunately, the palm trees suffered in 2021 and that still continue to affect the population of the island.
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