Madrid, 28 (European press)
This is the result of a study by researchers from Johannes Gutenberg University in Mainz (JGU) on the 2021 eruption, the longest and most turbulent in the recent history of the Canary island of La Palma. More than 1,600 buildings were destroyed or damaged, including about 1,300 apartment buildings. Images of lava flowing through settlements into the sea have been seen all over the world.
“The viscosity of the lava was one of the lowest ever observed for a basaltic eruption,” said Yves Wiesel, a doctoral candidate in Professor Jonathan Castro’s research group at the JGU Institute of Geosciences. Castro and Weisel measured the viscosity of lava from Cumbre Vega in the laboratory and report their findings in Nature Communications.
“In fact, it was possible through television and online images of the lava flows to see how fast the lava was moving, and thus inferred a decrease in its viscosity,” Wiesel said. From the images captured, the researchers calculated that in some cases, the velocity of the lava exit was greater than ten meters per second. In addition, the researchers were able to observe phenomena in lava flows that are usually more characteristic of turbulent flowing fluids, such as those within water bodies, for example the so-called hydraulic jumps or standing waves.
To more accurately determine the viscosity of lava, researchers collected ash particles that solidified as they fell from the sky at La Palma. Back at the University of Mainz, they were able to determine the temperature of the eruption through chemical analysis of these samples, and revealed that the magma must have been in the range of about 1,150 to 1,200 degrees Celsius. They also melted some samples and measured the viscosity of the molten at these temperatures using a device known as a rheometer.
“Shortly after the eruption began, the viscosity of the lava was about 10 to 160 Pas,” Wiesel explained. “This is 10 times lower, for example, than the viscosity of the lava discharged from Kilauea in Hawaii in 2018.” According to Feisel, the lava from Cumbre Vieja was very liquid primarily because of its specific chemical composition, in particular its relatively low content of silica, and the way this melt crystallized: “When the lava cooled, crystals formed and this may have helped to retain a low content of silica. Silica (SiO2) from the lava, allowing it to maintain its low viscosity for a longer period of time.”
The results of this research may help mitigate damage from volcanic eruptions in the future. “It is always difficult to predict when and how volcanoes will erupt,” Wiesel admitted. However, information regarding lava viscosity can be useful because liquid lava like Cumbre Vieja is typically discharged from a variety of locations, some of which may vary over time. Knowing that lava is low in viscosity and will flow rapidly, among other things, can help integrate eruption and terrain models to better predict the path and evolution of future lava flows.