Researchers from Mainz University came to the conclusion that the lava produced by the most recent volcanic eruption on La Palma had an exceptionally low viscosity.

The 2021 Cumbre Vieja eruption was the longest and most devastating volcanic outburst on La Palma, a Canary Island. Over 1,600 structures, including over 1,300 homes, were either destroyed or severely damaged. Around the world, people saw images of lava pouring over towns and into the sea.

The lava erupted during the eruption was particularly low in viscosity, forcing it to flow quickly, according to researchers at Johannes Gutenberg University Mainz (JGU).

Yves Feisel, a PhD candidate in Professor Jonathan Castro’s research group at the JGU Institute of Geosciences, noted that “the lava’s viscosity was among the lowest ever observed for a basaltic eruption”.

Castro and Feisel determined the viscosity of Cumbre Vieja lava in the laboratory and reported their findings in Nature Communications.

“It was actually possible from the footage of the lava flows on TV and online to see,” according to Feisel, “how fast the lava was moving and thus deduce its low viscosity.”

On the basis of the captured photos, the researchers determined that in certain instances the lava’s exit velocity exceeded ten meters per second. The researchers were also able to spot phenomena in the lava flows that are often more common in turbulent flowing fluids, like those in water bodies, like so-called hydraulic jumps or standing waves.

To more precisely quantify the viscosity of the lava, the researchers collected solidified ash particles as they dropped from the sky on La Palma. By chemically testing these samples at Mainz University, they were able to ascertain the eruption’s temperature, which showed that the magma must have been between 1,150 and 1,200 degrees Celsius.

Additionally, some of the samples were melted, and the viscosity of the melt at these temperatures was determined using a tool called a rheometer. The lava had a viscosity of between 10 to 160 Pascal seconds “shortly after the eruption began,” according to Feisel.

“That is a figure ten times lower than, say, the viscosity of the lava discharged from Kilauea in Hawaii in 2018.” 

Feisel asserts that the chemical makeup of the Cumbre Vieja lava, particularly its relatively low silica content and how this melt crystallized, is primarily responsible for its fluidity: “When the lava cooled, crystals were formed and this likely helped retain the low silica (SiO2) content of the lava, allowing it to maintain its low viscosity over a longer period of time.”

These findings could aid in the future mitigation of volcanic eruption damage. Feisel acknowledged that “It is always very difficult to predict when and how volcanoes will erupt.”

However, since fluid lava, like that from Cumbre Vieja, is typically discharged from a variety of places, some of which may change over time, the knowledge on lava viscosity may prove valuable.

Integrated eruption and terrain models can, among other things, benefit from knowing that the lava is low in viscosity and will flow quickly in order to better anticipate the path and evolution of subsequent lava flows.

Image Credit: Jonathan Castro

You were reading: New Study Explains Why The Cumbre Vieja Eruption Was So Destructive