When volcanoes erupt near the places where humans live, the costs can be devastating, but emergency responders and scientists have difficulty predicting the extent of the damage in advance. When a vent opened in November 2014 on the side of the Fogo volcano in Cape Verde, a chain of islands off the coast of Africa, local civil responders were concerned that lava would overrun the villages of Bangaeira and Portela. Emergency services, hoping to model the lava’s path, reached out to a team of scientists from across the globe who’d been developing a model for years.
Unlike many other volcanic models, which tend to rely on just a few sources of data to model aspects of an eruption, this team’s project incorporates data from satellites, three-dimensional (3-D) models of the Earth, and other sources to construct a comprehensive simulation of the eruption. This gives the model’s developers the rare capacity to predict where lava will flow in near-real time.
The team had tested an older version of its model against small eruptions high on the slopes of Mount Etna; Fogo offered a chance to try the model on a real-world disaster. The stakes were high, with around 1000 villagers’ property at risk, so the consequences would be serious if the model got it wrong. In a paper published recently in the Journal of Geophysical Research: Solid Earth (JGR: Solid Earth), the scientists described how they plotted the lava’s course.
An International Effort
The volcanic modeling began a week after the eruption started, when Cape Verde civil services reached out to a network of volcanologists—from the island of Tenerife in the Canary Islands, at Italy’s National Institute of Geophysics and Volcanology, and at the University of Cape Verde. By then, the lava on Fogo Island had crept to within just a few hundred meters of the edge of Portela, the closer of the two villages. No one knew whether the lava would bypass the village or destroy it and, if the lava kept going, whether Bangaeira was in danger as well.
To build their model, the international network of volcanologists relied mostly on satellite data to pinpoint the location of the volcanic vent and observe the lava flowing from it. “The topography can change during the volcanic eruption, and that can have a big impact on where the lava is going to go. And really the only way to get that information is by satellite, because nobody should be going up there during an eruption,” said Chuck Connor, a volcanologist at the University of South Florida in Tampa who was not involved with the study.
The researchers added the fresh, hot volcanic vent to a 3-D virtual map of the island using location information from an infrared satellite image. They used information from the volcano’s past eruption to compute approximations of the lava’s viscosity, how fast it was cooling, and other factors—all of which can change how lava behaves. Then the team ran simulations, allowing virtual lava to flow from the fissure onto the hillsides in multiple runs, during which different assumptions played out regarding how much lava would come out and how fast.
The team updated its model again and again as the eruption progressed. Sometimes, the volcanologists’ reliance on satellite observations became more of a hindrance than a help. “Ash clouds can totally or partially cover the view from satellites, making it impossible to estimate [lava] effusion rate,” noted Gaetana Ganci of the National Institute of Geophysics and Volcanology in Rome, Italy, a coauthor of the 5 April study.
Mostly Submerged by Lava
The virtual trials showed both villages in danger, members of the team said. If the lava came out slowly, the villagers would have about 5 days before their homes were destroyed. The scientists created Google Earth overlays of their predictions that showed where the lava was expected to travel and pool, and they shared those with the local Cape Verde civil protection services.
Local authorities evacuated more than 1000 people to temporary housing. Even though many villagers had time to save their belongings and the local winemakers rescued some of their wine, lava overran both villages. Many evacuees later returned to find their homes buried or swept away by molten rock. Later, some rebuilt their houses “on top of the still-warm 2014–2015 lava flows, with temperatures measured on the floor in the house up to 50°C,” Ganci wrote.
Model’s Accuracy and Usefulness Advance
After 2 weeks, during which the modelers tracked and mapped the Cape Verde eruption, the final outlines of the lava flow corresponded closely to the researchers’ simulations.
This research team wasn’t the only one observing the volcano: A different paper, published earlier this year, describes how another group of scientists used radar to track and model the lava’s flow beneath the ground, before it emerged from the volcano.
However, to model the eruption as it happened, as the authors of the JGR: Solid Earth paper did, “is really cutting-edge,” said Connor. It’s one thing to build predictive models far in advance of the eruption when you have time to run the simulations but quite another to attempt to model the lava as it flows, he said. The former requires a deeper knowledge of the individual volcano and its history, whereas the latter requires more raw computing power.
Connor said he expects models to continue the trend of becoming ever more comprehensive and a better tool for local governments to call upon. Eventually, they will likely incorporate ash cloud data to warn nearby towns of hazardous plumes, he added, noting that he and other lava modelers are excited about the possibilities of applying similar near-real-time models to future eruptions.
“Volcanology has really changed over the last couple of decades,” said Connor. “If you go back in time, it was more of a descriptive science.”
—Elizabeth Deatrick, Writing Intern
Citation: Deatrick, E. (2016), As lava flows, refined model predicts a path, Eos, 97, doi:10.1029/2016EO051871. Published on 4 May 2016.