Underestimated natural hazard – New findings based on the most recent eruption of the Cabo Verdean volcano Fogo

Underestimated natural hazard – New findings based on the most recent eruption of the Cabo Verdean volcano Fogo (photo: Nicole Richter, GFZ).

08.09.2016: Where a lightning stroke yesterday it won’t strike again today. People often act upon natural disasters based on this fatal logic. They settle within floodplains or on hillslopes, even if the potential of a future flooding or landslide remains high. A new study as published in the open access journal Natural Hazards and Earth System Sciences shows that this assumption can also have fatal consequences at active volcanoes. It investigates the lava flow hazard before and after the most recent eruption of Fogo Volcano, Cabo Verde. GFZs PhD student Nicole Richter is the lead author of the study.

The island of Fogo, also Ilha do Fogo, in English “the island of fire”, is one of the Cabo Verdean Islands located in the central Atlantic Ocean, off the coast of Northwest Africa. Fogo is one of the most active volcanoes on Earth. During the most recent eruption which occurred between November 2014 and February 2015, basaltic lava flows destroyed about 90 percent of the houses of the villages Portela and Bangaeira. Also the small settlement Ilhéu de Losna and as much as 25 percent of the agricultural area within the Chã das Caldeiras (i.e. the central high plain at an average altitude of 1700 meters above sea level) were destroyed. About one thousand people lost their homes. Shortly after the eruption had come to an end, reconstruction of the houses within the Chã had started again. The villagers build their houses on top of the cooling lava flow. They seem to assume that a future lava flow will not affect an area that was once overrun by a lava flow and is therefore now elevated above the surroundings.

This assumption was now disproved by an international team of scientists around Nicole Richter, GFZ section Physics of Earthquakes and Volcanoes. Applying computer simulations to topographic data that were acquired before and after the most recent eruption the team provided comprehensive lava flow hazard assessment for Fogo Volcano. The precise terrestrial laser scanning technique was used to analyze the new topography in the area affected by the eruption. Results were compared to the pre-eruptive topography. This way the scientists were able to estimate the erupted volume. Furthermore, they used remote sensing data collected by the German satellite TerraSAR-X to map the lava flow emplacement over time. The data were used to feed thousands of model simulation runs in order to estimate the most likely lava flow paths and to create a lava flow hazard map for Fogo Volcano. The lava flow model was suitable to reconstruct the most recent eruption which proofs the model results to be reliable.

Some of the areas that were overrun by the 2014-2015 lava flow are not necessarily safer now. The lava flow hazard remains high also at the location of the largely damaged villages of Portela and Bangaeira. „Our results highlight the importance of up-to-date topographic and hazard information in active volcanic regions. It is now important to communicate our results to the decision makers at Fogo and to provide hazard information also to other volcanic regions“, says Richter. Maybe, so hope the scientists, this study can support sustainable settlement activity and land use planning around active volcanoes. (ak)

Richter, N., Favalli, M., de Zeeuw-van Dalfsen, E., Fornaciai, A., da Silva Fernandes, R.M., Pérez, N.M., Levy, J., Silva Victória, S., Walter, T.R., 2016. Lava flow hazard at Fogo Volcano, Cabo Verde, before and after the 2014–2015 eruption. Natural Hazards and Earth System Sciences, 16, 1925-1951. DOI: 10.5194/nhess-16-1925-2016