The 2014-2015 eruption at Fogo volcano

Marco Bagnardi is a postdoctoral scientist at the University of Leeds. He works on measuring and modelling volcanic deformation, and is co-funded by COMET and the EU FUTUREVOLC project.

Understanding the impacts and highlighting future risks using Sentinel-1A

Between November 2014 and February 2015, after twenty years of inactivity, Fogo volcano – the most active in the Cape Verde archipelago – erupted for over two months.

Although the eruption received little attention from the international media, it caused the disappearance of two villages under tens of metres of rubbly lava, and the displacement of more than a thousand people.

1)The village of Portela in June 2015.  The village is almost entirely covered by a thick lava flow that travelled more than five kilometers from the eruption, leaving only a few roofs that were not entirely engulfed.  (Credit: Bagnardi)
The village of Portela in June 2015. The village is almost entirely covered by a thick lava flow that travelled more than five kilometers from the eruption, leaving only a few roofs that were not entirely engulfed. (Credit: Bagnardi)

Since the eruption began, we have been monitoring ground deformation using InSAR techniques.  InSAR is one of the best tools for characterising the inner workings of a volcano, particularly in terms of identifying where large volumes of magma are stored and how it moves through the Earth’s crust to reach the surface and feed eruptions.

Using data from Sentinel-1A, which had only been operating for a few weeks when the eruption began, meant that our study was the first to use the new satellite to investigate surface deformation associated with volcanic activity.

During the eruption, lava spewed for weeks in vigorous fire fountains which created fast-moving lava flows.  The data confirmed that there was no shallow (less than a few kilometres beneath the surface) magma reservoir within the volcano, meaning that magma was instead moving rapidly from depths of more than ten kilometres to feed the eruption at the volcano’s summit.

We focused our attention on the magmatic intrusion that was feeding the eruption.  Taking advantage of Sentinel-1A’s unique capabilities, particularly its TOPS (Terrain Observation by Progressive Scans) mode, we found that the deformation was probably being caused by the intrusion of a sub-vertical planar body, or dyke, from beneath the volcano to its surface.

 

Sentinel-1A TOPS interferogram showing deformation associated with the emplacement of a dike beneath the surface. The ground was displaced for tens of centimetres on both sides of the intrusion. Each color cycle represents approximately three centimetres of ground motion away from the eruptive fissure.
Sentinel-1A TOPS interferogram showing deformation associated with the emplacement of a dike beneath the surface. The ground was displaced for tens of centimetres on both sides of the intrusion. Each color cycle represents approximately three centimetres of ground motion away from the eruptive fissure.

 

We are now analysing the InSAR data to assess the stability of the entire volcanic structure.  The intrusion of magma through the volcano could push the volcano’s very steep flanks, making them unstable and potentially causing them to crumble, creating enormous landslides.  Importantly, Fogo experienced this kind of event 100,000 years ago and still shows scars on its landscape that evidence a giant landslide into the Atlantic Ocean, potentially causing a large tsunami.

Centre for Observation and Modelling of Earthquakes, Volcanoes and Tectonics