The cross : Specialists say you have to wait ten days before declaring the end of a rash. Is this the case with Cumbre Vieja? Did this one fall asleep on Christmas day?
Raphaël Paris:The rash is over. All the magma came back up. There is still a small residual seismicity and there is still a little magma stored mainly between 10 to 15 kilometers deep, but it does not rise. This means that there is no longer any deep seismicity, at a depth of about thirty kilometers, as was the case during the eruption. The source is clearly dried up.
What was the impact of the eruption on the inhabitants?
RP: The main impact is economic as it occurred in a heavily populated area. More than 7,000 people have been evacuated, of whom around 500 are still living in hotels, and nearly 3,000 buildings have been destroyed (figures given by local authorities). The quantity of ash was surprising as well as the volumes of lava flows. The gases emitted forced many people to stay locked in their homes.
What have you learned from these eighty-five days of heavy seismic activity?
RP: We had the remarkable opportunity to study a volcanic eruption with all current means, in very active oceanic islands which remain hot spots. The main lesson is that the process probably started about ten years ago.
→ EXPLANATION. In the Canaries, Cumbre Vieja, a very active volcano
Monitoring began from 2000-2011 with signals of gas and deformation of the island. During the following decade, specialists saw a change: the magmatic system of the island was re-energized.
On other eruptions, we had elements but no data. This time, we were able to follow the process from the start. In the Canaries, we often see the magma moving several kilometers deep without it coming out. Usually it cools down and solidifies inside.
Do we know when the volcano will wake up?
RP: It is impossible to say how long he will stay asleep. The Canary Islands remain considered geologically active volcanic islands, even though there is no ongoing eruption. They are independent of each other. The source of magma at depth, up to a hundred kilometers, is common to the other volcanoes on the island, but it cannot cause a chain explosion.
→ READ. A new tool to predict the eruption of volcanoes
We have a big project started with Spanish colleagues from the University of Las Palmas in Gran Canaria to study the ashes. In France, a team is studying the impact of ashes on health. Personally, I work on the mapping of lava flows, and colleagues do digital models of these flows. This is used to make predictive maps and to anticipate other eruptions.
You are a specialist in tsunamis that can be generated by volcanoes. About Cumbre Vieja, a study by researchers at University College London, in September 2000, on the risks of tsunami as far as the British coasts had raised fears? Is it credible?
RP: It is a scenario often mentioned. The risk is not to be taken lightly. But the British study was catastrophic, based on unreliable sliding volumes, which gave monstrous waves. Since then, work has been done on more serious models which show that, from the moment we have a mass of material that collapses in the sea, it causes significant waves for the other Canary Islands and could generate waves of 1 to 2 meters on the coasts of the Caribbean and the east coast of the United States. This is not trivial, but we do not know when it can happen and in what context
During the eruption of Cumbre Vieja, we were in contact with the group of experts from the Caribbean Tsunami Warning Center. It was unlikely that a tsunami would occur, but a watch was maintained. If any part of the island’s side had started to warp and slide, we would have been concerned.
Two peninsulas of 43.5 hectares to the south and 5 hectares to the north were created by the lava flows from Cumbre Vieja which slipped into the Atlantic Ocean. Will they be fertile?
RP: Lava can become fertile if ash falls regularly around the volcano as this enriches the soil from a mineral point of view. Otherwise, it takes human intervention to cultivate.
The priority for the inhabitants of La Palma is to repair the electricity and drinking water networks, to rebuild the roads, but it is necessary to wait for the soil covered with lava to stabilize. When the thickness reaches 40 meters, for example, it takes several years for it to cool down.