The largest underwater volcano ever discovered has been behind a mysterious string of earthquakes off the cost of the French island of Mayotte.
The mystery had lasted for over a year. On May 10, 2018, small seismic waves began to shake the region of Mayotte, this French archipelago wedged between Madagascar and the African coast. Five days later, the islands were hit by an earthquake bigger than the others, with a magnitude of 5.8 — a local record. Since then the small earthquakes have not stopped. Nearly 1,500 tremors of more than 3.5 magnitude were recorded during the year 2018, with a new peak of intensity at the end of December. In the last days of the year, the micro quakes, imperceptible to humans, never ceased: there were several per hour.
Another worrying sign: “Since July 2018, the island has moved eastward and sank more than 10 cm, which is considerable in such a short time.” Preliminary deformation patterns suggest that the source of this phenomenon is the deflation of a very large magma pocket located between 20 and 30 km deep, 50 km off the island”, says the Institute of physical world.
What could have been behind the mysterious phenomenon? The signals were atypical on the seismometer readings, and the origin of the seismic activity seemed to come from the sea, east of Mayotte, at 3,500 meters deep.
To better understand and anticipate this phenomenon, the French government mobilized, in June 2018, the National Committee for Scientific Research (CNRS), the Bureau of Geological and Mining Research (BRGM), the Institute of Earth Physics in Paris ( IPGP), the French Research Institute for the Exploitation of the Sea (IFREMER), the University of Reunion, the Institute of Earth Physics of Strasbourg (IPGS), the National Institute of Geographical Information and (NSA), the Ecole Normale Supérieure (ENS), the National Center for Space Studies (CNES) and the Hydrographic and Oceanographic Service of the Navy (SHOM) as well as the scientific vessel Marion Dufresne, which carried out an oceanographic campaign on place, baptized Mayobs.
These terrestrial and oceanic observations made it possible to highlight the birth of a new submarine volcano, 50 km from Petite-Terre. In addition, a number of instruments have been deployed to precisely locate the origin of the seismic swarm.
Located at a depth of 3,500 m, it is already 800 m high with a base of 4 to 5 km in diameter. In other words, it could be growing about 2 meters a day. It emits a plume of volcanic fluids 2 km high that does not reach the surface of the water yet. In addition, the population of Petite-Terre has discovered gas emissions on the coast, a common sign encountered in this type of volcanic activity.
It is now a matter of following and anticipating the development of this volcano. Scientists are mobilized to process, analyze and interpret the wealth of data acquired in recent months. This operation will require extensive work to assess the risks posed for Mayotte in terms of seismic, volcanic, and tsunami risks.
Since the beginning of the earthquake phenomenon, the French government has continuously adapted, according to the lighting of the scientists, the measures of surveillance and prevention to face this exceptional geological phenomenon which impacts the Mahoran population and more widely this part of Indian Ocean.
Already, the French government has defined the action plan composed of the following 5 axes:
- Establishing monitoring devices and measuring instruments (such as seismographs and GPS beacons) as soon as possible to continuously monitor the phenomenon
- Acquire extensive scientific knowledge through adapted missions
- Immediately update the knowledge of the risks posed by this phenomenon and the potential impacts for the Mahorese territory, the results of which can be presented within three months.
- Immediately strengthen the crisis management planning and preparation system. To this end, a mission to support civil security planning is dispatched to provide support to the island.
- Regularly inform the population, in connection with local elected officials. Finally, these new knowledge elements will be shared internationally in the Indian Ocean area.
The birth of an underwater volcano is an unusual phenomenon, as spectacular as it is dangerous.