On Tuesday evening, lava from the Cumbre Vieja volcano in the Canaries reached the ocean. “It happened at 11 p.m. (10 p.m. GMT),” said 20 minutes Raphaël Paris, CNRS researcher at Laboratoire Magmas et Volcans (LMV), present on site. A feared phenomenon since the volcano erupted on September 19 on the Spanish island of Palma and resulting in the evacuation of many inhabitants.
The lava flows have already caused material damage by destroying in their passages nearly 600 buildings and by covering some 258 hectares of land, according to the European system of geospatial measurements Copernicus. But their arrival in the waters of the Atlantic Ocean has quite other consequences, in particular the release of toxic gas feared by specialists. 20 minutes takes stock of the situation.
What is the chemical phenomenon caused by the contact of lava with the ocean?
“When they emerge from the eruptive cracks on Cumbre Vieja, the lava flows have a temperature close to 1050 ° C”, explains Pierre-Jean Gauthier, CNRS researcher at the Magmas and Volcanoes Laboratory. While the lava cools slightly during its journey, it is still extremely hot when it reaches the ocean. It is this extremely high temperature that will cause the famous phenomenon. “It breaks the chemical bonds of water molecules, which are hydrogen and oxygen. The hydrogen atom then binds to the chlorine present in the salt water and forms hydrochloric acid, ”explains Guillaume Boudoire, volcanologist at LMV and specialist in gas geochemistry.
This hydrochloric acid is then found in the air, because when the lava (at more than 1,000 ° C) meets sea water (at around 23 ° C) in the region, “the latter is instantly vaporized”, describes Audrey. Michaud-Dubuy, volcanologist at the Institut de Physique du Globe de Paris. “This sudden contact causes the formation of a noxious fog, or plume, called a ‘laze’. It is a contraction of the English words “lava” and “haze” which mean respectively “lava” and “fog” “, continues the expert.
What is the noxious smoke that escapes from the contact area between the lava and the ocean made of?
This is essentially made of seawater vapor, hydrochloric acid, but also ash. “These fine particles are formed when lava and water come into contact and cause what is called a phreatic explosion,” explains Guillaume Boudoire. “Sea water also contains sulphates, fluorine, iodine and carbonates which can form other toxic gases on contact with lava and rise into the atmosphere”, adds Audrey Michaud-Dubuy, which warns about the potential dangerousness of this cloud.
Are these gases toxic to humans?
Breathing this cloud directly is obviously dangerous for health and can cause various respiratory problems such as asphyxia, suffocation, irritation or even bronchopulmonary edema. However, unless you are within 300 meters of the contact zone, no risk. The danger varies, however, depending on the weather conditions, recalls Raphaël Paris. “The Alizée wind arrived at the right time, since it is blowing towards the ocean. This could be a problem if other winds pick up and push the gas plume towards populated areas. »The inhabitants could then feel some difficulty in breathing, irritations and have coughs.
If the chemistry of the island’s atmosphere will be impacted by the gases and the air quality is likely to be poorer, Pierre-Jean Gauthier insists that “the plume is diluted very quickly in the atmosphere and that the quantities of toxic elements remain low ”. The long-term effects will therefore remain negligible unless the volcano remains in eruption non-stop for years.
Are these gases harmful to the environment?
For Pierre-Jean Gauthier, it is obvious that the vegetation will not appreciate the sudden arrival of this acid gas. “This will cause plant pathologies with a whole gradation of symptoms depending on the concentration at the point of impact, ranging from simple yellowing of leaves for example, to plant necrosis, or even, ultimately, the death of the plant. . “
Again, the impact on the environment and animals will also depend on the weather. “If there is precipitation, it can interact with the gas plume and fall back into acid rain,” says Guillaume Boudoire, who mentions potential problems for agricultural production linked to the presence of these acid particles in the soil. These rains can also cause burns to the skin, mucous membranes or eyes of humans, such as animals, continues the specialist in gas geochemistry.
Is the situation necessarily going to get worse?
Concretely, toxic gases will escape into the air as long as the lava comes into contact with sea water. However, as Raphaël Paris present on site, since the eruption resumed last Sunday, “the flow of lava is well fed and stable ”. So there is no reason for it to stop. However, as Audrey Michaud-Dubuy points out, “one can imagine that if the lava flow always follows the same path, it will end up enlarging the island by creating new lands. Thus, it could end up no longer touching the sea but simply thickening ”.
Is the formation of toxic gas the only dangerous phenomenon caused by the meeting of lava and the sea?
Depending on the viscosity of the rocks and the topography of the coast, vaporized seawater can sometimes get trapped under the lava. “In this case, an excess pressure is created which will lead to coastal explosions which can sometimes be very violent and therefore dangerous, if there are observers nearby”, explains Pierre-Jean Gauthier. The CNRS researcher recalls that in Hawaii, where lava flows have already hit the ocean, there have already been accidents. “The unwary curious who came to watch the show by boat, and approaching too close, received projections of blocks and ashes. “