The explosive mixture of water and lava woke up a monster in Capelinhos. The science that explains the 1957 eruption in the Azores – Observer

In the Azores, shortly after having witnessed the emission of water vapor, carbon dioxide, sulfates and sulfur dioxide, the new volcano began to emit large pyroclasts — volcanic ash mixed with sand, dust and lapili, as well as pumice stone made of basalt — in pointed jets 1,400 meters high, composed of black bulbs due to the solidification of the lava; and other whites, on account of water vapor, which came to exceed four kilometers in altitude. The emission of these ash was so abundant that by October 10, about two weeks after the onset of volcanic activity, an islet 800 meters in diameter, 99 meters high and a crater opened to the sea had already formed. In that same place, before the eruption, the depth of the ocean was 70 meters.

These explosions of ash happened because of the contact of very cold water with the scalding lava, described to the Observer the volcanologist José Pacheco, director of the Institute of Investigation in Volcanology and Risk Assessment. It was the perfect mixture: an amount of water came into contact with the same amount of lava, magma pulverized at high speeds, giving rise to large volumes of ash. Impregnated with sodium chloride, resulting from this chemical reaction, the explosions spread through the air and condensed, increasing the rain of ash that covered Faial. Crops were damaged, some villages had to be evacuated, and the cone of the new volcano quickly rose in view of the Azoreans.

Until, at the end of October, peace returned to Faial. The volcano’s cone, made of very unstable material, suffered partial collapses and the islet around the mouth from which the pyroclasts came out was once again submerged. But it was only for a short time: at the beginning of the following month, the eruption reactivated to the point of creating a new island about 100 meters from the first. Its growth continued until the formation of an isthmus that connected the newly formed island to Faial, with a lagoon that was fed with materials dragged by the sea or by sand thrown by the volcano. In December, the isthmus was 600 meters wide and the explosive phase of Capelinhos, whose volcano was constantly fed by the combination of seawater and lava, reached a peak earlier in the same month.

It was always through short intervals of calm that the eruption continued until 1958. On one occasion, however, it took on different characteristics: as the volcano was already on the surface, and the sea water had no direct contact with the lava source, it began to seep down the flanks. That’s what happened on December 16, at 10:30 pm, when the light emitted by the glowing lava lit the clouds in a pink glow. In the eastern region of the volcano, a fracture opened which gave rise to seven lava fountains that rose from 10 to 15 meters in height. It was from them that the lava that was to reach the sea broke.