The eruption of the Cumbre Vieja volcano on La Palma occurred after several days of earthquakes in the area. When is a volcano considered active? Experts from the Smithsonian Global Volcanism Program believe that a volcano that has erupted in the last 10,000 years can be considered active. According to this definition, there are many active volcanoes in the world that do not have to be erupting, in fact they may not have erupted for thousands of years. Due to this, the term ‘sleeping volcano’ can be included, explained to us by the professor of the Department of Theoretical and Cosmos Physics of the Earth Physics Area at the University of Granada Janire Prudencio: “ Normally we differentiate between active volcano, dormant volcano , and extinct volcano. Extinct means that in historical time – last 10,000 years – it has not erupted. The challenge is to distinguish if a volcano is dormant or active. With some like Stromboli erupting every few minutes, there is no question, it is a fully active volcano. The ideal would be to identify all the dormant volcanoes, because at any moment they could erupt ”.
It is quite difficult to give a definitive number of volcanoes that could erupt: if, for example, only 100% confirmed historical eruptions are taken into account, it will probably not count eruptions from the past or for which there are uncertain records, and many times it will be a criterion that will depend on the opinion of each volcanologist. Smithsonian scientists, in fact, make it clear: “Because the dormant intervals between major eruptions in a single volcano can last from hundreds to tens of thousands of years, dwarfing the relatively short historical record in many regions, it is misleading to restrict the use of ‘active volcano’ to recorded human memories ”. A more precise term would be, according to them, ‘historically active volcanoes’.
According to this, there would be 1,356 volcanoes that are thought to have erupted during the Holocene, although 866 of these would be confirmed. “The numbers will change as new research is published, new dates are acquired or new criteria are applied.”
Predicting eruptions
Predicting whether any of these dormant volcanoes will soon erupt is a complex task and several different techniques are often used: seismographic detection of earthquakes and tremors that, as we have seen, usually precede eruptions, measurements of soil deformation that generally it precedes increased magma, changes in volcanic gas emissions, and changes in gravity and magnetic fields. Thus, if noticeable changes in background activity are observed, scientists may suspect that an eruption may be imminent. Unfortunately, however, there is still no way to know for sure whether a volcano has just erupted or will soon erupt again.
In 2021, 68 volcanoes have erupted and currently there are around 50, according to the weekly record of global volcanic activity published by the Smithsonian Global Volcanism Program. Some have been erupting for decades, such as Sheveluch in the Kamchatka region (Russia). In Europe, in addition to the La Palma volcano, at least three volcanoes are erupting in Iceland.
