Some volcanoes erupt without warning signs because the internal pressure of the magma can increase very rapidly, causing a sudden explosion. This situation can occur when gases are trapped under a layer of very viscous lava, thus preventing any early warning.
Many volcanoes surprise due to their very particular internal structure. These volcanoes generally have narrow conduits or are blocked by solid rocks or cooled magma: this acts like an airtight plug, quietly accumulating pressure. Additionally, some have very thick and viscous lava, often rich in silica, which struggles to escape easily. As a result, the pressure builds up in the magma chamber until it abruptly explodes the rocky plug without warning. Another common feature: these volcanoes sometimes hide small cracks or internal faults that are not easily detected on the surface, thus facilitating surprise eruptions with no visible signs beforehand.
Beneath the earth, magma can sometimes become trapped under pressure in buried magma chambers. When a crack or sudden weakness forms in the rock, bam, the magma quickly rises to the surface. This rapid movement causes a sudden drop in pressure, releasing the gases contained in the magma. The result: a violent release of energy that is often explosive. In some cases, the rapid crystallization of minerals can also affect the viscosity of the magma, leading to an unexpected eruption without the typical prior tremors or swelling of the volcano. Finally, sometimes it is the rapid arrival of fresh, hot magma from greater depths that disrupts the balance underground, abruptly triggering a surprise eruption.
Volcanic prediction mainly relies on measuring earthquakes, ground deformation, or gas emissions. However, some volcanoes catch everyone by surprise because their signals remain weak or almost nonexistent before eruptions. There is also a problem of monitoring coverage: not all volcanoes around the globe are monitored continuously, far from it. Some volcanoes located in remote areas, hard to access, or simply lacking observation resources, can awaken without anyone having detected the slightest anomaly beforehand. And even where advanced technical means exist, current instruments do not always capture the deep evolution of magmas. Technical monitoring has its limitations: some internal phenomena completely go under the radar, preventing any reliable anticipation.
In May 1980, the explosive eruption of Mount Saint Helens in the United States took everyone by surprise: without any real immediate warning signs, the entire flank of the mountain suddenly exploded. Another notable case is the Ontake volcano in Japan in 2014, a brutal and unexpected eruption that occurred during a tourist day, trapping numerous victims. In New Zealand, in 2019, the volcanic island of White Island also surprised experts; there were no clear signs before the explosion, yet many visitors were still present. These eruptions show how nothing is truly certain when it comes to volcanism: even when we think we know a volcano, nature always finds an unexpected way to remind us that it remains unpredictable.
Silent volcanic eruptions are all the more dangerous because local populations are generally not alerted in time, making risk management extremely difficult for the authorities.
Nearly half of the recent volcanic eruptions around the world were not preceded by detectable warning signs using traditional volcanic monitoring instruments.
The Ontake volcano in Japan, which unexpectedly erupted in 2014, showed no classic signs of previous seismic activity, completely surprising the volcanologists and hikers present on its slopes.
The analysis of emitted volcanic gases can sometimes reveal hidden underground activity that is not detectable through conventional means such as seismic analysis or visual observation of changes in the terrain.
Not necessarily. Although some volcanoes that have been dormant for a long time can experience unpredictable awakenings, even active volcanoes or those under regular monitoring can exhibit unexpected explosive phases. Ultimately, it is the composition of the magma and the internal dynamics of the volcano that determine the predictability of its eruptions.
The best protection often lies in pre-defined evacuation plans, regular awareness-raising among local populations, and careful observation of the instructions provided by local authorities in the event of a sudden emergency.
Although modern volcanic monitoring systems can significantly reduce risks, no current technology can completely eliminate unforeseen eruptions. Certain internal conditions, such as underground magmatic dynamics or structural fragility, still partially elude human observation.
Various instruments such as seismographs, inclinometers, GPS, gas sensors, and thermal cameras allow specialists to monitor volcanic activity in real time and potentially anticipate an eruption. However, even these advanced instruments have limitations when faced with geological unpredictability.
Yes, some volcanoes like Mount Ontake in Japan and Whakaari volcano in New Zealand have demonstrated their ability to erupt without obvious precursor signs, due to their geological composition and complex magmatic system, which makes their activity particularly difficult to predict.
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