(CNN Español) — The eruption on saturday of the Hunga Tonga-Hunga Ha’apai volcano, located near Tonga, put the issue of submarine volcanoes at the center of the discussion. Why?
To begin with, this volcano is of a submarine type, according to the Global Volcanism Program of the Smithsonian Institution. What’s more, your rash it was probably the largest recorded anywhere on the planet in more than 30 years, according to experts.
The eruption was so strong that images from space captured the blast in real time, as a huge plume of ash, gas and steam was thrown up to 20 kilometers into the atmosphere, and tsunami waves crashed into the Pacific. You can see these images in the following video:
It was such a violent eruption that triggered tsunamis that hit Hawaii, Japan and Tonga’s largest island, Tongatapu, sending waves that flooded the island nation’s capital.
Its strength is not due to the fact that it is an underwater volcano, but it does raise some doubts about this type of volcano.
What are underwater volcanoes?
Simply put, they are volcanoes that are underwater. According to Oregon State University (OSU for its acronym in English), “the most active volcanic systems on Earth are hidden under an average of 2,600 meters of water.”
Why are they the most active?
The OSU notes that undersea volcanoes are responsible for about three-quarters of Earth’s annual magma production.
“A global system of mid-ocean ridges generates approximately 75% of the annual magma production; it is estimated that 3 cubic kilometers of lava are emitted,” explains the Oregon university institution. It should be noted that the mid-ocean ridges are “mountain ranges or submarine mountain ranges of volcanic origin”, according to Seismology Chile, nonprofit organization.
Also, the publication Geophysics, from the Institute of Geophysics of the National Autonomous University of Mexico (UNAM), indicated in 2004 that submarine volcanoes represent 80% of the planet’s volcanism, which is more or less in accordance with the percentage of annual magma production.
How many underwater volcanoes are there in the world?
The OSU mentions that it is estimated that there are about 4,000 volcanoes for every million square kilometers on the bottom of the Pacific Ocean.
So if you apply this estimate to all the world’s oceans, says the OSU, “then there are more than a million underwater volcanoes.”
“Perhaps as many as 75,000 of these volcanoes rise more than half a mile (1 kilometer) above the ocean floor,” he adds.
How are underwater volcanoes formed?
As in the case of continental volcanoes (those that can be seen with the naked eye on land), submarine volcanoes are more common where tectonic plates are moving closer or farther apart, the OSU says.
Actually, the tectonic plates are rigid and, when they move and interact with each other, they do not deform greatly, except at their edges, where there are very relevant changes, according to the Mexican Geological Service (SGM).
So, we talk about divergent edges when tectonic plates move apart and converging edges when they get closer. These movements of both separation and approach result in “most of the Earth’s volcanic and seismic activity, as well as the origin of mountain systems,” adds the SGM.
In addition to the formation of volcanoes by the movements of the tectonic plates, there is also the formation of submarine volcanoes in the so-called “hot spots”, which are “conduits, immobile or relatively immobile, that communicate the surface with the depths (up to 2,900 km) of the Earth and in which a vertical movement of the magma occurs”, according to the Costa Rica university.
“Hot spots leave linear seamount ‘footprints’ across ocean basins and build some of the largest volcanoes on Earth,” explains the USO.