It's a bit as if we discovered the elephant after all listed species of ants ... At a time when the satellite scan each point of the Earth, at a time when Google Maps zooms in your garden, there is something paradoxical about announce the discovery of what is - for now - the largest volcano world. Yet this is what has happened, Thursday, September 5, by means of publication in the journal Nature Geoscience . As explained in US-Japanese team who is the author, there is a good reason not to be identified geological structure such that at the beginning of the third millennium: off for a long time, the "monster", as well as the researchers describe it, hiding under the surface of the Pacific Ocean.
We must throw some 1500 km east of Japan and dive 2000 meters deep to see the top of Shatsky Rise. It is, in the language of geophysics, an oceanic plate and can be described as a chain of underwater about 900 km long mountain. Shatsky Rise is composed of three main massifs, Tamu, Ori and Shirshov. The first is by far the largest and the oldest. Coring showed that dated back to 145 million years. His name Tamu may seem exotic, but it is actually an acronym for the Texas A & M University, who led several campaigns about her and where William Sager work, the first author of the study published by Nature Geoscience.
Tamu is a species of large, rounded oblong tray with enough gentle slopes, 450 km wide and 650 long. The cores that were conducted say that it is composed of volcanic rocks, huge flows of low viscosity basalt. Until now, it was believed that this huge bulge was due to the juxtaposition of the merger of several neighboring volcanoes each other. This kind of phenomenon is quite common and has for example led to the island of Hawaii, consisting of five volcanoes, or, closer to home, Iceland. But William Sager and his colleagues had another idea. The information provided by cores are limited, they switched to another method of exploration, the seismic method, commonly used by the oil industry in search of new deposits . They had the chance to participate in two research cruises over Shatsky Rise, in 2010 and 2012, during which they "sounded" massive underwater explosions through by air guns.
The analysis of waves reflected by the rock has to ultrasound Tamu Massif and realize that it was obviously not a conglomerate of volcanoes. Instead, all the lava seemed well come from the top of the range, implying a magmatic and one fireplace.One volcano then, and gigantic. Covering an area of over 300 000 km 2 , equivalent to the size of a country like Italy or Poland, Tamu almost on a par with the giant of the solar system what the Martian volcano Olympus Mons. If it had landed in France, he would go to Paris to Montpellier and the mouth of the Gironde to the Swiss border.That said, there is a big difference between Tamu and Olympus Mons: if both are "shield volcanoes", the first difficulty reaching 4 km high, while its Martian counterpart, much curved, exceeds 20 km! Although William Sager do not despair of being able to find even larger than the Tamu, it is unlikely that the height of Olympus Mons is never exceeded.
If we put aside the race a little futile to record, the study is interesting in that it shows that the Martian giant has at least one counterpart on Earth. A building such as Tamu also a challenge to researchers who must explain how it was possible to combine in one place as magma in a relatively short time, since the construction of Shatsky Rise (2.5 million kilometers cubes) was done in a few million years. Beyond these scientific considerations, one can also question the ultimately superficial knowledge we have of our own planet. Indeed, only a few days, we discover in quick immense canyon 750 km long and 800 meters deep under the Greenland icecap and the largest volcano in the world. Earth, we are you hiding other elephants?
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