Volcanism on the seabed is still poorly understood. However, the eruptions are sometimes violent and very large. Proof of this is the presence of this huge volcanic plateau that covers more than a third of France and whose formation turns out to be much more complex than one would imagine.
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Volcanic eruptions occur every day on Earth. On the continents, the activity of volcanoes cannot go unnoticed and is usually the subject of great attention, either because it directly threatens the population or simply to enjoy the spectacle. fascinating forces of nature in action.
A volcanic plateau whose area reaches 40% of the area of mainland France
The oceanic world also experiences a series of eruptions. In fact, the seabed is dotted with numerous volcanoes, some of which are in no way inferior in size and power to those on land. Deep beneath the surface, massive volcanic eruptions even occur without us really being aware of it. A massive lava flow has been forming at the bottom of the Pacific Ocean for 120 million years. This is the Melanesian border plateau. This superstructure of volcanic origin near the Solomon Islands covers approximately 222,000 km2, equivalent to 40% of mainland France! And its growth is clearly not over yet.
The story of a tectonic drift
The origin of this huge volcanic plateau has been a mystery until now. Did it happen all at once or over several episodes? However, in 2013, a team of scientists conducted a series of dredging operations to better understand its history. The analysis results, published this year in the journal Earth and Planetary Science Letters, show that it formed gradually over the last 120 million years during four major pulses of volcanic activity associated with highly geodynamic processes. The first phase appears to have been particularly dramatic, with large-scale outflow of basalt-basalt lava. Over time and thanks to the movement of the Pacific Plate, this primary plateau gradually shifted until it found itself over a hotspot called Rurutu-Arago 45 million years ago.
The intense volcanism would have resulted in the formation of a series of volcanic islands across the plateau. Erosion will eventually take over these islands, which will gradually disappear underwater as the Pacific plate continues its migration. Thus, 13 million years ago, the plateau thickened by recent events was located above another hotspot, the same one that is currently involved in the formation of the Samoa Islands. New islands form only to disappear again over time.
However, the story of the plateau is not over yet. His tectonic journey eventually takes him to the level of the Tonga Islands subduction trench. Here the Pacific Plate sinks into the Earth's mantle and is recycled. This geodynamic context also generates volcanism, which adds to and participates in the construction of the pre-existing plateau.
This study thus reveals the complex history of this vast oceanic plateau and shows the extent to which its formation was discontinuous and linked to multiple magmatic processes linked to the movement of the Pacific Plate.