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French scientists have witnessed the birth of a newborn underwater volcano. Rising from the Indian Ocean floor between Africa and Madagascar is a giant edifice 800 meters high and 5 kilometers across, according to initial results obtained by the research vessel Marion Dufresne and released last week. In previous maps there had been nothing. The quarter-million people living on the French island of Mayotte in the Comoros archipelago knew for months that something was happening. From the middle of last year they felt small earthquakes almost daily. Now, data retrieved from ocean-bottom seismometers reveal why. They show, east of the island, a tightly clustered region of earthquake activity, ranging from 20 to 50 kilometers deep in Earth's crust. The research team suspects a deep magma chamber fed molten rock to the surface and then contracted. The size of the volcano indicates that as much as 5 cubic kilometers of magma erupted onto the sea floor—the largest such event ever witnessed.
Volcanic tsunamis are generated by a variety of mechanisms, including volcano-tectonic earthquakes, slope instabilities, pyroclastic flows, underwater explosions, shock waves and caldera collapse. In this review, we focus on the lessons that can be learnt from past events and address the influence of parameters such as volume flux of mass flows, explosion energy or duration of caldera collapse on tsunami generation. The diversity of waves in terms of amplitude, period, form, dispersion, etc. poses difficulties for integration and harmonization of sources to be used for numerical models and probabilistic tsunami hazard maps. In many cases, monitoring and warning of volcanic tsunamis remain challenging (further technical and scientific developments being necessary) and must be coupled with policies of population preparedness.
Mount Mayuyama is a peripheral dome of Unzen volcano, which was active, but the 340×106 m3 failure was probably triggered by a strong earthquake . The failure pore fluid pressurization may have contributed to the development of the collapse structure . Tsunami run-ups ranged between 8 and 24 m on the opposite side of the Ariake Bay and 15 030 people were killed .
For instance, the bulk volume of the 1991 caldera collapse at Pinatubo, Philippines, might have subsided in 34 min . Ulvrová et al.  demonstrated that caldera collapse of the Kolumbo submarine volcano, Aegean Sea, would produce significant wave heights (more than 1 m) on the shorelines of Santorini Island if the bulk subsidence lasted less than 10 min (figure 5).
Can you post a link to the story you referenced, about the ship spotting a newborn volcano beneath the surface?
Researchers used multibeam sonar to find the underwater volcano. The reflected sonar waves revealed the outline of the underwater volcano (red) and the gassy plume rising from it.
In previous maps there had been nothing.