Extensive volcaniclastic deposits at the Mid‐Atlantic Ridge axis: results of deep‐water basaltic explosive volcanic activity?

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Abstract
A recent mapping survey followed by submersible diving investigations revealed the existence of extensive volcaniclastic deposits on three adjoining, progressively deeper, segments of the Mid‐Atlantic Ridge, south‐west of the Azores. The maximum water depth at which subaqueous magmatic and hydro‐magmatic explosive processes can occur is controversial. This discovery provides fundamental constraints on the dynamics of deep subaqueous volcanic eruptions. Using multibeam bathymetry, sonar image interpretations, submersible observations, volcaniclastic sample descriptions and chemical analysis, evidence of extensive deep water (up to –1700 m) magmatic explosive activity of basalt at the axis of a spreading Mid‐Ocean Ridge is documented for the first time.