Reconstruction of Subaqueous Eruption-Fed Current Characteristics and Source Location Using Anisotropy of Magnetic Susceptibility (AMS) at Otapahi, Dunedin Volcano, New Zealand

Abstract

Information about birth and early eruptions of composite volcanoes is scarce, but erosion has revealed very early deposits of the Dunedin Volcano, and we apply anisotropy of magnetic susceptibility (AMS) techniques to retrieve information about the earliest known, submarine, eruptive centre. Although AMS has been used to recover information from subaerial eruptions, and to examine turbidites, this is its first use in investigating depositional processes and the source location for submarine volcaniclastic deposits. AMS fabrics of the deposits, emplaced by submarine eruption-fed density currents, show basal portions of the currents were decoupled from more-buoyant upper parts. Triangulation of AMS vectors and orientations yields a vent site location, with some imprecision reflecting the chaotic nature of deposits rapidly aggraded within 500 m of the source vent. This method elucidates depositional processes of subaqueous volcanic currents as well as subaerial ones, while still yielding sufficient consistency for triangulation of flow source sites.