High-resolution bathymetry using Alvin scanning sonar at the Southern East Pacific Rise and its implication to the formation of collapsed lava lakes

Akiko Tanaka,Severine Rosat,Kiyoyuki Kisimoto,Tetsuro Urabe

doi:10.1186/bf03353101

Akiko Tanaka, Severine Rosat + Show 2 more

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https://doi.org/10.1186/bf03353101

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Abstract

Abstract A high-resolution bathymetric map of a collapsed lava lake on the ridge crest of the superfast-spreading Southern East Pacific Rise was constructed. The data were acquired during the MOAI’98 Cruise using a pencil-beam scanning sonar that was installed on the submersible Alvin. The map covers an area of 200 × 350 m at the Oasis hydrothermal site (17°25.4′S, 113°12.3′W) where low-temperature fluids are venting from a collapsed lava lake. The collapsed lava lake is 250 m long, with a mean width of 10 m in parallel to the spreading axis on the western flank of the ridge crest. The estimated volume of lava that has drained out is about 7000 m3 erupted from a single event. This small amount of melt and frequent contacts between “young” and “younger” flows indicate that volcanism at the superfast-spreading ridge system is characterized by frequent eruptions of very small volumes of magma.

Highlights

The superfast-spreading East Pacific Rise (EPR), situated between 13◦S and 19◦S (Fig. 1(a)), has the highest magmatic, hydrothermal (Urabe et al, 1995; Baker and Urabe, 1996) and biological (Maruyama et al, 1998) fluxes of the mid-oceanic ridges
The finest scale bathymetric information from the MESOTECH depth profiles shows steeply dipping walls, lava pillars and irregular floor bathymetry. Based on these observations and information, the central depression is interpreted to be a collapsed lava lake. This collapsed lava lake is elongated almost parallel to the ridge axis and in en echelon, and it may have been formed by a single eruptive event because it is found within young lobate and pillow lavas without a dusty sediment cover, which in turn are surrounded by pillow lavas with a dusty sediment cover (Fig. 2(c))
The blue area denotes the collapsed lava lake, pink indicates the area of sheet and/or lobate lava flows and the green and white areas are pillow lava flows with and without a dusty sediment cover, respectively

Summary

Introduction

The superfast-spreading East Pacific Rise (EPR), situated between 13◦S and 19◦S (Fig. 1(a)), has the highest magmatic, hydrothermal (Urabe et al, 1995; Baker and Urabe, 1996) and biological (Maruyama et al, 1998) fluxes of the mid-oceanic ridges. The resolution of ship-mounted bathymetric mapping at mid-oceanic ridge depths of 2000–3000 m is typically 30–100 m, which is one to two orders of magnitude larger than that of visual observations of the seafloor from submersibles. Kurras et al (1998) constructed high-resolution bathymetric maps of two biologically and geologically active areas within the axial summit collapse trough on the EPR at 9◦49 N–9◦51 N using scanning sonar data during 23 Alvin dives over a 5-year period.

Results

Conclusion