Intra-flow morphology variations within a single submarine flow: the 2005-2006 East Pacific Rise eruption

A.T. Fundis¹*, S.A. Soule², D.J. Fornari², M.R. Perfit¹

Corresponding author: afundis@ufl.edu
¹University of Florida, Department of Geological Sciences, Gainesville, FL, 32601
²Woods Hole Oceanographic Institution, Geology and Geophysics Dept., Woods Hole, MA, 02543

Abstract:
The 2005-2006 eruption at the EPR ISS marked the first observed repeat eruption at a mid-ocean ridge and provided a unique opportunity to deduce the emplacement dynamics of a single eruptive event. Since this new flow was documented in April 2006, a total of 41 deep-towed imaging surveys have been conducted with the Woods Hole Oceanographic Institution’s TowCam system. These surveys collected more than 60,000 digital color images and high-resolution (+ 10 cm) bathymetric profiles. We have analyzed the surface morphology of the flow using this data at a level of detail that has never before been possible. This analysis quantifies the spatial distributions of lava flow surface morphologies and allows us to investigate how these various morphologies relate to the physical characteristics of the ridge and dynamics of flow emplacement. Images of the 2005-2006 flow from each of the TowCam surveys were analyzed for lava flow morphology, the orientation of flow direction indicators, and for the presence of kipukas, collapse, faults and fissures. Our results support previous studies (Fornari et al. 1998,2004; Soule et al., 2005) that suggest the 2005-2006 flows originated from continuous fissures as discrete flow units and followed pre-existing bathymetric lows and flow channels away from the AST. These flow channels, found predominantly on the eastern flank of the ridge axis at ~950, are primarily composed of transitions between sheet and hackly flows. The flows north of 953 and south of 949 are predominantly lobate flows with a high abundance of kipukas (<1 – 5 m diameter). The centers of lava channels that served as distribution pathways during the flow tend to be characterized by sheet flows, while hackly flows that transition into lobate define the edges of the channels. Pillows are most abundant at the termini of the flow lobes. Using previously collected bathymetric data with WHOI’s Autonomous Benthic Explorer and 30 kHz Simrad EM300 multibeam system, we conclude that the pre-existing slope did not influence the development of various morphologies of the 2005-2006 eruption.

Contributions to Integration and Synthesis:
Understanding the volumes of individual eruptions and the modes of lava distribution across the seafloor is crucial in order to understand the construction of the upper oceanic crust and the evolution of a mid-ocean ridge. The mapping of seafloor morphology of a single eruption at the EPR ISS will provide context for interpreting the complex relationships between volcanic and hydrothermal features, emplacement dynamics and related processes at mid-ocean ridges. In conjunction with geochemical and seismic data, the characterization of the various flow morphologies throughout the 2005-2006 eruption will help to define the individual flow units that comprise the eruption in addition to providing context for deducing the organization of the volcanic plumbing system at the EPR ISS.