Submarine inflated flows at the East Pacific Rise, 16°N

The East-Pacific Rise (EPR) is a fast spreading ridge. Between 15°22'N and 16°15'N the spreading rate is 87 mm/year. This segment is the most inflated of the EPR due to its interaction with the Mathematician hotspot. The French PARISUB ("Panache Ridge Submersible") cruise in 2010 acquired high-resolution geophysical data using the Autonomous Underwater Vehicle (AUV) Aster-X and the manned submersible Nautile (Ifremer). The goal was to investigate in detail the magmatic and tectonic processes at the intersection between the hotspot and the ridge. We investigate the lava flow dynamics, using high-resolution (2 m) bathymetry acquired using Aster-X, and photos and videos acquired during Nautile dives. High-resolution bathymetry is used to characterize details of the lava flow geometry (e.g., length and width) and to measure their thickness, the slope on which they are emplaced, etc. Photos and videos are used to determine the lava flow morphologies (e.g., pillows, lobate flows, sheet flows). This study allows us to distinguish the different lava flow morphologies using the roughness and geometry of flow surfaces imaged by bathymetry. For example, our observations show that pillows are characterized by rough terrain on the high resolution bathymetry, whereas lobate lava flows are smoother and often display collapsed lava channels. Here we focuse on submarine lava flows that display a smooth, relatively flat or slightly depressed surface. These smooth flows are interpreted as inflated flows, and their surfaces are comprised of sheet flows. At the flow boundaries, levees with cracks at their summit are observed, which we interpret as inflation clefts. Flow boundaries are steep (up to 45°) and are tens of meters high. Flow dimensions reach 9 km². Their depressed upper surfaces are likely due to lava draining during emplacement. Our theoretical model of flow dynamics show that they emplaced within a few hours to a few days.