Small-Scale Bathymetric Changes Associated with 2005-2006 Eruptions at the East Pacific Rise Near 9 50'N

Volcanic eruptions that occurred in 2005-2006 along the East Pacific Rise (EPR) axis between 9 46'N and 9 56'N have been mapped preliminarily using near- bottom sonar systems on the WHOI TowCam and Alvin. The recent surveys confirmed that eruptions were focused within and proximal to the Axial Summit Trough (AST), a known locus of hydrothermal and volcanic activity in this area that has been mapped over the past few years using near-bottom scanning altimetric sonar. Although no large-scale systematic mapping program has yet been conducted at the post-eruptive EPR, near-bottom high-resolution scanning altimetric sonar data have been collected with Alvin that can be compared with previous data to determine the physical changes to the AST and the volcanic and hydrothermal features it contains. These data can help constrain areas where the eruptions filled or partially filled the AST and can provide information on the location of primary eruptive fissures within and proximal to the AST. Near-bottom high-resolution bathymetry data were collected with a scanning altimetric sonar system (675 kHz) mounted on the submersible Alvin. This sonar system is a permanent sensor on Alvin and provides a low- impact means for acquiring high-resolution bathymetric data. Coordinated survey efforts during multiple dive programs in June and Oct.-Nov. 2006 provided the data necessary to create bathymetry maps of portions of the post-eruptive AST. Merged with high-precision navigation, these data can be used to quantify sub-meter resolution morphologic details of the seafloor. By comparing these micro-bathymetry data with pre-eruptive micro-bathymetry, we can quantify morphologic changes due to the recent activity and relate the location of new hydrothermal vents to key volcanic features displayed in the maps. Continued, repeat surveys at this site will allow us to further document the extent of the 2005-06 lava emplacement as well as the morphologic evolution of the post-eruptive AST due to hydrothermal, volcanic and tectonic activity.