VERTICAL DEFORMATION OF THE AXIAL SEAMOUNT SUMMIT FROM REPEATED 1-M SCALE BATHYMETRY SURVEYS WITH THE MBARI MAPPING AUV

Axial Seamount is an intensely studied submarine hotspot volcano on the Juan de Fuca Ridge that has erupted in 1998, 2011, and 2015, and is now a site for a cabled seafloor observatory as part of the Ocean Observatory Initiative. A series of MBARI Mapping AUV surveys from 2006-2009 obtained nearly complete 1-m-resolution topographic coverage of the Axial Seamount summit, including the caldera, the caldera rim, and the south rift zone. The Mapping AUV fields a 200 kHz multibeam sonar, 110 kHz sidescan sonar, and a 1-6 kHz chirp subbottom profiler for 17.5 hour duration missions. Flying at 1.5 m/s (5.4 km/hr) at a 50 m altitude, the AUV bathymetry achieves a 0.1 m vertical precision and a 1 m lateral resolution. Following the 2011 eruption, additional Mapping AUV surveys were performed in 2011 and 2014 to survey all of the new lava flows and to extend the coverage of the caldera rim and the north and south rifts. The detailed morphology and volume of the 2011 lava flows resolved by the repeated AUV surveys have been previously reported. Comparison of repeated components of the 2011 and 2014 surveys have now revealed a pattern of vertical deformation associated with the reinflation of the sub-caldera magma chamber between the 2011 and 2015 eruptions. The uplift has a maximum of 1.8 m near the caldera center over the three year period between surveys, and diminishes steadily away from this site. The comparison assumes zero uplift at the south end of the repeat surveys, 8 km from the caldera center. These results are consistent with observations of uplift by Chadwick and Nooner using biannual pressure measurements at a small set of seafloor benchmarks in the caldera and on the south rift. This result demonstrates that AUV seafloor mapping can be used to map deformation on submarine volcanoes. The AUV method is less precise than point pressure measurements but can measure the deformation pattern over a large, spatially continuous area.