Brief Report of Side-Scan Sonar Observations Around the Yokoniwa NTO Massif

Abstract

We conducted the side-scan sonar observations of the Yokoniwa Rise, a non-transform offset massif at the southern Central Indian Ridge using the autonomous underwater vehicle AUV-r2D4 fitted with a 100 kHz sidescan sonar system. We identified two terrain types with high backscattering signals; one terrain type exhibited typical volcanic features, while the other appeared to correspond to peridotite outcrops. The orientation of linear features identified in the survey area was highly variable, but appeared to be affected by local bathymetry. The standard deviations of the orientation and average length of these linear features were larger and smaller, respectively, than those of similar features observed along the East Pacific Rise. These observations showed that the linear features on the sonar image were likely to be flow channels or areas of the seafloor that had experienced gravitational collapse. A few small chimney-like structures were also detected.