In sidescan sonar images, young lava flows have a bright appearance while older ones are covered by sediments and thus appear darker, and structures identified as lava coils, lava rubble, lava tumuli, pillow lavas, polygons and sheet flows have been observed on young flows. The lava flows have buried the pre-existent seafloor topography, smoothening it, and in one place a flow front rises about from the seafloor. The lava flows erupted in the South Arch volcanic field were probably fluid and were produced at high rates. There is no evidence for the presence of a magma chamber at the South Arch volcanic field.