Volcanism in the Azores region of extension between Europe and Africa has created giant volcanic
ridges, in particular those forming the islands of Sao Jorge and Pico. In July 1999, we surveyed
submarine ridges adjacent to the central group of islands using deeply towed TOBI sidescan sonar and
recently developed swath bathymetry. The images show that the ridges are comprised of many small
seamounts, much like axial volcanic ridges (AVRs) of the Mid-Atlantic Ridge. Seamounts vary in form
from nearly circular in plan to more elongate ridges. These small ridges are several kilometres long and
are aligned with the main ridges - we interpret these as caused by eruption over dykes, as similarly
proposed for hummocky ridges on AVRs and therefore as evidence for dyke intrusion parallel to the
main ridges. In addition, our new data reveal a massive network of extensional fractures in an area of
low magmatic output southeast of Terceira.
Abstract presented at Fall Meeting of the American Geophysical Union, 1999.