Surveying an ultra‐fast spreading ridge along the East Pacific Rise (EPR), explorers aboard the submersible Nautile examined features such as lava pillows and tubes, sulfide chimneys, black smokers, hot shimmering waters, and colonies of animals living in hydrothermal vents to learn more about the processes of accretion and tectonics on the ocean floor. Taken together, the observations of the EPR between 17°S and 19°S from the 1993 NAUDUR cruise (a French acronym for Nautile on Ultra‐fast Ridge) indicate recent volcanic eruptions occurring as frequently as every few years.

The NAUDUR cruise was designed to study the interaction between magmatic, tectonic, and hydrothermal processes at an ultra‐fast spreading axis of the EPR. Researchers performing twenty three dives in five regions (Figure 1) along the axis of the Garrett fracture zone collected more than 150 rock samples and made 52 gravity measurements [Auzende et al., 1994]. The Garrett fracture zone (13°S) and the Easter Microplate limit a large segment of the East Pacific Rise where the accretion rate is near the upper limit for present‐day spreading values (141 to 162mm/yr) [Perram et al., 1993]. The five dive regions with distinct morphological characteristics represent different stages in the accretion process.