Processes associated with ocean crustal formation: The Juan De Fuca Ridge

Recent geophysical, geological and geochemical studies on the Juan de Fuca Ridge have been gathered into a special collection of manuscripts that demonstrate the interdisciplinary nature of the crustal formation and evolutionary processes. On the ridge axis, these new studies include long‐term sea floor and water column measurements that indicate ‘real‐time’ changes due to volcanic activity and related hydrothermal flux, sea floor measurements of seismic activity detecting swarms of earthquakes near the axial zone, and submersible observations of a 2‐km along‐strike spacing of large‐scale hydrothermal fields. Detailed sampling of axial basalts show that, in spite of abundant evidence of ‘excess’ volcanic activity, the Juan de Fuca Ridge is not a traditional hot spot. On a larger scale, geophysical surveys of the ridge flanks show that the upper crust can vary in thickness by a factor of two, that crustal porosity systematically decreases with age, and the topographic forcing is the dominant control of off‐axis hydrothermal circulation. Finally, the Juan de Fuca Ridge has long been a testing ground for innovative survey techniques, and this issue includes reports on the development of acoustic backscatter as a quantitative measure of basement roughness and as an indicator of the presence of lithified sediments overlying zones of fluid upwelling.