Article Abstract
Since 1991, over 30 borehole observatories have been installed by the Ocean Drilling Program (ODP), the Integrated Ocean Drilling Program, and the International Ocean Discovery Program (IODP), mostly in young oceanic crust and in subduction zones. These installations have provided a sustained presence in the subseafloor environment, enabling collection of a new generation of long-term, time-series data sets of temperature, pressure, and deformation, as well as continuous fluid sampling and in situ active experimentation. These multidisciplinary observations have pushed the frontiers of knowledge about Earth’s linked geodynamic, hydrological, geochemical, and biological processes.