The hydrogeologic properties of igneous ocean crust have been tested directly in only a few locations during IODP, but more common studies of crustal structure and rock alteration (using core samples and wireline logs) provide insight as to how water-rock interactions modify the crust over time. Collectively these studies reveal strong lithologic and hydrogeologic control on the nature of water-rock interactions, with hydrogeology following crustal architectures and histories. Permeability is generally greatest in the upper crust, but is heterogeneously distributed with depth and (at least in one location) may be azimuthally anisotropic. There appears to be a spreading rate dependence of basic patterns of rock alteration in the upper oceanic crust, with more variable and extensive alteration observed in crust created at slow- and medium-rate spreading centers. There may also be a spreading rate dependence of hydrogeologic properties, but we currently lack direct observations to test this hypothesis. The evolution of crustal properties with age is consistent with sustained ridge-flank water-rock interactions, and a continued dependence on fluid flow rates and reaction temperatures.

A new International Continental Drilling Program (ICDP) project will drill through the 50-year-old edifice of Surtsey Volcano, the youngest of the Vestmannaeyjar Islands along the south coast of Iceland, to perform interdisciplinary time-lapse investigations of hydrothermal and microbial interactions with basaltic tephra. The volcano, created in 1963-1967 by submarine and subaerial basaltic eruptions, was first drilled in 1979. In October 2014, a workshop funded by the ICDP convened 24 scientists from 10 countries for 3 and a half days on Heimaey Island to develop scientific objectives, site the drill holes, and organize logistical support. Representatives of the Surtsey Research Society and Environment Agency of Iceland also participated. Scientific themes focus on further determinations of the structure and eruptive processes of the type locality of Surtseyan volcanism, descriptions of changes in fluid geochemistry and microbial colonization of the subterrestrial deposits since drilling 35 years ago, and monitoring the evolution of hydrothermal and biological processes within the tephra deposits far into the future through the installation of a Surtsey subsurface observatory. The tephra deposits provide a geologic analog for developing specialty concretes with pyroclastic rock and evaluating their long-term performance under diverse hydrothermal conditions. Abstracts of research projects are posted at http://surtsey. icdp-online.org.