Addressing Geohazards Through Ocean Drilling

Natural geohazards, such as earthquakes, volcanic eruptions, landslides, and volcanic collapse, are of immediate societal concern. In an oceanic setting (Fig. 1), all are capable of generating tsunami that threaten coastal zones at distances of many thousands of kilometers. This power and its effects were forcefully shown by the giant earthquake (Mw 9.2) and tsunami of 26 December 2004 off the coast of northern Sumatra. Smaller magnitude submarine earthquakes andlandslides occur with shorter recurrence intervals and the capability of tsunami generation, creating hazards for local coastal communities as well as for offshore industry and infrastructure. At the other end of the scale, the geologic record suggests that less common, large-volume volcanic collapses and extraterrestrial meteorite and comet impacts in ocean basins have the potential to initiate tsunami ofextraordinary power that can threaten huge sections of coastlines with growing populations. These events also disperse enormous volumes of ash, steam, and ejecta into the atmosphere, with short- and long-term consequences, including climate change. All of these processes, which have operated throughout the Earth’s history, are instrumental in shaping the Earth system today. However, they are characteristically difficult to predict, and viable risk assessmentand hazard mitigation depend on a clearer understanding of the causes, distributions, and consequences of such natural events.