Observations of fresh lava flows coupled with the injection of biogenic particles into the water column and seismicity demonstrated that eruptions can trigger seismic, hydrothermal, and biologic activity. Understanding the factors that control eruptions is critical to understanding the linkages between volcanic eruptions, faulting (earthquakes), hydrothermal venting, and biological activity. Yet, few data are available that document the volume, timing, and spatial extent of volcanic eruptions, and this paucity of direct evidence makes it difficult to investigate linkages with other ridge processes.

To maximize the probability of catching an eruption in the act, the Ridge2000 strategy has been to focus investigations at “bull’s eyes”, sections of the ridge axis that display large cross-sectional areas. Indeed, inflated segments are generally thought to be subject to more frequent and/or more voluminous eruptions. The common occurrence along such segments of fresh-looking lava flows, of shallow melt lenses (as revealed from seismic surveys) and of hydrothermal plumes support this model. However, the paucity of investigations at counterpart magmatically starved segments (i.e., segments with small cross-sectional areas) makes for an uncomplete test. Some linkages may be overlooked because factors other than magmatic “robustness” probably also control the timing and styles of volcanic eruptions. For example, static stress changes induced by the intrusion of a dike or by an earthquake may sometime be sufficient to trigger diking at a neighboring segment. A diking event without associated seafloor eruption would also affect hydrothermal circulation, and therefore biological activity.

I am interested in discussing existing evidence for linkages between eruptions and seismic, hydrothermal, and biological activities. Two recent and on-going experiments will contribute material for such discussion. A linear array of 19 bottom pressure recorders (BPRs) have been deployed since March 2007 between 9°N and 10°N along the EPR that will be recovered early in 2011 (coPIs Cormier, Buck, and Webb). BPRs can detect vertical motion of the seafloor with a resolution of just a few cm and should capture any diking event that occurred during that 4 year-period over a 100 km section of the ridge axis. The other dataset include repeat water column profiling (“tow-yo” surveys) along that same length of the EPR. It documents large variations in the intensity of hydrothermal plumes that seem correlated with time since last eruption.