Axial Seamount is a hotspot volcano superimposed on the Juan de Fuca Ridge (JdFR) in the Northeast Pacific Ocean. Due to its robust magma supply, it rises ~ 800 m above the rest of JdFR and has a large elongate summit caldera with two rift zones that parallel and overlap with adjacent segments of the spreading center (Figure 1). Submersible dives at Axial in 1983–1984 discovered the first active black smoker vents in the Northeast Pacific (Chase et al., 1985). The New Millennium Observatory (NeMO; http://www.pmel.noaa.gov/vents/nemo) was established at Axial in 1996 to study volcanic events and the perturbations they cause to hydrothermal and biological systems. As if on cue, Axial erupted in January 1998 and was the first seafloor eruption detected remotely and monitored by in situ instruments (Embley et al., 1999). In fact, one instrument caught in a 1998 lava flow was later recovered with data intact, providing new insight into the emplacement of submarine lavas (Chadwick, 2003). Initially, research focused on mapping, sampling, and documenting the impact of the eruption on the hydrothermal vents and biological communities (Figure 2). The emphasis has gradually shifted to long-term geophysical, geochemical, and biological monitoring of the volcano in anticipation of its next eruption.