Compositionally variable limu o Pele occurs in widely distributed sediments collected during ROV Tiburon dives along the Gorda Ridge axis. The fragments formed deeper than the critical depth of seawater and are unlikely to be formed by supercritical expansion of seawater upon heating in contact with hot lava. Discharge of CO 2 through erupting lava is the most likely way to make such bubbles at >298 bars pressure. The distribution and composition of limu o Pele fragments indicate that low-energy strombolian activity is a common, although minor, component of eruptions along mid-ocean ridges. Combined dissolved and exsolved volatile contents of N-MORB from the Gorda Ridge with 12.8-15.6% spherical vesicles are about 0.78% CO 2 and 0.18 wt% H 2 O and exceed estimates of primary CO 2 of only 0.07 to 0.095 wt% calculated from whole rock Nb concentrations. This discrepancy suggests that the magmas accumulated an exsolved volatile phase prior to eruption. The evidence that a separated volatile phase drives strombolian eruptions on the seafloor also implies that volatile bubbles coalesce during storage or transport to the surface. The combination of large bubbles in otherwise dense magma suggests nearly complete coalescence of small bubbles and is most consistent with accumulation of the exsolved volatile phase, most likely near the tops of crustal magma chambers, prior to upward transport in shallow conduits to the eruptive vents on the seafloor. A portion of this CO 2 -rich separated fluid phase is released in brief bursts during eruptions where it becomes part of event plumes.