Event Plumes Formation Impacts and Dispersal
Dike injections/eruptions have been long recognized as the “quantum event” of upper oceanic crustal accretion. Yet the most profound oceanic impact of an eruption, the generation of event (mega-) plumes and greatly enhanced chronic venting, still lacks full understanding.
Observations over the last 30 years show that event plumes inevitably accompany seafloor eruptions. The consistent and unique chemistry of event plumes implies a consistent formation process, but this process remains undefined. Proposed hypotheses include the “instantaneous” release of mature hydrothermal fluids residing in the crust, magmatic gases from a melt, crustal fluids heated by the intruding dike, and seawater heated by the erupting lava. Developing a convincing hypothesis is challenged not only by the consistent chemistry of event plumes, but by the common occurrence of multiple event plumes, variation of the volume and heat content by a factor of ~100, the rough correlation between event plume and lava heat content, and eruptions that range from thin effusive flows to thick pillow mounds.
The importance of eruptions to the transfer of heat, chemicals, and perhaps life from the crust to the ocean is emphasized by observations at multiple eruption sites. These observations show that eruptions create event plumes and enormously invigorate chronic venting for ~1 year, creating an “eruption flux” that may rival the between-eruption flux. Axial Volcano offers a unique opportunity to test this idea, though not without additional instrumentation to properly monitor the overlying ocean.