Thermal fluxes associated with the 1993 diking event on the CoAxial segment, Juan de Fuca Ridge: A model for the convective cooling of a dike

The 1993 diking event on the CoAxial segment, northern Juan de Fuca Ridge, generated at least three hydrothermal event plumes high in the water column and lower chronic plumes along similar to 40 km of the ridge axis. A 2-year time series of temperature and light attenuation measurements within the water column shows a rapid decay of the maximum rise height of the chronic plumes over the first 3 months following the eruption. We use these measurements to estimate the hydrothermal heat fluxes into the chronic plumes at two different sites. We hypothesize that the chronic plumes resulted from the convective cooling of a dike and construct a simple two-dimensional, numerical model of this process for a vertical dike intruded into a cold, saturated porous layer. The width of the dike and the permeability and thickness of the porous layer control the transfer of heat from the dike to the seafloor. We investigate the effects of these parameters on the temporal evolution of the surficial heat fluxes. The results show that simple convective cooling of the dike can reproduce the observed temporal evolution of the heat fluxes for permeabilities in the range 10(-11)-10(-12) m(2) and a 3- to 5-m-wide dike. The high permeabilities obtained are consistent with flow through highly permeable extrusives or with the creation of a zone of high permeability near the dike walls due to fracturing. The width of the dike may well be overestimated by our model because of the limitations of the continuum approximation for the permeability in the narrow upflow zone adjacent to the dike.