Vertical and lateral splitting of a hydrothermal plume at Steinaholl, Reykjanes Ridge, Iceland

Ernst, G.G.J., Cave, R.R., German, C.R., Palmer, M.R. and Sparks, R.S.J. (2000) Vertical and lateral splitting of a hydrothermal plume at Steinaholl, Reykjanes Ridge, Iceland. Earth and Planetary Science Letters, 179 (3/4), 529-537. (doi:10.1016/S0012-821X(00)00140-0).

Abstract

The generation of multiple, neutrally-buoyant intrusions by a single, bubble-rich plume [Asaeda and Imberger, J. Fluid Mech. 249 (1993) 35–57] and plume bifurcation [Ernst et al., Bull. Volcanol. 56 (1994) 159–169; Lavelle, J. Geophys. Res. 102 (1997) 3405–3420], are predicted from theory and experiments but have yet to be documented for hydrothermal plumes. In contrast, bifurcation of volcanic plumes (which are dynamically analogous to hydrothermal plumes) is very common [Ernst et al., Bull. Volcanol. 56 (1994) 159–169] and thus bifurcation of hydrothermal plumes should be expected [Lavelle, J. Geophys. Res. 102 (1997) 3405–3420; Ernst et al., BRIDGE Newslett. 10 (1996) 76–77]. Recent 38 kHz echo-sounder and water-column chemical tracer studies near the Steinahóll vent site (Reykjanes Ridge, Iceland), identified a bubble-rich hydrothermal plume intruding at three levels (two main ones and a subsidiary one) before reaching the sea surface and spreading there [Ernst et al., BRIDGE Newslett. 10 (1996) 76–77; Olafsson et al., RIDGE Events 2 (1991) 35–38; German et al., Earth Planet. Sci. Lett. 121 (1994) 647–654]. The two main intrusions (ca. 100 and 200 m above the vent) show lateral development of two lobes away from the vent and are consistent with the 350 m rise of a bubble plume yielding seafloor and surface gas fluxes of ~2.5×10?3 and 0.75×10?1 m3/s, respectively. The bubble-rich core of the hydrothermal plume also penetrates the 150 m deep thermocline and generates an intrusion visible at the sea surface. Although bifurcation of the bent-over plume could have been initiated by crossflow alone [Ernst et al., Bull. Volcanol. 56 (1994) 159–169], several other processes may also have enhanced plume bifurcation; including interaction with the thermocline and entrainment of the plume lobes by horseshoe eddies in the lee of a 150 m high hill on the seafloor.

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