The dynamics of mid-ocean ridge hydrothermal systems: Splitting plumes and fluctuating vent temperatures

Department of Earth Science & Engineering, Imperial College London, RSM Building, Exhibition Road, London, SW7 2AZ
Earth and Planetary Science Letters (Impact Factor: 4.72). 05/2006; 245(1-2):218-231. DOI: 10.1016/j.epsl.2006.02.044

ABSTRACT We present new, accurate numerical simulations of 2D models resembling hydrothermal systems active in the high-permeability axial plane of mid-ocean ridges and show that fluid flow patterns are much more irregular and convection much more unstable than reported in previous simulation studies. First, we observe the splitting of hot, rising plumes. This phenomenon is caused by the viscous instability at the interface between hot, low-viscosity fluid and cold, high-viscosity fluid. This process, known as Taylor–Saffman fingering could potentially explain the sudden extinguishing of black smokers. Second, our simulations show that for relatively moderate permeabilities, convection is unsteady resulting in transiently varying vent temperatures. The amplitude of these fluctuations typically is 40 °C with a period of decades or less, depending on the permeability. Although externally imposed events such as dike injections are possible mechanisms, they are not required to explain temperature variations observed in natural systems. Our results also offer a simple explanation of how seismic events cause fluctuating temperatures: Earthquake-induced permeability-increase shifts the hydrothermal system to the unsteady regime with accompanying fluctuating vent temperatures. We demonstrate that realistic modelling of these high-Rayleigh number convection systems does not only require the use of real fluid properties, but also the use of higher order numerical methods capable of handling high-resolution meshes. Less accurate numerical solutions smear out sharp advection fronts and thereby artificially stabilize the system.

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    • ") and numerical models (Kaminski and Jaupart, 2003; Homma et al., 2006). Similar geometry is often associated with jets originating from submarine chimneys that exhale hot hydrothermal fluids with high velocities into relatively colder oceanic water (Fig. 1a) (Coumou et al., 2006). Other common examples of natural plumes range from large-scale meteorological plumes rising over the desert to explosive volcanic eruptions or saline plumes descending from melting sea ice. "
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    International Journal of Multiphase Flow 07/2014; 63. DOI:10.1016/j.ijmultiphaseflow.2014.02.007 · 1.94 Impact Factor
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    • "Hydrothermal vents are highly dynamic ecosystems, characterized by great spatial and temporal instability. Super-heated fluid emitted from hydrothermal vents can reach temperatures of $400 1C, and the cooling effects of surrounding seawater create acute thermal gradients (Coumou et al., 2006). Additionally, the venting of fluids is often unstable and sudden bursts of hot vent fluid are common, meaning vents display great thermal heterogeneity (Desbruy eres et al., 2000; Hourdez and Lallier, 2007). "
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    Deep Sea Research Part II Topical Studies in Oceanography 11/2012; 92(in press). DOI:10.1016/j.dsr2.2012.12.003 · 2.76 Impact Factor
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    • "In contrast, seafloor spreading at a fast spreading ridge where the crust moves at half rates of 50 km/Myr, so that 5 km of lower crustal flow away from the ridge axis occur on a timescale of ~ 10 5 yrs. Models of hydrothermal processes tend to use a model time step of less than a year and are typically limited in size to a crustal thickness-scale (Coumou et al., 2006) while numerical experiments describing the process of crustal accretion and subaxial mantle flow (Morgan and Chen, 1993b) need to model thermal evolution over timescales of several million years. Our model aims to simultaneous resolve the development of hydrothermal convection cells while solving for crustal and mantle flow associated with seafloor spreading. "
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