HR: 0800h
AN: T31B-0498    [Abstracts]
TI: Timescales of Thermal Fluctuations and of Vent Location Changes in Mid-Ocean Ridge Hydrothermal Systems From Numerical Modelling.
AU: * Coumou, D
EM: coumou@erdw.ethz.ch
AU: Geiger, S
EM: geiger@erdw.ethz.ch
AU: Driesner, T
EM: driesner@erdw.ethz.ch
AU: Heinrich, C A
EM: heinrich@erdw.ethz.ch
AB: We performed 2D numerical simulations of hydrothermal systems in the high-permeability axial plane of mid-ocean ridge systems. By using realistic fluid properties, second order accurate transport schemes and high-resolution meshes we observe new features, which potentially explain some of the key-observations at black smokers. The high viscosity contrast between hot and cold fluids causes rising plumes to split (Taylor-Saffman fingering) making fluid flow patterns much more irregular. This can result in a single upflow zone to vent at different locations for a limited period of time, after which one of the plumes becomes unstable and merges with its direct neighbour. Besides, our simulations show that already for relatively moderate permeabilities, convection is unsteady resulting in transiently varying vent temperatures (typically ~40°C). The period of those fluctuations ranges from months for high-permeability systems (10^-12m²) to decades for moderate-permeability systems (10^-14m²). For even lower permeabilities convection becomes steady. Several studies have reported the onset of fluctuations in black smoker temperatures directly after an earthquake. We propose a very simple mechanism to explain those fluctuations: The earthquake-induced permeability increase shifts the sub-seafloor convection cells from the stable to the unstable regime with accompanying fluctuations in vent-temperatures. Potentially, clogging of fractures reduces permeability again over time, shifting the system back towards constant vent-temperatures. The simulations predict that changes in vent location occur on much larger timescales, ranging from decades to thousands of years.
DE: 1805 Computational hydrology
DE: 3017 Hydrothermal systems (0450, 1034, 3616, 4832, 8135, 8424)
DE: 4255 Numerical modeling (0545, 0560)
DE: 8411 Thermodynamics (0766, 1011, 3611)
DE: 8424 Hydrothermal systems (0450, 1034, 3017, 3616, 4832, 8135)
SC: Tectonophysics [T]
MN: Fall Meeting 2005