Plume head flow

The presence of a lithosphere with a thickness up to 100 km above the plume head obscures observations that could be made in terms of heat flow, gravity field or seismic structure. Establishing the temperature and flow fields beneath a hotspot thus becomes a difficult exercise. Several key parameters (Fig. 2) are poorly constrained and mostly result from theoretical fluid dynamics model, which underlines their large uncertainty. The temperature anomaly within the hotspot region is generally estimated to be approximately 200 100°C with large uncertainties (Shilling 1991 Sleep 1990). These temperature anomalies will induce smaller densities in the plume and the flux of the density anomalies is called buoyancy flux as defined in (Sleep 1990) ... 

Fig. 2. Graph of plume material thickness v. distance (normalized) from plume s centre for several lithospheric geometries. For linear flow (e.g. along a channel at the LAB below a pre-existing rift zone) and radial flow (e.g. plume arising beneath a flat-keeled craton) material from the plume head is relatively uniform in thickness, except at its edges where viscosity increases associated with cooling retard flow. The shape of the radial curve is similar for topography of limited (small craton) or infinite extent (large craton). Unlike the top two cases, the flow from the plume tail thins more rapidly with distance from the centre (continuous line).

Powerful inorganic feedbacks do exist. If a volcanic event degasses huge amounts of carbon dioxide (e.g. eruption of a major plume head), then the air will become warmer and hence wetter, and more acid. Weathering will become more intense bicarbonate will flow off the land and eventually carbonate will be deposited in sediment and in new oceanic plate, to return the carbon dioxide to the deep continental crust and to the mantle. But this process depends on the availability of exposed land to be weathered, on the rate of erosion, and on the rate of plate motion. Weathering reaches only a certain depth ... 

The numerical demonstrator showed that the 3D SMART model is capable to simulate atmosphere and sea within a joint simulation. The numerical demonstrator showed that the sea and atmosphere plume head in different directions due to different hydrodynamic and atmospheric flow fields. Expected back coupling between sea and atmosphere distribution has been observed due to the Henry coefficient based mass exchange between sea and atmosphere. An error analysis will be performed in a separate publication. Requirements are bathymetry and shoreline data, supercomputer access, and a triangle mesh for the Arabian Gulf. Short dated natural gas plume simulations require the availability of an Arabian Gulf model which has been caUbrated with current and tidal data. 

In situ oxygen supply requires aeration wells for the injection of oxygen. The criteria are that the aeration well zone must be wide enough to allow the total plume to pass through, and the flow of air must be sufficient to produce a substantial radius of aeration while small enough so as not to create an air barrier to groundwater flow. The required residence time tr for aeration can be calculated from Darcy s law as a function of the groundwater head and hydraulic conductivity ... 

Two questions arise from this result. Do lobsters use only chemical and not mechanosensory information, and why do lobsters not use ground reference and head up-current Since turbulent odor dispersal is based on water flow patterns, we must investigate the role of microflow patterns in plume orientation behavior. As for ground reference, we speculate that the flow patterns of the lobster s natural environment may be too complex to allow for efficient rheotactic behavior in odor source localization. This complexity is most likely caused by a mismatch between turbulent scales and animal body size and sampling scales. 

The second box contains a peristaltic pump and a servoactuator. Both the pump and servo are controlled electrically from the sensing head and are powered from the same power supply. The separation of the sensing head from the pump and servo provide electrical and mechanical isolation and address space constraints associated with mounting the system on the autonomous underwater vehicle. The peristaltic pump enables operation at a variable flow rate and has bidirectional flow capability. The servo actuates a movable sample inlet tube that can be raised or lowered by remote control to enable precise positioning of the inlet relative to the source or in the source plume. 

The results are compared with solutions determined using fixed-length management periods. The hypothetical homogeneous, isotropic, confined aquifer is comprised of 60 finite elements and 77 nodes, with dimensions 1500 m by 900 m (Culver and Shenk, 1998). The initial contaminant plume, which has a maximum toluene concentration of 40 mg/L, is shown in Figure 1. An easterly steady flow was maintained with a constant hydraulic head of 12.0 m and contaminant concentration of 0.0 mg/L on the left side, a constant hydraulic head of 0.0 m and contaminant concentration of 0.0 mg/L on the right side, and no flow at the top and bottom boundaries. In this example, the sorbed phase is assumed to remain in equilibrium with the... 

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