Figure A. Flow of a gravity current down a slope of 3 degrees into a uniformly density stratified environment, B₀ = 0.055, Holmboe waves. The dense fluid is marked with green fluorescene dye, which also marks fluid that is mixed with the environment. Mixing occurs through the process of Holmboe instability (see Baines (1995, Chapter 4)), which causes wisps of dense fluid to be swept off the top of the dense downflow and mix into the overlying fluid. This causes a steady build-up of detrained fluid, made visible through the accumulating concentration of dye above the main downflow (see Baines 2001a). The fluid is illuminated by a scanning laser beam giving a thin two-dimensional vertical cross-section.

Figure A. Flow of a gravity current down a slope of 3 degrees into a uniformly density stratified environment, B₀ = 0.055, Holmboe waves. The dense fluid is marked with green fluorescene dye, which also marks fluid that is mixed with the environment. Mixing occurs through the process of Holmboe instability (see Baines (1995, Chapter 4)), which causes wisps of dense fluid to be swept off the top of the dense downflow and mix into the overlying fluid. This causes a steady build-up of detrained fluid, made visible through the accumulating concentration of dye above the main downflow (see Baines 2001a). The fluid is illuminated by a scanning laser beam giving a thin two-dimensional vertical cross-section.

Figure B. Flow of dense fluid down a slope of 30 degrees into a uniformly density-stratified environment, B₀ = 0.028, a turbulent plume. Here the flow has the character of a turbulent plume, which entrains environmental fluid into the descending boundary current. The plume overshoots its level of equilibrium density, and springs back to spread out around its equilbrium level. Some of this fluid is entrained into the downflow and recirculated.

Figure B. Flow of dense fluid down a slope of 30 degrees into a uniformly density-stratified environment, B₀ = 0.028, a turbulent plume. Here the flow has the character of a turbulent plume, which entrains environmental fluid into the descending boundary current. The plume overshoots its level of equilibrium density, and springs back to spread out around its equilbrium level. Some of this fluid is entrained into the downflow and recirculated.

Figure C. Flow of dense fluid down a slope of 30 degrees into a uniformly density-stratified environment, B₀= 0.004, a case of double outflow. For 30 degrees slopes with B₀ < 0.007 the downflow was observed to have unusual structure in which the effect on the environment was outflow near the top and bottom, with inflow in between. Over much of the downflow it behaved like an entraining plume, except that partially mixed fluid leaving the boundary current at lower levels rose through the central entraining region to form the upper outflow. This film shows an example of the development of this flow. In the fully developed stage near the end of the film, the buoyant fluid is seen traversing the central gap where entrainment keeps it close to the boundary current, and upward "bubbling motion" is apparent.

Figure C. Flow of dense fluid down a slope of 30 degrees into a uniformly density-stratified environment, B₀= 0.004, a case of double outflow. For 30 degrees slopes with B₀ < 0.007 the downflow was observed to have unusual structure in which the effect on the environment was outflow near the top and bottom, with inflow in between. Over much of the downflow it behaved like an entraining plume, except that partially mixed fluid leaving the boundary current at lower levels rose through the central entraining region to form the upper outflow. This film shows an example of the development of this flow. In the fully developed stage near the end of the film, the buoyant fluid is seen traversing the central gap where entrainment keeps it close to the boundary current, and upward "bubbling motion" is apparent.