Subglacial Channel Formation from a Single Moulin (SHAKTI)
Goals
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Mesh GenerationRun step 1 in ParameterizationRun step 2 in The model domain is set up as a 500 m thick slab of ice, with bed and surface slope of 0.02. We begin by assuming the hydraulic head is such that the water pressure is equal to 50% of the ice overburden pressure, Re=1,000 everywhere, and the initial gap height is 0.01 m. The outflow boundary (x=0 m) is set to atmospheric pressure () with a "Type 1" (Dirichlet) condition. We set the distributed input from the englacial system to the subglacial system as zero (for this example, we will define the moulin input in the next step). To look at the bed topography, ice surface, initial head, and initial gap height, you can plot them in MATLAB: plotmodel(md,...
'data',md.geometry.base,'title','Bed Elevation [m]',...
'data',md.geometry.surface,'title','Surface Elevation [m]',...
'data',md.hydrology.head,'title','Initial Head [m]',...
'data',md.hydrology.gap_height,'title','Initial Gap Height [m]')
Hydrology solutionIn step 3, we specify which machine we want to run the model on, including number of processors to be used, define the model time step, final time, and prescribe the moulin inputs. In this example, we put a steady moulin input of 4 m s at the center of the domain (x=500 m, y=500 m). We also impose a no-flux "Type 2" (Neumann) boundary condition at all boundaries (except the outflow, where we have our Dirichlet condition defined already in step 2). Now that the set up is complete, we can run the model: md=solve(md,'Transient');
The final steady configurations for effective pressure, hydraulic head, basal water flux, and gap height can be visualized by plotting: plotmodel(md,'data',md.results.TransientSolution(end).EffectivePressure,'title','Effective Pressure [Pa]',...
'data',md.results.TransientSolution(end).HydrologyHead,'title','Head [m]',...
'data',md.results.TransientSolution(end).HydrologyBasalFlux,'title','Basal Water Flux [m^2 s^{-1}]',...
'data',md.results.TransientSolution(end).HydrologyGapHeight,'title','Gap Height [m]')
You can see that a distinct pathway has formed from the moulin at the center to the outflow at the left. Hydraulic head (related to water pressure) is highest directly around the moulin, and the head is lower in the channel than in the areas above and below it in the y-direction. To watch the evolution through time in an animation, use the command: plotmodel(md,'data','transient_movie')
You will be prompted to select which parameter to animate, and can watch an efficient subglacial channel emerge from the moulin to the outflow! References
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