Hello there,

I’m currently using version 2.2.0 of ASPECT and I’m trying to model a plume whose path is driven by mantle flow (see Steinberger et al. (2019): Yellowstone Plume Conduit Tilt Caused by Large-Scale Mantle Flow, esp. figure 3 and 4). In order to achieve this I’d like to implement a velocity field split in two, namely a left-oriented velocity field in the lower part of the figure and a right-oriented velocity field in the upper part of the figure, using the function Prescribed Velocity Boundary Indicators. However, in the simulation, the plume immediately gets dragged to the right and the effect of the lower boundary condition just described is not really visible anymore and, in addition, the setup leads to multiple convection cells I didn’t aim for. Below you can find the code I used.

Do you have any ideas what I can do in order to see the effect of both velocity field directions on the plume, both in the left and in the right direction? Thank you in advance for your answers!

Dina

```
set Dimension = 2
set Start time = 0
set End time = 2e7
set Use years in output instead of seconds = true
#set Maximum time step = 1e7
set Output directory = NGP-vm5a
set Use conduction timestep = true
subsection Geometry model
set Model name = box
subsection Box
set X repetitions = 4
set Y repetitions = 1
set X extent = 12e6
set Y extent = 3e6
end
end
##################### Boundary conditions
subsection Boundary velocity model
set Prescribed velocity boundary indicators = left x: function , right x: function
subsection Function
set Variable names = x,y
set Function constants = cm=0.1
set Function expression =if(y<1.5e6, -0.45*cm, 0.45*cm); 0
end
set Zero velocity boundary indicators = bottom
end
subsection Boundary temperature model
set Fixed temperature boundary indicators = bottom, top
set Model name = box
subsection Box
set Top temperature = 1600
set Bottom temperature = 4000
end
end
subsection Initial temperature model
set Model name = function
subsection Function
set Variable names = x,z
set Function expression = 3100 - z*0.5e-3 + if (x>9.5e6 & x<10e6 & z<0.5e6,2000,0)
end
end
subsection Material model
set Model name = multicomponent
subsection Multicomponent
set Densities = 3300,3600
set Viscosities = 1e21,1e22
set Viscosity averaging scheme = harmonic
end
end
## Use compositional field to simulate a lower mantle of different composition
subsection Compositional fields
set Number of fields = 1
end
subsection Initial composition model
set Model name = function
subsection Function
set Variable names = x,z
set Function expression = 1
end
end
subsection Gravity model
set Model name = vertical
subsection Vertical
set Magnitude = 10.0
end
end
subsection Heating model
set List of model names = shear heating
end
subsection Mesh refinement
set Initial adaptive refinement = 0
set Initial global refinement = 5
set Time steps between mesh refinement = 10
set Strategy = temperature,density
end
subsection Postprocess
set List of postprocessors = visualization
subsection Visualization
set Number of grouped files = 0
set Output format = vtu
set List of output variables = density,viscosity,heating
set Time between graphical output = 1e5
set Interpolate output = true
end
end
```