Hello, thank you very much for your response 

1) Can you please provide more information or screenshot of geometry?

Here is my computational domain. There is an inlet on the lower surface, from where phase 2 is extruded into the model domain, the outlet is the upper surface (blue), from where phase 1 exits the domain to guarantee the incompressibility condition.

2) What is volume fraction of phase2?

phase2 is the lava Volume of fraction = 1

phase1 is the air Volume of fraction = 0

3) Please share the details of vof model and model use for phase interaction?

VOF model, implicite, implicite body force,Interface modelling Sharp + interfacial Anti-diffusion. I dont consider phase interaction. 

3) How you patch phase 2 after initialization?

I suppose that at the initial time the model domain is filled by air(phase 1), hence there is no phase 2 in the model domain.

Thank you very much for your help!