Shrink part of the landscape in UE5

I am trying to achieve this behavior if it is possible:
In a top down game, on the map there is a ground in the center (shaped like O for example) and outside of that center is lava (or anything for context). after some time I want this central O to shrink (if it had radius 10, after certain time it goes to radius 8) and what’s left gets filled by lava (or whatever material is outside of the center)

In case my explanation is not clear I’ll add a photo of what I mean