Moving sponge is trippy. If you want it to work, you need either a perfect circle or a perfect square that has ABOSLUTELY NO PARTICLES near it. I have no idea why this is true, but it is. It is probably best to just draw the sponge in the general location of where it needs to be and later paste/draw the landscape.

Once these factors have been controlled, enter the desired velocity command into the console, press "F" a couple of times to advance the frames, then carve the desired shape. Paste landscape around the sponge, and you should be fine.