We'll be obscuring some of the roads and livening up the larger areas of the board with a couple of well placed craters. After a little discussion about size and dimensions, we're going to make them of a size that equates roughly to that of a Space Marine drop pod hitting the ground. The reason being that this is a reformed Imperial world and you'd expect those power armoured pansies to be on the frontline of bringing about compliance, plus Eldar are a little more graceful and my Orks haven't a clue how they arrived there.

Some Small Craters

The first type of crater I experimented with were a simple result of having finished filling in the base of one of the boards with filler, and being filled with the urge to destroy the nice smooth finish.

First, make a small round hole into the base, which is easy if done at the start to the fact that the filler is still wet.  This makes the bottom of the crater lie lower than the surrounding land, which doesn't make a huge difference with a 3mm deep base, but every little counts.

Next, heap a small ring of filler around the hole, trying not to fill the hole up in the process.  It doesn't matter too much at this point what the effect is, as this is simply to make the raised edge of the crater, and will be worked into the correct shape in the next step.

Now, draw the raised edge outwards, with the aim of not making a perfectly even cone, but a rougher splash-effect. Some rays should be bigger than others, and extend out further.

Finally, fill in the centre in such a way as to make a spherical depression - imagine a marble sitting neatly in the hole.