The world map in Sacred 2 not just opened up. It burned in and out! How this looks, is proudly presented by this little GIF animation:

Source: Sacred 2

So how is such an effect possible? I can’t tell you the deep technical details, because i didn’t understand them. But let me try to explain it in artist words.
First you paint a height map. There should be one dominant spike in it, depending how you want the map to burn in/out. And now imagine how this map would look like in geometry:
When you think about to press this “mountain” from below through a paper it would look like that:
And this is exactly what happens. Of course not with a 3D model but the shader checks the height map and the current “paper” height, generates a alpha mask from it and this mask is then used for the map animation.

If you now raise your hand and ask “But where comes the burning border from?”, then you’re a A+ pupil. As before i can’t explain how it really works, but there’s just one small gradient texture which is “wrapped” around the borders of the generated alpha mask:

Source: Sacred 2

Update 1

Kyle just posted his breakdown of his burning-paper-effect in the comments!

Source: A Burning Paper Shader