You can't. I don't know what you think you saw, but you cannot. You can add units with locust and a doodad model to "make" doodads during the game, you can remove blight and show terrain underneath it, but you can't change terrain with a trigger.
in the first cin, the ground has a shockwave type thing
and then i know if you go to the top left to fight, the ground raises every once in a while. (not sure if it works on other isdes, i jus fight there usually)
Yea, that is a Terrain Deformation, there are triggers for it somewhere, search for em.
*EDIT* They are in the Environment Category. There are 4 Different ones, Crater, Ripple, Wave, and Random. If you want the hill like in that map, make a Crater with a negative value for the depth.