Thanks.
As for depth, simpy place lava on ground, select it and hold Ctrl + PageDown, make sure it is a doodad. This way it will go down beneath texture.
I used one model for chains, it was downloaded from XGM.ru website. I created a doodad for each piece of chain, rotated it just like I did with rocks, by opening Object editor, holding Shift pushed on Roll and Pitch Angle to set it into minus by typing '-' without ( ' ) in front of value, this way doodad rotated based on the negative value entered. -1.57 will rotate 90 degrees, -3.15 will rotate 180 degrees and so on. Same with rocks, I put them to -3.15 so it is up side down. As for chain, I adjusted necessary value and using Ctrl + PageUp rised it into position imitating chains.