40d:Cave-in

A cave-in will occur if constructions or ground tiles are detached from all supporting tiles (bridges and the like do not support constructions). Since it is only a placeholder, the system is highly unrealistic – you can hold up a giant megafortress by a slender pillar of soap. Toady has stated he intends to implement more realistic cave-ins in future versions.

Cave-ins can be disabled through the init file, by changing [CAVEINS:YES] to [CAVEINS:NO].

How cave-ins work

Any unconnected section of terrain (rock, dirt, or construction that is completely disconnected from the rest of the world) will cave in. The game checks for terrain connections along the X, Y, and Z axes (that's left/right, up/down, and high/low). Diagonal connections are not taken into account yet. Stairs and supports will hold up the terrain. There are not (m)any bridges that will hold up the terrain.

Results of a cave-in

• Any creature caught under the falling material is crushed and killed.
• Any item caught under falling natural terrain is encased in stone and must be dug out destroyed completely.^[Verify]
• Anything standing on the area that caves in falls and may be wounded. The fall victim has a chance of being unable to walk away, somewhat proportional to the distance fallen but not set in stone. No pun intended.
• A large amount of dust is generated. Any creature caught by the dust from the collapse is knocked unconscious and thrown a few tiles, which may cause them to fall off a narrow bridge fifty z-levels above the ground.
• All buildings and constructions under and above the falling area are destroyed
• Natural terrain will remain intact during the cave-in; the only effect is they are revealed.
• Constructions will deconstruct when they collide with solid terrain.
• Any terrain crashes through multiple floors, and stops only upon reaching solid ground, where natural terrain piles up and constructions deconstruct.
• Mined stairs and ramps will settle like unmined rock; Stairs down that fall onto previously empty floors will reveal the level below. If there's rock or floor above them, it'll cover the stairs.
• Anything falling into a flow (like water) sinks to the bottom. Therefore, it is not a good idea to punch a skylight into your meeting area if you forgot that e.g. your gem pile was directly below and you had a magma tube three Z levels afterward... you get the idea.
• If your dwarves, animals, items, or even the seven simultaneous goblin sieges at your door are unfortunate enough to be caught in a cave-in flow (which, by the way, travels up Z levels quite often) they will be pushed around and likely sucked into a lower level.

• This can be used to an advantage (i.e. drop a wooden floor such that the cave-in flow will push the invaders into your magma moat).

Avoiding cave-ins

Do not make unconnected sections of rock.

Actually, you're quite unlikely to cause cave-ins unless you are actively trying to cause them. In which case, you'd be wondering how to avoid cave-ins that cause damage to your folks. That's simple: Add a support under the stone mass, and link it to a distant lever. When you're done, hide everyone, pull the lever and watch the fireworks.

One of the more common accidental cave-ins results when you're taking out the floor in a checker-pattern (dwarves channeling may sometimes tend to make this mistake) and the area below isn't supported, resulting in a situation like the diagram below:

Floor -1
▒▒▒▒▒▒
▒    ▒
▒ X +▒ <-- The X is a floor tile. It's not attached, so it will fall down.
▒  +>▒
▒    ▒
▒▒▒▒▒▒

Floor -2
▒▒▒▒▒▒
▒....▒
▒...▒▒ <-- Causing this area to receive a cave-in flow and knocking out any dwarves in its reach.
▒...<▒
▒....▒
▒▒▒▒▒▒

Another thing to watch out for is if you want to dig away a hill above ground, to make room for your fancy overground fort. You may dig away the hill on one level, and then have a huge platform of "floor" on the z-level above that falls on your miner if they get disconnected from the ground. Easy thing to miss the first time you do it.

The solution here is to dig ramps instead, since these take away both the soil on the level you are digging on and the floor on the level above. This is not foolproof, however, as trees will prevent the floor it's on from being removed, resulting a free-hanging floor when you carve the ramp around it. In addition, ramps do not provide support for other tiles on the higher z-level; depending upon the order they are constructed, cave-ins may still occur.

Using cave-ins

Intentional cave-ins serve four purposes:

• Dams. Dropping a section of natural rock above an underground river can provide a way to dam the river. Similarly, causing a cave-in is probably the easiest way to be able to dig beneath an aquifer you can't dig around. This only works with natural rock; constructions will revert to their components, and not block the river at all.
• Death. Since a cave-in kills most creatures instantly, it can provide a convenient or amusing way to off a group of creatures.
• Easy removal of floor tiles. Causing a cave-in will destroy non-reinforced (no wall or support underneath) floor tiles directly underneath the falling terrain - this is a good way to e.g. hollow out a large area. All that's left to do is a little bit of cleanup on the edges, but look at all the channeling you save yourself!
• Destroying items. Elven siege left behind a bunch of worthless wooden weapons? Got some fire imp fat in your butcher's shop? Need an amusing way to off your stone? Smash it with a cave-in and you'll never see it again.

Mining FAQ
How do I get my dwarves to haul stones only from certain areas?
How do I find ores to mine?
How do I get my dwarves to haul ores and ignore useless stones?
How do I get rid of all this stone?
How do I stop miners from falling in channels as they dig them?
What causes a cave-in?
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