Magma is red-hot molten rock present in volcanoes, as well as magma pools and magma pipes. It serves as an energy source, powering magma forges, magma glass furnaces, magma kilns, and magma smelters, which do not "use it up" in any way. It is extremely dangerous, and has led to the death of many dwarves, and many fortresses.
Magma never cools, but can evaporate if left at a depth of 1/7 for long enough. If mixed with water it can form obsidian (see below).
Lava is the same substance. Magma is what it is called underground, while it is called Lava if it is above ground.
 Magma sources
Magma almost exclusively occurs in two different features; magma pools and magma pipes.
- A magma pool is a reservoir of magma that occupies only a few Z-Levels in the mountain, without reaching the surface. Magma pools can be very small, and may have few suitable locations for buildings that rely on magma. Magma in these pools is limited, and pools will not refill with magma once emptied.
- A magma pipe starts at the lowest z-level of the map from a magma (or lava) flow and extend in a pipe shape upwards, sometimes reaching the surface but often not. Magma Pipes gradually refill with magma.
- Hidden Fun Stuff also contains a very very very small amount of magma, enough for a smelter or two.
Also, note that...
- A volcano is identical in gameplay to a magma pipe, but it has the advantage of being a geographical feature that is visible on the location screen. This means that it is a lot easier to find. However, it IS actually possible for a volcano that shows up on the "local" and region screen in the starting location chooser to be entirely underground - although you could see it in the starting location chooser, it would not be visible from the surface once your dwarves have arrived at the fort's site.
- A magma "vent" is the generic, non-game term for either a pipe or pool. When the distinction doesn't matter, it's commonly referred to as a vent.
 Finding magma
Volcanoes are visible on the "local" screen in the starting location chooser. It is represented as a red ≈ mark (a double tilde) - essentially it looks like red water. Note that red ≈ marks in the "region" screen mean something different entirely (e.g. red sand). If you are using a certain utility, you can also see magma pools and magma pipes on the local screen in the embark menu. After you have embarked for a place that has a volcano, and once your dwarves have arrived at their target destination, you should see a large red pool of lava on your map. If you don't, you should expect your volcano to be somewhere underground. You then have to use exploratory mining to find it. If you can find a large patch of obsidian on the surface that is devoid of boulders, chances are there is a magma vent below, so that would be a good place to start your mining.
While picking a starting location, the easiest place to look for magma is on or near a volcano (a red ^ mark in the "region" screen). There are often volcanic islands (easy to find, since they are the sole land in the middle of oceans), but since sea travel is not yet implemented, trade with other races may not be possible on such islands. Instead, find a volcano on land, and (optionally) start looking for a vent in nearby squares. "Nearby squares" can mean anything from literally on top of the volcano, to adjacent, to quite a long distance away indeed. The placement of magma seems to be related to the distance from volcanoes, but is still essentially random.
Magma vents occur exclusively in world map tiles that are primarily igneous extrusive. That is to say, if you select an entire tile on the embarkation screen and press F1 to highlight the most common terrain, the tile will only have magma if the top stone is dark gray, signifying igneous extrusive rock. Magma does not necessarily form in this geological zone/biome, rather anywhere in the tile. Even if magma is not evident on the surface, it's almost certain to be underground somewhere, though the chances of finding it without reveal.exe are still slim.
Much harder than simply finding a magma vent is finding a magma vent that is also near suitable terrain for building. Depending on your requirements - you may be looking for a source of running water, or a mountain for minerals, or a healthy tree population, a layer of flux for steel production or even all four - suitable building sites can be extremely scarce.
Since volcanoes show up on the region finder, and magma vents do not, you may find it easier to simply check all volcanoes on a map for suitability, and generate a new world if none are suitable, rather than scouring tile after tile for magma vents.
If you're willing to search exhaustively, you might want to consider finding magma vents that are not near volcanoes at all. Very occasionally, magma will be visible in the middle of forests, plains, or other terrain nowhere near a volcano or even mountains. There is no way to spot these on the region map, so you have to review the local maps. This can be done from DF, but since it involves a lot of scrolling and is very tedious, you can try exporting the local map of the world which can be much more quickly searched for the distinctive red ≈ symbol.
You can also occasionally find magma that does not extend all the way to the surface, and therefore is not visible on the local map. These are in fact much more numerous than surface-visible magma vents; however, they are almost impossible to find without cheating via one of the utilities like "reveal.exe", since unlike proper magma vents these smaller deposits must be almost literally mined into to see (you will get a warning about "warm stone" before you actually breach the deposit). These smaller magma deposits appear in the same places as normal magma vents - near volcanoes, or, failing that, near other known magma.
The newly-added "Site Finder" feature neatly sidesteps all of this legwork, allowing you to search for a site with a magma pool or pipe without having to manually check each tile on the world map. Note that unless you edit the .init file so that magma features are shown on the local map, you won't know exactly where the lava is prior to embarking- just that it exists. Depending on whether or not you like a little mystery, this can be turned on or off at will.
 Using magma
On a map with a magma vent, the magma will be clearly visible from every level ground and below, unless the map is in a Freezing area. In Freezing areas, the top few levels of the vent will have cooled to form an obsidian "cap". This should still be readily recognizable however, as it will comprise a circular area. The minerals directly adjacent to the magma vent will also be immediately visible, even at the lowest level of the map, which can give some hints about where to prospect for ores.
The vent has a similar, circular shape on each level. However, it is not identical from one level to the next; some levels will have a larger or somewhat misshapen circle of magma.
The primary use for magma is to power magma smelters, magma glass furnaces and magma forges. (There are other uses, including defense, obsidian production, and possibly even garbage disposal.) To build forges, etc. on magma, at least one of the external eight squares must be above a square of magma.
This can be done most easily by simply building on ground level. The magma is visible from ground level but is actually contained one level below ground level, just like any ground-level water source.
To build underground, you will need to dig at least one tile of a channel down from the location you wish to build the smelter or forge. Eventually, flowing into this channel (on that lower z-level immediately below the forge or smelter), there must be magma, either from the pipe/pool itself or channeled from the vent. You can simply build a tunnel straight into the magma (and lose the miner who digs it 99% of the time), or use channeling to tap into the magma safely from the level above - this latter requires the lower level to be wider than the upper, to jut out so that last tile can be channeled away from above to free the magma into the tunnel system on that level.
Tapping into magma directly is usually safe provided that you are prepared for it (see Pressure note below). Unpressurized Magma is much slower than water from a river source, and can be stopped by any magma-safe floodgate, door or etc. with a bauxite mechanism. Take care however if you are using a screw pump to pump magma into a tunnel/funnel with a cistern below - the pump will make the magma overflow as it would with water.
Volcanoes and magma pipes slowly replenish their supply of magma. A miner with less than Unbelievably Agile will die when breaching a magma tube as he can't move away quick enough.
 Producing Obsidian
Magma can also be used to produce obsidian, a stone which has a base value of 3 (compare with 1 for normal stone and 2 for flux stones), and which can be used to make swords at a Craftsdwarf's workshop.
See Obsidian farming.
 Creature Safety
Volcanoes do not house nice things. Fire men, Magma men, and Fire imps all have their habitats in magma. All of these are attributed to innumerable cases of fun, especially with newer players and forts starting off a bit too close to their volcano perches.
There are several things you can do to prevent fun.
- Channel water in a moat around the the top of the volcano. This will prevent creatures from venturing too far from their homes, but they can still chuck fire at your wood cutters and fisherdwarves. Losing these early on can easily damn your efforts.
- Build far enough away from the volcano as to not catch the attention of what lurks inside. It is perfectly alright to dig several screens away from the volcano and then tunnel up along side it. Magma does not exert pressure and will not follow the rules of equilibrium.
- Use magma-safe grates to filter out unwanted creatures. This works for fire imps, but fire men and magma men are building destroyers and will knock down grates. Fortifications will not work, since creatures will be able to swim through them freely once they are submerged to a depth of 7/7.
 Magma flow
Magma is a non-Newtonian fluid and as such will not be affected by pressure under normal circumstances.
Thus it can be safely passed through tunnels to be used at a lower point in the fortress.
A frequent mistake, however, is to assume that a channel is sufficient to cause magma to fall. While magma will not rise out of a channel, it can flow over the top once the channel fills up.
Another common mistake has to deal with magma pipes and volcanos in Freezing areas. Many people will channel into the obsidian cap and then into the magma through there. However, once a tile of the obsidian 'cap' is breached, the tile directly above the breach will then be included as part of the magma pipe and the magma will begin rising until it has filled that square. For fortresses that tapped into the magma, this can result in waves of magma slowly filling up the fortress from the bottom level up to the magma pipe's new top level. The magma can continue to rise all of the way to the surface if an entire section of the obsidian cap is channeled. The magma will not harden into obsidian again, though, just from the cold temperatures.
Also note that screw pumps can cause magma to behave oddly. Magma that is emerging pumped from a screw pump will behave as if pressurized, and be forced upwards to the same level as the pump. However, this pressure is only exerted by the pump itself - once on the other side, the magma will flow normally again. It is possible to use this effect to channel magma from distant source. If you happen to have constructed your fortress very far from the magma source, you can use a screw pump to "pressurize" the magma to force to flow much more quickly. Where unpressurized magma might take years to flow across the map, pressurized magma would just take a few days.
 Magma pipe refilling
Magma pipes are not pressurized and will flow predictably (Magma#Magma_flow).
Magma pipes refill itself slowly to its original z-level if there is nothing obstructing its path. Tiles above the magma flow tiles will randomly increase magma flow until its original z-level is at 7/7.
There are exceptions to this rule. If there is a floor or wall above a magma flow tile, it will not produce magma above the floor/wall.
Note that since the addition of magma is quite slow, if you intend to breach only a few tiles to fill with magma, it might evaporate at a faster rate than replenishing. A single tile of replenishing magma will most likely evaporate with as little as 5-10 open tiles.
 Magma compared to water
Magma is a non-Newtonian fluid. As such, it acts like water in certain circumstances, but acts differently in others.
- Magma fills a tile and has seven possible depths.
- Magma flows outward and downward to expand into clear space.
- Screw pumps work in magma.
- Floodgates and pressure plates work in magma.
- Constructed walls of all kinds safely contain magma.
- Objects thrown into magma sink to the bottom.
- Magma that is only 1 deep "evaporates" over time.
- Magma will create mist.
- Magma is extremely hot, and capable of melting objects and buildings made of most materials (see Magma vs. built objects) and thus destroying them.
- Magma is not normally pressurized, it seeps out of holes slower than water and slow enough for any dwarves to outrun, unless they are the ones digging into it. That is to say, digging into a volcano core is likely to result in the death of the miner unless he is sufficiently agile or has another immediately pending task - otherwise, he will pause for a moment, think of what to do next, then burst into flames as the magma flows onto him. It is recommended that you tell any prized miners to no longer mine and give a peasant or otherwise less desirable dwarf the sole responsibility of breaking the barrier holding back magma. It is also usually safe to carve a fortification into the wall.
- Magma only spawns directly above the "Magma Flow" tiles at the bottom of a magma pipe, and only up to the original top level. Otherwise, its level may rise only by dripping more magma from above, and new magma may only distribute itself by moving down or to the sides, but never up.
- Magma reacts violently with water, releasing steam and leaving behind tiles of solid obsidian which can be mined, smoothed or engraved like any natural tile.
- Magma cannot be used to satisfy thirst.
- Magma mist is not generated by falling magma, but only by a cave-in.
- Magma mist will not generate happy thoughts, but will instead burn whatever it touches.
 Magma vs. built objects
Some objects that come in contact with magma will function fine, no matter what their material. Others will melt or cease to work properly unless they're made of magma-safe materials.
- Workshops that are powered by magma need not be built of magma-safe materials to function - fire-safe materials are sufficient.
- Constructed objects like walls, floors, stairs and ramps can be made of any material, even those that are not "Magma-safe", and can come into contact with magma without issues.
- Like walls, doors can also be built out of any material and still hold back lava as long as it's in the "closed" position. It may be wise to make sure hallways/rooms close to an engineering project involving magma have plenty of doors, just in case you have a little too much fun when you forget to build that last floodgate.
- Bridges that are built over magma may be constructed of any material. However, bridges that are submerged in magma must be constructed of a magma-safe material.
- Most machines must be made of magma-safe materials to function for more than a few minutes in magma. This includes floodgates. Unsafe materials will function for a while, but then melt or burn away. Screw pumps made from flammable materials (wood, possibly also graphite, lignite, or bituminous coal blocks) can catch fire, though stone and metal components need not be magma-safe unless the rear tile of the pump is submerged.
- Stone mechanisms attached to a construction will melt in magma unless made of bauxite or raw adamantine, even if the construction itself is made of steel.
If even a single component of a submerged building melts (whether a chalk mechanism on a steel floodgate or a copper sword in a weapon trap), the entire building will deconstruct.
 Magma creatures
Fire imps, firemen, magma men, and fire snakes inhabit Magma. Fire snakes are a type of vermin that can set your fortress on fire with little to no warning. Like all other vermin, they may spawn a short distance outside their native environment, meaning they can appear in any region near a magma pipe, even if the region and magma have no physical connection. However, they only spawn near natural formations. They will not spawn at a channel you have dug to another section of your fortress.
 Temperature settings
Magma is almost harmless if temperature is disabled in the Dwarf Fortress init file. It can still trap and suffocate or simply starve your dwarves in some situations. It will not melt bridges, etc. constructed of non-magma-proof materials.
 Magma reactions
- Flowing water: If magma happens to contact water it produces some steam and obsidian. Steam is no longer deadly (as in the old 2D version) so steam traps are ineffective; however, it is now much safer to cast large volumes of obsidian inside mined or constructed molds. The resulting slabs of obsidian are functionally identical to native stone.
- Pond water: A bucket of water dumped onto magma from directly above will cause all of the magma in the tile to disappear in a puff of steam. If dropped from more than one Z-level up, obsidian will be created as expected.
- Brooks: If magma comes in contact with a brook, it will not produce steam, but will turn the water tile below the brook to obsidian, and give the brook tile the appearance of a dried-up brook.
- Rocks: Rocks left over from mining will melt if magma covers them. During the season change, all molten rock is automatically removed (at the same time as blood/vomit).
- Magma-safe items: Magma-safe items in magma (iron, adamantine, raw bauxite, etc) will never melt or be destroyed by the magma. One way to recover them it to turn the magma into obsidian using water and dig them out when it is safe, as encasing them in stone will also not destroy them.
- Trees: Trees will not burn or be destroyed by magma.
- Pressure: Magma does not transmit pressure diagonally, but can in orthogonal directions.
- Speed: Magma flows at the same rate as unpressurized water.
- In a volcano or a magma pipe, magma will occasionally appear in small columns above its surface  if it is below its original level. It will not be created above floors. It will be created in 7s, and will probably spread around in few seconds. This may be deadly to unlucky dwarves standing around. Therefore, to be sure to avoid casualties, do not build workshops inside the pipe itself except at the highest level of magma.
- Cave-in: A cave-in of natural tiles or (more than one) constructed tiles landing in magma will cause potentially lethal magma mist.