|This article is about the current version of DF.|
Magma pools are a type of underground feature, essentially deep pits reaching into the magma sea and filled with magma. They are basically pipes of magma extending up from the magma sea itself, identifiable by their obsidian walls (the regular magma sea is surrounded by warm stone). Magma pools can be just about any height; they might not even reach past the top layer of the magma sea, but can be up to a hundred and some z-levels high, reaching up about as far as the first cavern layer.
Extremely tall magma pools provide the second shallowest source of magma in the game, beat only by volcanoes (which reach the surface entirely). They are thus very rare, very desirable embark features, making a fuel-less metal industry much easier, as well as simplifying the pump stacks for applications in !!SCIENCE!!.
Magma pools will very slowly refill if drained, and thus can occasionally be sloughed off when needed. Use caution when digging into the magma sea near a magma pool: the same refill mechanism can apply to exposed magma sea tiles that are not apparently part of the pipe. Rather than rising slowly, a block of 7/7 magma will be created one or more levels above the current level, resulting in much fun for dwarves who happen to be nearby. This effect seems to extend 10 or more tiles from the tube, so it is best to dig into the magma sea a fair distance away from any magma pools.
 Exploiting magma pools
Since dangerous creatures can lurk in magma pools, and in the surrounding caverns, walking around an open magma pool can be hazardous. Instead, you can cap some or all of the magma pool by pouring water on top of it and forming a layer of obsidian. You can then tunnel into the obsidian from the side, and safely channel to the layer of magma below to gain access to magma with a minimum of interference from the local crundle population.