Magma is a special type of terrain that appears within the volcano. It can be created elsewhere by using a Staff of minor volcano summoning. In ASCII it appears as an = that flickers between red, yellow, and brown.
Magma causes a large amount of fire damage to PC and monsters while they stand in it. If the PC kicks magma or levitates over it they will also take fire damage. It is treated the same as water for the purposes of the PC drowning. If volcanoes are active in the Drakalor chain, magma will gradually expand into adjacent squares. Magma can only be removed by the falling rocks from earthquakes.
Fire immune monsters will ignore magma, but all other monsters will avoid or attempt to leave it.