Vortices are a special type of creature in ADOM that is notorious for their deadliness, especially to unprepared and careless adventurers. They are semi-sentient elemental constructs that only know one combat strategy: violent self-combustion, dealing considerable amounts of damage (and also item destruction) depending on the type.
There are four different kinds of vortices: The fire vortex, the ice vortex, the lightning vortex and the acid vortex. Of these the fire vortex tends to appear the earliest, the lightning vortex is the fastest and thus hardest to escape, and the acid vortex is the most damaging overall. The ice vortex is relatively tame compared to the others in raw damage and does have the additional perk that it freezes any water caught in its explosive radius, but to consider it harmless would be a grave mistake.
Especially dangerous are masses of vortices, as created in threat rooms. Even with resistance they will still deal considerable damage if they explode around the PC in masses, and being immune to each other's explosions ensures that they will all get their turn. Vortex artifact guardians are possible; they will explode much more violently than regular vortices, so even resistance might not save the PC's life. In such cases, high HP will also be needed.
The easiest way to deal with vortices would be to have the proper elemental resistance handy, through ring(s) or even intrinsically. Barring that, the player can take advantage of several strategies. One of these is missile combat; the vortex' explosion will only trigger in place of a melee attack, so PCs that can do so are encouraged to destroy the vortex before it gets the chance. Especially reliable, in the case of fire and ice vortices, is the use of the correct bolt or ball spell. PCs that have pets or companions available can also send them off to fight the vortex and make a run for it. All vortices are diagonal-walking monsters, which can sometimes be exploited to deal with them safely.
A quite effective way of dealing with any vortex is the Darkness spell, as this might render the vortex unable to find the PC and thus not explode on him/her; as of v. 1.2.0, though, even enemies that cannot see in the dark can still stumble around dark areas and can bump into the PC. Vortices cannot see invisible and will generally not explode upon contact with an invisible PC (but may if they happen to stumble into them), but will nonetheless track the PC's movements very persistently. Note that vortices except for fire vortices can cross rivers to pursue PCs, and vortices except for ice vortices cannot be hindered by webs as they will destroy them as soon as they are entered.