A chronal wave was a destructive pulse of time energy that usually resulted from a fault while time travelling.

Chronal waves were created whenever anyone attempted to operate the SKARDIS, since it was an imperfect version of the Doctor's TARDIS, created by the Skith from the Tenth Doctor's stolen knowledge.

The SKARDIS' use in 21st century Sydney Australia caused it to release a chronal wave each time the Skith tried to fly it. One chronal wave aged the crew and passengers of a plane it hit by hundreds of years, another froze Sydney in ice from the Ice Age, and others brought prehistoric creatures such as dinosaurs and mammoths into 21st century Sydney. The SKARDIS was destroyed by UNIT, and the Doctor ultimately helped alleviate the effects of the chronal damage. (COMIC: The Age of Ice)

The planet Chronos would be flooded with chronal waves that would sweep everyone on the planet into the future to the Cybermen. They were a result of the Cybermen travelling between the far future of Chronos to its past. (WC: Real Time)