An event level chronal distortion was a volatile event that could destroy a TARDIS.
When the Doctor's TARDIS collided with an Acari ship, it split the fifth dimension in two, causing chaos and allowing Emily Winter to meet the Tef'Aree. Before she could return, the TARDIS was destroyed in the distortion, and the huon radiation was too strong to transport her to another planet. They returned her to the TARDIS a few seconds before it was destroyed, enabling her to prevent it. (COMIC: Tesseract)