Loop collapse is a phenomenon that occurs when a loop is not reset, or ten to twelve ymbrynes join together to destroy one. If done successfully, the process can destroy a loop permanently.
Non-Complete Destruction of a Loop[]
A loop typically collapses when it is not able to be reset by an ymbryne, demi-ymbryne or loop-keeper after a certain amount of time. This type of loop collapse will not destroy the loop completely and will leave it open to leapfrogging. When a loop is collapsed like this, it does not repeat the last day of its existence. Peculiars inhabiting it at the time become a part of the loop itself, though the only example shown in the series is Miss Tern. They will be unaware that they are in a collapsed loop, and their memories reset with the loop each day much like looped normals.
Complete Destruction of a Loop[]
One previously largely forgotten procedure, rediscovered by Myron Bentham, can quickly and permanently destroy a loop, but it is rarely done because of how dangerous it is. The procedure requires twelve ymbrynes to form a tight circle and join hands. They do a thirty second chant in Old Peculiar before separating. The main reason the procedure is considered so dangerous is because after the ymbrynes have completed the procedure, any peculiars inside will only have a minute to escape. Anyone who remains in the loop when the minute is completed will be turned into a hollowgast (this is only supported by one instance, the Experiment of 1908). While the minute is ticking a small vortex of shimmering silver, like a miniature hurricane, will appear and being to shrink, spinning faster and faster. When it became too small to see, a sound like the crack of a sonic boom will happen. Those who escape the loop in time, if they have spent a number of years in a loop, will have their internal clocks reset and age naturally again.
The procedure is known to have been used by the Claywings on an abandoned Siberia loop (the Experiment of 1908, which did not work as intended and caused a catastrophic explosion), and by the twelve ymbrynes kidnapped by the wights in the first trilogy on Abaton, during Library of Souls. In the second trilogy, a safer process that involves ten ymbrynes would be discovered. It was tested on Miss Babax's old loop before being used on the pocket loop in Jacob Portman's backyard to reset the internal clocks of the Devil's Acre peculiars.