What is believed to cause the colossal flares released by magnetars?

Snapping and reconnecting of unstable magnetic field lines

The origin of the most dramatic energetic outbursts—the colossal flares observed from magnetars—is attributed to instabilities developing within the structure of the object's super-intense magnetic field. When these field lines become sufficiently strained due to twisting and restructuring, they are thought to snap violently and then reconnect. This sudden reconfiguration instantaneously releases vast quantities of stored magnetic energy, resulting in the observed bursts of X-rays and gamma rays. This mechanism highlights that the energy driving these flares comes directly from the configuration and decay of the magnetic field, distinct from rotational energy loss.