may yield at significantly lower breaking stresses [@Chugonov2010]. In that case, it would effectively deform as a plastic flow, and, depending on its (unknown) properties, cease to yield altogether [@Lyutikov2015; @Lander2019]. @Thompson2017 has argued that even in this case the crust could yield.

The [*magnetospheric instability*]{} model requires a strongly twisted magnetosphere that becomes unstable and leads to a rapid reconnection event [@Lyutikov2003]. The existence of long-lived magnetospheric twists is supported by the observation of hard X-ray emission in persistent magnetars [@Beloborodov2013b; @Hascoet2014]. During the magneto-thermal evolution of the crust, the displacement of the magnetic field footprints can generate large twists in the magnetosphere [@Akgun2017; @Akgun2018b]. Above a critical twist, the magnetosphere becomes unstable and undergoes a rapid rearrangement where energy is dissipated by reconnection [@Lyutikov2003; @Gill2010; @Elenbaas2016] in a similar fashion as in the crustquake model. The main challenge of this scenario is the ability of the crust to produce significant twists in the magnetosphere. @Beloborodov2009 estimated that currents supporting magnetospheric twist are bound to dissipate on timescales of years, effectively leading to a progressive untwisting. Therefore, Hall evolution is required to proceed relatively fast in order to allow for significant twists. Plastic viscosity may also be a problem 