  This paper presents a model to unify the diverse range of magnetar activity,
through the building and release of elastic stress from the crust. A cellular
automaton drives both local and global yielding of the crust, leading to
braiding of coronal loops and energy release. The model behaves like a real
magnetar in many ways: giant flares and small bursts both occur, as well as
periods of quiescence whose typical duration is either $\lesssim 1$ yr or $\sim
10-30$ yr. The burst energy distribution broadly follows an earthquake-like
power law over the energy range $10^{40}-10^{45}\,{\rm erg}$. The local nature
of coronal loops allows for the possibility of high-energy and fast radio
bursts from the same magnetar. Within this paradigm, magnetar observations can
be used to constrain the poorly-understood mechanical properties of the
neutron-star crust.
