  We investigate the evolution of string order in a spin-1 chain following a
quantum quench. After initializing the chain in the Affleck-Kennedy-Lieb-Tasaki
state, we analyze in detail how string order evolves as a function of time at
different length scales. The Hamiltonian after the quench is chosen either to
preserve or to suddenly break the symmetry which ensures the presence of string
order. Depending on which of these two situations arises, string order is
either preserved or lost even at infinitesimal times in the thermodynamic
limit. The fact that non-local order may be abruptly destroyed, what we call
string-order melting, makes it qualitatively different from typical order
parameters in the manner of Landau. This situation is thoroughly characterized
by means of numerical simulations based on matrix product states algorithms and
analytical studies based on a short-time expansion for several simplified
models.
