  We show that the neutron star's crust-core interface acts as a potential
barrier on the peripheral neutron vortices approaching this interface and thus
prevents their continuous decay on it in the course of equilibrium state
deceleration. The barrier arises due to the interaction of vortex magnetic flux
with the Meissner currents set up by the crustal magnetic field at the
interface. When the non-balanced part of the Magnus force reaches the value at
which the vortices are able to annihilate at the interface, the rapid transfer
of angular momentum from the superfluid spins-up the observable crust on short
dynamical coupling times.
