We study the evolution of the Gregory-Laflamme instability for black
strings in global AdS spacetime, and investigate the CFT dual of the
formation of a bulk naked singularity. Using an effective theory in the
large D limit, we uncover a rich variety of dynamical behaviour,
depending on the thickness of the string and on initial perturbations.
These include: large inflows of horizon generators from the asymptotic
boundary (a `black tsunami'); a pinch-off of the horizon that likely
reveals a naked singularity; and competition between these two
behaviours, such as a nakedly singular pinch-off that subsequently gets
covered by a black tsunami. The holographic dual describes different
patterns of heat flow due to the Hawking radiation of two black holes
placed at the antipodes of a spherical universe. We also present a model
that describes, in any D, the burst in the holographic stress-energy
tensor when the signal from a bulk self-similar naked singularity
reaches the boundary. The model shows that the shear components of the
boundary stress diverge in finite time, while the energy density and
pressures from the burst vanish.