  We report a time-resolved study of the dynamics associated with the slow
compaction of a granular column submitted to thermal cycles. The column height
displays a complex behavior: for a large amplitude of the temperature cycles,
the granular column settles continuously, experiencing a small settling at each
cycle; By contrast, for small-enough amplitude, the column exhibits a
discontinuous and intermittent activity: successive collapses are separated by
quiescent periods whose duration is exponentially distributed. We then discuss
potential mechanisms which would account for both the compaction and the
transition at finite amplitude.
