  Using parsec-resolution simulations of a typical galaxy merger, we study the
triggering of starbursts by connecting the (inter-)galactic dynamics to the
structure of the interstellar medium. The gravitational encounter between two
galaxies enhances tidal compression over large volumes, which increases and
modifies the turbulence, in particular its compressive mode with respect to the
solenoidal one. This generates an excess of dense gas leading to intense star
formation activity. Along the interaction, the compressive turbulence modifies
the efficiency of gas-to-star conversion which, in the Schmidt-Kennicutt
diagram, drives the galaxies from the sequence of discs to that of starbursts.
