  In the colour string picture with fusion and percolation it is shown that
long range azimuthal-rapidity correlations (ridge) can arise from the
superposition of many events with exchange of clusters of different number of
strings and not from a single event. Relation of the ridge with the flow
harmonics coefficients is derived. By direct Monte-Carlo simulations, in the
technique previously used to calculate these coefficients, ridge correlations
are calculated for AA, pA and pp collisions. The azimuthal anisotropy follows
from the assumed quenching of the emitted particles in the strong colour fields
inside string clusters. It is confirmed that in pp collisions the ridge
structure only appears in rare events with abnormally high multiplicity.
Comarison with the experimental data shows a good agreement. Also a good
agreement is found for pPb collisions. For AA collisions a reasonable agreement
is found for both near-side and away-side angular correlations although it
worsens at intermediate angles.
