  Cold fronts have been observed in a large number of galaxy clusters.
Understanding their nature and origin is of primary importance for the
investigation of the internal dynamics of clusters. To gain insight on the
nature of these features, we carry out a statistical investigation of their
occurrence in a sample of galaxy clusters observed with XMM-Newton and we
correlate their presence with different cluster properties. We have selected a
sample of 45 clusters starting from the B55 flux limited sample by Edge et al.
(1990) and performed a systematic search of cold fronts. We find that a large
fraction of clusters host at least one cold front. Cold fronts are easily
detected in all systems that are manifestly undergoing a merger event in the
plane of the sky while the presence of such features in the remaining clusters
is related to the presence of a steep entropy gradient, in agreement with
theoretical expectations. Assuming that cold fronts in cool core clusters are
triggered by minor merger events, we estimate a minimum of 1/3 merging events
per halo per Gyr.
