  Recently, high-resolution Chandra observations revealed the existence of very
sharp features in the X-ray surface brightness and temperature maps of several
clusters (Vikhlinin et. al., 2001). These features, called ``cold fronts'', are
characterized by an increase in surface brightness by a factor >2 over 10-50
kpc, accompanied by a drop in temperature of a similar magnitude. The existence
of such sharp gradients can be used to put interesting constraints on the
physics of the intracluster medium (ICM), if their mechanism and longevity are
well understood. Here, we present results of a search for cold fronts in
high-resolution simulations of galaxy clusters in cold dark matter (CDM)
models. We show that sharp gradients with properties similar to those of
observed cold fronts naturally arise in cluster mergers when the shocks heat
gas surrounding the merging sub-cluster, while its dense core remains
relatively cold. The compression induced by supersonic motions and shock
heating during the merger enhance the amplitude of gas density and temperature
gradients across the front. Our results indicate that cold fronts are
non-equilibrium transient phenomena and can be observed for a period of less
than a billion years. We show that the velocity and density fields of gas
surrounding the cold front can be very irregular which would complicate
analyses aiming to put constraints on the physical conditions of the
intracluster medium in the vicinity of the front.
