i will discuss the metric behavior of the kahler-ricci flow on hirzebruch surfaces assuming that the initial metric is invariant under a maximal compact subgroup of the automorphism group. i will describe how, in the sense of gromov-hausdorff, the flow either shrinks to a point, collapses to $p^1$ or contracts an exceptional divisor. this confirms a conjecture of feldman-ilmanen-knopf. this is a joint work with jian song.