Splash singularity for water waves
  We exhibit smooth initial data for the 2D water wave equation for which we prove that smoothness of the interface breaks down in finite time. Moreover, we show a stability result together with numerical evidence that there exist solutions of the 2D water wave equation that start from a graph, turn over and collapse in a splash singularity (self intersecting curve in one point) in finite time. 
Angel Castro, Diego C\'ordoba, Charles Fefferman, Francisco Gancedo   and Javier G\'omez-Serrano
math.AP