2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/35575We have developed a powerful and efficient method for locating the event horizon of a black hole spacetime, making possible the study of the dynamics of event horizons in numerical relativity. We describe the method and apply it to a colliding black hole spacetime.3 pages, uuencoded gziped ps file including 1 Fig. Also available at http://jean-luc.ncsa.uiuc.edu/Papers/ To appear in the MG7 proceedingsGeneral Relativity and Quantum Cosmologytext