  The dynamics of apparent and event horizons of various black hole spacetimes,
including those containing distorted, rotating and colliding black holes, are
studied. We have developed a powerful and efficient new method for locating the
event horizon, making possible the study of both types of horizons in numerical
relativity. We show that both the event and apparent horizons, in all dynamical
black hole spacetimes studied, oscillate with the quasinormal frequency.
