Complex sentence: At this point in its journey, the train was overwhelmed by a tsunami caused by the 2004 Indian Ocean earthquake, estimated to be 6m high--the train was derailed and its carriages filled with water.
Split into simpler sentences: At this point in its journey, the train was overwhelmed by a tsunami caused by the 2004 Indian Ocean earthquake, estimated to be 6m high. The train was derailed and its carriages filled with water.