Complex sentence: If the first part of a tsunami to reach land is a trough--called a drawback--rather than a wave crest, the water along the shoreline recedes dramatically, exposing normally submerged areas.
Split into simpler sentences: If the first part of a tsunami to reach land is a trough--called a drawback--rather than a wave crest. The water along the shoreline recedes dramatically, exposing normally submerged areas.