The topography of the park is strongly influenced by several faults, particularly the north-east trending of the Klong Marui fault. This offsets the eastern terrain from the central mountain ranges by a right lateral movement. This fault movement resulted in the formation of a large graben parallel to the fault. This graben is marked by the present bay. The high ground is produced by massive limestone blocks displaying classic karst scenery. These blocks extend southward into Phangnga bay where they form islands with vertical cliffs, mainly orientated in a north-south direction. Phangnga bay slopes seaward and is filled with tidal sediments. The bay itself is composed of large and small tidal channels which originally connected with the fluvial system of the mainland. The main tidal channels for instance Klong Ko Panyi, Khlong Phangnga, Klong Bang Toi and Klong Bo Saen all run in a northsouth direction. They consist of several tidal creeks or tidal channel distributaries. Most of the tidal channels are meandering with well developed point bars. Mangrove forests grow around the whole area of the Phangnga bay, they differ in species depending on elavation and relative tidal range. The landward boundary of Phangnga bay is marked by a gentle erosion slope, limestone cliffs and transition forest between mangrove and upland forest which extends beyond the bay margin.