New Guinea is situated between the stable land mass of Australia and the deep ocean basin of the Pacific and is thus part of one of the most mobile zones of the earth’s crust, the circum Pacific Mobile Belt. It is characterized by high seismic activity, widespread volcanism, young folded and faulted mountain chains and curved chains of islands and oceanic rises, so called island arcs. Typical New Guinea landforms are high mountain ridges with sharp narrow crests separated by deeply incised V-shaped valleys. Structurally controlled landforms like homoclinal ridges, hogback ridges are also important in certain areas, as are large areas of limestone karst.