Landslide-driven drainage network evolution in a pre-steady-state mountain belt: Finisterre Mountains, Papua New Guinea

The emergence of an orogen is generally characterized by an early phase of rapid surface uplift and the concomitant evolution of montane topography, leading in some cases to a steady state in which tectonic mass flux is balanced by erosion. This early phase of mountain growth is exemplified in the Finisterre Mountains of Papua New Guinea, a propagating growth fold whose catchments can be observed at a range of stages in their temporal evolution. Watersheds appear to initiate by isolated gorge incision, to expand by large-scale landsliding in a manner controlled by ground-water seepage, and to entrench by fluvial incision of landslide scars and deposits. Once a montane system of ridges and valleys is established, only rare, major landslides can modify the drainage pattern. The steady-state morphology of a mountain belt is therefore intimately related to its initial phase of growth.