The evolution of topography over subduction zones exhibits high rates of tectonic activity, surface uplift and topographic change. At short time scales (102 yr), surface uplift is dominated by cycles of uplift and subsidence modulated by the elastic loading during the earthquake cycle. At longer time scales (106-7yr), the evolution of topography shows phases and patterns of uplift and subsidence related to changes in the dynamics of the down-going plate and upper plate deformation. There are thus three main processes contributing to subduction zone topography: mantle geodynamics, crustal deformation and mass transfer by erosion and sedimentation. Mantle geodynamic processes are dominated by the downwelling of lithosphere into subduction zones producing vertical motions of the Earth’s surface, but also driving plate tectonics and crustal deformation. Crustal deformation, in turn, manifests itself as vertical motion through isostatic equilibration of thickened or thinned crust. Once elevated, the Earth’s surface erodes, producing sediment that is transferred back to the oceans. The morphology and topography of the continental margin overlying a subduction zone reflects all these processes. Focussed study of this topography and its sources will provide new constraints on subduction and earthquake processes. This requires a diverse set of methods and field sites and the expertise to be assembled for such multi-disciplinary study will provide a perfect learning environment for a set of early stage researchers through an ETN.

Addressing the problem of evolving topography in subduction settings requires interdisciplinary approaches. Many of the individual disciplines considering these processes have seen significant recent advances in both observational fidelity and modelling capability. At global or continental scales, rapid progress has been made in the understanding of dynamic topography. At the crustal and lithosphere scale, tectonic models incorporating the complex viscous and brittle rheology of the lithosphere have been developed to investigate plate boundary processes and crustal deformation. In landscape evolution, advances in modelling surface processes, such as river incision and mass wasting, have permitted models with resolution of metres to be applied over entire mountain belts. Increasingly complex surface and climatic processes have been included in these models. Digital topography data are now widely available and their analysis has become a standard tool in field studies. There have also been advances in the linkages between these fields, particularly the coupling of geodynamic, tectonic and surface processes through numerical models. Although these have only been done at a large scale for relatively simple scenarios, they have documented the importance of the coupling between Earth deformation, surface processes and climate.

These efforts have brought the field to the point that more focused studies can now be applied, a challenge envisaged by SUBITOP.