Thesis (MSc (Computer Science))--University of Stellenbosch, 2009. / Super cially realistic worlds can easily be created using fractal landscapes. Such landscapes are limited in that real-world geological features such as caves and overhangs are impossible using a standard height eld representation. Interactive, realistic simulation of terrain evolution on such landscapes has proved elusive and does not generally provide direct control over the placement of landscape features. This thesis presents an interactive terrain design system, which enables the user to generate localised, speci c terrain features, as well as generalised global characteristics. A fully volumetric terrain representation is used to allow varied three dimensional terrain features. A hybrid rendering algorithm is employed to e ciently render the volumetric data set, while allowing interactive terrain deformation. Small terrain deformation is enabled using voxel carving, while larger terrain features is generated using an adoption of the Wires algorithm. A fractal river network generation technique is presented and adopted for voxel terrain. These tools provide the user with interactive feedback to allow for more dynamic terrain design.