The late Cenozoic episode of crustal shortening in the South Island, New Zealand, which has caused present day uplift rates of greater than 10 mm/yr and has formed the Southern Alps, may have also caused clockwise rotation of the Alpine Fault by up to 20°. In contrast to the northern end of the Alpine Fault, which appears to have remained fixed relative to the Australian plate, increasing westward movement of the Fault trace has occurred southward along the fault. This westward movement may exceed 100 km where the Fault crosses the coastline in northern Fiordland. Most shortening adjacent to the southern end of the Alpine Fault has occurred within Australian plate continental crust which has been thrust beneath Pacific plate continental crust. This zone of continental underthrusting merges with the Fiordland subduction zone further south, where Australian plate oceanic crust is being subducted. Gravity modelling of the continental collision zone beneath the Southern Alps indicates that the leading edge of underthrust Australian plate crust may be close to a relatively sharp 10 km change in Moho depth. Inward dipping thrust faults on both plates mark the outer limits of the collision zone, which is over 300 km wide near the southern end of the Alpine Fault. The probable increase in crustal thickness due to the late Cenozoic shortening suggests that the amount of crustal thickening is similar in size to the amount of eroded crust