Geomorphic events and landform response in south-eastern Taranaki, New Zealand

Abstract

South-eastern Taranaki is a tectonically rising area of hill country and marine terraces cut into Plio-Pleistocene marine sediments in the North Island of New Zealand. It is argued that the geomorphic development of the region is more satisfactorily explained with resort to concepts of 'dynamic metastable equilibrium' and 'unsteady behaviour' than by concepts of steady equilibrium behaviour. The region is constantly adjusting in part or in whole to a spectrum of geomorphic events including: sea-level change, tectonic uplift, aeolian deposition, large landslide-triggering earthquakes, deforestation and landslide-triggering rainstorms. The record of these events, in terms of frequency and magnitude, is established and the consequential landform response is discussed. Twelve high sea-level events within the last 700 ka are recorded in the landscape each with associated phases of aeolian deposition. Large earthquakes with terrain-forming capability occur on average once every 1000 to 10 000 years. As a result of slope destabilization by recent deforestation, erosion rates appear to have increased by three times their previous rate. The agents involved in this process are rainstorms with a return period of about 10 years which, during a single event, can strip the regolith from 5 to 15 percent of hillslopes over areas of up to 100 km2. Show more