The Mamaku Plateau is a large, forest-covered ignimbrite plateau in the North Island of New Zealand. This study was launched to aid inquiries into the evolu-tion of the plateau by classifying its valleys (which con-stitute Mamaku’s main geomorphological feature).An automatic classification of the valley forms in the Mamaku Plateau was made using a Digital Elevation Model (DEM). A new algorithm was created for the Arc/Info Geographic Information System, to extract the valleys from the DEM. Preliminary results from this phase of the inquiry indi-cated that it was difficult to do a computer-aided classi-fication of valleys based only on valley form. Conven-tional classification of the plateau’s valleys had also been done using stereoscopy to assist in the geomorphological interpretation. The results of these classifications were compared, and it was concluded that DEMs are useful in landscape analysis especially if combined with traditional geomorphological analysis.