ABSTRACT
Four landslides in Tertiary-age sandstone and mudstone hills of the North Islands East Coast are described, and their movement modes discussed. Active tectonics of the region suggest earthquake triggering mechanisms. The 275 m thick, 1.3 km3 block-slide component of the Waikaremoana landslide accelerated 2 km down a slope of 7° ~2,200 years ago, reaching ~26 m/s before impacting and deforming 1.2 km3 of earlier rock-avalanche debris, thus forming the barrier ponding the present-day, 250 m deep lake. The 200 m thick, 0.9 km3 block-slide at Te Putere traveled 2 km along a 3° basal surface, blocking some adjacent valleys. The 29 km3, complex block and debris Waikareiti landslide moved ~3.5 km down a 7° backscarp 25,000 years ago, affecting an area of 70 km2. Several large lakes are ponded in its surface folds. The 1.5 km3, 100 m thick Tiniroto landslide flowed down a basal slope of 3° 6,500 years ago. Numerous small lakes are ponded on its hummocky surface.
