Geology of the Okataina Volcanic Centre

Abstract

This publication describes and illustrates the volcanic and tectonic processes that formed the Okataina Volcanic Centre over the last half-million years. The map covers the area between Rotorua, Waiotapu and Kawerau, including part of Rotorua Caldera (which collapsed about 220,000 years ago), and all of the Okataina Volcanic Centre, where the last major caldera collapsed about 60,000 years ago. Rotorua Caldera was last active about 20,000 years ago. The Okataina centre is still active, with 80 cubic kilometres of molten rock erupted from the caldera in eleven major eruption episodes over the last 22,000 years. The latest (and smallest) eruption occurred at Tarawera-Rotomahana in 1886 AD.

Deciphering the eruption history of the Okataina Volcanic Centre has involved more than seventy years of geological observations by many people. The lavas and widespread ash and pumice deposits of prehistoric eruptions have been traced back to their vents, and their ages established by varied editing methods. The sequence of volcanic events described and illustrated will prove a valuable source of geological information for scientists, engineers, hazard management agencies and the general public.