The Rotorua Caldera, now in filled with Lake Rotorua, is a large rhyolitic caldera. It is one of several large volcanoes located in the Taupō Volcanic Zone on the North Island of New Zealand. Geography The major regional settlement of Rotorua is located in the caldera. There is geothermal activity in the city of Rotorua and the geothermal areas of Tikitere and Whakarewarewa are associated with the caldera. These areas are still associated with small hydrothermal eruptions. Geology Eruption history The caldera was formed in a single event paired major eruption, that lasted only weeks, is now dated about 240,000 years ago, and which ejected more than of rhyolitic Mamaku ignimbrite giving it a Volcanic Explosivity Index of 7. The eruption has been reinterpreted as a paired eruption with a very slightly later, slightly smaller southerly eruption from the same mush body feeding the Ohakuri Caldera. Ignimbrite, up to thick covering about , was deposited in the surrounding area, particularly towards the west. A small but rather thick outcrop named Mokai Ignimbrite exposed to the south-west, but beyond the known boundaries of much thinner at these boundaries, Mamaku ignimbrite, was erupted at close to the same time but likely from a different source. A different source would explain interlayered ash not present in northern Mamaku ignimbrite but there was close composition homogeneity suggesting a similar magma melt source. Perhaps rather than a very directional pyroclastic flow during the eruption events from a southern vent near Rotorua this formation is explained by more complex pairing with an unknown vent in the area of the Kapenga Caldera. Whatever the Rotorua eruption was paired with one from the Ohakuri Caldera away, possibly through tectonic coupling, as paired events are being increasingly recognised and ignimbrite from Ohakuri has travelled at least 17km towards Rotorua. The outflow dense-rock equivalent (DRE) of the Mamaku ignimbrite Rotorua eruption alone was up to . The maximum DME of the Ohakuri eruption alone is . Caldera collapse occurred particularly during the eruption of middle layer of Mamaku Ignimbrite and in later stages of the eruption as the magma chamber underneath the volcano empted. A circular depression left behind is now filled with Lake Rotorua but the current caldera is more like two ovoids offset from each other, about in maximum diameter. Mokoia Island, close to the centre of the lake, is a rhyolite dome that later erupted. There are