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21-533: The Kapenga Caldera has a western boundary defined by the Horohoro Cliffs and an eastern boundary marked by volcanic domes, including those in the Ōkareka Embayment , some of which are buried by the younger activity of the Ōkataina Volcanic Centre . The Horohoro Cliffs rise to 817 m (2,680 ft) in what is a mountain range, and the caldera contains Haparangi a volcanic dome that is 668 m (2,192 ft) high. Its southern boundary of volcanic activity

42-523: 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 that also feed the Ohakuri Caldera . Ignimbrite , up to 145 metres (476 ft) thick covering about 3,100 km (1,200 sq mi), was deposited in the surrounding area, particularly towards the west. A small but rather thick outcrop named Mokai Ignimbrite exposed to

63-543: A lower in the mantle common mush body, as paired events are being increasingly recognised. The maximum outflow dense-rock equivalent (DRE) of the Ohakuri ignimbrite is 100 cubic kilometres (24 cubic miles) which means the combined eruptions produced 245 cubic kilometres (59 cu mi) of material. It has been postulated that the drainage of the linked deep magma mush body between Rotorua and Ohakuri resulted in more than 250 metres (820 ft) of vertical displacement on

84-497: A much lower displacement rate of the order of 0.14 millimetres (0.0055 in)/year. It has been assigned by some as the outer western fault of the modern Taupō Rift although most think this is further to the east. Understanding that there is volcanotectonic interrelationship lead to a complete reinterpretation of events in the Taupō Volcanic Zone in the last 250,000 years. List of large volcanic eruptions This

105-715: 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 definitely paired with an eruption from the Ohakuri Caldera 30 kilometres (19 mi) away, possibly through tectonic coupling, as paired events are being increasingly recognised. The ignimbrite from Ohakuri travelled at least 17 km towards Rotorua. The outflow dense-rock equivalent (DRE) of

126-467: Is a sortable list of large eruptions that occurred between 11.7 Ka and 450+ Ma . Uncertainties as to dates and tephra volumes are not restated, and references are not repeated. The inclusion criteria here only covers entries with a Volcanic explosivity index (VEI) of 5 or greater. The given values for events in the Miocene epoch sometimes lack references, and are given as VEI-equivalent, as an estimate of

147-632: Is ill-defined but does not extend into areas of continuing low residual gravity anomaly in the Paeroa Graben. The Kapenga Caldera, located just south of the Rotorua Caldera and between it and the Maroa Caldera , is believed to have been buried by subsequent eruptions, including those of the Tarawera volcanic complex which is one factor in making it difficult to define its boundaries. The eastern area of

168-424: Is now filled with Lake Rotorua but the current caldera is more like two ovoids offset from each other, about 22 km (14 mi) in maximum diameter. Mokoia Island , close to the centre of the lake, is a rhyolite dome that later erupted. There are other domes, including Hinemoa Point, Ngongotahā, Pohaturoa and Pukeroa. The most recent magmatic eruption occurred less than 25,000 years ago, creating some of

189-631: The Horohoro Fault scarp. This formed the Paeroa Graben, coincident to the north with the Kapenga Caldera between it and the Paeroa Fault to the east. The formation is known as the Horohoro Cliffs escarpment and displaced Mamaku ignimbrite from the Rotorua Caldera eruption by this amount, presumably shortly after at least the initial the eruption. This fault, in the present day, while active has

210-468: The Mamaku ignimbrite Rotorua eruption alone was up to 145 cubic kilometres (35 cu mi). The maximum DME of the Ohakuri eruption alone is 100 cubic kilometres (24 cu mi). 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. The circular depression left behind

231-632: The Ngakuru Graben, onwards to the Waikato River as it existed then. Subsequent volcanic activity has buried much of the evidence of this phase in the caldera's history. A large number of intra-rift faults called the Taupo Fault Belt are associated with the modern Taupō Rift , and they exist in the Paeroa Graben and Kapenga Caldera, making it a tectonically active area. The paired, in time, Rotoiti eruption and Earthquake Flat Breccia eruptions had

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252-414: The city, and the geothermal areas of Tikitere and Whakarewarewa are associated with the caldera. These areas are still associated with small hydrothermal eruptions. The caldera was formed in a single event paired major eruption , lasting only weeks, that is now dated to 240,000 ± 11,000 years ago. It ejected more than 340 cubic kilometres (82 cu mi) of rhyolitic Mamaku ignimbrite giving it

273-458: The difficulties noted. Often, such issues can be resolved by compositional analysis. Bowyer noted that the Earthquake Flat eruptives were distinct from the earlier Chimp eruptives. While more compositional analysis exists, the issue is unresolved. Its known eruptions were: Rotorua Caldera The Rotorua Caldera is a large rhyolitic caldera that is filled by Lake Rotorua . It

294-522: The ignimbrite flare-up of the Taupō Volcanic Zone, between 350,000 to 240,000 years ago. The boundary between the Kapenga Caldera and the Ōkataina Caldera is debated, which particularly affects more recent Earthquake Flat activity. The Kapenga Caldera occupies the northern part of the Paeroa Graben, between the uplift caused by the now fairly inactive Horohoro Fault and the uplift associated with

315-408: The latter initially assigned to the Kapenga Caldera, as it was within the old caldera's margins. However, some have assigned it to the magma mush body underlying the magma bodies of the Ōkataina Volcanic Centre , suggesting it belongs to a different volcanic centre. An attempt to address the controversy of which caldera was responsible for the Earthquake Flat eruption was made in 2001 by DA Bowyer, with

336-457: The postulated caldera has experienced, relative to much of the rest of the central Taupō Volcanic Zone, many smaller eruptions after caldera formation. Unfortunately, to date, no definite assignment of the up to seven ignimbrites attributed to it can be related to a specific caldera-forming event or documented collapse, despite geological evidence suggesting that such an event may have occurred. The caldera had several very large eruptive events during

357-422: The smaller lava domes. Mokoia Island has been assigned an age of less than 50,000 years. {{maplink|frame=yes |frame- The first major volcanic event 240,000 years ago was the initial Mamaku eruption followed within an hours/days/weeks of a smaller eruption (phase 1) from the same mush body feeding the Ohakuri Caldera about 30 km (19 mi) to the south. Ignimbrite , up to 180 metres (590 ft) thick

378-426: The south-west, but beyond the known boundaries of the much thinner at these boundaries, Mamaku ignimbrite, was erupted at close to the same time. This is likely from a different source to either the Mamaku or Ohakuri ignimbrite. A different source would explain interlayered ash not present in northern Mamaku ignimbrite but there is close composition homogeneity, suggesting a similar magma melt source. Perhaps rather than

399-585: The still very active Paeroa Fault . It has been speculated that the Horohoro Cliffs represent the edge of the caldera. To the south of the caldera is the Ngakuru Graben . For an unknown period between the Mamaku Ignimbrite eruption of the Rotorua Caldera 240,000 years ago and about 60,000 years ago, Lake Rotorua drained via the Hemo Gorge into the Kapenga Caldera, which likely contained a lake, and through

420-457: Was deposited in the surrounding area to the south of Rotorua. Between Rotorua and Ohakuri, crosssections of the ash and ignimbrite from the two eruptions have been able to be sequenced completely. The layers have relationships that can only be explained by a sequence of eruptions separated on occasions by days or less (e.g. no rainfall between eruptions). The pairing was possibly through tectonic coupling of separate magma bodies that co-evolved from

441-460: Was formed by an eruption 240,000 years ago that produced extensive pyroclastic deposits . Smaller eruptions have occurred in the caldera since, the most recent less than 25,000 years ago. It is one of several large volcanoes in the Taupō Volcanic Zone on the North Island of New Zealand . The major regional settlement of Rotorua city is located in the caldera. There is geothermal activity in

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