Rotorua Caldera
Rotorua Caldera | |
---|---|
Highest point | |
Elevation | 757 m (2,484 ft) |
Coordinates | 38°05′S 176°16′E / 38.08°S 176.27°E |
Dimensions | |
Width | 22 kilometres (14 mi)[1] |
Geography | |
Country | Ma)[2] |
Mountain type | Caldera |
Volcanic arc/belt | Taupō Volcanic Zone |
Last eruption | < 25,000 years ago[3] |
The Rotorua Caldera is a large
Geography
The major regional settlement of Rotorua city is located in the caldera. There is geothermal activity in the city, and the geothermal areas of Tikitere and Whakarewarewa are associated with the caldera. These areas are still associated with small hydrothermal eruptions.[4]
Geology
Eruption history
The caldera was formed in a single event paired
The outflow dense-rock equivalent (DRE) of the Mamaku ignimbrite Rotorua eruption alone was up to 145 cubic kilometres (35 cu mi).[2] The maximum DME of the Ohakuri eruption alone is 100 cubic kilometres (24 cu mi).[5]
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.[1] The circular depression left behind 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
240,000 years ago Ohakuri paired eruption
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.[2] Ignimbrite, up to 180 metres (590 ft) thick was deposited in the surrounding area to the south of Rotorua.[1] 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).[7] The pairing was possibly through tectonic coupling of separate magma bodies that co-evolved from a lower in the mantle common mush body, as paired events are being increasingly recognised.[5] 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.[2]
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 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.[7] 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 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.[8] Understanding that there is volcanotectonic interrelationship lead to a complete reinterpretation of events in the Taupō Volcanic Zone in the last 250,000 years.[5]
See also
- Geology of New Zealand – Overview of the geology of New Zealand
- Geothermal areas in New Zealand
- Geothermal power in New Zealand – Overview of geothermal power in New Zealand
- List of volcanoes in New Zealand
- North Island Volcanic Plateau – A pyroclastic volcanic plateau on the North Island of New Zealand
- Taupō Volcanic Zone
- Taupō Volcano
- Volcanism of New Zealand
References
- ^ a b c d e f Milner, David M (2001). The structure and eruptive history of Rotorua Caldera, Taupo Volcanic Zone, New Zealand (Thesis).
- ^ .
- ^ a b c "Rotorua". Global Volcanism Program. Smithsonian Institution.
- ^ Klemetti, Erik. "Steam Explosions Rock New Zealand's Rotorua Caldera". Wired.
- ^ doi:10.1130/B25924.1.
- ^ Loame, Remedy Charlotte (2016). Using a tephrostratigraphic framework to determine the past 40,000 yrs of fault rupture and paleohydrothermal activity on the east strand of the Whirinaki Fault, Ngakuru Graben, central Taupo Volcanic Zone (PDF) (Thesis).
- ^ a b c Gravley, Darren MClurg (2004). "The Ohakuri pyroclastic deposits and the evolution of the Rotorua-Ohakuri volcanotectonic depression" (PDF). Retrieved 17 August 2022.
- .