Rotorua Caldera

2025-09-07T07:01:05Z

2404:4400:4138:7400:C443:53EE:66DD:D7C6: /* 240,000 years ago Ohakuri paired eruption */ Deleted what looked like the first half of a template expression that was included in the article text

{{Short description|Volcanic caldera in New Zealand}}
{{Use dmy dates|date=July 2019}}
{{Use New Zealand English|date=March 2024}}
{{Infobox mountain
| name = Rotorua Caldera
| photo = Rotorua.Caldera.Mount.Tarawera.JPG
| photo_caption = NASA image of the caldera. The town of [[Rotorua]] is south of the lake that fills much of the apparently circular caldera. The caldera is a more complex shape with areas of collapse and the [[Tikitere Graben]] at its outlet. [[Mount Tarawera]] is in the lower right corner south east of the caldera and it and the lakes to the east are features of the adjacent active [[Ōkataina Caldera]]. The eruption products are thickest towards the north east.
| map = New Zealand#North Island
| elevation_m = 757
| elevation_ref =
| prominence =
| location = [[North Island]]
| country = [[New Zealand]]
| region = [[Bay of Plenty Region|Bay of Plenty]]
| coordinates = {{coord|38.08|S|176.27|E}}
| topo =
| type = [[Caldera]]
| age = {{Geological range|0.24|prefix=[[Pleistocene]] (|ref=)<ref name="Bégué2014">{{cite journal|first1=F. |last1=Bégué|first2=C. D. |last2=Deering|first3=D. M. |last3=Gravley |first4=B. M. |last4=Kennedy |first5=I. |last5=Chambefort |first6=G. A. R. |last6=Gualda |first7=O. |last7=Bachmann |title=Extraction, Storage and Eruption of Multiple Isolated Magma Batches in the Paired Mamaku and Ohakuri Eruption, Taupo Volcanic Zone, New Zealand |journal=Journal of Petrology |volume=55 |issue=8 |year=2014 |pages=1653–1684 |doi=10.1093/petrology/egu038 |url=https://academic.oup.com/petrology/article/55/8/1653/1486635|doi-access=free |hdl=20.500.11850/88102 |hdl-access=free }}</ref>}}
| width = {{convert|22|km}}<ref name="Milner2001">{{cite thesis|last1=Milner |first1=David M |title=The structure and eruptive history of Rotorua Caldera, Taupo Volcanic Zone, New Zealand |url=https://ir.canterbury.ac.nz/handle/10092/12722 |year=2001}}</ref>
| volcanic_zone = [[Taupō Volcanic Zone]]
| last_eruption = < 25,000 years ago<ref name="GVP">{{cite gvp|vn=241816|name=Rotorua}}</ref>
}}

The '''Rotorua Caldera''' is a large [[rhyolitic]] [[caldera]] that is filled by [[Lake Rotorua]]. It was formed by an eruption 240,000 years ago that produced extensive [[Pyroclastic rock|pyroclastic deposit]]s. Smaller eruptions have occurred in the caldera since, the most recent less than 25,000 years ago. It is one of several large [[volcano]]es in the [[Taupō Volcanic Zone]] on the [[North Island]] of [[New Zealand]].

==Geography==
[[Image:RotoruaAerial.jpg|thumb|left|230px|Downtown [[Rotorua]], Lake Rotorua, and Mokoia Island]]
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.<ref>{{cite magazine |url=https://www.wired.com/2016/12/steam-explosions-rock-new-zealands-rotorua-caldera/ |title=Steam Explosions Rock New Zealand's Rotorua Caldera|magazine=Wired |last1=Klemetti |first1=Erik }}</ref>

==Geology==
===Eruption history===
The caldera was formed in a single event paired [[List of large volcanic eruptions|major eruption]], lasting only weeks, that is now dated to 240,000 ± 11,000 years ago.<ref name="Gravley2007">{{cite journal|first1=D.M. |last1=Gravley|first2=C.J.N.|last2= Wilson|first3= G.S.|last3= Leonard|first4=J.W. |last4=Cole|title= Double trouble: Paired ignimbrite eruptions and collateral subsidence in the Taupo Volcanic Zone, New Zealand|journal= GSA Bulletin| year=2007|volume=119 |issue=1–2 |pages=18–30 |doi=10.1130/B25924.1|bibcode=2007GSAB..119...18G |url=https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/119/1-2/18/125353/Double-trouble-Paired-ignimbrite-eruptions-and|url-access=subscription}}</ref> It ejected more than {{convert|340|km3}} of rhyolitic Mamaku [[ignimbrite]] giving it a [[Volcanic Explosivity Index]] of 7.<ref name="GVP"/> 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]].<ref name="Bégué2014"/> [[Ignimbrite]], up to {{convert|145|m}} thick covering about {{convert|3100|sqkm|sqmi|abbr=on}}, was deposited in the surrounding area, particularly towards the west.<ref name="Milner2001"/> A small but rather thick outcrop named Mokai Ignimbrite exposed to 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.<ref name="Milner2001"/> 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 definitely paired with an eruption from the Ohakuri Caldera {{convert|30|km}} away, possibly through tectonic coupling, as paired events are being increasingly recognised. The ignimbrite from Ohakuri travelled at least 17 km towards Rotorua.<ref name="Loame2016">{{cite thesis|first1=Remedy Charlotte |last1=Loame |title=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 |year=2016 |url=https://researchcommons.waikato.ac.nz/bitstream/handle/10289/10537/thesis.pdf }}</ref><ref name="Gravley2007"/><ref name="Bégué2014"/>

The outflow [[dense-rock equivalent]] (DRE) of the Mamaku [[ignimbrite]] Rotorua eruption alone was up to {{convert|145|km3}}.<ref name="Bégué2014"/> The maximum DME of the Ohakuri eruption alone is {{convert|100|km3}}.<ref name="Gravley2007"/>

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.<ref name="Milner2001"/> 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 {{convert|22|km|mi|abbr=on}} 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 the smaller lava domes.<ref name="GVP"/> Mokoia Island has been assigned an age of less than 50,000 years.<ref name="Milner2001"/>

===240,000 years ago Ohakuri paired eruption===
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| frameless =1|align=right
|text=Map centered between the Ohakuri caldera and Rotorua caldera (light green shading) so as to show selected surface volcanic deposits including all the present surface Mamaku and Ohakuri ignimbrites. {{Wikipedia:Map data/Northern North Island Volcanics/key}}
|width=295
|height=500
|latitude=-38.16
|longitude=176.03
|icon=no
|zoom=9
}}
[[File:Ohakuri.Rotorua.Paired.Eruptions.Rift.Zone.North.Island.NZ.jpg|thumb|left|alt=Paired eruptions Rotorua(Mamaku) and Ohakuri |Approximate location and outlines (white) of the paired single event Rotorua and [[Ohakuri Caldera|Ohakuri]] calderas with approximate known surrounding Mamaku (blue)<ref name="Bégué2014"/> and Ohakuri [[ignimbrite]]s (yellow phase 1 and dark yellow phase 2).<ref name="Gravley2004">{{cite web|title=The Ohakuri pyroclastic deposits and the evolution of the Rotorua-Ohakuri volcanotectonic depression |url=https://ir.canterbury.ac.nz/bitstream/handle/10092/5465/gravley_thesis.pdf |year=2004 |first1=Darren MClurg |last1=Gravley |access-date=2022-08-17}}</ref> The relationship to the inactive southern portion (red dots) and currently active northern portion (red line) of the [[Horohoro Fault]] is shown. Relationships also shown to old [[Taupō Rift]] (light yellow shading), modern Taupō Rift (light red shading) and [[Hauraki Rift]] (light purple shading). The present landmarks of [[Lake Taupō]] and [[Mount Tarawera]] are labelled for orientation]]

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 {{convert|30|km|abbr=on}} to the south.<ref name="Bégué2014"/> [[Ignimbrite]], up to {{convert|180|m}} thick was deposited in the surrounding area to the south of Rotorua.<ref name="Milner2001"/> 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).<ref name="Gravley2004"/> The pairing was possibly through tectonic coupling of separate magma bodies that co-evolved from a lower in the [[Mantle (geology)|mantle]] common mush body, as paired events are being increasingly recognised.<ref name="Gravley2007"/> The maximum outflow dense-rock equivalent (DRE) of the Ohakuri ignimbrite is {{convert|100|km3|mi3|abbr=off}} which means the combined eruptions produced {{convert|245|km3}} of material.<ref name="Bégué2014"/>

It has been postulated that the drainage of the linked deep magma mush body between [[Rotorua]] and Ohakuri resulted in more than {{convert|250|m}} 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.<ref name="Gravley2004"/> 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 {{convert|0.14|mm}}/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.<ref name="Zachariasen2001">{{cite journal|first1=Judith |last1=Zachariasen |first2=Russ |last2=Van Dissen |title=Paleoseismicity of the northern Horohoro Fault, Taupo Volcanic Zone, New Zealand |journal=New Zealand Journal of Geology and Geophysics |doi=10.1080/00288306.2001.9514946 |year=2001 |volume=44 |issue=3 |pages=91–40|doi-access=free |bibcode=2001NZJGG..44..391Z }}</ref> Understanding that there is volcanotectonic interrelationship lead to a complete reinterpretation of events in the [[Taupō Volcanic Zone]] in the last 250,000 years.<ref name="Gravley2007"/>

==See also==

* {{annotated link|Geology of New Zealand}}
* {{annotated link|Geothermal areas in New Zealand}}
* {{annotated link|Geothermal power in New Zealand}}
* [[List of volcanoes in New Zealand]]
* {{annotated link|North Island Volcanic Plateau}}
* [[Taupō Volcanic Zone]]
* [[Taupō Volcano]]
* [[Volcanism of New Zealand]]

==References==
{{reflist}}

==External links==
* [http://volcano.und.nodak.edu/vwdocs/volc_images/australia/new_zealand/rotorua.html Rotorua at Volcano World]

[[Category:Taupō Volcanic Zone]]
[[Category:Rotorua]]
[[Category:Calderas of New Zealand]]
[[Category:VEI-7 volcanoes]]
[[Category:Volcanoes of the Bay of Plenty Region]]
[[Category:Rotorua Volcanic Centre]]
[[Category:Pleistocene calderas]]
[[Category:Geothermal areas in New Zealand]]

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Rotorua Caldera