Reporoa Caldera

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|text=The Reporoa Caldera is outlined approximately in red. Also shown are approximate sizes (dark blue shading) of the temporary Lake Reporoa's created transiently after the 232 ± 10 CE Hatepe eruption. The Taupō-Reporoa Basin includes both the lakes and caldera and is not shown specifically.

}}

The Reporoa Caldera is located in the northern part of the Taupō-Reporoa Basin, which extends north-east from Lake Taupō in the south to the Waiotapu geothermal area, and whose southern features are distinct from the caldera.{{rp|189}} The Waikato River where it leaves Lake Taupō enters the south east corner of the basin and is flanked by geothermal areas developed for power near Wairakei. In the north-west, the basin rises up to the Paeroa Range whose western limit is defined by the Paeroa Fault scarp.{{rp|189}} The hills of the eastern basin margin are mostly covered by the Kaingaroa Forest. The Waikato River loops to the north before exiting the basin at its south-west but is always south of the caldera.

The basin has been the location of several temporary lakes during its volcanic history and one long term lake that lasted about 200,000 years.{{cite journal|last1 =Rosenberg|first1 =MD|last2 =Wilson|first2 =CJ|last3 =Bignall|first3 =G|last4 =Ireland|first4 =TR|last5 = Sepulveda|first5 =F|last6 =Charlier|first6 =BL| title = Structure and evolution of the Wairakei–Tauhara geothermal system (Taupo Volcanic Zone, New Zealand) revisited with a new zircon geochronology| journal = Journal of Volcanology and Geothermal Research|date=15 January 2020| volume = 390| number =106705| doi =10.1016/j.jvolgeores.2019.106705}}{{rp|loc=Tables 1 & 2}} The long term lake was Lake Huka which was destroyed in the 25,600 years ago Oruanui eruption.{{Cite journal | doi = 10.1080/00288306.2004.9515074| title = The 26.7 ka Oruanui eruption, New Zealand: A review of the roles of volcanism and climate in the post‐eruptive sedimentary response| journal = New Zealand Journal of Geology and Geophysics| volume = 47| issue = 3| pages = 525–546| year = 2004| last1 = Manville | first1 = V. | last2 = Wilson | first2 = C. J. N. | author-link2 = Colin J. N. Wilson|doi-access=free}}{{rp|541}} After the Oruanui eruption there is evidence for a temporary lake in the Reporoa Basin with a shoreline terrace at about {{convert|360|m|abbr=on}} and lake deposits at up to {{convert|400|m|abbr=on}} above today's sea level but this was either drained before the main break-out flood from Lake Taupō, or was destroyed during the break-out flood that followed the Oruanui eruption.{{rp|535}}

The largest recent temporary lake was Lake Reporoa, formed after the Taupō Hatepe eruption about 1,800 years ago.{{cite book|last1=Manville |first1=V| title=Sedimentology and history of Lake Reporoa: an ephemeral supra‐ignimbrite lake, Taupo Volcanic Zone, New Zealand in Volcaniclastic sedimentation in lacustrine settings| editor1=James D. L. White|editor2= N. R. Riggs | publisher=Wiley| date= 2001-04-18| pages=109–40|isbn=1444304267}}{{rp|109}} This lake occupied up to {{convert|190|km2|abbr=on}} of the basin impounding about {{convert|2.5|km3|abbr=on}} of water.{{rp|109}} In due course its natural dam was breached with a resulting initial flood down the Waikato River and this is known to have been before the later breaching of the ignimbrite dam, also formed by the same eruption, at present outlet of the Lake Taupō.{{rp|109}} This larger breach released about {{convert|20|km3|abbr=on}} of water,{{cite journal| last1=Manville| first1=V.| last2=Segschneider| first2=B.| last3=Newton| first3=E.| last4=White| first4=J.D.L.| last5=Houghton| first5=B.F.| last6=Wilson| first6=C.J.N.| year=2009 | title= Environmental impact of the 1.8 ka Taupo eruption, New Zealand: Landscape responses to a large-scale explosive rhyolite eruption| journal=Sedimentary Geology| volume=220| issue=3–4| pages=318–336| doi=10.1016/j.sedgeo.2009.04.017}}{{rp|327}} temporarily flooded some of the area of the former Lake Reporoa.{{rp|109}}

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|text=Map to show surface volcanic deposits of Kaingaroa ignimbrite and Reporoa Caldera (light green shading). {{Wikipedia:Map data/Northern North Island Volcanics/key}}

|width=300

|height=290

|latitude=-38.49

|longitude=176.33

|icon=no

|zoom=9

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It was first recognised as a volcanic caldera in 1994{{rp|1}} and later work has defined it as a single major event caldera within the Taupō Rift.{{rp|471}} Initially the age was thought to be 0.23 Ma{{cite journal

| doi = 10.1080/00288306.2000.9514903

| author = S. W. Beresford

|author2=J. W. Cole

| year = 2000

| title = Kaingaroa Ignimbrite, Taupo Volcanic Zone, New Zealand: evidence for asymmetric caldera subsidence of the Reporoa Caldera

| journal = New Zealand Journal of Geology & Geophysics

| volume = 43

| issue = 3

| pages = 471–481

| s2cid = 129243910

| doi-access =

}}{{rp|pp=471,473}} but is now thought to be about 50,000 years older at 281 ± 21 ka BP.{{rp|197}} This age is more consistent with argon–argon dating on the tephra, ignimbrite and samples from the later smaller rhyolite dome eruptions that happened after caldera formation.{{rp|197}} One of these was at Deer Hill, which is just to the south of the caldera margin and is dated at 264 ± 4 ka BP. Within the southern area of the caldera proper Pukekahu (263 ± 5 ka BP), and Kairuru (247 ± 2 ka BP) formed.{{rp|pp=197,203}} Gravitational{{cite web| last1=Soengkono| first1=S.| year=2012| title=Gravity Modelling Of Reporoa Basin, Eastern Taupo Volcanic Zone (TVZ), New Zealand: In Proceedings of the 34th New Zealand Geothermal Workshop, Auckland, New Zealand|url=https://www.geothermal-energy.org/pdf/IGAstandard/NZGW/2012/46654final00065.pdf |access-date=2023-09-01}}{{rp|pp=1–6}} and magnetic{{cite web| last1=Soengkono| first1=S.| last2=Hochstein| first2=M.P.| year=1996| title=Interpretation of Magnetic Anomalies over the Reporoa Geothermal Field, Taupo Volcanic Zone, New Zealand: In Proceedings of the 18th New Zealand Geothermal Workshop, Auckland, New Zealand|url=https://www.geothermal-energy.org/pdf/IGAstandard/NZGW/2012/46654final00065.pdf |access-date=2023-09-01}} studies have been used to define the caldera to being north of the present Waikato River course in the Taupō-Reporoa Basin.{{cite journal| last1=Kaya| first1=E.| last2=O'Sullivan| first2=M.J.| last3=Hochstein| first3=M.P.| year=2014| title=A three dimensional numerical model of the Waiotapu, Waikite and Reporoa geothermal areas, New Zealand| journal=Journal of Volcanology and Geothermal Research| volume=283 |pages= 127–142| doi=10.1016/j.jvolgeores.2014.07.008}}{{rp|loc=Fig. 1.(a)}}{{rp|187}} A relative gravity low does exist south-west of the river and caldera in the Mihi area and has been called the Mihi volcanic depression, although there is presently no evidence of a related volcanic event.{{rp|4}} The Reporoa Caldera is associated with three geothermal fields. These are the active Reporoa geothermal field in the caldera, the Waiotapu geothermal area north of the caldera rim, and the Broadlands thermal area to the south.{{rp|loc=Fig. 1.(a & b)}}

• List of volcanoes in New Zealand
• {{cite gvp|vnum=241060|name=Reporoa}}

{{reflist}}

Category:Taupō Volcanic Zone

Category:Calderas of New Zealand

Category:VEI-7 volcanoes

Category:Rotorua Lakes District

Category:Volcanoes of Waikato

Category:Pleistocene calderas

Category:Geothermal areas in New Zealand