Omanawa Caldera

Omanawa Caldera is inferred by an area of magnetic anomaly that exists to the north-west of the Rotorua Caldera.^[2][1] It is also located to the north west of the present boundary of the modern Taupō Volcanic Zone but its existence would be compatible with activity in the area of intersection of Taupo Rift and Hauraki Rift before 1.9 million years ago. The area of the caldera is covered by Mamaku Ignambrite from the Mamaku eruption of 240,000 years ago that formed the Rotorua Caldera. Eruptions from the Omanawa Caldera would explain formations such as the Waiteariki ignimbrite which covers much of the Bay of Plenty and forms the bulk of the Whakamarama Plateau. This would date the major caldera formation to 2.1 million years ago.^[3] However, there are at least eight large eruptions that occurred in the Tauranga Volcanic Centre between 2.4 and 1.9 million years ago and at this time which ones relate to this caldera can not be definite. However to date there is no other obvious closer inferred volcanic structure to assign a super volcanic eruption to, so at least some of these eruptions are likely to be associated with the Omanawa Caldera magnetic anomaly.^[4]

Omanawa Caldera
The approximate size and position of the largely buried (in ignimbrites from the modern Taupō Volcanic Zone) Omanawa Caldera relative to other nearby features of the Taupō Volcanic Zone[1]
Highest point
Coordinates	37°56′29″S 176°02′38″E
Geography
Omanawa Caldera North Island, New Zealand
Geology
Age of rock	between 2.4 to 1.9 million years[1]
Mountain type	Caldera
Volcanic arc/belt	Taupo Volcanic Zone

References

1. Pittari, Adrian; Prentice, Marlena L.; McLeod, Oliver E.; Zadeh, Elham Yousef; Kamp, Peter J. J.; Danišík, Martin; Vincent, Kirsty A. (2021). "Inception of the modern North Island (New Zealand) volcanic setting: spatio-temporal patterns of volcanism between 3.0 and 0.9 Ma" (PDF). New Zealand Journal of Geology and Geophysics. 64 (2–3): 250–272. doi:10.1080/00288306.2021.1915343. S2CID 235736318.
2. Stagpoole, V; Miller, C; Caratori, Tontini F; Brakenrig, T; Macdonald, N (2021). "A two million-year history of rifting and caldera volcanism imprinted in new gravity anomaly compilation of the Taupō Volcanic Zone, New Zealand". New Zealand Journal of Geology and Geophysics. 64 (2–3): 358–371. doi:10.1080/00288306.2020.1848882. S2CID 230527523.
3. Prentice, Marlena; Pittari, A.; Kamp, P; Lowe, David J. (2020). "The 2.1 Ma Waiteariki Ignimbrite: Defining a new super-eruption at the onset of TVZ volcanism". Geoscience NZ 2020.
4. Prentice, Marlena; Pittari, Adrian; Lowe, David J.; Kilgour, Geoff; Kamp, Peter J.J.; Namaliu, Miriam (2022). "Linking proximal ignimbrites and coeval distal tephra deposits to establish a record of voluminous Early Quaternary (2.4–1.9 Ma) volcanism of the Tauranga Volcanic Centre, New Zealand". Journal of Volcanology and Geothermal Research. 429 (107595): 107595. doi:10.1016/j.jvolgeores.2022.107595. ISSN 0377-0273. S2CID 249264293.