Kapenga Caldera

The Kapenda Caldera, just south of the Rotorua Caldera and between this and the Maroa Caldera, is believed to have been buried by subsequent eruptions including those of the Tarawera volcanic complex. Problematically to date no definite assignment of the up to seven ignimbrites attributed to it can be related to a definite caldera-forming event or documented collapse.[2] It had several very large eruptive events during the ignimbrite flare-up of the Taupō Volcanic Zone between 350,000 to 240,000 years ago.[1] The boundary between the Kapenda Caldera and the Ōkataina Caldera is debated which particularly affects more recent Earthquake Flat activity. The Kapenda Caldera occupies the northern part of the Paeroa Garben between the uplift caused by the now fairly inactive Horohoro Fault and the uplift associated with the still very active Paeroa Fault. It contains the Ngakuru Graben. A large number of intra-rift faults called the Taupo Fault Belt and associated with the modern Taupō Rift exist in the Paeroa Garben and Kapenga Caldera so it is quite a tectonically active area now. The recently paired in time Rotoiti eruption and Earthquake Flat Breccia eruptions had the later assigned as it was within the old caldera's margins but with greater understanding is best assigned to the magma mush body that underlays the magma bodies of the Ōkataina Volcanic Centre and so presently to this active volcanic centre.

There are two rhyolite domes of note. These are the Horohoro Cliffs at 817 m (2,680 ft), a rim-fracture dome associated with the Horohoro Fault that marks the northwestern edge of the Kapenda Caldera, and Haparangi a late-stage intra-caldera dome that rises above the Ngakuru Graben to 688 m (2,257 ft).[3] Haparangi Rhyolite has been a term used since 1937 to any rhyolite flows/lavas of Pliocene-Pleistocene origin in the Taupo Volcanic Zone and does not imply any origin from the Kapenda Caldera.[3]

Its known eruptions were:

• 890,000 - 680,000 years ago
  • Tikorangi Ignimbrite (sometime known as Pukerimu Ignimbrite). Erupted at 0.89 ± 0.04 Ma[4]
  • Rahopaka Ignimbrite (0.77 ± 0.03 Ma)[3]
  • Waiotapu Ignimbrite (0.71 ± 0.06 Ma)[3]
  • Matahana Ignimbrite (0.68 ± 0.04 Ma) [3]
• 310,000 - 275,000 years ago
  • The caldera is not a source of some of the Mamaku ignimbrite as previously speculated - this all originates from Rotorua Caldera.[5]
  • Neither is the caldera the source of the Ohakuri Ignimbrite as previously speculated.[3] This comes from the Ohakuri Caldera[6]
  • Pokai ignimbrite (0.275 ± 0.01 Ma)[1] (previously assigned 0.23 - 0.22 Ma)[3]
    • Eruptive volume 100 cubic kilometres (24 cu mi)[1]
    • Welded hard deposit almost reached Tokoroa in west and about Tauriko in north east.[1]
    • The vent still has some uncertainity[1]
  • Waihou (Chimp, Chimpanzee) Ignimbrite (0.31 ± 0.1 on stratographic grounds)[1] (previously assigned 0.26 - 0.25 Ma) [3]
    • Eruptive volume 50 cubic kilometres (12 cu mi)[1]
    • Loose unwelded deposit reached Tauranga in north east and almost to Tokoroa in west[1]
    • The vent still has some uncertainity[1]
• (felt misassigned)[3] 47,400 ± 1500 years ago (Earthquake Flat Breccia)[7]
  • The historical ages in the literature were close to those now accepted.[8][9] Some composition[3] does not match well Waihou (Chimp) Ignimbrite or earlier. Current ages are based on 20 years revision work.[1]