Ōkataina Caldera (Ōkataina Volcanic Centre, also spelled Okataina) is a massive active volcanic caldera and its associated volcanoes located in Taupō Volcanic Zone of New Zealand's North Island, just east of the smaller Rotorua Caldera and southwest of the much smaller Rotomā complex which is usually regarded as part of the same volcano. Confusingly the Haroharo Caldera contained within it has sometimes been described in almost interchangeable terms with the Ōkataina Caldera or volcanic complex or centre and by other authors as a separate complex.

Ōkataina Caldera
Ōkataina Volcanic Centre, Okataina Caldera, Okataina Volcanic Centre
Okataina Volcanic Centre relationships to other nearby volcanic and tectonic structures
Highest point
Coordinates	38°10′S 176°30′E
Dimensions
Length	28 km (17 mi)[1]
Width	15 km (9.3 mi)[1]
Geography
Ōkataina Caldera North Island Show map of New Zealand Ōkataina Caldera Ōkataina Caldera (North Island) Show map of North Island
Country	New Zealand
Region	Bay of Plenty
Geology
Age of rock	approximately 625,000 years
Mountain type	Caldera
Volcanic region	Taupō Volcanic Zone
Last eruption	1886 Tarawera, 1973 Hydrothermal in Waimangu Volcanic Rift Valley

Geography

The caldera covers an area of about 450 square kilometres (170 sq mi), stretching from Lake Rotoehu in the north to Lake Rotomahana in the south.[2]The north east boundary bisects Lake Rotoiti and the north east includes all of Lake Rotomā. The south west corner is defined by the domes of the Ōkareka Embayment and the Waimangu Volcanic Rift Valley while the south east aspect is dominated by Mount Tarawera and the volcanic badlands of the Puhipuhi Basin. The caldera also contains several lakes, including part or all of Lake Ōkareka, Lake Ōkataina, Lake Rotoehu, Lake Rotomā, Lake Rotoiti, Lake Rotomahana, Lake Tarawera and Lake Tikitapu.[2]

Geology

The caldera contains the first major event Matahina Caldera, the large Haroharo Caldera, and the Rotomā Caldera. The Ōkareka Embayment is another, now in-filled caldera.

Eruptions

The caldera has seen six eruptions in the past 10,000 years, most recently the 1886 Mount Tarawera eruption in the caldera's southeastern corner. The caldera contains two major lava dome complexes, Haroharo in the north and Mount Tarawera in the south. Other volcanoes connected with the caldera include Putauaki (Mount Edgecumbe) [3] and the maar crater of Lake Rotokawau which is most likely to have formed from a basaltic dike extrusion associated with the common magma mush body.[4]

While most New Zealand volcanoes produce small eruptions relatively frequently, Ōkataina's volcanoes tend to erupt very violently after intervals of centuries. As such, they pose significant potential threats to the Bay of Plenty Region.[3] During the last 20,000 years, pyroclastic and lava eruptions have occurred of several types; low-silicate basalt eruptions, high-silicate rhyolite eruptions, and intermediate andesite and dacite eruptions. The most common magma type at Ōkataina is rhyolite.[3]

It is likely that the volcanic history of the area began some 625,000 years ago.[5] The caldera was formed by at least five huge eruptions between 400,000 and 50,000 years ago, causing the collapse of the ground. The most significant collapse event with an eruptive volume of 150 cubic kilometres (36 cu mi) was 230,000 years ago and associated with eruption of the Matahina Ignimbrite which covers over 2,000 km² (770 sq mi).[1] The shape of the Matahina caldera was then modified (and buried/destroyed) by eight smaller eruptions which occurred between 50,000 and 24,000 years ago. The paired 47,400 ± 1500 years ago[6] Rotoiti eruption and Earthquake Flat eruption (previously timed 65,000 years ago) at far ends of the caldera had eruptive volumes of 120 cubic kilometres (29 cu mi) and 10 cubic kilometres (2.4 cu mi) respectively.[1] Between this eruption and 21,000 years ago over 81 km³ (19 cu mi) of Mangaone silicic plinian tephras or pyroclastic flow deposits occurred but eruptive centres can not be assigned. However one of these events can be assigned to the Kawerau Ignimbrite eruption of 33,000 years ago as a location within the central part of the Matahina Caldera at level of the Puhipuhi Basin. [1] Volcanoes within the caldera are known to have erupted eleven times in the last 21,000 years, with all but two of those eruptions being rhyolite.[7][3] Of these eruptions, two, both at Tarawera, occurred within the last 2000 years (in 1886 and c. 1314AD). The most explosive of the eruptions in the last 21,000 years is likely to have been that of Haroharo in about 5500 BCE, which ejected some 17 cubic kilometres of magma.[3] During the same period Ōkataina volcanos have contributed a total magma eruptive volume of about 80 km³ (19 cu mi) in all its eruptions.[7][8] In summary the more significant eruptions have been:[5][1]

• 1886 CE Mount Tarawera
• 1314±12 CE Tarawera Kaharoa
• 1390±70 BCE Rotokawau[9]
• 3550 BCE Haroharo Whakatane[10]
• 5929 BCE Haroharo Mamaku
• 7412 BCE Haroharo Rotamā
• 13,800 years ago Tarawera Waiohau[11]
• 15,700 years ago Ōkareka Embayment Rotorua
• 17,700 years ago Tarawera Rerewhakaaitu[12]
• 21,900 years ago Tarawera Okareka[11]
• 33,000 years ago Kawerau (previously called Kaingaroa and miss-assigned to be 200,000 years older)[1]
• 47,500 to 21,000 years Mangaone deposits
• 47,400 ± 1500 years ago Rotoiti[6] (paired with Earthquake Flat, previously timed 65,000 years ago)[1]
• 48,000+ years ago Puhipuhi Dacite[1]
• 280,000 years ago Matahina[1] (previously timed 322,000 - large as caldera collapse)
• 557,000 years ago Utu
• 625,000 years ago Ōkataina

Tectonics

Faults are not defined under this very active caldera but the existence of at least one paired eruption at the far north and south extremes of the caldera 47,000 years ago at Earthquake Flat and at Rotoiti suggest potential volcanicotectonic interaction. The active Paeroa Fault terminates at the caldera edge and the active Ngapouri-Rotomahana Fault is just to the south. It is notable that the two recently active main vent alignments in the Ōkataina Caldera being the Horahora and Tarawera vents align with identifiable faults outside the caldera.[1]

References