The Whakamaru Caldera which was created in a massive eruption with a VEI of 8 is approximately 30 by 40 km (19 by 25 mi) in size and is located in the North Island of New Zealand. It now contains active geothermal areas as well as the later Maroa Caldera.

Whakamaru Caldera
The approximate immediate impact of the Whakamaru Caldera (red shading) eruptions of about 335,000 years before present. Light white shading shows where 10cm or more tephra detected noting that for example 25cm tephra is found against prevailing wind patterns well to north west of present New Zealand and 10cm south east of Banks Peninsular suggesting multiple significant events contributed. Similarly the light yellow shading does not consider all discontinuities but rather assumes that most discontinuities are due to subsequent erosion rather than landforms of this long ago, which is likely incorrect, but from immediate biosphere impact likely not significantly so. It is possible that ultimately there was worldwide biosphere impact.
Highest point
Elevation	744 m (2,441 ft)
Coordinates	38.42°S 175.80°E / -38.42; 175.80
Dimensions
Width	40 kilometres (25 mi)
Geography
Whakamaru Caldera North Island, New Zealand Show map of New Zealand Whakamaru Caldera Whakamaru Caldera (North Island) Show map of North Island
Geology
Age of rock	Over 500,000 but mainly 335,000 years[1]
Mountain type	Caldera
Volcanic arc/belt	Taupo Volcanic Zone
Last eruption	Hydrothermal eruptions are contemporary, last volcanic 14,000 years ago (Puketarata)

Geography

The Whakamaru Caldera covers an area larger than the younger Taupo Volcano to its south and indeed the rims overlap. To its north the more recent eruptive centres have sometimes been grouped as the Mokai Ring Complex or Maroa Volcanic Centre. It contains to its north east the more recently active Maroa Caldera with the Ben Lomond Dome being outside the southern border of the Maroa Caldera but definitely a feature of the Whakamaru Caldera.[2] Domes within the caldera include the Western Dome Complex, including Pokuru which defines its north western borders (which likely overlap with those of the older Mangakino caldera complex), Forest Road Dome, Puketarata (which is the last Maroa Caldera eruption at 14,000 years ago),[3] Ngangiho which is 629 metres (2,064 ft) high but beaten by Ben Lomond 744 metres (2,441 ft) and Marotiri 733 metres (2,405 ft) just to the west of Kinloch.

Geology

The first eruptions may have occurred half a million years ago but the period 320,000 to 340,000 years before the present have been characterised as:

1. Whakamaru Eruption
   • massive eruption sequence over less than a thousand years with a VEI of 8 producing 1,200 to 2,000 km³ (287.9 to 479.8 cu mi) of tephra about 335,000 years ago (330 - 340 ka). [1][4] This is the largest known in the Taupō Volcanic Zone and had at least three rhyolytic and one basaltic eruption in its sequence.[5]
   • Although accumulation of the magma mush may have been over more than 200,000 years there is increasing evidence that eruption only became possible over a period that may have been as short as 10 years through a rapid thermal pulse or pressure change.[5][6]
   • From sea core sediment studies it is known that it deposited the widespread Mount Curl/Rangitawa Tephra, dominantly to the southeast (in addition to occurrences northwest), extending across the landmass of New Zealand, and the South Pacific Ocean and Tasman Sea. The eruption has been calculated to have been 1,500 km³ (360 cu mi) dense-rock equivalent (DRE) and modelled to have produced a Plinian column approximately 45 km (28 mi) high.[7] At the Chatham Islands which is more than 900 kilometres (560 mi) from the Whakamaru Caldera the deposits are up to 30 cm (12 in) thick. About 200 kilometres (120 mi) from the source in New Zealand itself the Rangitawa Tephra is up to 70 cm (28 in) thick[7] so a large area of the planet's biosphere would have been impacted.
   • Whakamaru ignimbrite
     • Found over an area of 13,000 km² (5,000 sq mi) mainly to west of caldera
     • Up to 1 km (0.62 mi) thick[2]
   • Rangataiki ignimbrite
     • Found mainly to east of caldera
2. Mananui eruption (also termed Whakamaru 2 eruption about 330,000 to 320,000 years ago
   • Mananui ignimbrite found mainly to west of caldera
   • Te Whaiti ignimbrite found mainly to east of caldera and likely to be same eruptive sequence as Mananui[2]
3. Paeroa eruption by 320,000 years ago
   • Paeroa ignimbrite found mainly to east of caldera[2]
4. The Western Dome Belt eruptions
   • These represent separate younger magmas that were emplaced over an extended period, from 340,000 to 240,000 years ago[2]

The Maroa Caldera eruptions can be regarded as a separate sequence of rholite eruptions commencing from 305,000 years ago continuing to as recently as 14,000 years ago:[2]

• 305,000 ± 17,000 oldest Maroa dome
• 283,000 ± 11,000 Korotai deposits from northern Maroa
• 275,000 to 240,000 years ago small-scale pyroclastic eruptions
• 272,000 ± 10,000 Putauaki pyroclastics from a central Maroa source
• 256,000 ± 12,000 Orakonui pyroclastics from a central Maroa source
• 251,000 ± 17,000 onward two large parallel dome complexes developed
• 229,000 ± 12,000 Atiamuri deposits from northern Maroa
• 220,000 unclear where Mokai ignimbrite that outcrop in some of Maroa area comes from
• 229,000 to 196,000 Pukeahua deposits and dome building
• 16,500 years ago Puketarata tuff ring formed with total volume of 0.25 km³ (0.060 cu mi)[3] in a complex series of eruptions including maar formation[8]

References