Taupō Volcano

Lake Taupō, in the centre of New Zealand's North Island, is the caldera of the Taupō Volcano, a large rhyolitic supervolcano. This huge volcano has produced two of the world's most powerful eruptions in geologically recent times.

Horomatangi ReefHatepe eruptionMotutaiko IslandHoromatangi ReefMotutaiko IslandMotutaiko IslandAcacia Bay

Not to be confused with the Taupo Bank which is an extinct volcano about 400 km (250 mi) off the east coast of Australia.
Taupō Volcano
Volcano, lake, and caldera locations in the Taupō Volcanic Zone
Highest point
Elevation452 m (1,483 ft)[1]
ProminenceMotutaiko Island
Coordinates38°48′20″S 175°54′03″E
Dimensions
Width33 km (21 mi)
Geography
Taupō Volcano is located in New Zealand
Taupō Volcano
Taupō Volcano
Taupō Volcano is located in North Island
Taupō Volcano
Taupō Volcano
Taupō Volcano (North Island)
CountryNew Zealand
RegionWaikato
Geology
Age of rock
Mountain typeCaldera
Volcanic regionTaupō Volcanic Zone
Last eruptionAbout 250 CE
Climbing
AccessState Highway 1

The volcano is in the Taupō Volcanic Zone, a region of rift volcanic activity that extends from Ruapehu in the south, through the Taupō and Rotorua districts, to Whakaari/White Island, in the Bay of Plenty.

Taupō began erupting about 300,000 years ago. The main eruptions that still affect the surrounding landscape are the dacitic Mount Tauhara eruption 65,000 years ago, the Oruanui eruption about 26,500 years ago,[2] which is responsible for the shape of the modern caldera, and the Hatepe eruption, dated 232 ± 10 CE.[3][4] There have been many more eruptions, with major ones every thousand years or so (see timeline of last 10,000 years of eruptions).[5][6][7]

Taupō Volcano has not erupted for approximately 1,800 years; however, with research beginning in 1979 and published in 2022, the data collated over the 42-year period shows that Taupō Volcano is active with periods of volcanic unrest and has been for some time.[8] Some volcanoes within the Taupō Volcanic Zone have erupted more recently. Mount Tarawera had a moderately violent VEI-5 eruption in 1886, and Whakaari/White Island is frequently active, erupting most recently in December 2019.

Rhyolitic eruptions

The Taupō Volcano erupts rhyolite, a viscous magma, with a high silica content.

If the magma does not contain much gas, rhyolite tends to just form a lava dome. However, when mixed with gas or steam, rhyolitic eruptions can be extremely violent. The magma froths to form pumice and ash, which is thrown out with great force.

If the volcano creates a stable plume, high in the atmosphere, the pumice and ash are blown sideways, and eventually fall to the ground, draping the landscape like snow.

If the material thrown out cools more rapidly and becomes denser than the air, it cannot rise as high, and suddenly collapses back to the ground, forming a pyroclastic flow, hitting the surface like water from a waterfall, and spreading sideways across the land at enormous speed. When the pumice and ash settle, they are sufficiently hot to stick together as a rock called ignimbrite. Pyroclastic flows can travel hundreds of kilometres an hour.

Earlier eruptions

Earlier ignimbrite eruptions occurred further north than Taupō. Some of these were enormous, and two eruptions around 1.25 and 1.0 million years ago were big enough to generate an ignimbrite sheet that covered the North Island from Auckland to Napier.

While Taupō has been active for 300,000 years, explosive eruptions became more common 65,000 years ago.

Oruanui eruption
Main article: Oruanui eruption
Oruanui eruption impact
Oruanui eruption impact North Island in terms of approximate 10cm ash deposit (white shading) and approximate ignimbrite from pyroclastic flow (yellow shading).[9] The central red area is the Oruanui caldera with surrounding collapse crater in lighter red. It is superimposed on present day New Zealand although at the time New Zealand land mass was larger, as sea level was much lower.
A large eruption column during the Oruanui eruption as it may have appeared from space

The Oruanui eruption of the Taupō Volcano was the world's largest known eruption in the past 70,000 years, with a Volcanic Explosivity Index of 8. It occurred around 26,500 years ago[2] and generated approximately 430 km3 (100 cu mi) of pyroclastic fall deposits, 320 km3 (77 cu mi) of pyroclastic density current (PDC) deposits (mostly ignimbrite) and 420 km3 (100 cu mi) of primary intracaldera material, equivalent to 530 km3 (130 cu mi) of magma.[10][9][11]

Modern Lake Taupō partly fills the caldera generated during this eruption.

Tephra from the eruption covered much of the central North Island with ignimbrite up to 200 m (660 ft) deep. The ignimbrite eruption(s) were possibly not as forceful as that of the later Hatepe eruption but the total impact of this eruption was somewhat greater. Most of New Zealand was affected by ashfall, with an 18 cm (7.1 in) ash layer left even on the Chatham Islands, 1,000 km (620 mi) away. Later erosion and sedimentation had long-lasting effects on the landscape, and caused the Waikato River to shift from the Hauraki Plains to its current course through the Waikato to the Tasman Sea.

Hatepe eruption
Main article: Hatepe eruption
Hatepe eruption
Hatepe eruption impact of a 10-cm ash deposit (white shading) and ignimbrite from pyroclastic flow (yellow shading). The collapse caldera is in light red. It is superimposed on the present day North Island.
The Hatepe eruption's main vents (three of the vents in red) ran parallel to Lake Taupō's current southeastern shore. Present active geothermal systems are in light blue.

The Hatepe eruption (also known as the Taupō or Horomatangi Reef Unit Y eruption) represents the most recent major eruption of the Taupō Volcano, and occurred about 1,800 years ago. It was the most powerful eruption in the world in the last 5,000 years.[12][13]

Stages of eruption

The eruption went through several stages.

  • A minor eruption occurred beneath the ancestral Lake Taupō.
  • A dramatic increase in activity produced a high eruption column from a second vent, and pumice was deposited over a wide area.
  • Water entered the first vent and mixed with the magma, producing a white ash-rich pumice fall.
  • A new vent formed and produced a dark ash- and obsidian-rich fall deposit.
  • A larger eruption ensued, producing pumice over a huge area, and a small ignimbrite deposit.
  • The most destructive part of the eruption then occurred. Part of the vent area collapsed, unleashing about 30 km3 (7.2 cu mi) of material, that formed a fast-moving, 600–900 km/h (370–560 mph) pyroclastic flow.
  • Rhyolitic lava domes were extruded some years later, helping form the Horomatangi Reefs and Waitahanui bank.[14] These later smaller eruptions of unknown total size also created large pumice rafts and terminated within decades of the major eruption.[15]

The main pyroclastic flow devastated the surrounding area, climbing over 1,500 m (4,900 ft) to overtop the nearby Kaimanawa Ranges and Mount Tongariro, and covering the land within 80 km (50 mi) with ignimbrite from Rotorua to Waiouru. Only Ruapehu was high enough to divert the flow.

The power of the pyroclastic flow was so strong that in some places it eroded more material off the ground surface than it replaced with ignimbrite. Valleys were filled with ignimbrite, evening out the shape of the land.

All vegetation within the area was flattened. Loose pumice and ash deposits formed lahars down all the main rivers.

The eruption further expanded the lake, which had formed after the much larger Oruanui eruption. The previous outlet was blocked, raising the lake 35 m (115 ft) above its present level until it broke out in a huge flood, flowing for more than a week at roughly 200 times the Waikato River's current rate.

Dating the Hatepe eruption

Many dates have been given for the Hatepe eruption. One estimated date was 181 CE from ice cores in Greenland and Antarctica.[16] It is possible that the meteorological phenomena described by Fan Ye in China and by Herodian in Rome[17] were due to this eruption, which would give a date of exactly 186.[18] However, ash from volcanic activity does not normally cross hemispheres,[19] and radiocarbon dating by R. Sparks has put the date at 233 CE ± 13 (95% confidence).[20] A 2011 14C wiggle-matching paper gave the date 232 ± 5 CE.[3] A 2021 review based on five sources reports 232 ± 10 CE.[4]

New Zealand was unpopulated at that time, so the nearest humans would have been in Australia and New Caledonia, more than 2,000 km (1,200 mi) to the west and northwest.

Current activity and future hazards

From May through December 2022 there was increased earthquake activity with lakeside slumping and inundation from a small tsunami and ground deformation.[21] The Volcanic Alert Level for Taupō Volcano was raised to Volcanic Alert Level 1 (minor volcanic unrest) on 20 September 2022.[22]

While no witnessed eruptive event has been recorded from Taupō, there have been seventeen episodes of volcanic unrest since 1872, with the most recent being in 2019 and 2022–2023.[4] This manifested as swarms of seismic activity and ground deformation within the caldera. The present-day magma reservoir is estimated to be at least 250 km3 (60 cu mi) in volume and have a melt fraction of >20%–30%.[4]

While Taupō is capable of very large eruptions these remain very unlikely as the majority of the 29 eruptions of various magnitudes in the last 30,000 years have been much smaller.[23] Many have been dome-forming, which may have contributed to lake features such as Motutaiko Island and the Horomatangi Reefs.

Earthquake and tsunami hazards also exist. While most earthquakes are relatively small and associated with magma shifts, the moderate earthquakes associated with eruptions or the numerous rift-associated faults historically have produced tsunami events. The intra-rift Waihi fault, for example, has been associated with 6.5 magnitude earthquakes at recurrence intervals of between 490 and 1,380 years and at least one tsunami related to landslip at the Hipaua steaming cliffs.[24]

GNS Science continuously monitors Taupō using a network of seismographs and GPS stations.[23] The Horomatangi Reefs area of the lake is associated with active hydrothermal venting and high heat flow.[4] Monitoring of a volcano situated under a lake is challenging, and an eruption might occur with little or no meaningful notice.[23] Live data can be viewed on the GeoNet website.

See also

References
  1. "NZTopMap:Motutaiko Island". Archived from the original on 27 August 2022. Retrieved 27 August 2022.
  2. Dunbar, Nelia W.; Iverson, Nels A.; Van Eaton, Alexa R.; Sigl, Michael; Alloway, Brent V.; Kurbatov, Andrei V.; Mastin, Larry G.; McConnell, Joseph R.; Wilson, Colin J. N. (25 September 2017). "New Zealand supereruption provides time marker for the Last Glacial Maximum in Antarctica". Scientific Reports. 7 (1): 12238. Bibcode:2017NatSR...712238D. doi:10.1038/s41598-017-11758-0. PMC 5613013. PMID 28947829.
  3. Hogg, Alan; Lowe, David J.; Palmer, Jonathan; Boswijk, Gretel; Ramsey, Christopher Bronk (2011). "Revised calendar date for the Taupo eruption derived by 14C wiggle-matching using a New Zealand kauri 14C calibration data set". The Holocene. 22 (4): 439–449. Bibcode:2012Holoc..22..439H. doi:10.1177/0959683611425551. hdl:10289/5936. S2CID 129928745.
  4. Illsley-Kemp, Finnigan; Barker, Simon J.; Wilson, Colin J. N.; Chamberlain, Calum J.; Hreinsdóttir, Sigrún; Ellis, Susan; Hamling, Ian J.; Savage, Martha K.; Mestel, Eleanor R. H.; Wadsworth, Fabian B. (1 June 2021). "Volcanic Unrest at Taupō Volcano in 2019: Causes, Mechanisms and Implications". Geochemistry, Geophysics, Geosystems. 22 (6): 1–27. Bibcode:2021GGG....2209803I. doi:10.1029/2021GC009803.
  5. A continent on the move: New Zealand geoscience into the 21st century. Graham, Ian J. et al.; The Geological Society of New Zealand in association with GNS Science, 2008. ISBN 978-1-877480-00-3. page 66, 168.
  6. "Taupo the volcano" (a single sheet pamphlet), C.J.N. Wilson and B.F. Houghton, Institute of Geological & Nuclear Sciences, c2004.
  7. "Information from GNS Science on the Taupō Volcano". Archived from the original on 5 February 2018. Retrieved 21 October 2011.
  8. "Bed of Lake Taupō rising and falling as magma moves around in active volcano below - study". Newshub. Archived from the original on 12 July 2022. Retrieved 12 July 2022.
  9. Manville, Vern; Wilson, Colin J. N. (2004). "The 26.5 ka Oruanui eruption, New Zealand: a review of the roles of volcanism and climate in the post-eruptive sedimentary response". New Zealand Journal of Geology & Geophysics. 47 (3): 525–547. doi:10.1080/00288306.2004.9515074.
  10. Wilson, Colin J. N. (2001). "The 26.5 ka Oruanui eruption, New Zealand: an introduction and overview". Journal of Volcanology and Geothermal Research. 112 (1–4): 133–174. Bibcode:2001JVGR..112..133W. doi:10.1016/S0377-0273(01)00239-6.
  11. Wilson, Colin J. N.; et al. (2006). "The 26.5 ka Oruanui Eruption, Taupō Volcano, New Zealand: Development, Characteristics and Evacuation of a Large Rhyolitic Magma Body". Journal of Petrology. 47 (1): 35–69. Bibcode:2005JPet...47...35W. doi:10.1093/petrology/egi066.
  12. "Taupo the eruption" (a single sheet pamphlet), C.J.N. Wilson and B.F. Houghton, Institute of Geological & Nuclear Sciences, c2004.
  13. Wilson, C.J.N. and Walker, G.P.L., 1985. The Taupō eruption, New Zealand I. General aspects. Philosophical Transactions of the Royal Society of London, A314: 199–228.
  14. Houghton, B.F. (2007). Field Guide – Taupo Volcanic Zone Archived 3 March 2016 at the Wayback Machine.
  15. von Lichtan, I.J.; White, J.D.L.; Manville, V.; Ohneiser, C. (2016). "Giant rafted pumice blocks from the most recent eruption of Taupo volcano, New Zealand: Insights from palaeomagnetic and textural data". Journal of Volcanology and Geothermal Research. 318: 73–88. Bibcode:2016JVGR..318...73V. doi:10.1016/j.jvolgeores.2016.04.003.
  16. Lake Taupō Official Site Archived 12 March 2007 at the Wayback Machine
  17. Herodian of Antioch. "Chapter 14". History of the Roman Empire. Vol. Book 1. Archived from the original on 16 September 2019. Retrieved 8 August 2009. Stars remained visible during the day; other stars, extending to an enormous length, seemed to be hanging in the middle of the sky.
  18. Barton, John (2001). The First New Zealand Book? — an Eyewitness account of the Taupō eruption of AD 186. New Plymouth: Trustees of the Dalberton Library. ISBN 0-473-08268-3.
  19. "Iridium: tracking down the extraterrestrial element in sedimentary clays". New Scientist: 58. 1989. Archived from the original on 12 July 2022. Retrieved 4 December 2020.
  20. Sparks, R.J.; Melhuish, W.H.; McKee, J.W.A.; Ogden, J.; Palmer, J.G. (1995). "14C calibration in the Southern Hemisphere and the date of the last Taupō eruption: evidence from tree-ring sequences". Radiocarbon. 37 (2): 155–163. doi:10.1017/s0033822200030599.
  21. Kilgour, Geoff (7 December 2022). "No further unusual activity since the M5.6 earthquake beneath Lake Taupō. Volcanic Alert Level remains at Level 1". GeoNet. New Zealand: GeoNet. Retrieved 7 December 2022.
  22. "GeoNet Volcanic Activity Bulletin". www.geonet.org.nz. Archived from the original on 20 September 2022. Retrieved 20 September 2022.
  23. "GeoNet volcano data underpins new research of Taupō volcano". Geonet NZ. Archived from the original on 13 February 2022. Retrieved 13 February 2022.
  24. Gómez‐Vasconcelos, Martha; Villamor, Pilar; Procter, Jon; Palmer, Alan; Cronin, Shane; Wallace, Clel; Townsend, Dougal; Leonard, Graham (2018). "Characterisation of faults as earthquake sources from geomorphic data in the Tongariro Volcanic Complex, New Zealand". New Zealand Journal of Geology and Geophysics. 62: 131–142. doi:10.1080/00288306.2018.1548495. S2CID 134094861.
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