Hatepe eruption

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The Hatepe eruption's three main vents ran parallel to Lake Taupo's current southeastern shore.
The Hatepe eruption's three main vents ran parallel to Lake Taupo's current southeastern shore.

The Hatepe eruption (named for the Hatepe Plinian pumice fall deposit[1]; sometimes imprecisely referred to as the Taupo eruption) around 180 CE was Lake Taupo's most recent major eruption, and New Zealand's largest eruption during the last 20,000 years. It ejected some 120 cubic kilometres of material (rating a 7 on the Volcanic Explosivity Index scale),[2] of which 30 cubic kilometres was ejected in the space of a few minutes. It is believed that the eruption column was 50 kilometres high, twice as high as the eruption column from Mount St. Helens in 1980. This makes it one of the most violent eruptions in the last 5000 years (alongside the Tianchi eruption of Baekdu at around 1000 and the 1815 eruption of Tambora). The resulting ash turned the sky red over Rome and China.[3]

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[edit] Stages of eruption

The eruption went through several stages, with six distinct fall units identified. Despite the uniform composition of the erupted magma, a wide variety of eruptive styles were displayed, including weak phreatomagmatism, Plinian eruptions, and a huge pyroclastic flow. Rhyolitic lava domes were extruded some years or decades later, forming the Horomatangi reefs and Waitahanui bank.[4]

The main pyroclastic flow devastated the surrounding area, climbing over 1500 metres (5000 feet) to overtop the nearby Kaimanawa Ranges and Mount Tongariro, and covering the land within 80 kilometres (50 miles) with ignimbrite. Since New Zealand was not settled by the Māori until at least several centuries later, the area had no human inhabitants when the eruption occurred. Tsunami deposits of the same age have been found on the central New Zealand coast, evidence that the eruption caused local tsunamis, but much more widespread waves may have been generated (like those observed after the 1883 Krakatoa eruption).[5]

The Hatepe eruption further expanded the lake, which had formed after the much larger Oruanui eruption around 26,500 years ago. The previous outlet was blocked, raising the lake 35 metres 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.

[edit] Dating

With regard to the dating of the Taupo eruption, the earlier date of c130 CE based on radioactive carbon14 from carbonized vegetation enclosed in the eruption products. The 22 selected samples used to obtain an average of 1,819 plus or minus 17 years BP, or CE 131, have much larger standard deviations than the average date itself.[3] This article showed, as now accepted by most if not all geologists, that the tephra or pumice fall was far greater than previously thought (150 cubic km instead of 14) and so could have been visible from China and Rome. On this basis, it was posited by Wilson et al., and is now generally accepted, that meteorological phenomena described by Fan Ye in China and by Herodian in Rome were due to the eruption, which therefore can be dated exactly to 186 CE.[6]

[edit] References

  1. ^ Talbot, J. P.; Self, S.; Wilson, C. J. N. (1994). "Dilute gravity current and rain-flushed ash deposits in the 1.8 ka Hatepe Plinian deposit, Taupo, New Zealand". Bulletin of Volcanology 56 (6-7): 538–551. doi:10.1007/BF00302834. 
  2. ^ Taupo - Eruptive History. Global Volcanism Program. Smithsonian Institution. Retrieved on 2008-03-16.
  3. ^ a b Wilson, C. J. N.; Ambraseys, N. N.; Bradley, J.; Walker, G. P. L. (1980). "A new date for the Taupo eruption, New Zealand". Nature 288: 252–253. doi:10.1038/288252a0. 
  4. ^ Houghton, B.F. (2007). Field Guide - Taupo Volcanic Zone.
  5. ^ Lowe, D. J.; de Lange, W. P. (2000). "Volcano-meteorological tsunamis, the c. AD 200 Taupo eruption (New Zealand) and the possibility of a global tsunami". The Holocene 10 (3): 401–407. doi:10.1191/095968300670392643. 
  6. ^ Barton, John (2001). The First New Zealand Book? - an Eyewitness account of the Taupo eruption of 186 A.D.. New Plymouth: Trustees of the Dalberton Library. ISBN 0473082683. 

[edit] External links