Hatepe Eruption

The Hatepe eruption, named for the Hatepe Plinian pumice tephra layer, sometimes referred to as the Taupō eruption or Horomatangi Reef Unit Y eruption, is dated to 232 CE ± 10 and was Taupō Volcano's most recent major eruption. It is thought to be New Zealand's largest eruption within the last 20,000 years. The eruption ejected some of material, of which just over was ejected in a few minutes. This makes it one of the largest eruptions in the last 5,000 years, comparable to the Minoan eruption in the 2nd millennium BCE, the 946 eruption of Paektu Mountain, the 1257 eruption of Mount Samalas, and the 1815 eruption of Mount Tambora.

Stages of the eruption

The eruption went through several stages, with six distinct marker horizons 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.Houghton, B.F. (2007).
Field Guide—Taupo Volcanic Zone
'. ''.

The main pyroclastic flow devastated the surrounding area, climbing over to overtop the nearby Kaimanawa Ranges and Mount Tongariro, and covering the land within with ignimbrite. As New Zealand was not settled by the Māori until more than 1,000 years later, the area had no known 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).

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

After the eruption rhyolitic lava domes were extruded, these smaller eruptions of unknown total size also created large pumice rafts that were later discovered deposited on the lake shoreline.

Dating the eruption

For many years it was believed, following research by Colin J. N. Wilson and others, that the eruption could be dated almost exactly to 180 AD. This meant that it coincided with meteorological phenomena described by Fan Ye in the Han dynasty and by Herodian of Antioch in the Roman Empire.

The 180 AD date has since been debated. Estimated dates suggested for the Taupō eruption have ranged from 131 to 538 CE. The earlier date was based on from carbonized vegetation enclosed in the eruption products. However, the 22 selected samples used to obtain an average date of 1,819 ± 17 years BP (131 CE) had much larger standard deviations than the average date itself. Most, if not all, geologists now accept that the tephra or pumice fall from the eruption was far greater than previously thought, approximately instead of . A middle date of 233 CE ± 13 years (95% confidence) was a result of radiocarbon dating by R. Sparks (1995).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. . page 66, 168. The presence of contaminating ¹⁴C-less magmatic carbon in pre-eruption groundwaters has been proposed as skewing towards older dates, leading to suggested dates for the Hatepe eruption decades or even centuries younger (eg 538 CE) than previously thought. It may be relevant to note despite the issue that the carbon dating data might be considered in dating ice core data, that the high resolution ice core series now available have an eruption detectable in both northern and southern hemispheres at approx 229 CE -7+3 and an event confined to the southern hemisphere around 190  CE. Greenland NGRIP data and Antarctic Law Dome data dates are much more consistent than Antarctic South Pole and Dronning Maud Land at this time from the present which may have errors ± 20 years.

The date is currently accepted to be 232 CE ± 10. If the timing is changed by other validation due to the potential systematic error produced by carbon released by the eruption itself it will be towards a more recent date. Humans had not settled in New Zealand at the time of the eruption, and would not for more than 1,000 years. The nearest human populations at the time were in Tonga, more than to the northeast.

Post-eruption soil deficiencies

The tephra soils associated with the eruption were deficient in several essential minerals, with cobalt deficiency being the cause of bush sickness in animals that precluded productive livestock farming until this issue was identified and addressed. This identification by New Zealand government scientists in 1934 was probably the most significant single advance in New Zealand agriculture ever, but was not able to be fully exploited until the 1950s with the deployment of cobalt ion containing superphosphate fertiliser from aircraft.

See also

* North Island Volcanic Plateau

References

External links

Lake-floor relief map
from {{cite journal , url=http://www.niwa.co.nz/publications/wa/vol10-no3-october-2002/high-tech-tools-for-tackling-fisheries-problems-in-lakes , title=Volume 10: High-tech Tools for Tackling Fisheries Problems in Lakes , journal=Water & Atmosphere , volume=10 , issue=3 , author1=Dave Rowe Gavin , author2=James Gavin Macaulay , author3=Ude Shankar , date=October 2002 Summary: the main Hatepe eruption vents are marked by submarine peaks on the far eastern side of Lake Taupō called the Horomatangi Reefs.

Taupō Volcanic Zone
Volcanic eruptions in New Zealand
2nd-century natural disasters
Ancient natural disasters
Prehistoric volcanic events
Events that forced the climate
VEI-7 eruptions
Phreatomagmatic eruptions
Plinian eruptions
Lake Taupō