Английская Википедия:Hatepe eruption

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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 Шаблон:Convert of bulk tephra, of which just over Шаблон:Convert was ejected in approximately 6–7 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

Hatepe eruption

Hatepe eruption impact on the North Island 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 present day New Zealand.

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. Most of the stages only affected the immediate surrounds of the caldera and regions to its east due to prevailing wind patterns. The main extremely violent pyroclastic flow travelled at close to the speed of sound and devastated the surrounding area, climbing over Шаблон:Convert to overtop the nearby Kaimanawa Ranges and Mount Tongariro, and covering the land within Шаблон:Convert with ignimbrite. There is evidence that it occurred on an autumn afternoon and its energy release was about 150 megatons of TNT equivalent. The eruption column penetrated the stratosphere as revealed by deposits in ice core samples in Greenland and Antarctica. 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 stages as reclassified from 2003 are:

Hatepe eruption stages

Stage	Deposit	Type	Volume	Timing
1	unit Y1	phreatomagmatic fine ash	Шаблон:Convert	hours
2	unit Y2	mainly magmatic dry ash	Шаблон:Convert
3	unit Y3	mainly phreatoplinian ash but interrupted by dry magmatic ash	Шаблон:Convert	up to tens of hours with towards end heavy rain
4	unit Y4	Rotongaio fine phreatoplinian ash	Шаблон:Convert
5	unit Y5a	Dry vesicular pumice and ash	Шаблон:Convert	up to 17 hours
	unit Y5b	Dry pyroclastic flow	Шаблон:Convert	collapse of 5a eruptive column
6	unit Y6	Taupō ignimbrite	Шаблон:Convert	no more than 15 minutes
7	Horomatangi Reefs and Waitahanui Bank	rhyolite lava domes	Шаблон:Convert	up to decades after

After

Шаблон:Maplink It is estimated that it might have taken as much as 30 years to refill the emptied lake in the caldera. There were massive changes in the landscape for Шаблон:Convert around with all life sterilised and prior landforms evened out, with beyond the ignimbrite sheet likely forest fires and ash associated die back especially to the west. The Waikato River had been blocked by ignimbrite deposits with the lowest being at Orakei Korako and the temporary lake that was formed over perhaps 2 to 3 years after the eruption in the older Reporoa Caldera had an area of about Шаблон:Convert and a volume of about Шаблон:Convert.Шаблон:Rp This broke through in a massive flood with peak flow believed to be 17,000 m³/s, over 100 times the current river maximum flood flow.

In due course 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 after about 20 years in a huge flood. Over Шаблон:Convert of waterШаблон:Rp escaped down river in less than 4 weeks, with peak discharge of the order of 30,000 m³/s so flowing for more than a week at roughly 200 times the Waikato River's current rate.

Following 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. The volcano continues to be classified as active with periods of volcanic unrest.

Dating the eruption

Early radiocarbon dating effort on 22 selected carbonized samples yielded an uncalibrated average date of 1,819 ± 17 years BP (131 CE ± 17). Research by Colin J. N. Wilson and others remarked that ongoing calibration pushes the radiocarbon result to a more recent date, and they proposed 186 CE as the exact year of eruption based on ancient Chinese and Roman records of unusual atmospheric phenomena in about this year.

In an effort led by R.S.J. Sparks and others to investigate interhemispheric calibration offset in 1995, the team analyzed the uncalibrated ages of tree rings of a single tree killed in Taupo eruption, cross-matched the uncalibrated tree ring chronology to Northern Hemisphere calibration curve, and extrapolated the calibrated tree ring dates to obtain the outermost ring date of 232 CE ± 15, i.e. the last moment the tree was alive.

In 2012, to circumvent interhemispheric calibration offset, the uncalibrated dates of tree rings of a single tree killed in Taupo eruption were wiggle-matched to New Zealand-derived calibration data set to obtain the currently most precise eruption date of 232 CE ± 8 (95.4% confidence). This date is statistically indistinguishable from that of 1995 study and is the currently accepted date. It is suggested that the presence of magmatic carbon in pre-eruption groundwaters may have contaminated radiocarbon ages. However, rhyolitic shards derived from the Taupo eruption have been identified in the Roosevelt Island ice core and are independently dated to 230 CE ± 19, thus firmly refuting propositions of a potential age bias.

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

External links

• Lake-floor relief map, from Шаблон:Cite journal Summary: the main Hatepe eruption vents are marked by submarine peaks on the far eastern side of Lake Taupō called the Horomatangi Reefs.