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The Hatepe eruption, named for the Hatepe Plinian
pumice Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular v ...
tephra layer Tephra is fragmental material produced by a volcanic eruption regardless of composition, fragment size, or emplacement mechanism. Volcanologists also refer to airborne fragments as pyroclasts. Once clasts have fallen to the ground, they rem ...
, sometimes referred to as the Taupō eruption or Horomatangi Reef Unit Y eruption, is dated to 232 CE ± 10 and was
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 violent eruptions in geologically recent times. ImageSize ...
's most recent major
eruption Several types of volcanic eruptions—during which lava, tephra (ash, lapilli, volcanic bombs and volcanic blocks), and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are often ...
. It is thought to be
New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island coun ...
'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 The Minoan eruption was a catastrophic volcanic eruption that devastated the Aegean island of Thera (also called Santorini) circa 1600 BCE. It destroyed the Minoan settlement at Akrotiri, as well as communities and agricultural areas on ne ...
in the 2nd millennium BCE, the
946 eruption of Paektu Mountain The 946 eruption of Paektu Mountain in Korea and China, also known as the Millennium Eruption or Tianchi eruption, was one of the most powerful volcanic eruptions in recorded history and is classified as a VEI-7 event. The eruption resulted in a ...
, the 1257 eruption of Mount Samalas, and the
1815 eruption of Mount Tambora Mount Tambora is a volcano on the island of Sumbawa in present-day Indonesia, then part of the Dutch East Indies, and its 1815 eruption was the most powerful volcanic eruption in recorded human history. This volcanic explosivity index (V ...
.


Stages of the eruption

The eruption went through several stages, with six distinct marker horizons identified. Despite the uniform composition of the erupted
magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natura ...
, a wide variety of eruptive styles were displayed, including weak phreatomagmatism, Plinian eruptions, and a huge
pyroclastic flow A pyroclastic flow (also known as a pyroclastic density current or a pyroclastic cloud) is a fast-moving current of hot gas and volcanic matter (collectively known as tephra) that flows along the ground away from a volcano at average speeds of b ...
.
Rhyolitic Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals ( phenocrysts) in an otherwise fine-grained groundmass. The ...
lava dome In volcanology, a lava dome is a circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano. Dome-building eruptions are common, particularly in convergent plate boundary settings. Around 6% of eruptions ...
s were extruded some years or decades later, forming the Horomatangi Reefs and Waitahanui Bank.Houghton, B.F. (2007).
Field Guide—Taupo Volcanic Zone
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The main pyroclastic flow devastated the surrounding area, climbing over to overtop the nearby Kaimanawa Ranges and
Mount Tongariro Mount Tongariro (; ) is a compound volcano in the Taupō Volcanic Zone of the North Island of New Zealand. It is located to the southwest of Lake Taupō, and is the northernmost of the three active volcanoes that dominate the landscape of th ...
, and covering the land within with
ignimbrite Ignimbrite is a type of volcanic rock, consisting of hardened tuff. Ignimbrites form from the deposits of pyroclastic flows, which are a hot suspension of particles and gases flowing rapidly from a volcano, driven by being denser than the surro ...
. As New Zealand was not settled by the
Māori Māori or Maori can refer to: Relating to the Māori people * Māori people of New Zealand, or members of that group * Māori language, the language of the Māori people of New Zealand * Māori culture * Cook Islanders, the Māori people of the Co ...
until more than 1,000 years later, the area had no known human inhabitants when the eruption occurred.
Tsunami deposit A tsunami deposit (the term tsunamiite is also sometimes used) is a sedimentary unit deposited as the result of a tsunami. Such deposits may be left onshore during the inundation phase or offshore during the 'backwash' phase. Such deposits are u ...
s 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 The Oruanui eruption of New Zealand's Taupō Volcano (also known as the Kawakawa eruption or Kawakawa/Oruanui event) was the world's most recent supereruption.} Eruption With a Volcanic Explosivity Index of 8, it is one of the largest eruptio ...
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 The Waikato River is the longest river in New Zealand, running for through the North Island. It rises on the eastern slopes of Mount Ruapehu, joining the Tongariro River system and flowing through Lake Taupō, New Zealand's largest lake. It th ...
's current rate. After the eruption
rhyolitic Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals ( phenocrysts) in an otherwise fine-grained groundmass. The ...
lava dome In volcanology, a lava dome is a circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano. Dome-building eruptions are common, particularly in convergent plate boundary settings. Around 6% of eruptions ...
s were extruded, these smaller eruptions of unknown total size also created large
pumice Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular v ...
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 Colin James Ness Wilson (born 19 July 1956) FRS FRSNZ is Professor of Volcanology at Victoria University of Wellington in New Zealand. Education Wilson was educated at Imperial College London where he was awarded a Bachelor of Science degree ...
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 The Han dynasty (, ; ) was an Dynasties in Chinese history, imperial dynasty of China (202 BC – 9 AD, 25–220 AD), established by Emperor Gaozu of Han, Liu Bang (Emperor Gao) and ruled by the House of Liu. The dynasty was preceded by th ...
and by Herodian of Antioch in the
Roman Empire The Roman Empire ( la, Imperium Romanum ; grc-gre, Βασιλεία τῶν Ῥωμαίων, Basileía tôn Rhōmaíōn) was the post-Roman Republic, Republican period of ancient Rome. As a polity, it included large territorial holdings aro ...
. 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 deviation In statistics, the standard deviation is a measure of the amount of variation or dispersion of a set of values. A low standard deviation indicates that the values tend to be close to the mean (also called the expected value) of the set, whil ...
s than the average date itself. Most, if not all, geologists now accept that the
tephra Tephra is fragmental material produced by a volcanic eruption regardless of composition, fragment size, or emplacement mechanism. Volcanologists also refer to airborne fragments as pyroclasts. Once clasts have fallen to the ground, they r ...
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 Tonga (, ; ), officially the Kingdom of Tonga ( to, Puleʻanga Fakatuʻi ʻo Tonga), is a Polynesian country and archipelago. The country has 171 islands – of which 45 are inhabited. Its total surface area is about , scattered over in ...
, more than to the northeast.


Post-eruption soil deficiencies

The tephra soils associated with the eruption were deficient in several essential minerals, with
cobalt Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, p ...
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 Triple superphosphate is a component of fertilizer that primarily consists of monocalcium phosphate, Ca(H2PO4)2. Triple superphosphate is obtained by treating phosphate rock with phosphoric acid. Traditional routes for extraction of phosphate roc ...
fertiliser from aircraft.


See also

*
North Island Volcanic Plateau The North Island Volcanic Plateau (often called the Central Plateau and occasionally the Waimarino Plateau) is a volcanic plateau covering much of central North Island of New Zealand with volcanoes, lava plateaus, and crater lakes. It contains ...


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