Hatepe eruption
Encyclopedia
The Hatepe eruption around the year 180 CE was Lake Taupo
Lake Taupo
Lake Taupo is a lake situated in the North Island of New Zealand. With a surface area of , it is the largest lake by surface area in New Zealand, and the second largest freshwater lake by surface area in geopolitical Oceania after Lake Murray ....

's most recent major eruption, and New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

's largest eruption during the last 20,000 years. It ejected some 120 km³ (28.8 cu mi) of material (rating a 7 on the Volcanic Explosivity Index
Volcanic Explosivity Index
The Volcanic Explosivity Index was devised by Chris Newhall of the U.S. Geological Survey and Stephen Self at the University of Hawaii in 1982 to provide a relative measure of the explosiveness of volcanic eruptions....

 scale), of which 30 km³ (7.2 cu mi) was ejected in the space of a few minutes. It is believed that the eruption column was 50 km (31.1 mi) high, twice as high as the eruption column from Mount St. Helens
Mount St. Helens
Mount St. Helens is an active stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United States. It is south of Seattle, Washington and northeast of Portland, Oregon. Mount St. Helens takes its English name from the British diplomat Lord St Helens, a...

 in 1980. This makes it one of the most violent eruptions in the last 5000 years, comparable to the Tianchi eruption of Baekdu
Baekdu Mountain
Baekdu Mountain, also known in China as Changbai Mountain and Baitou Mountain , is a volcanic mountain on the border between North Korea and China, located at...

 at around 1000 CE and the 1815 eruption of Tambora
Mount Tambora
Mount Tambora is an active stratovolcano, also known as a composite volcano, on the island of Sumbawa, Indonesia. Sumbawa is flanked both to the north and south by oceanic crust, and Tambora was formed by the active subduction zone beneath it. This raised Mount Tambora as high as , making it...

). The resulting ash turned the sky red over Rome
Rome
Rome is the capital of Italy and the country's largest and most populated city and comune, with over 2.7 million residents in . The city is located in the central-western portion of the Italian Peninsula, on the Tiber River within the Lazio region of Italy.Rome's history spans two and a half...

 and China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

.

Stages of eruption

The eruption went through several stages, with six distinct marker horizon
Marker horizon
Marker horizons or chronohorizons or marker beds are stratigraphic units of the same age and of such distinctive composition and appearance, that, despite their presence in separate geographic locations, there is no doubt about their being of equivalent age and of common origin...

s identified. Despite the uniform composition of the erupted magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...

, a wide variety of eruptive styles were displayed, including weak phreatomagmatism, Plinian eruption
Plinian eruption
Plinian eruptions, also known as 'Vesuvian eruptions', are volcanic eruptions marked by their similarity to the eruption of Mount Vesuvius in AD 79 ....

s, and a huge pyroclastic flow
Pyroclastic flow
A pyroclastic flow is a fast-moving current of superheated gas and rock , which reaches speeds moving away from a volcano of up to 700 km/h . The flows normally hug the ground and travel downhill, or spread laterally under gravity...

. Rhyolitic lava dome
Lava dome
|250px|thumb|right|Image of the [[rhyolitic]] lava dome of [[Chaitén Volcano]] during its 2008–2009 eruption.In volcanology, a lava dome is a roughly circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano...

s were extruded some years or decades later, forming the Horomatangi reef
Reef
In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....

s and Waitahanui bank.

The main pyroclastic flow devastated the surrounding area, climbing over 1500 m (4,921.3 ft) to overtop the nearby Kaimanawa Ranges and Mount Tongariro
Mount Tongariro
Mount Tongariro is a volcanic complex in the North Island of New Zealand. It is located 20 kilometres to the southwest of Lake Taupo, and is the northernmost of the three active volcanoes that dominate the landscape of the central North Island....

, and covering the land within 80 km (49.7 mi) with ignimbrite
Ignimbrite
An ignimbrite is the deposit of a pyroclastic density current, or pyroclastic flow, a hot suspension of particles and gases that flows rapidly from a volcano, driven by a greater density than the surrounding atmosphere....

. Since New Zealand was not settled by the Māori until more than a thousand years later, the area had no human
Human
Humans are the only living species in the Homo genus...

 inhabitants when the eruption occurred. Tsunami deposit
Tsunami deposit
A tsunami deposit is a sedimentary unit deposited as the result of of a tsunami. Such deposits may be left onshore during the inundation phase or offshore during the 'backwash' phase. Such deposits are being used to identify past tsunami events and thereby better constrain estimates of both...

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
Krakatoa
Krakatoa is a volcanic island made of a'a lava in the Sunda Strait between the islands of Java and Sumatra in Indonesia. The name is used for the island group, the main island , and the volcano as a whole. The island exploded in 1883, killing approximately 40,000 people, although some estimates...

 eruption).

The Hatepe eruption further expanded the lake that had formed after the much larger Oruanui eruption
Oruanui eruption
The Oruanui eruption of New Zealand's Taupo Volcano was the world's largest known eruption in the past 70,000 years, with a Volcanic Explosivity Index of 8...

 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
Waikato River
The Waikato River is the longest river in New Zealand. In the North Island, it runs for 425 kilometres from the eastern slopes of Mount Ruapehu, joining the Tongariro River system and emptying into Lake Taupo, New Zealand's largest lake. It drains Taupo at the lake's northeastern edge, creates the...

's current rate.

Dating the event

The Taupo eruption was at one time dated to c. 130 CE based on from carbonized vegetation
Vegetation
Vegetation is a general term for the plant life of a region; it refers to the ground cover provided by plants. It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic characteristics. It is broader...

 enclosed in the eruption products. However, the 22 selected samples used to obtain an average date of 1,819 plus or minus 17 years BP (131) had much larger standard deviation
Standard deviation
Standard deviation is a widely used measure of variability or diversity used in statistics and probability theory. It shows how much variation or "dispersion" there is from the average...

s than the average date itself. Most if not all geologist
Geologist
A geologist is a scientist who studies the solid and liquid matter that constitutes the Earth as well as the processes and history that has shaped it. Geologists usually engage in studying geology. Geologists, studying more of an applied science than a theoretical one, must approach Geology using...

s now accept that the tephra
Tephra
200px|thumb|right|Tephra horizons in south-central [[Iceland]]. The thick and light coloured layer at center of the photo is [[rhyolitic]] tephra from [[Hekla]]....

 or pumice fall from the eruption was far greater than previously thought, approximately 150 km³ (36 cu mi) instead of 14 km³ (3.4 cu mi). This means the event would have been visible from China and Rome. It was therefore posited by Wilson et al. (and is now generally accepted) that the meteorological phenomena described by Fan Ye
Fan Ye (historian)
Fan Ye , courtesy name Weizong , was a Chinese historian and the compiler of Book of Later Han of Liu Song. Fan came from an official family background, he was born in present-day Shaoxing, Zhejiang, his ancestry was from Nanyang, Henan. His father was Fan Tai .-References:*Tan, Jiajian, ....

 in China and by Herodian
Herodian
Herodian or Herodianus of Syria was a minor Roman civil servant who wrote a colourful history in Greek titled History of the Empire from the Death of Marcus in eight books covering the years 180 to 238. His work is not entirely reliable although his relatively unbiased account of Elagabalus is...

 in Rome were due to this eruption, which therefore can be dated exactly to 186 CE. However, recent radiocarbon dating by R. Sparks has put the date at 233 CE ± 13 (95% confidence).

Humans had not permanently settled in New Zealand at the time, and would not for another thousand years, although some scholars have suggested that New Zealand was discovered not long before the eruption. The nearest humans at the time may have been those in Australia, more than 2000 kilometres (1,242.7 mi) to the west.

External links

  • Lake-floor relief map, from The main Hatepe eruption vents are marked by submarine peaks on the far side of Lake Taupo.
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