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Historic volcanic activity

by  Eileen McSaveney, Carol Stewart and Graham Leonard

The world’s most dramatic volcanic eruption in 5,000 years occurred in New Zealand about 200 AD. The Taupō eruption devastated much of the central North Island, emptying Lake Taupō in the process. Since people have settled in the volatile land, they have seen its active volcanoes – Tarawera, Rangitoto, Taranaki (Egmont), Tongariro, Ngāuruhoe, Ruapehu and White Island – intermittently and unpredictably spew fountains of hot ash and lava.


Eruptions in early history

The Taupō eruption

The serene waters of Lake Taupō in the central North Island mask a violent past – beneath the lake lies an enormous volcano. About 200 AD it unleashed the world’s most powerful eruption in 5,000 years.

During the main eruption, the volcano sent up a plume of dust and gases 50 kilometres into the stratosphere. Vast clouds of gases and 30 cubic kilometres of glowing-hot pumice and ash were blasted into the sky. The towering column collapsed suddenly, and hot ground-hugging pyroclastic flows raced away from the vents at 600–900 kilometres per hour. These incandescent clouds incinerated everything in an area of 20,000 square kilometres. These would have caused spectacular sunsets and several years of cooler temperatures worldwide.

No people lived in New Zealand at the time of the Taupō eruption – Polynesian seafarers did not settle the country for another 1,000 years.

Polynesian settlement

Volcanoes provide clues as to when the first Polynesians, the ancestors of Māori, came to New Zealand. They are thought to have arrived about 1250–1300 AD. When Tarawera erupted around 1314 AD it deposited a widespread layer of ash, known as Kaharoa ash. Pollen lying just below the ash at a few sites suggests that small areas of forest may have been cleared before the eruption, and remains of occupation found by archaeologists immediately above the ash indicate that small numbers of Polynesians may have been living there.

Māori people living in New Zealand before Europeans arrived would have witnessed the eruptions of Tarawera, Rangitoto, Taranaki (Mt Egmont), Tongariro, Ngāuruhoe, Ruapehu and Whakaari (White Island).

Rangitoto

Rangitoto Island, immediately east of Auckland City, is the youngest and largest of the region’s volcanic cones. Māori living there witnessed its formation. From radiocarbon and other dating methods, the eruption has been dated around 1400 AD. On nearby Motutapu Island, ash from Rangitoto was found lying above stone tools used for hunting and fishing, and the footprints of adults and children were found within the ash.

Mt Taranaki (Mt Egmont)

On the slopes of Mt Taranaki, Māori umu (ovens made of stones in a hollow) lie between ash deposits from eruptions around 1450, 1500 and 1655, indicating that people were travelling through Taranaki’s forests before 1450. According to Māori oral history Karakatonga , on the northern side of the mountain, was destroyed when the volcano erupted. The first Pākehā settlers did not realise that Taranaki was recently active, until in 1883 a local settler, A. W. Burrell, discovered pumice lodged in the forks of large mataī trees near the mountain.

Steaming hot

In the mid-1800s Captain Byron Drury, in the Pandora, carried out a hydrographic survey around White Island. He described the crater:

‘[I]n the centre is a boiling spring about 100 yards in circumference, sending volumes of steam full 2,000 feet high in calm weather; round the edges of the crater are numerous small geysers, sounding like so many high-pressure engines, and emitting steam with such velocity that a stone thrown into the vortex would immediately be shot into the air.’ 1

White Island (Whakaari)

White Island (Whakaari) is New Zealand’s most active volcano, constantly venting steam and gases, blasting out new small vents, and intermittently discharging clouds of ash. The island is a feature of Māori traditions, and has probably been active since the ancestors of Māori arrived.

In 1820 the missionary Samuel Marsden, standing on a Tauranga hilltop, saw ‘immense columns of smoke’ from White Island. However, because the volcano is 48 kilometres off the Bay of Plenty coast its effect on the mainland has been minor, mostly infrequent dustings of ash. White Island is one of the few privately owned volcanoes in the world, and more than 10,000 tourists visit by boat or helicopter each year. The island’s abundant sulfur deposits were once mined, until a collapsing crater wall killed 11 miners in 1914.

Footnotes
  1. Quoted in W. T. Parham, Island volcano: White Island, or Whakaari, New Zealand. Auckland: Collins, 1973, pp. 35–36. › Back

Tarawera

Lying 24 kilometres south-east of Rotorua, Tarawera is a curious-looking mountain, with several large domes and a broad, flat top. Its distinctive profile formed during eruptions around 1314 AD. Early Māori and the Europeans who arrived in the 1800s did not realise that Tarawera was an active volcano. In June 1886, however, it came to life in a violent one-day eruption – the deadliest in the history of New Zealand settlement.

The famous terraces

In the 1880s, tourists were drawn to the thermal regions of Rotorua and Tarawera. A stellar attraction was the Pink and White Terraces, on the shores of Lake Rotomahana. Their tiers of delicately tinted silica and cascading hot pools were considered one of the wonders of the world.

An omen

In the days before Mt Tarawera erupted there was an increase in hot spring activity, but otherwise there were no warning signs. Eleven days before, however, Māori and Pākehā tourists reported a phantom Māori war canoe sailing across Lake Tarawera, and surges in the water.

The eruption

At Te Wairoa village, 7.5 kilometres from the terraces, people were woken after midnight on 10 June 1886 by a series of increasingly violent earthquakes. Around 2 a.m., a fissure through Ruawāhia Dome on Mt Tarawera erupted, and by 2.30 a.m. the craters along the summit were venting fountains of glowing scoria and a cloud of ash up to 10 kilometres high, through which intense lightning flickered. At 3.20 a.m. the explosions spread. Craters were blasted open on the south-west side of the mountain and through Lake Rotomahana and the Waimangu area. A 17-kilometre rift spewed steam, mud and ash. The eruptions were over by about 6 a.m.

Night of a thousand stars

Rumblings from the Tarawera eruption were heard as far south as Blenheim, in the South Island. In the Waikato and Bay of Plenty, people woken by the explosions saw distant flashes on the horizon. Aboard the Glenelg, moored in the Bay of Plenty, Captain Stephenson saw hovering over the land ‘large balls of fire, which suddenly appeared, and then broke into a thousand stars.’ 1

Te Wairoa

At Te Wairoa, people went outside to watch Tarawera erupt, but soon had to retreat indoors. Many sought shelter in the Hinemihi meeting house and McCrae’s Hotel. When wet mud began to fall, the roof and upper floor of the hotel gradually gave way under the weight. More than 60 people found safety in the sturdy house of the tourist guide, Sophia Hinerangi. When the home of the local schoolmaster collapsed, three people escaped and took refuge in a hen house.

Mud skies

The Tarawera eruption was unusual – it initially ejected molten basalt scoria. However, the rising magma mixed with groundwater and several lakes, turning the water to steam, and causing powerful explosions that pulverised the land and blasted it out as huge volumes of hot mud.

The aftermath

Soon after daybreak, rescue parties were dispatched. They found that the settlements of Te Tapahoro, Moura, Te Ariki, Totarariki and Waingongongo had been completely destroyed, or buried by falling hot mud. At Te Wairoa 15 were dead, but many had survived, huddled inside the stronger buildings. Four days after the eruption the high priest Tūhoto Ariki was dug out alive from a house, but died several weeks later. The official death toll was put at around 150, but it is more likely between 108 and 120 people were killed.

The landscape around Rotomahana and Tarawera was stripped of vegetation. Thick mud and ash blanketed hundreds of square kilometres of land, and large cracks crossed the region. The Pink and White Terraces had vanished, reduced to dust and fragments of sinter.

The site of the terraces became a crater over 100 metres deep. Steam eruptions continued in the crater for several months, but within 15 years it filled with water, forming a new Lake Rotomahana, much larger than its predecessor. The chain of craters at the Waimangu end of the rift became the site of many new geothermal features, including Waimangu Geyser, the largest in the world, and New Zealand’s largest hot spring, Frying Pan Lake.

Footnotes
  1. Bay of Plenty Times, 12 June 1886, p. 2. › Back

Tongariro and Ngāuruhoe

Mt Tongariro

Mt Tongariro is not a single volcano, but a complex of craters that have been active at different periods. In 1868, violent earthquakes marked the eruption that formed the upper Te Maari crater, named after a Māori chieftainess. Upper Te Maari erupted again in 1896–97, dumping 50 millimetres of ash on the Desert Road, and wafting ash as far as Napier.

Mt Ngāuruhoe: young and active

Although regarded as a separate volcano, Mt Ngāuruhoe is Tongariro’s main active vent. The remarkable symmetry of Ngāuruhoe’s steep cone is the result of regular eruptions.

Ngāuruhoe frequently belches out clouds of ash. Over 70 ash eruptions have occurred between 1839 and 1975, on average about six years apart. Eruptions of lava are less common – they have been witnessed only in 1870, 1949 and 1954.

In 1867, Māori people told the scientist and explorer James Hector that in May ash from Ngāuruhoe had covered the ground with a white dust, like snow. They said that during a previous eruption, in 1865, the Taupō district – and even the water of the lake – was covered with several inches of black dust. The showers of ash that fell into Rotoaira, a small lake between the volcano and Lake Taupō, had poisoned the fish there.

The 1870 eruptions

Many eye-witness accounts describe the eruption of Ngāuruhoe on 7 July 1870, which followed about 30 years of intermittent ash eruptions. Two lava flows travelled down the north side of the mountain, and loud detonations continued for three months, heard as far as Hamilton, Rotorua, New Plymouth and Napier. The lava was also visible from distant areas. In July 1870 Colonel J. M. Roberts, at a constabulary post on the Napier–Taupō road, wrote of the event:

One night a glow was observed spreading down the cone, comparable to a tree fern fire on a distant hill, and the following day three great columns of steam were seen rising, one from the summit crater and the others from the lower slopes. 1

The 1948–49 eruptions

In 1948, explosive eruptions tossing out blocks many metres thick culminated in a three-week eruption in February 1949. The eruptions were accompanied by loud blasts, and a small lava flow. A plume of ash rose 6 kilometres into the air.

The 1954 eruptions

In 1954 Mt Ngāuruhoe produced more than six million cubic metres of lava – the largest flow ever seen in New Zealand in historic times. Spectacular lava fountains played above the summit, and a sizeable scoria cone built up within Ngāuruhoe’s crater.

Lava flow

During Ngāuruhoe’s 1954 eruption, D. R. Gregg of the New Zealand Geological Survey observed a lava flow on 30 June at close quarters:

‘The more rapidly moving parts of the flow were moving forward bodily. Boulders were tumbling from the face and exposing the red-hot interior of the flow as it slowly advanced over the fallen debris. As the blocks fell off, incandescent dust trickled out. The finer dust particles remained suspended in the air, producing a reddish-brown smoke most irritating to the eyes. As the flow moved, it produced continual grating and clanking noises.’ 2

Eruptions 1973–75

The discharge of red-hot blocks of lava in January 1973 heralded the most recent major eruption of Ngāuruhoe. Sporadic activity continued through the year, building up to highly explosive eruptions of ash in January and March 1974, and in February 1975. One of these threw a 3,000-tonne block of lava 100 metres out of the crater. During the last and most violent eruption, gases streamed from the crater for several hours, producing a churning plume of ash that towered up to 13 kilometres above the crater. This column collapsed under its own weight, forming ash and scoria avalanches that swept down the flanks of Ngāuruhoe, leaving trails of rubble in their wake.

Although Ngāuruhoe’s eruptions have seldom been more than nine years apart, the mountain has been quiet since 1975 – the longest break in activity in its recorded history. Its steam vents have temporarily cooled, suggesting that the main vent has become blocked.

Footnotes
  1. Quoted in D. R. Gregg, ‘The geology of Tongariro subdivision.’ New Zealand Geological Survey Bulletin 40 (1960): 59. › Back
  2. ‘The geology of Tongariro subdivision’: 64–65. › Back

Ruapehu, 1861–1945

Early eye-witness accounts

To New Zealand’s earliest European settlers, snow-capped Mt Ruapehu appeared benign and too remote to pose any danger. The earliest written accounts of activity are from 1861, when it was reported in the New Zealand Spectator and Cook’s Strait Guardian that, ‘dense volumes of smoke were seen issuing from the crater, and at night a lurid glare was reflected by the heavens’. 1 The settler Henry Sarjeant witnessed an outburst from Ruapehu’s Crater Lake surging down the Whangaehu River:

I suddenly saw … a huge wave of water and tumbling logs ... [the wave] appeared to be covered with what we first thought to be pumice but the intense cold which made us shiver and turn blue caused us to discover that this was no less than frozen snow. Mixed with this was a mass of logs and debris. Very soon a bridge passed us stuck in the roots of a giant tree and a few minutes later about a dozen canoes came down. 2

In the 19th century Ruapehu’s activity was low-key, limited to occasional small steam and ash eruptions from the summit Crater Lake. In 1889, 1895, 1903 and 1925, eruptions spilled water out of the lake, creating volcanic mud flows known as lahars.

Ruapehu eruptions, 1945

In March 1945 Mt Ruapehu stirred, beginning a series of eruptions that continued intermittently through the year.

On 8 March the pilot of a plane reported a plume of steam rising from the crater, and ash dusting the mountain’s eastern slopes. On 19 March a dome of lava emerged from Crater Lake, accompanied by steam explosions visible from about a hundred kilometres away. A week later, however, in another large explosion, the lava dome disappeared.

In the first two weeks of May, steam and ash rose in a continuous column. Activity then slackened. But by 19 June ash was pouring from the volcano, covering a large region as far north as Taupō. Another lava dome appeared on 7 May, and it grew through June, spilling all the water out of Crater Lake.

In July, August and early September explosive eruptions ejected rocks and columns of steam and ash. Wind carried the ash as far south as Upper Hutt, near Wellington, and as far north as Whakatāne. Noisy eruptions during the first week of August made authorities briefly consider evacuating communities around the mountain.

A lucky escape

In May and June 1945 geologist Robin Oliver observed Mt Ruapehu’s growing lava dome. During a quieter period, he and J. Witten Hannah camped overnight inside the crater. An explosion on the evening of 1 July showered them with red-hot rocks and ash. Both men received burns and Oliver was knocked unconscious. Hannah hauled him some distance from the crater, left him in a sleeping bag, and descended the mountain in the dark for help. A rescue party found Oliver the next day. The men were lucky to survive – the explosion had blasted out rocks weighing up to 8 tonnes.

On 1 September a group of sightseers barely escaped injury when they ventured up to the summit and were bombarded by small rocks. Volcanic activity continued through September at a moderate level. In late September and October ash fell on Taupō, Rotorua, Whakatāne, Napier and Hastings. Eruptions in November and early December spread ash on communities around the mountain and in Hawke’s Bay.

Ash fall

In 1945 Chateau Tongariro, 9 kilometres from Ruapehu’s crater, was a wartime mental hospital. Its electricity failed repeatedly when ash penetrated the hospital’s generators, and the streams supplying water eventually became too muddied to be filtered. The hospital closed in December, and 180 patients had to be relocated.

Ruapehu’s outbursts caused more wide-ranging disruption. The wind spread ash for hundreds of kilometres. In heavy ashfalls, asthmatics suffered and many people remained indoors. Hundreds of cases of ‘Ruapehu throat’ were reported to doctors and pharmacists, and eye irritations were common wherever ash fell.

Dry ash was easily stirred up by passing vehicles. Gritty clouds drifted into houses and buildings, and played havoc with machinery. Wet ash stuck like cement to roofs, windows and flat surfaces. It contaminated rainwater tanks if people did not disconnect their downpipes before the ash fell.

Cars were vulnerable, their paintwork and windscreens scratched by ash. The New Zealand Army were forced to move some 700 vehicles from Waiōuru. Crops around Ōhakune withered, and stock did not like the taste of ash-covered pastures. Farmers around Taihape found ash in the wool of the sheep they sheared.

Footnotes
  1. Quoted in Karen Williams, Volcanoes of the south wind. Tūrangi: Tongariro Natural History Society, 2001, p. 72. › Back
  2. David Johnston and Vince Neall, Ruapehu awakens. Palmerston North: Science Centre and Manawatū Museum, 1995, p. 4. › Back

Ruapehu and the Tangiwai disaster

Poised for disaster

Mt Ruapehu erupted in 1945, but by the end of the year the excitement was over. The crater, about 300 metres deep, slowly refilled with water. The mountain did not seem dangerous, and it was no longer being monitored. By 1953, however, Crater Lake was 8 metres higher than its level before 1945. Few realised that the water was now held in by an unstable mass of ice and volcanic rubble and ash.

The lahar

At 8 p.m. on Christmas Eve 1953, the debris at the outlet of Crater Lake collapsed. About 340,000 cubic metres of water poured into the head of the Whangaehu River and swept down the valley, picking up sand, silt and boulders as it went. Soon after 10 p.m. this volcanic mud flow, known as a lahar, smashed into the main trunk railway bridge at Tangiwai. The concrete piers were knocked out and the bridge partially collapsed.

Driving through the darkness, Cyril Ellis stopped when he saw that the bridge ahead was under water, even though there had been no rain. Realising that a train was approaching the nearby rail bridge, he ran along the track towards it, waving a torch to flag it down. It was the passenger express from Wellington, packed with 285 people heading to Auckland for the holidays.

The train reaches the bridge

The driver saw him and applied the brakes, but the train’s momentum carried it out onto the bridge. The engine and first carriage nosedived, landing against the opposite bank. Four more carriages plunged into the river, floating in the torrent briefly before sinking. Another four carriages remained on the track, but one of them dangled over the river. Ellis and guard William Inglis attempted to help people off, but the coupling snapped and the carriage toppled into the river. Rolling several times, it came to rest on its side, with water flowing through it. Ellis knocked out several windows and hoisted people outside as passenger John Holman lifted fellow travellers out to him. In all, 26 people escaped, huddled on the carriage for over an hour until the torrent subsided. The men then formed a human chain in waist-deep water, helping everyone reach the bank safely.

On the other side of the flooded road bridge, Arthur Bell and his wife had also seen the train crash into the river. Mrs Bell went for help, while Arthur assisted 15 people from the carriage that had hit the riverbank.

One carriage was carried more than 2 kilometres downstream. The others were swept across the flooded main road or rammed into the riverbanks. Some people had escaped and swam to the banks, but dozens drowned in the tangles of gorse there.

The work of recovering victims went on for several days along 60 kilometres of the river. Twenty bodies were never found; it was assumed they had washed out to sea, some 120 kilometres away.

New Zealand in mourning

New Zealanders woke on Christmas morning to the shocking news that 151 lives had been lost. Tangiwai had lived up to its Māori name – ‘weeping waters’.

Queen Elizabeth II and Prince Philip were visiting New Zealand at the time. Prince Philip attended the state funeral for 21 unidentified victims, and the queen presented Cyril Ellis and John Holman with the George Medal, and William Inglis and Arthur Bell with the British Empire Medal.

A commission of inquiry into the disaster later determined that the lahar could not have been anticipated. Since then, Ruapehu’s Crater Lake has been carefully monitored.


Ruapehu since 1945

An uneasy quiet

Following the 1945 eruption Mt Ruapehu settled into a fitful slumber. Between 1945 and 1986, scientists reported 61 volcanic disturbances, mostly small steam eruptions that splashed water and mud within the summit crater.

A few were more substantial. Shortly after midnight on 22 June 1969, the volcano produced a lahar that destroyed the kiosk at the Whakapapa ski field. On 8 May 1971 a party surveying the crater rim saw the lake surface bulge, then burst skyward. Two of the men were drenched with acid water, blasted by choking ash and toxic gas, and bombarded with rocks. In 1975, eruptions sent lahars down the Whangaehu River and through the Whakapapa ski field.

Acid bath

Swimming in Ruapehu’s Crater Lake was popular during the 1950s and 1960s. The water was usually warm due to volcanic gases streaming up from the magma chamber below, and a gentle ramp of snow allowed easy access. However, volcanic gases bubbling up from below slowly began to acidify the water. Swimming was discouraged once scientists discovered the increasing acidity, and also because eruptions in the lake could occur without warning.

The 1995–96 eruptions

From January 1995, scientists monitoring Ruapehu detected a growing restlessness. On 18 and 20 September, small eruptions produced mud flows from Crater Lake. Around 5 p.m. on 23 September, hundreds of skiers were on the slopes when lake water, steam and ash were suddenly blasted into the sky. Rocks were tossed up to 1.5 kilometres from the crater. Most of the skiers dropped their gear and fled. A cloud of steam and some volcanic ash rose 12 kilometres, and lahars raced down three valleys. One narrowly missed Whakapapa’s Far West T-Bar and its queuing area, where only an hour earlier hundreds of people had thronged.

A series of explosions just a few minutes apart followed on 24 and 25 September, sending half the water in Crater Lake down the Whangaehu River. A 10-kilometre-high plume of ash rose skyward, falling to smother the Desert Road.

Nevertheless, skiers were quick to return to the slopes once the mountain quieted. But on 7 October they were once again threatened when earthquakes accompanied a new series of eruptions that lasted until 15 October. Crater Lake was emptied of its remaining water.

Activity dropped off and by mid-November lakes were re-forming in the crater. But in June 1996 Ruapehu once again began blasting out plumes of ash, blocks of hot rock, and lava bombs. On 20 July fountains of hot lava were seen, and sonic booms shook the area. An 11-kilometre-high cloud dispersed ash as far as Ōpōtiki, on the East Coast. By early September, Ruapehu was quiet once more.

A costly spectacle

Ruapehu’s 1995–96 eruptions were similar in size to those of 1945, but their social and economic impacts were much greater. New Zealand’s population had doubled since 1945, and visitors to the mountain had increased dramatically. In 1945 there was one ski area, and no ski lifts; by 1995 there were three ski areas and 36 ski lifts. On some days up to 10,000 skiers swarmed the slopes, and when the three ski areas closed it cost the region $100 million.

Avoiding an erupting volcano made travel difficult. The main highway and railway line connecting Wellington and Auckland skirt Ruapehu. During eruptions the central North Island also became off-limits to aircraft. Detours were lengthy and costly. Drifting ash intermittently closed airports, including Auckland and Wellington; the value of cancelled flights alone was $2.4 million.

Electricity suppliers lost $22 million as ash shorted out power pylons and later wrecked the turbines of the Rangipō power station.

Future volcanic activity

Impressive as they were, the 1995–96 eruptions were relatively minor, and scientists of the future are unlikely to find evidence of them in the long-term geological record. Existing deposits around the mountain from lava flows, pyroclastic flows (clouds of hot gas, pumice and rock fragments) and avalanches of volcanic debris suggest that Ruapehu is capable of much more violent activity.

As in 1945, the 1995–96 eruptions added unstable debris to the rim of Crater Lake, setting the scene for another breakaway flood down the Whangaehu River. However, the hazard is now continuously monitored, and systems are in place to give early warnings of lahars moving towards the Desert Road and Tangiwai. These protective measures were effective when there was a lahar from the lake on 18 March 2007, and there was little damage.


Raoul Island

Raoul Island is the largest of the Kermadec Islands, over 1,000 kilometres north-east of the North Island. It is the emergent part of a large volcano, almost 20 kilometres in diameter. Although apparently isolated, the island lies on the Kermadec ridge, a chain of submarine volcanoes.

The island’s irregular anvil shape is due to a combination of volcanic activity and marine erosion. Detailed onshore and offshore investigations show that there are two large collapse calderas (Raoul and Denham), both of which have erupted frequently over the last few thousand years.

Recorded eruptions

Eruptions have been observed and recorded in 1814, 1870, 1964 and 2006.

1814

On 9 March 1814 Captain Barnes of the Jefferson, who had landed in Denham Bay several days earlier, reported a thick, dark cloud above Raoul. Returning two months later, he found that there was a volcanic island made of scoria in the middle of Denham Bay. Explosive activity occurred at the same time in Raoul caldera.

The scoria island had disappeared by 1854, when a survey in Denham Bay was made by HMS Herald.

Heading for the hills

William Covat and his family were living in Denham Bay when eruptions started in June 1870. Alarmed by earthquakes, volcanic explosions and suffocating fumes they fled to the hills, and were very pleased to be rescued in early October. They never returned.

1870

Primary records indicate that there were eruptions in both the Denham Bay and Raoul calderas between June and October 1870. Captain Preble of the Ellen Goodspeed described an erupting volcano in Denham Bay on 5 July that blasted a dark column of ash and steam up to 1,000 metres. In early October 1870, there were two separate volcanic islands in Denham Bay.

During the same period there was an eruption in Raoul caldera which blasted a crater 600 metres across, knocking over trees and covering the floor of the crater with mud and boulders.

There was no further volcanic activity for the next 90 years, and Raoul Island has been occupied almost continuously. The area devastated in the centre of the Raoul caldera was soon covered in trees that grow rapidly in the subtropical environment.

Nuclear tests

In 1954 the British government requested permission to test a hydrogen bomb in the Kermadec Islands. Although there had been eruptions in 1814 and 1870, no one recognised that Raoul was an active volcano. Indeed, the central flat area surrounded by steep cliffs (now recognised as the Raoul caldera) seemed an excellent testing spot. Fortunately the request was declined by the New Zealand government – for political reasons.

1964

A series of strong earthquakes started on 10 November 1964, and by 15 November volcanic tremor was recorded. At about the same time Green Lake started to heat up, and the level rose several metres. An explosive eruption commencing about 6am on 22 November opened a large vent near Green Lake which devastated the immediate area, and there were eleven other small vents within the Raoul caldera. Activity gradually tailed off after early February 1965. Mud ejected from the vents was confined to the central part of the Raoul caldera.

A plume of discoloured bubbling water containing pumice fragments was observed in Denham Bay in November and December.

2006

An earthquake swarm started near Raoul Island on Sunday 12 March 2006, but the tremors rapidly declined over the next few days. Then on 17 March at 8.21 a.m. there was a sudden explosive eruption near Green Lake. Mud and rocks were ejected, together with a plume of steam and gas. Mark Kearney, a Department of Conservation observer, was killed by the explosion. Green Lake was heated, and the level rose several metres during the next few days.

Pattern of eruption

All historic eruptions include explosive activity within the Raoul caldera close to Green Lake, probably caused by disruption of the geothermal system as magma moves upwards. There appears to be a close connection with vents in the Denham caldera, as the 1814, 1870 and 1964 eruptions occurred there at the same time. It is highly probable that there will be future eruptions from the same vents.

Acknowledgements to Ted Lloyd (formerly New Zealand Geological Survey, DSIR), Vince Neall (Massey University), Brad Scott and David Johnston (GNS Science), and David J. Lowe and Richard Smith (University of Waikato).


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How to cite this page: Eileen McSaveney, Carol Stewart and Graham Leonard, 'Historic volcanic activity', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/en/historic-volcanic-activity/print (accessed 22 November 2017)

Story by Eileen McSaveney, Carol Stewart and Graham Leonard, published 12 Jun 2006