Raoul Island
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| Raoul Island | |
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| Elevation: | 516 m |
| Coordinates: | |
| Location: | Kermadec Islands |
| Type: | Stratovolcano |
| Last eruption: | 2006 |
Anvil-shaped Raoul Island (Sunday Island), the largest and northernmost of the Kermadec Islands, (located at , 900 km SSW of Ata Island of Tonga and 1100 km NNE of New Zealand's North Island), has been the source of vigorous volcanic activity during the past several thousand years that was dominated by dacitic explosive eruptions.
The area of the island, including fringing islets and rocks mainly in the Northeast, but also a few smaller ones in the Southeast, is 29.38 km². The highest elevation is Moumoukai peak, at an elevation of 516 m.
The island is uninhabited, except for the permanently manned Raoul Island Station, a government meteorological and radio station and hostel for Department of Conservation (DOC) officers and volunteers that has been maintained since 1937 on the northern terraces of the island, about 50 m in elevation above the cliffs of Fleetwood Bluff. Raoul Island Station represents the northernmost outpost of New Zealand.
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[edit] 2006 eruption
On March 17, 2006 at 8:21 a.m. NZDT, a 40-second long volcanic eruption occurred at the Green Lake. At the time, Mark Kearney, a 33-year-old DOC worker, was at the crater taking water temperature measurements. A five-hectare area around Green Lake was affected with ash, mud and boulders. Two DOC workers were forced to turn back after going to the crater to search for Kearney.
Following the eruption, DOC decided to evacuate the remaining five staff members. A Mil Mi-17 helicopter and Piper PA-31 Navajo aircraft took off from Taupo at 11 a.m. that morning.[1] They arrived at the island in the early afternoon and undertook a 45 minute search for Kearney but no sign was seen. The evacuated staff members were brought back to Auckland that evening.
A Royal New Zealand Air Force P-3 Orion made an overflight on 21 March to provide further information on how safe it is to approach Green Lake. The Volcanologists aboard decided the area was still unsafe, and that the crater lake had risen by about 8 metres compared to footage taken on 17 March. There was no cloud or ash plume.[2]
A group of police, the five evacuated DOC workers and scientific staff left Tauranga on 18 March for the three-day boat trip to Raoul aboard the RV Braveheart to recover his body.[3] They were able to undertake a limited search, but decided that it was extremely unlikely that Kearney survived given the amount of devastation in the area around Green Lake. The Braveheart began the journey back to the mainland on 25 March, with three of the DOC workers staying on the island to continue research.[4] The three were joined by the other four evacuated workers at the start of May 2006. Two of the three will return to the mainland after the handover.[5]
Five hours after the eruption, the Aura satellite passed over and found an estimated 200 tonnes of sulfur dioxide had been released.[6] This confirmed that there were magmatic gases in the eruption, and the presence of degassing magma within the volcano. By the end of April, the activity in the area had decreased significantly and the "Alert Level" was lowered to 1.[7]
As a geographically active 'hotspot', the Kermadec Islands also experience frequent earthquakes, the most recently significant of which occurred at 22:39 NZST on May 16, 2006.[8] The epicentre was approximately 290 km SSW from Raoul and measured 7.4 on the moment magnitude scale, and as such is classified as a 'major' earthquake by the United States Geological Survey. It was felt as far away as Christchurch, New Zealand some 1500 km from the epicentre.
HMNZS Te Mana left for Raoul on 24 August 2006 on a resupply mission. Also on board where Kearney's sister, Merryn McDermott; three representatives of the Ngati Kuri iwi; and Chris Carter, the Minister of Conservation. During a service held on 28 August, the Ngati Kuri representatives performed a tapu lifting ceremony.[9] A plaque was erected to honour Kearney. Te Mana also allowed some volcanic monitoring to be undertaken using its SH-2G Super Seasprite helicopter. During a dawn flight, sample bottles were filled with crater lake water.[10]
A report by the New Zealand Department of Labour into the death was released on 14 October 2006. It cleared the Conservation Department and Geological and Nuclear Sciences of any negligence related to the death of Kearney. The report stated that the eruption was unpredictable and there was no indication of imminent seismic activity.[11]
[edit] Geography
Two Holocene calderas are found at Raoul. The older caldera cuts the center of Raoul Island is about 2.5 x 3.5 km wide. Denham caldera, formed during a major dacitic explosive eruption about 2200 years ago, truncated the western side of the island and is 6.5 x 4 km wide. Its long axis is parallel to the tectonic fabric of the Havre Trough that lies west of the volcanic arc. Historical eruptions at Raoul during the 19th and 20th centuries have sometimes occurred simultaneously from both calderas, and have consisted of small-to-moderate phreatic eruptions, some of which formed ephemeral islands in Denham caldera. A 240 m high unnamed submarine cone, one of several located along a fissure on the lower NNE flank of Raoul volcano, has also erupted during historical time, and satellitic vents at Raoul are concentrated along two parallel NNE-trending lineaments. The Denham caldera was named for the nearby Denham Bay, itself named for Captain Denham from HMS Herald, an early explorer of the island.
Three small lakes, Blue Lake (1.17 km², about 40 % overgrown), Green Lake (160,000 m²) and Tui Lake (5,000 m², drinking water quality) are located in the Northern caldera of Raoul Island. The plains surrounding the lakes are called Pumice Flats.
[edit] Flora and fauna
Raoul is part of the Kermadec Islands subtropical moist forests ecoregion, and is largely covered with closed-canopy forest, predominantly of the evergreen tree Metrosideros kermadecensis and the islands' endemic palm, Rhopalostylis cheesemanii. The island has no native land mammals, and was formerly home to vast colonies of seabirds who nested in the forests. Polynesian visitors introduced Polynesian Rats in the 14th century, and norway rats, cats, and goats were introduced by European and American visitors in the 19th and 20th centuries. The rats and cats greatly reduced the seabird colonies, which mostly withdrew to offshore islets, and although the goats did not eliminate the tree canopy as they did on other islands, they greatly reduced the understory vegetation.
Goats were removed from the island in 1984; in 2004 rats, and probably also cats, were successfully eradicated from the island. A large scale weeding programme has also been under way for a number of years involving teams of DOC workers and volunteers. The island is part of the Kermadec Islands Marine Reserve, New Zealand's largest marine reserve, which was created in 1990.
[edit] Satellite islands and rocks
The two largest satellite islands are North Island and South Island of Meyer Islands
- Islands and Rocks in the Northeast of Raoul Island
- Fishing Rock
- Egeria Rock
- Meyer Islands
- North Island
- South Island
- Napier
- Nugent
- Herald Islets
- Dayrell Island
- Chanter Islands
- Chanter (North) Island
- South Island
- West Island
- Islands and Rocks in the Southwest of Raoul Island
- Milne Islands
- Dougall Rocks
[edit] Notes
- ^ "DoC evacuates as Raoul Island erupts, 'one missing'", New Zealand Press Association, 17 March 2006.
- ^ "Raoul crater ruled unsafe", The Press, 22 March 2006.
- ^ "Raoul five return to look for mate", The Dominion Post, 20 March 2006.
- ^ "DOC searchers on Raoul Island to head home", Radio New Zealand, 25 March 2006.
- ^ "Raoul survivors return to island", NZPA, 25 March 2006.
- ^ Alert Bulletin, Raoul Island volcano, 24 March 2006
- ^ Alert Bulletin, Raoul Island volcano, 26 April 2006
- ^ Magnitude 7.4 - KERMADEC ISLANDS REGION, United States Geological Survey
- ^ "A place of death, and reconnection", Dominion Post, 2006-08-26. Retrieved on 2006-08-26.
- ^ "Frigate leaves for Raoul Island", Dominion Post, 2006-08-24. Retrieved on 2006-08-26.
- ^ "Family 'let down' by Raoul report", The Dominion Post, 2006-10-14. Retrieved on 2006-10-21.
