Macauley Island

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Macauley Island
View from the north-east, 2003
Macauley Island in the Kermadec Islands
Geography
LocationSouth Pacific Ocean
Coordinates30°14′S 178°26′W / 30.233°S 178.433°W / -30.233; -178.433
ArchipelagoKermadec Islands
Area3.06 km2 (1.18 sq mi)
Length2.5 km (1.55 mi)
Width1.8 km (1.12 mi)
Highest elevation238 m (781 ft)
Highest pointMount Haszard
Administration
New Zealand
Demographics
Population0
Additional information
Nature Reserve

Macauley Island is a

grasses
.

The island was formed during several volcanic episodes that produced mainly

lava flows. During the Holocene, a large explosive eruption produced the Sandy Bay Tephra; this eruption may have had a volume of more than 100 cubic kilometres (24 cu mi) and the Macauley caldera might have formed during that occasion. Later, the Haszard Formation built most of the current surface of Macauley Island. Two uncertain eruptions took place during the 19th century offshore Macauley Island; a hydrothermal vent
system is active on Macauley Cone in the caldera.

Macauley Island is an important breeding place for numerous seabirds, which come on land only to reproduce. While the island is uninhabited, Polynesians, and during the 19th century whalers, introduced goats, pigs and rats which damaged the island's ecosystem. During the 20th and 21st century these invasive species were largely eradicated, leading to a recovery of the previous vegetation. The island is part of a protected area.

Geography and geomorphology

Macauley Island is in the

New Zealand Department of Conservation.[8] The islands are, with the exception of the weather station on Raoul Island, uninhabited.[9]

The volcano rises from a depth of 1,700 metres (5,600 ft) where it is 23–30 kilometres (14–19 mi) wide;[10] it is elongated in east-southeast direction[11] and features a 10.5 by 7 kilometres (6.5 mi × 4.3 mi) wide submarine caldera northwest of Macauley Island. The caldera floor lies at 1,100 metres (3,600 ft) depth and its rim at 600 metres (2,000 ft).[12] The caldera is elongated in east-northeast direction[3] and features north-northeast trending lineaments that extend to Macauley Island. Jumbled blocks, presumably from landslides or slumps, cover the portions of the caldera adjacent to Macauley Island,[11] and there is evidence of collapses on the western caldera margin.[13] A fault runs inside the caldera next to its southeastern margin.[14] The caldera floor is covered with pumice,[14] and thick pumice deposits occur on the flanks of Macauley volcano.[15]

North-northwest of the caldera is a 9 kilometres (5.6 mi) long structure called Lloyd dome

lava flows[12] that extend into the caldera and down the flanks.[13]

The seafloor on the slopes of Macauley volcano is covered with sand, rock,

bacterial mats.[21] "Sediment waves" up to 1 kilometre (0.62 mi) long and 100 metres (330 ft) wide occur on the submarine slopes[22] and extend over 55 kilometres (34 mi) away from the volcano.[23] These waves appear to have formed in part during sector collapses and in part during density flows triggered by eruptions;[24] the size of the latter waves may be indicative of the large size of eruptions.[25] The submarine slopes are dissected by canyons and channels.[16] The total volume of the volcano is about 269 cubic kilometres (65 cu mi),[10] of which less than five percent are emergent.[14]

Macauley Island

Parts of the volcano emerge above sea level, forming Macauley Island, Haszard Island and Newcombe Rock. Together they have an area of about 3 square kilometres (1.2 sq mi), making it the second-largest island in the Kermadec Islands.[26] Macauley Island was also known as Green Island.[27]

Macauley Island is about 2.1 kilometres (1.3 mi) wide with a roughly circular[1] to rectangular shape[28] and rises from an average elevation of about 100 metres (330 ft) to the 238 metres (781 ft) high Mount Haszard in the northern part of the island.[26] Seen from the north the island has the shape of a wedge, while it has a more rounded shape when seen from the east.[29]

The island has a surface area of 3.06 square kilometres (306 ha).[30] Most of the island is a gently tilted plateau, cut by gullies and ravines which are the only way to reach the inside of the island.[31] The deepest of these gullies is 45 metres (148 ft) deep Grand Canyon on the eastern side of Macauley Island;[30] there is evidence that the gullies have become deeper in historical times. Flowing water only occurs after rainfall.[32] The island is geologically unstable, with beaches and landforms frequently shifting due to erosion[33] during rainfall and tropical cyclones, but also due to earthquakes.[5] A castaway depot was established on the northeastern side of[32] Macauley Island in 1888.[34]

Cliffs with heights of over 61 metres (200 ft) surround most of Macauley Island

lava flows, tephra and two volcanic craters crop out in the cliff.[26] South and southwest of Mount Haszard are two more craters[37] known as Haszard Crater and Macauley Crater.[4]

Haszard Island lies 0.23 kilometres (250 yd)[1] east of Macauley Island, next to Sandy Bay.[37] Its name is derived from Henry Douglas Morpeth Haszard (at first, it was named Roaches' Isle),[38] and, like that of Mount Haszard, is often spelled as Hazard.[39] It has a surface of about 0.032 square kilometres (8 acres)[1] and is entirely surrounded by cliffs, making access difficult.[40] Newcombe Rock - also known as Haszardette - is located northeast of Haszard Island and may be part of the same edifice, separate from the Macauley Island one.[41][4] Three more emergent rocks are found northeast and southwest of Haszard Island and south of Macauley Island,[32] and a shallow rock named Mac Donald lies reportedly a few kilometres off Mount Haszard.[42]

Geology

In the

Louisville seamount chain subducts in the trench) in the northern Tonga and the southern Kermadec arc.[45] In the Kermadec arc, subduction proceeds at a rate of 50–70 millimetres per year (2.0–2.8 in/year).[48]

The Kermadec arc consists mainly of 33

hydrothermal activity.[18] Because of its mostly submarine location, volcanism in the Kermadec arc is poorly understood.[53]

The

backarc-volcanic arc system.[53]

Composition

Most of the rocks on Macauley Island have a

alumina-rich to tholeiitic suite[56] with intermediate potassium contents.[57] The rocks contain olivine and pyroxene phenocrysts with rare glass,[58] and the Sandy Bay Tephra contains augite, hypersthene, ilmenite, magnetite and plagioclase.[59] There is a single instance of dacite[3] and rhyolite in Sandy Bay Tephra,[60] and evidence for earlier felsic eruptions;[52] with the exception of that Macauley Island rocks have a largely uniform composition.[61][60] Magma mingling processes appear to have occurred prior to the eruption of the Sandy Bay Tephra.[62]

natroalunite and tridymite. The altered rocks have pink and red colours[37] and there are occurrences of palagonite.[64] Hyaloclastite is found in the sea at shallow depths[65] and ferromanganese crusts have been dredged from the submarine flanks of Macauley Island.[66]

The volcano is believed to consist mostly of basaltic rocks.

backarc extension in the Havre Trough, where tectonic lineaments match the trend of the Macauley caldera and of Denham Caldera on Raoul Island, may also have influenced the explosive activity at both calderas.[71]

Climate and oceanic conditions

The climate of Macauley Island is expected to resemble that of Raoul Island, where temperatures range between 12–25 °C (54–77 °F) and about 1,500 millimetres (60 in) of precipitation fall each year. In summer, winds blow from east and southeast and the rest of the year from northwest. Mean sunshine duration per year is about 2100 hours.[32]

The Kermadec Islands are largely exposed to oceanic swells coming from all directions.[6] Ocean current regimes in this area of the Pacific Ocean are poorly known and appear to be seasonal, with northerly currents during summer and southeasterly ones the rest of the year.[72] Sea surface temperatures at Raoul Island to the north range between 16–26 °C (61–79 °F) and these at L'Esperance Rock south between 14–26 °C (57–79 °F),[73] thus they are considered too cold to be tropical.[46] Waters are salty and clear.[72]

Ecosystem

Most of the island is covered by

artist's conk.[80] There have been historical changes in vegetation due to the introduction and eradication of pigs and goats and a spread of ferns that may be due to climatic changes.[81]

Macauley Island has the largest

Balls Pyramid and Lord Howe Island.[90]

Invertebrates reported from the islands include

flies, moths, orthopterans, snails and spiders[91] although centipedes were not recorded in 2011 and millipedes and earthworms were absent as well.[92]

Marine organisms

Unlike the land-based fauna,

algae with proper corals covering less than one percent of the ground;[95] there are no proper coral reefs at Macauley Island[93] presumably owing to the only marginally suitable water temperatures, as has been observed at other subtropical sites.[96] Spiny kelp occur at Macauley Island, the northernmost occurrence of this species.[97]

Brothers volcano),[106] the crustacean Munidopsis maunga (Macauley caldera),[107] and the mussel Vulcanidas isolatus (at Macauley Island and Giggenbach volcano).[108]

Human activity and ecological impacts

The

flotsam/marine debris arriving from New Zealand is frequently reported.[72]

In the late 20th century, there have been efforts to eradicate introduced species from the Kermadec Islands.

New Zealand Department of Conservation began an effort to eradicate the Polynesian rat.[109] This eradication programme was probably successful, leading to the recovery of a more diverse fern-sedge vegetation that may be still underway as of 2015[78] and could lead to a future reduction of fern occurrences.[120] Rats and other rodents have never been reported from Haszard Island.[38] Since the establishment of the Kermadec Islands Marine Reserve, certain activities such as discharging wastewaters, fishing, mining and laying submarine cables are prohibited around Macauley Island.[7]

Eruption history

The history of Macauley Island is easily

marine cores around Macauley Island may originate from eruptions there.[16][123][124]

Rocks dip away from the northwestern side of the island

last glacial period, a much larger area of the island was exposed above sea level.[16]

Pumices dredged from Macauley Island bear evidence of having formed through a unique process ("Tangaroan eruption"), where expanding magma forms a foam-like structure that fragments into numerous spherical pieces. These pieces upon contacting water solidify on the outside but remain molten on the inside. These pumice deposits are distinct from the Sandy Bay Tephra deposits and probably formed during additional eruptions.[126] The chemistry and density of Macauley Island pumices indicate a complex volcanic history.[127]

Pre-Sandy Bay activity

The lava flows of the North Cliff Lavas are the oldest formation that crops out,

phreatomagmatic eruptions emplaced the tephras and lavas of the Boulder Beach Formation,[64] presumably after water had entered the vent.[129] Dykes, most of which are correlated to the Annexation Lavas, are intruded into the Boulder Beach Formation.[64]

The Annexation Lavas are widespread on Macauley Island and also occur at Haszard Island and Newcombe Rock.

summit crater was left.[130] At this time, Macauley Island may have had a diameter of 4 metres (13 ft) and maximum elevation of 150 metres (490 ft).[61]

Sandy Bay eruption

The Sandy Bay Tephra was erupted 7,200

scrubby vegetation on Macauley Island, leaving wood casts in the rocks.[137]

The Sandy Bay Tephra has a conspicuous white colour, contrasting with the dark colours of the rest of Macauley Island. It consists of dacitic

plutonic rocks are found embedded in the Sandy Bay rocks[130] and reach sizes of 1.5 metres (4 ft 11 in);[132] they indicate that older rocks were integrated into the erupting magma.[59] The total volume of Sandy Bay Tephra on Macauley Island is about 0.1–0.2 cubic kilometres (0.024–0.048 cu mi) but it is likely that the total volume of the tephra was considerably larger.[134] Erosion has affected the Sandy Bay Tephra,[138] leaving cliffs around Haszard Islet.[133]

Southwest Pacific.[134] Caldera collapse and collapses of caldera flanks perhaps produced tsunamis which may have hit the Bay of Plenty region of New Zealand.[140] The Sandy Bay Tephra is the only demonstrated felsic eruption at Macauley volcano;[141] the presence of obsidian and pitchstone in the Sandy Bay Tephra indicate that earlier felsic eruptions took place,[121] but their dates are unknown.[142]

Haszard Formation

The Haszard Formation makes up the bulk of exposed Macauley Island rocks.

phreatomagmatic activity generated the Parakeet Tuff, which was erupted along with the Haszard Scoria and consists of lapilli and volcanic ash.[144] Both the Haszard Scoria[143] and the Parakeet Tuff include rafted blocks with diameters of 2 metres (6 ft 7 in).[144]

The Parakeet Tuff and Haszard Scoria

Plinian dimensions; the crater eventually collapsed below sea level, perhaps during the slumping of the southeastern flank of Macauley Caldera, but the eruption continued as a Surtseyan eruption. Several small phreatic craters on southern Macauley Island probably relate to the Haszard Formation, as does the Grand Canyon Formation formed in a lake formed through the damming of a valley at the eastern end of the island.[11][145]

Historical eruptions and hydrothermal activity

Macauley Island is considered to be a

earthquakes,[5][40] and a faint smell of sulfur was reported at the northern cliffs, next to the oldest rocks of Macauley Island.[37]

isotope ratios appear to vary between observations.[150] The influence of the hydrothermal emanations extend 7 kilometres (4.3 mi) from the volcano. One or two additional vent sites are suspected to exist in the Macauley Caldera.[151] There is evidence that a lake of molten sulfur once filled the Macauley Cone crater[152] and left sulfur deposits with thicknesses exceeding 1 metre (3 ft 3 in).[153]

A

Sea stars prey on them while crabs and tonguefish graze at the sulfurous crater walls.[155] The hydrothermal activity occurs at shallow depths,[156] thus fluids can enter the photic zone where biological productivity is highest.[157]

History

Macauley Island was first discovered on 30 June 1788 by the

archaeological evidence[109] other than an obsidian flake discovered in 2015.[159] They may have obtained obsidian from the island.[160] The island was originally named Macaulay,[161] after George Mackenzie McCaulay, alderman of the City of London who had contracted the voyage of the Lady Penrhyn.[162]

Macauley Island and other Kermadec islands are part of New Zealand's territory since the 19th century;[163] early explorers envisaged planting trees on Macauley Island and using the Kermadec islands as places to settle from New Zealand,[164] and in 1957 were briefly considered as a potential testing ground for the British nuclear weapons programme.[165] Archaeological excavations were conducted in 1990.[166]

See also

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Sources

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