Product Code Database
Macauley Island is a volcano island in New Zealand's Kermadec Islands, approximately halfway between New Zealand's North Island and Tonga in the southwest Pacific Ocean. It is part of a larger submarine volcano that features a wide underwater caldera northwest of Macauley Island. Two islets, Haszard Island and Newcome Rock, lie east offshore of Macauley Island. The island is mostly surrounded by high that make accessing it difficult; the inland parts are mostly gently sloping terrain covered with and .
The island was formed during several volcanic episodes that produced mainly rocks as . During the Holocene, a large explosive eruption produced the Sandy Bay Tephra; this eruption may have had a volume of more than 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 , which come on land only to reproduce. While the island is uninhabited, Polynesians, and during the 19th century whaling, 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 several .
Macauley Island and other Kermadec islands are part of New Zealand's territory since the 19th century; early explorers envisaged planting trees on Macauley Island and using the Kermadec islands as places to settle from New Zealand, and in 1957 were briefly considered as a potential testing ground for the British nuclear weapons programme. Archaeological excavations were conducted in 1990.
The seafloor on the slopes of Macauley volcano is covered with sand, rock, breccia and . "Sediment waves" up to long and wide occur on the submarine slopes and extend over away from the volcano. These waves appear to have formed in part during and in part during density flows triggered by eruptions; the size of the latter waves may be indicative of the large size of eruptions. The submarine slopes are dissected by canyons and channels. The total volume of the volcano is about , of which less than five percent are emergent.
Macauley Island is about wide with a roughly circular to rectangular shape and rises from an average elevation of about to the high Mount Haszard in the northern part of the island. Seen from the north the island has the shape of a wedge, while it has a more rounded shape when seen from the east.
The island has a surface area of . 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. The deepest of these gullies is deep Grand Canyon on the eastern side of Macauley Island; there is evidence that the gullies have become deeper in historical times. Flowing water only occurs after rainfall. The island is geologically unstable, with beaches and landforms frequently shifting due to erosion during rainfall and , but also due to earthquakes. A castaway depot was established on the northeastern side of Macauley Island in 1888.
Cliffs with heights of over surround most of Macauley Island and allow landing only at Sandy Bay, a long beach. Boulder, gravel and sand occur at some places, while others have steep rocky slopes at subtidal depths with crevices, caves and overhangs. At its northwestern end west of Mount Haszard, the steep Perpendicular Cliff drops into the southern part of the caldera. The structure of the shield volcano with , tephra and two crop out in the cliff. South and southwest of Mount Haszard are two more craters known as Haszard Crater and Macauley Crater.
Haszard Island lies east of Macauley Island, next to Sandy Bay. Its name is derived from Henry Douglas Morpeth Haszard (at first, it was named Roaches' Isle), and, like that of Mount Haszard, is often spelled as Hazard. It has a surface of about and is entirely surrounded by cliffs, making access difficult. 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. Three more emergent rocks are found northeast and southwest of Haszard Island and south of Macauley Island, and a shallow rock named Mac Donald lies reportedly a few kilometres off Mount Haszard.
The Kermadec arc consists mainly of 33 submarine volcanoes and and extends from White Island next to New Zealand to Raoul Island; most of these volcanoes however are submarine. The volcanoes are formed principally by and andesitic magmas and are lined up in a wide zone west of the trench. The volcanoes are located west of the ridge, except for Macauley, Raoul and Curtis Islands which are on it, and rise on an oceanic crust of Eocene age. Volcanism began in the Pliocene and has occurred at the present-day location of the Tonga-Kermadec Ridge for about one million years. Many of the volcanoes were discovered using bathymetry, and about 80% show hydrothermal activity. Because of its mostly submarine location, volcanism in the Kermadec arc is poorly understood.
The Kermadec Islands are the emergent part of the Kermadec arc, and most of the ridge lies at over depth. The islands are usually found on ridges perpendicular to the main ridge, implying that local lineaments control the position of volcanoes; they are separated from each other by water depths of over . west-northwest of Macauley Island lies Giggenbach, a submarine volcano, and even farther west ares the Havre Trough and a caldera. This trough separates the Kermadec microplate from the Australian plate and it and the Lau Basin began to form through crustal spreading 6 million years ago; the lineaments of the Macauley caldera appear to match these of the Havre Trough. The Kermadec-Havre system is considered to be an archetype of a backarc-volcanic arc system.
Gabbro and basalts with different compositions occur as and resemble Raoul Island rocks. Chemical alteration has given rise to gypsum, hematite, kaolinite, montmorillonite, natroalunite and tridymite. The altered rocks have pink and red colours and there are occurrences of palagonite. Hyaloclastite is found in the sea at shallow depths and ferromanganese crusts have been dredged from the submarine flanks of Macauley Island.
The volcano is believed to consist mostly of basaltic rocks. The occurrence of felsic rocks at Macauley Island and elsewhere in the Tonga-Kermadec volcanic arc is unexpected. Processes where magma ascending into the lower crust heats it until it melts (anatexis) and dehydrates have been invoked to explain the felsic volcanism in the Kermadec arc. In contrast, an origin through fractional crystallization of basaltic magmas is unlikely for a number of reasons. The 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.
The Kermadec Islands are largely exposed to oceanic swells coming from all directions. 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. Sea surface temperatures at Raoul Island to the north range between and these at L'Esperance Rock south between , thus they are considered too cold to be tropical. Waters are salty and clear.
Macauley Island has the largest seabird population of New Zealand. live on the sea and come to land only to breed; birds found breeding on Macauley Island include Black noddy, black-winged petrels, Grey noddy, Kermadec parakeets, , little shearwaters, masked boobies, red-tailed tropicbirds, , wedge-tailed shearwaters, white-bellied storm petrels and white-naped petrels. Of these, the Kermadec parakeet is the only land bird on Macauley Island. Catastrophic volcanic eruptions that periodically wipe the animals out may be the reason why Macauley Island and other Kermadec islands lack endemic birds. In 1988, 5.2 million breeding birds were reported. They nest mainly in the sedgelands and cliffs, and both Macauley and Haszard Island are heavily burrowed by nesting seabirds. Birds may fly from the colonies on Macauley Island to islands farther west, such as Balls Pyramid and Lord Howe Island.
Invertebrates reported from the islands include , , butterflies, , crickets, flies, , , and although centipedes were not recorded in 2011 and and were absent as well.
, , and crown-of-thorns starfish occur at Macauley Island. Other animal taxa include , , bony fish, cartilaginous fish, , , , , , , , jellyfish, , , polychelida, Porifera, , , , Octocorallia, , and . Animal density is higher in the areas of hydrothermal venting. About 105 mollusc taxa and numerous bryozoan species have been identified in the surrounding sea. Species discovered at Macauley Island and other Kermadec volcanoes are the crabs Gandalfus puia (Macauley Island and submarine volcanoes farther south) and Xenograpsus ngatama (Macauley Island and Brothers volcano), the crustacean Munidopsis maunga (Macauley caldera), and the mussel Vulcanidas isolatus (at Macauley Island and Giggenbach volcano).
In the late 20th century, there have been efforts to eradicate introduced species from the Kermadec Islands. Pigs had died out by 1910 and goats were removed in the 1960s by the New Zealand Wildlife Service; about 3,200 goats were killed during that occasion. After an initial delay due to concerns that toxic baits used for rat removal could impact parakeet populations, in 2006 the New Zealand Department of Conservation began an effort to eradicate the Polynesian rat. This eradication programme was probably successful, leading to the recovery of a more diverse fern-sedge vegetation that may be still underway and could lead to a future reduction of fern occurrences. Rats and other rodents have never been reported from Haszard Island. Since the establishment of the Kermadec Islands Marine Reserve, certain activities such as discharging wastewaters, fishing, mining and laying are prohibited around Macauley Island.
Rocks dip away from the northwestern side of the island and all the rocks appear to have been emplaced above sea level; there is no evidence for orogenic deformation although the presence of subaqueous lava flows indicates that recent eruptions occurred during a time of low sea level. During the sea level lowstand of the last glacial period, a much larger area of the island was exposed above sea level.
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. The chemistry and density of Macauley Island pumices indicate a complex volcanic history.
The Annexation Lavas are widespread on Macauley Island and also occur at Haszard Island and Newcombe Rock. Hawaii-like eruptions of vents located northwest of present-day Macauley Island produced lava flows with average thicknesses of or less intercalated with brown tephra. Dykes fed lava to additional vents, including the Newcombe Rock volcanic plug. Lava also ponded in a crater that crops out in Perpendicular Cliffs; the ponded lava which was originally interpreted as a volcanic intrusion. The total volume of the Annexation Lavas is about , they reach total thicknesses of about . Along with volcanic activity, tectonic activity increased during the Annexation Lavas stage, giving rise to and subsidence; at the end of the stage a summit crater was left. At this time, Macauley Island may have had a diameter of and maximum elevation of .
The Sandy Bay Tephra has a conspicuous white colour, contrasting with the dark colours of the rest of Macauley Island. It consists of dacitic tephra, which forms layered deposits containing lapilli, pumice, sand and fine volcanic ash. The total thickness of the Sandy Bay Tephra ranges from about in the south to in the north, with evidence of thicker deposits in topographic depressions. and rocks are found embedded in the Sandy Bay rocks and reach sizes of ; they indicate that older rocks were integrated into the erupting magma. The total volume of Sandy Bay Tephra on Macauley Island is about but it is likely that the total volume of the tephra was considerably larger. Erosion has affected the Sandy Bay Tephra, leaving cliffs around Haszard Islet.
Tephra from the Sandy Bay eruption has been identified in taken around the island and formed concentric ridges on the western flank of submarine Macauley. It is likely that the eruption produced large amounts of pumice, which would have been transported by to other islands in the Southwest Pacific. Caldera collapse and collapses of caldera flanks perhaps produced which may have hit the Bay of Plenty region of New Zealand. The Sandy Bay Tephra is the only demonstrated felsic eruption at Macauley volcano; the presence of obsidian and pitchstone in the Sandy Bay Tephra indicate that earlier felsic eruptions took place, but their dates are unknown.
The Parakeet Tuff and Haszard Scoria are thought to have originated in the southeastern sector of the caldera, northwest of Macauley Island. Their emplacement may have begun decades or centuries after the Sandy Bay Tephra eruption, during which rainfall eroded the Sandy Bay Tephra and formed valleys later filled by the Haszard Formation. The eruption was centred at the crater of the Annexation Lavas and on flank vents and reached sub-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.
Hydrothermal activity occurs in the submarine Macauley Cone, where white fluids and occasional bubbles emanate from rocks and chimney-shaped vents. Elemental sulfur occurs around the vents, which release warm () acidic mineral-rich waters with a brine-like composition and intense hydrothermal plumes. These waters may be derived from magmatic fluids and their helium appear to vary between observations. The influence of the hydrothermal emanations extends from the volcano. One or two additional vent sites are suspected to exist in the Macauley Caldera. There is evidence that a lake of molten sulfur once filled the Macauley Cone crater and left sulfur deposits with thicknesses exceeding .
A vent biota has become established around the hydrothermal vents consisting of : Vulcanidas isolatus at shallow depths and Gigantidas gladius at both shallow and intermediate depths. prey on them while and tonguefish graze at the sulfurous crater walls. The hydrothermal activity occurs at shallow depths, thus fluids can enter the photic zone where biological productivity is highest.
|
|
