Macauley Island is a volcanic 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 cliffs that make accessing it difficult; the inland parts are mostly gently sloping terrain covered with ferns and grasses.
The island was formed during several volcanic episodes that produced mainly basaltic rocks as lava flows. 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 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 Kermadec Islands, south-southwest of Raoul Island and roughly halfway between Tonga and New Zealand. Cheeseman Island and Curtis Island lie south-southwest of Macauley Island, and Havre and L'Esperance Rock are even farther south; together these islands form the southern group of the Kermadec Islands, of which Macauley Island is the largest. Under good conditions Raoul Island can be seen from Macauley Island. Located within the exclusive economic zone of New Zealand, the islands are since 1990 within the Kermadec Islands Marine Reserve and the Kermadec Benthic Protected Area administered by the New Zealand Department of Conservation. The islands are, with the exception of the weather station on Raoul Island, uninhabited.
The volcano rises from a depth of where it is wide; it is elongated in east-southeast direction and features a wide submarine caldera northwest of Macauley Island. The caldera floor lies at depth and its rim at . The caldera is elongated in east-northeast direction 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, and there is evidence of collapses on the western caldera margin. A fault runs inside the caldera next to its southeastern margin. The caldera floor is covered with pumice, and thick pumice deposits occur on the flanks of Macauley volcano.
North-northwest of the caldera is a long structure called Lloyd dome or Curtis Ridge; it is surmounted by a lineament of cones that rise to below sea level. high and wide Macauley Cone is located on the southeastern caldera margin and rises to depth. It is capped by a wide and deep crater with a floor covered with ash and sulfur, while its slopes are covered with talus. Parasitic vents and structures have been identified on the caldera rim and submarine slopes of Macauley Island volcano during bathymetric analysis, some are the source of lava flows that extend into the caldera and down the flanks.
The seafloor on the slopes of Macauley volcano is covered with sand, rock, breccia and bacterial mats. "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 sector collapses 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
Parts of the volcano emerge above sea level, forming Macauley Island, Haszard Island and Newcombe Rock. Together they have an area of about , making it the second-largest island in the Kermadec Islands. Macauley Island was also known as Green Island.
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.