Curtis Island (New Zealand)

About

Curtis Island is an island in the southwest Pacific. It is a volcanic island which, together with neighbouring Cheeseman Island, belongs to the Kermadec Islands, an outlying island group of New Zealand. It is a volcanic island with a fumarolically active crater, while vegetated slopes are nested by seabirds. There are uncertain reports of eruptions and the island has been uplifted by about 18 m (59 ft) during the past 200 years.

Lieutenant John Watts, RN was the first European to visit the Macauley and Curtis Islands – which he named after patrons George Mackenzie Macaulay and William Curtis – on the Lady Penrhyn on 1 July 1788. In 1888 castaway depots were established on both Curtis and Cheeseman islands, for the use of shipwrecked crews. Count von Luckner, commander of the German raider Seeadler during the First World War, stopped off at Curtis Island in 1917 to replenish his stores from the castaway depot while attempting to make good his escape from New Zealand to South America.

Curtis Island lies in the Kermadec Islands, between Tonga in the north and New Zealand in the south. The four other islands are Raoul Island and Macauley Island 35 km (22 mi) north of Curtis, Cheeseman Island next to Curtis and L'Esperance 83 km (52 mi) to its south. Cheeseman Island lies west-northwest from Curtis and is separated from the latter by the less than 1 km (0.62 mi) wide Stella Passage. The island has a surface area of 42–52 ha (0.42–0.52 km2). Cliffs surround a central plateau at about 100 m (330 ft) elevation and on the northeastern side continue below sea level. There are no known beaches. Two gaps in the cliffs are The Chasm to the southeast and former Macdonald Cove to the northwest. The island lies at the western side of a 6.5 km (4.0 mi) wide shoal at less than 250 m (820 ft) depth on the Kermadec Ridge. Bouldery reefs occur at 25 m (82 ft) depth. The total volume of the volcano, including its submarine sector, is about 41 km3 (9.8 cu mi), and it features a 7 by 6 kilometres (4.3 mi × 3.7 mi) wide caldera. The deepest point of the caldera is 400 metres (1,300 ft) below sea level. At the centre of the island, slightly offset to the northwest, lies a 120–140 m (400–450 ft) deep, elliptical, maximally 200 m (660 ft) wide volcanic crater with a surface area of 31,000 m2 (330,000 sq ft) at 10 m (33 ft) above sea level. North-south trending fractures in the island appear to have influenced the formation and shape of the crater. There is a breach on the northern side and a warm stream drains the crater into the sea northwest of the island. A second crater is found on the southeastern side of the island. This highest elevation is 47 m (154 ft).

The 2,550 km (1,580 mi) long Tonga-Kermadec arc extends from New Zealand's North Island to Tonga and lies between the Havre Trough to the west and the Kermadec Trench to the east. It occurs where the Pacific Plate subducts beneath the Australian Plate in the Kermadec Trench giving rise to magmas from depleted mantle with minor quantities of melted sediments that drive volcanism. Generally, the geology of the Kermadec arc is poorly known, as most of it is submerged. The emergent parts form the Kermadec Islands. The Havre Trough is a backarc basin where crustal spreading takes place; it is the southern continuation of the Lau basin where seafloor spreading is underway and the entire system formed due to a southwestward movement of the Kermadec arc. Of the volcanoes in the Kermadec arc, Raoul Island has had historical eruptions and active submarine volcanoes have been discovered.

Most of the island is formed by pyroclastic rocks, which in some places are intruded by dykes. The pyroclastic rocks are mainly tuff-like, with embedded pumice and rock fragments and only weak bedding. Volcanic rocks from Curtis Island include andesite with plagioclase and pyroxene phenocrysts. Dacites have also been reported, while there are no reported mafic rocks. Hydrothermal deposits such as silica and sulfur occur in the crater. Hydrothermal alteration by hydrothermal waters and the condensation of sulfuric acid has yielded aluminite, alunite, anhydrite, chlorite, cristobalite, diaspore, gibbsite, hematite, kaolinite, metahalloysite, natroalunite, pyrite, quartz and smectite, with chlorite, diaspore, natroalunite and sulfur being the most common.

Adapted from Wikipedia (CC BY-SA). Photography via Wikimedia Commons.