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.

Macauley Island is an important breeding place for numerous seabirds, which come on land only to reproduce.

[12] The caldera is elongated in east-northeast direction[3] and features north-northeast trending lineaments that extend to Macauley Island.

[15] North-northwest of the caldera is a 9 kilometres (5.6 mi) long structure called Lloyd dome[16] or Curtis Ridge;[17] it is surmounted by a lineament of cones that rise to 80 metres (260 ft) below sea level.

[28] Boulder, gravel and sand beaches occur at some places, while others have steep rocky slopes at subtidal depths with crevices, caves and overhangs.

[36] At its northwestern end[37] west of Mount Haszard, the steep Perpendicular Cliff drops into the southern part of the caldera.

[2] twenty-four kilometres (15 mi) [12] west-northwest of Macauley Island lies Giggenbach, a submarine volcano, and even farther west ares the Havre Trough[47] and a caldera.

[53] Most of the rocks on Macauley Island have a basaltic composition,[26] which define an 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.

[64] Hyaloclastite is found in the sea at shallow depths[65] and ferromanganese crusts have been dredged from the submarine flanks of Macauley Island.

[68] 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.

[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.

[75] Several vegetation associations occur, such as turf along the coasts, lichens and mosses on the northwestern cliffs, sedgelands mostly at the periphery of the island, shrubs at various sites[76] and dwarf ngaio[77] and Homalanthus forests.

[79] 68 plant species were recorded on Macauley Island in 2008,[31] and there are bryophytes, lichens, lycophytes, pteridophytes, seaweeds and spermatophytes.

[37] Tephra layers dating to 130,000, over 40,000, 30,000, 8,400 and 5,600 years ago identified in marine cores around Macauley Island may originate from eruptions there.

[16][124][125] Rocks dip away from the northwestern side of the island[41] and all the rocks appear to have been emplaced above sea level;[126] 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.

[37] Little erosion took place before phreatomagmatic eruptions emplaced the tephras and lavas of the Boulder Beach Formation,[64] presumably after water had entered the vent.

Hawaii-like eruptions of vents located northwest of present-day Macauley Island produced lava flows with average thicknesses of 1 metre (3 ft 3 in) or less intercalated with brown tephra.

It consists of dacitic tephra,[131] which forms layered deposits containing lapilli, pumice, sand and fine volcanic ash.

[134] Tephra from the Sandy Bay eruption has been identified in sediment cores taken around the island[140] and formed concentric ridges on the western flank of submarine Macauley.

[13] It is likely that the eruption produced large amounts of pumice, which would have been transported by ocean currents to other islands in the Southwest Pacific.

[37] It includes the Parakeet Tuff, Haszard Scoria and Cascade Lava Members,[64] which probably were produced by the same eruptive episode.

[144] Submarine phreatomagmatic activity generated the Parakeet Tuff, which was erupted along with the Haszard Scoria and consists of lapilli and volcanic ash.

[145] The Parakeet Tuff and Haszard Scoria[145] are thought to have originated in the southeastern sector of the caldera, [3] 0.75 kilometres (0.47 mi) northwest of Macauley Island.

[37] Hydrothermal activity occurs in the submarine Macauley Cone, where white fluids and occasional bubbles emanate from rocks[18] and chimney-shaped vents.

[148] Elemental sulfur occurs around the vents,[18] which release warm (112 °C (234 °F)) acidic mineral-rich waters[149] with a brine-like composition[150] and intense hydrothermal plumes.

[156] The hydrothermal activity occurs at shallow depths,[157] thus fluids can enter the photic zone where biological productivity is highest.

[161] The island was originally named Macaulay,[162] after George Mackenzie McCaulay, alderman of the City of London who had contracted the voyage of the Lady Penrhyn.