It consists of a volcanic cone that reaches a depth of 1,150 metres (3,770 ft) below sea level, two 2–2.5 kilometres (1.2–1.6 mi) and 1.3 kilometres (0.81 mi) wide calderas and a parasitic cone that reaches a depth of 950 metres (3,120 ft) below sea level.

The flanks of the volcano are covered with pumice and volcanic rocks, and hydrothermal venting occurs inside the caldera.

Parts of the "Loisels Pumice" in New Zealand are suspected to have originated in this eruption, which took place 590±80 years before present (1950).

[15] It is a 7 kilometres (4.3 mi) wide and 15 kilometres (9.3 mi) long northeast-southwest trending submarine volcano[16] consisting of three individual edifices, Healy Caldera, Healy Edifice[11] and Cotton Volcano,[16] and was discovered in 1965 by HMNZS Tui (T234).

[11] The surface of the volcano consists of felsic rock outcrops, lapilli and pyroclastic breccia.

[19] There is widespread evidence for ocean current-driven erosion of bottom sediments both on the slopes of the volcano[20] and in its caldera.

[31] The formation of silicic magmas in oceanic volcanic arcs has been interpreted either as a consequence of fractional crystallization processes or the remelting of crustal materials; processes which yield similar magma compositions and are thus difficult to distinguish,[32] although an origin through fractional crystallization is possible at Healy.

[33] The development of felsic magma and calderas at Healy and some other Kermadec volcanoes appears to be a consequence of a thicker crust which facilitates crustal melting.

[35] The eruption would have occurred at about 500–900 metres (1,600–3,000 ft) depth[40] and involved about 5 cubic kilometres (1.2 cu mi) of pyroclastic material,[41] which formed about 10–15 cubic kilometres (2.4–3.6 cu mi) of pumice and caused the collapse and formation of the Healy Caldera.

Part of the eruption column could have risen to the surface, possibly creating a pumice raft that would have been transported to New Zealand by oceanic currents and eddies.

[51] This pumice has a scientific importance stemming from its age, which directly post-dates the arrival of Maori people on New Zealand and can be used to correlate coastal sites.

[58] Hydrothermal venting occurs on the southern floor of Healy Caldera[11] and produces metal-rich discharges[59] and iron oxide mounds.

[60] There is no evidence for hydrothermal activity at Cotton,[61] and unlike all other Kermadec arc volcanoes there are no known chemosynthetic animal communities at Healy.

[65] A tsunami-generating eruption of Healy has been considered in disaster modelling scenarios of cities in northern New Zealand.