Macauley

Geography & Climate

Macauley is located in New Zealand, within the Middle Kermadec Volcanic Arc of the broader Tonga-Kermadec Volcanic Regions. Situated at 30.21° S, 178.47° W in the Southern Hemisphere, the volcano lies within a subtropical climate zone. At just 238 meters above sea level, Macauley is a relatively low-elevation volcanic feature. Despite its modest height, it remains an active geological formation with the same underlying magmatic processes as its taller counterparts. The volcanic landform is characterized as a caldera, which describes the physical shape and structure of the volcanic edifice as observed from the surface.

Geological Context

Macauley sits in a subduction zone, where one tectonic plate dives beneath another, creating intense heat and pressure that generates magma. Subduction zones are responsible for many of the world's most explosive volcanoes and deadliest eruptions. For communities in New Zealand near Macauley, this tectonic setting means the volcano is capable of producing powerful explosive eruptions, pyroclastic flows, and lahars that can threaten populated areas within tens of kilometers of the summit. The dominant rock type is basalt / picro-basalt, a dark, fine-grained volcanic rock that forms from rapidly cooling, low-viscosity lava. Basaltic eruptions tend to be less explosive and produce fluid lava flows that can travel long distances. While less immediately dangerous than explosive eruptions, basaltic lava flows can destroy structures and infrastructure in their path, and volcanic gases released during these eruptions can affect air quality over a wide area.

Eruption History Summary

Macauley has 3 recorded eruptions in the geological database, spanning from 4360 BCE to 1887 CE. The most powerful recorded event was a colossal eruption capable of affecting global climate for years in 4360 BCE, reaching VEI 6 on the Volcanic Explosivity Index. These eruptions span roughly 6,247 years of volcanic history.

Significance

Macauley has produced at least one eruption of VEI 6 or higher, placing it among the most powerful volcanic systems on Earth. Eruptions of this magnitude inject massive quantities of sulfur dioxide into the stratosphere, affecting global climate by lowering average temperatures for one to three years after the event.

GVP Reference Summary

Macauley Island is a rim remnant of a large submarine caldera centered 8 km to the NW. The 2-km-diameter island consists of a low, gently sloping surface of rhyolitic pumice from the caldera-forming eruption truncated by steep cliffs formed of underlying basaltic lava flows. The pre-caldera edifice consisted of two generations of shield volcanoes separated by a period of pyroclastic cone growth. Eruption of the voluminous Sandy Bay Tuff about 6,300 years ago truncated the NW side of the Annexation shield volcano and formed a 12-km-wide, 1.1-km deep caldera. Following formation of the caldera and substantial marine erosion, a partly submarine and partly subaerial eruption centered about 2 km N of present-day Macauley Island produced basaltic scoriae and lava flows. A reported possible eruption in 1825 from "Brimstone Island," 45 km W of Macauley at a location with a depth of about 2,000 m and SW of Giggenbach submarine volcano, is likely a location error and could refer to an eruption from the submarine flank of Macauley caldera (Lloyd et al., 1996).

— Smithsonian Institution, Global Volcanism Program