The eruption of Mt Tarawera
The Mt Tarawera eruption in 1886 is probably the most devastating eruption to occur in Aotearoa New Zealand since Polynesian settlers arrived in the 14th century.
The Okataina Volcanic Complex
Tarawera Volcano, southeast of Rotorua, is part of the large Okataina Volcanic Complex which is responsible for some of the biggest volcanic eruptions in New Zealand's volcanic history. Other eruptions from the wider Taupo Volcanic Zone rhyolitic super volcanoes, such as the 180AD Hatepe eruption from Taupo Volcano, have been big enough to have a global effect on climate due to enormous volumes of ash injected into the upper atmosphere.
The 1886 eruption was unusual for Okataina Volcanic Complex in being a basaltic eruption that, while sizeable, was small compared to more typical previous rhyolitc eruptions which were enormous.
One such earlier rhyolitic eruption from Tarawera Volcano in AD1314, known as the Kaharoa Tephra, provides an important datum because Polynesian artefacts first occur above this ash layer.
Volcanoes are generally produced by three types of magma - basaltic, andesitic and rhyolitic and are related to their particular plate tectonic setting. Each of these magmas has a distinct geochemistry, behaves differently when they erupt and produces different types of volcanoes.
It is a generalisation but at one end of the spectrum basaltic volcanoes behave in a relatively calm way (for a volcano) and erupt relatively small volumes of material at any given time (eg. Rangitoto Volcano). Rhyolitic volcanoes (eg. Taupo Volcano) at the other end behave badly, erupting huge volumes of material laying waste to hundreds and thousands of square kilometres instantaneously. Andesitic volcanoes (eg. Mt Taranaki and Mt Ruapehu) lie somewhere in the middle in terms of explosivity and menace.
In the Taupo Volcanic Zone, where continental crust above a subduction zone is being "stretched" and made thinner, all three types of volcanoes / eruptions are possible.
A sudden eruption
The 1886 eruption of Mt Tarawera and neighbouring Rotomahana began with little or no warning in the early hours (about 2.15am) on 10 June. It was over by 6am, although ash continued to fall for a few more hours. Had the eruption occurred during the day, the loss of life would have been greater than the estimated 108 to 120 people killed. The settlements of Te Tapahoro, Moura, Te Ariki, Totarariki, Waingongongo and Te Wairoa were badly damaged or buried.
The eruption opened up a rift system of multiple vents extending from Mt Tarawera across Lake Rotomahana and through the Waimangu Volcanic Valley, a distance of more than 15 kilometres. It spewed steam, mud and ash of various thicknesses.
Ash was deposited as far east as East Cape and on ships at sea in the Bay of Plenty. Professor Algernon Phillips Withiel Thomas, Auckland University geologist and past president of the Auckland Museum Institute, collected ash from a number of locations; now part of Auckland Museum's geology collection.
Thomas published his Report on the Eruption of Tarawera and Rotomahana, N.Z in 1888, which includes a map of the fissure caused by the eruption. A second map shows the effect of the eruption on the surrounding districts. They can be compared to geologist Dr Ferdinand von Hochstetter's map of the area when he visited in 1859, before the destruction took place.
The destruction of the 'Eighth wonder of the world'
The spectacular Pink Terrace, or Te Otukapuarangi ("The fountain of the clouded sky") in Māori, and the White Terrace, also known as Te Tarata ("the tattooed rock") were on the shores of Lake Rotomahana.
Mineral rich hot water flowed down from hot springs above the lake creating a cascade of stepped pools. At the time they were often referred to as "the Eighth Wonder of the World".
In hot pools which are mineral rich, a variety of silica rich sinters can be deposited as flowstone or entomb and preserve plants and animals by "petrifying" them (turning to stone). The images show some examples of this.
When the Lake Rotomahana vents erupted the Terraces were thought to have been completely destroyed. But recent research by GNS Science shows they still partly exist, albeit mostly covered by mud and under water.
Campbell, H. (n.d.). What's good about volcanoes: Mt Tarawera. Volcanoes. Auckland Museum.
GNS Science (2011). White Terraces Rediscovered.
Yarwood, V. (2003.) The night Tarawera awoke. New Zealand Geographic.
Cite this article
The eruption of Mt Tarawera. Auckland War Memorial Museum - Tāmaki Paenga Hira. First published: 8 June 2016. Updated: 31 August 2016.