Volcanic Zone
A Thermal Wonderland
The Lake Taupo region is part of the volcanic wonderland which stretches from White Island to Tongariro National Park, and is known as the Taupo Volcanic Zone.
Lake Taupo is not always recognised as a volcano, yet its history has been fiery and violent. A total of 28 eruptions in the past 27,000 years have occurred, however the majority of these have only been small. The most recent Taupo eruption was 181AD. The shape of Lake Taupo was largely created by the Oruanui eruption 26,500 years ago. A 500 metre deep caldera was created by this eruption and was enlarged by the 181AD Taupo eruption. Both of these two eruptions were extremely complex and violent, where as the other 26 eruptions were small.
The different between Cone and Caldera Volcanos
There are two different types of volcanoes - cones and calderas. Cone volcanoes have many small eruptions and are all generated from the same site, where as caldera volcanoes produce larger and less frequent eruptions. Due to the frequent amount of eruptions that cone volcanoes have, an accumulation of large volumes of volcanic debris builds up close to the vent, producing steep-sided cones like Ruapehu, Egmont, and Ngauruhoe. Caldera eruptions can form new caldera structures. This is because caldera-forming eruptions drain the magma reservoir beneath the volcano, causing the ground to collapse which creates a depression in the earth's surface.
New Zealands two most active caldera volcanoes are Taupo and Okataina (which last erupted from Mt Tarawera in 1886, killing 108 people). All caldera volcanoes have associated geothermal systems, where large bodies of underground water are heated by the volcano.
The Oruanui Eruption
The 26,500 year-old Oruanui eruption produced hugh volumes of ash and other volcanic material that buried parts of the central North Island. Close to the vent the ash reached depths of about 100m. The size of the eruption is difficult to grasp, but roughly 800km³ of pumice and ash were ejected in this one event. The ash blanketed a huge area of ocean floor to the east of New Zealand with a layer that varied in thickness from 20cm to 1cm. Even the Chatham islands, 800km to the east of New Zealand, received an 11cm coating. The rapid eruption of so much material caused several hundred km² of the area around the vent to collapse to form the Lake taupo basin, now partly filled by the lake.
The 181AD Taupo Eruption
This eruption took place from one or more vents near the Horomatangi Reefs (now submerged on the eastern side of Lake Taupo) and lasted for approximately several days to several weeks, producing a sequence of pumice deposits that blanketed the landscape east of Taupo. In total 100km³ was erupted. During the climax of this eruption, about 30km³ of pumice, ash and rock fragments was erupted in only a few minutes and travelled horizontally as a liquid flow, moving at speeds estimated to be between 600-900km. It crossed every obstacle in its path except the top of Mt Raupehu. The eruption column that was produced was 50 metres high (twice as high as the 1980 Mt St Helens eruption column), and effects were able to be seen in the sky as far away as Europe and China. This eruption was the most violent in the world for the past 5,000 years and if it occurred today, ashfall and other debris would cause chaos from Hamilton to Palmerston North, and the buildings in Rotorua and Gisborne could be damaged or destroyed.