The Oruanui eruption of New Zealand's Taupo Volcano, the world's largest known eruption in the past 70,000 years, had a Volcanic Explosivity Index of 8. It is the largest eruption in the history of New Zealand. It occurred around 25,360� years ago in the Late Pleistocene and generated approximately 430 km3 (100 cu mi) of pyroclastic fall deposits, 320 km3 (77 cu mi) of pyroclastic density current (PDC) deposits (mostly ignimbrite) and 420 km3 (100 cu mi) of primary intracaldera material, equivalent to 530 km3 (130 cu mi) of magma, totaling 1,170 km3 (280 cu mi) of total deposits. The eruption is divided into 10 different phases on the basis of nine mappable fall units and a tenth, poorly preserved but volumetrically dominant fall unit.
Modern Lake Taupo partly fills the caldera generated during this eruption; a 140 km2 (54 sq mi) structural collapse area is concealed beneath the lake, while the lake outline reflects coeval peripheral and volcano-tectonic collapse. Early eruption phases saw shifting vent positions; development of the caldera to its maximum extent (indicated by lithic lag breccias) occurred during phase 10.
The Oruanui eruption shows many unusual features: its episodic nature, wide range of depositional conditions in fall deposits of very wide dispersal, and complex interplay of falls and pyroclastic flows.
Tephra from the eruption covered much of the central North Island, with ignimbrite up to 200 metres (660 ft) deep. Ashfall affected most of New Zealand, with even an 18 cm (7 in) ash layer deposited on the Chatham Islands, 1,000 km (620 mi) away. Later erosion and sedimentation had long-lasting effects on the landscape, and caused the Waikato River to shift from the Hauraki Plains to its current course through the Waikato to the Tasman Sea.
- Wilson, C. J. N. (2001). "The 26.5ka Oruanui eruption, New Zealand: An introduction and overview". Journal of Volcanology and Geothermal Research 112: 133. doi:10.1016/S0377-0273(01)00239-6.
- Manville, V.; Wilson, C. J. N. (2004). "The 26.5 ka Oruanui eruption, New Zealand: A review of the roles of volcanism and climate in the post‐eruptive sedimentary response". New Zealand Journal of Geology and Geophysics 47 (3): 525. doi:10.1080/00288306.2004.9515074.
- Wilson, C. J. N. (2005). "The 26.5 ka Oruanui Eruption, Taupo Volcano, New Zealand: Development, Characteristics and Evacuation of a Large Rhyolitic Magma Body". Journal of Petrology 47: 35. doi:10.1093/petrology/egi066.
- Richard Smith, David J. Lowe and Ian Wright. 'Volcanoes - Lake Taupo', Te Ara - the Encyclopedia of New Zealand, updated 16-Apr-2007.