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The 26.5 ka Oruanui eruption, New Zealand: an introduction and overview

2001; Elsevier BV; Volume: 112; Issue: 1-4 Linguagem: Inglês

10.1016/s0377-0273(01)00239-6

1872-6097

Colin Wilson,

earthquake and tectonic studies

The 26.5 ka Oruanui eruption, from Taupo volcano in the central North Island of New Zealand, is the largest known 'wet' eruption, generating 430 km3 of fall deposits, 320 km3 of pyroclastic density–current (PDC) deposits (mostly ignimbrite) and ∼420 km3 of primary intracaldera material, equivalent to ∼530 km3 of magma. Erupted magma is >99% rhyolite and 90%). PDC deposits range from mm- to cm-thick ultra-thin veneers enclosed within fall material to >200 m-thick ignimbrite in proximal areas. The farthest travelled (∼90 km), most energetic PDCs (velocities >100 m s−1) occurred during phase 8, but the most voluminous PDC deposits were emplaced during phase 10. Grain size variations in the PDC deposits are complex, with changes seen vertically in thick, proximal accumulations being greater than those seen laterally from near-source to most-distal deposits. Modern Lake Taupo partly infills the caldera generated during this eruption; a ∼140 km2 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 fall and PDC activity.