New Zealand Journal of Geology and Geophysics abstracts

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Seismic reflection imaging of the Haraharo Caldera boundary beneath Lake Tarawera, Okataina Volcanic Centre, New Zealand

Bryan Davy
Hugh Bibby

Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand
email: b.davy@gns.cri.nz

Abstract  The Okataina Volcanic Centre forms one of the most active volcanic centres of the Taupo Volcanic Zone, New Zealand, having erupted c. 400 km³ of magma over the last 380 000 yr. Lake Tarawera lies within the Haroharo collapse caldera formed by two major Okataina ignimbrite eruptions at 0.28 Ma and 65 ka.
    Marine seismic surveying has imaged the Mamaku Ignimbrite basement horizon dipping east beneath Lake Tarawera. This horizon terminates mid-lake at a fault with a throw >300 m, interpreted as the caldera collapse boundary associated with the 65 ka Rotoiti eruption. The dip of the Mamaku Ignimbrite and overlying sediment are the result of subsidence peripheral to the >60 km3 of collapse deduced within the central Haroharo Caldera.
    Two prominent, highly reflective, reversed phase sedimentary interfaces are interpreted as gas-charged pumice layers deposited as late phases of the 5 ka Whakatane and 7.5 ka Hainini eruptions. Island-like stratigraphy suggests a shallow (<10 m) lake level at the conclusion of the Whakatane eruption.
    Lake-floor mounds and gas-charged disrupted sediments are interpreted to have formed by the passage of water, with entrained volcaniclastic sediment and gas, up faults to the near surface.

Keywords  Okataina Volcanic Centre; Haroharo Caldera; Lake Tarawera; marine seismic reflection; Mamaku Ignimbrite; gas; lake floor mounds

G03033; Received 29 September 2003; accepted 21 April 2004; Online publication date 23 March 2005
New Zealand Journal of Geology & Geophysics, 2005, Vol. 48: 153–166
0028–8306/05/4801–0153 © The Royal Society of New Zealand 2005

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