New Zealand Journal of Geology and Geophysics abstracts
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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