Distribution, stratigraphy, and history of proximal deposits from the c. AD 1305 Kaharoa eruptive episode at Tarawera Volcano, New Zealand

The Okataina Volcanic Centre forms one of the most active volcanic centres of the Taupo Volcanic Zone, New Zealand, having erupted c. 400 km 3 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 km 3 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.

Section: Recent Eruptionsmentioning

confidence: 99%

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

Davy¹,

Bibby

2005

“…yr BP Kaharoa eruption vents at Tarawera Complex in the southern part of the Haroharo caldera (Nairn et al 2001), the Whakatane episode vents do not lie on a near-straight line. The Tapahoro vent is 0.4 km southeast of a line drawn between the Makatiti and Pararoa vents; the Haroharo vent lies 1.4 km to northwest from such a line.…”

Section: Vent Locations and Eruption Triggering Processesmentioning

confidence: 99%

Proximal stratigraphy and event sequence of the c. 5600 cal. yr BP Whakatane rhyolite eruption episode from Haroharo volcano, Okataina Volcanic Centre, New Zealand

Kobayashi

Nairn²,

Smith

et al. 2005

The c. 5600 cal. yrBP Whakatane eruption episode consisted of a sequence of intracaldera rhyolite eruptions from at least five vents spread over 11 km of the Haroharo linear vent zone within Okataina Volcanic Centre. Initial ventopening eruptions from the Haroharo vent produced coarse lithic clast "blast beds" and pyroclastic density currents (surges). These were immediately followed by eruption of very mobile pumiceous pyroclastic surges from the Makatiti vent 6 km to the southwest. Major plinian eruptions from the Makatiti vent then dispersed Whakatane Tephra pumice fall deposits (bulk volume c. 6 km 3 ) across the northeastern North Island while smaller explosive eruptions produced pyroclastic flows and falls from the Haroharo-Rotokohu vents and at the Pararoa vent on the caldera rim 11 km northeast from Makatiti. The pyroclastic eruptions at all vents were followed by the extrusion of lava flows and domes; extruded lava volumes ranged from 0.03 km 3 for the Pararoa dome to 7.5 km 3 for the Makatiti-Tapahoro lava flows and domes. Minor variations in whole rock and glass chemistry show that the three main vent areas each tapped a slightly different high-silica rhyolite magma. About 10 km 3 of M-type magma was erupted from the Makatiti-Tapahoro vents; c. 1.3 km 3 of H-type magma from the Haroharo-Rotokohu vents, and 0.04 km 3 of P-type magma from the Pararoa vent.There are no significant weathering or erosional breaks within the Whakatane eruptive sequence, which suggests that all Whakatane eruptions occurred within a short time interval. However, extrusion of the Haroharo dome within the Makatiti pyroclastic eruption sequence suggests a duration of c. 2 yr for the main pyroclastic eruption phase. Emplacement of the following voluminous (7.5 km 3 ) lavas from the MakatitiTapahoro vents would have occurred over >10 yr at the c. 10-20 m 3 /s inferred extrusion rates.

“…The TaVC is an 8 km long linear vent zone that has extruded lava domes and flows, as well as being the site of plinian eruptions and pyroclastic flows. Okataina is one of the most active rhyolitic centres on Earth (Wilson et al 1995), and the TaVC was the site of the most recent rhyolitic eruption in New Zealand, the AD 1305 Kaharoa event (Nairn et al 2001). The most recent activity from this centre was a basaltic plinian eruption in 1886.…”

Section: Introductionmentioning

confidence: 99%

Volcanic stratigraphy and phase chemistry of the 11 900 yr BP Waiohau eruptive episode, Tarawera Volcanic Complex, New Zealand

Speed

Shane

Nairn

2002

The 11 900 yr BP Waiohau eruptive episode is a moderately sized rhyolitic event of the Tarawera Volcanic Complex. Subdivision of the pyroclastic fall deposits previously mapped as Waiohau Tephra has allowed the chronology of the eruption to be deciphered. At least 15 events (units A-O) with volumes in the range <0.01-1.7 km 3 can be recognised in proximal to medial settings. The eruption commenced with a series of minor pyroclastic falls and surges, which rapidly changed to a major phase of pyroclastic surges (unit D) that reached up to 14 km from the vent with ash clouds recognisable up to 30 km. Eastern Dome is considered to have been extruded early in the episode. Several prominent plinian phases (unit E, L, M) followed, two of which are estimated to have had column heights of c. 30 km. One event was associated with the destruction of an obsidian dome and dispersal of obsidian lapilli (unit F). These plinian events were accompanied by thin pyroclastic flows punctuated by minor magmatic and phreatomagmatic fall eruptions. There is no evidence for prolonged quiescence during these eruptions. The climactic pyroclastic fall phase (unit M) was followed by a major failure of the northeast flanks of the Tarawera massif, either by a series of block and ash flows or debris avalanche. Effusive activity resulted in the emplacement of Waikakareao lava flows, and voluminous and widespread pyroclastic flows (unit N) to the north and northeast. The Waiohau episode concluded with effusive activity producing the Pokuhu flow and Kanakana Dome. A new volume estimate for the combined units A-O is 4.5 km 3 . This is a minimum because it does not properly incorporate distal ash (>50 km) poorly preserved in paleosols. Previous volume calculations are considered overestimates because they included tephric loess. Effusive activity represents 3.9 km 3 , and pyroclastic debris in the northern sector adds another 2.4 km 3 , but much of the latter is xenolithic. G01020; published 27 September 2002 Received 22 June 2001; accepted 8 May 2002Deposits from the entire Waiohau eruptive episode were derived from a hypersthene (+ minor hornblende) rhyolite magma that lacked compositional (SiO2 = 78 ± 0.2 wt%) and mineralogic gradients. Electron microprobe analyses reveal that phenocrystic phases lack compositional variation. The bulk of the magma also lacked physical gradients (T= 780-790°C; logfO 2 = c. -15) as determined by Fe-Ti oxide geothermometry. Eastern Dome and the Pokohu lava display lower temperature (<740°C) and log fO2 (c. -16). There is no evidence for mafic triggering of the Waiohau eruption, unlike other eruptive episodes of Tarawera, and the magma represents a separate batch, unrelated to earlier and later biotite-bearing magmas. The Waiohau eruptive products appear to have been derived from a rapidly convecting, low aspect ratio magma body that did not reside in the crust for a prolonged time.