Post Eruption Deposition from the 10 June 1886 Mt Tarawera Eruption
Year:
Project type:
Advisers:
Abstract:
The uppermost tributary catchment area below the Tarawera falls along the upper Tarawera River Valley is mantled by up to 90cm of fallout deposits from the 1886 Tarawera eruption. These products are sub-divided into three units: (1) Tarawera scoria; (2) Tarawera scoria with Rotomahana mud, and; (3) Late-stage fall deposits. The deposition of the finer-grained latestage fall deposits, and of layers of intercalated Rotomahana mud, produced horizons within and at the top of the Tarawera scoria unit that were sufliciently less permeable than underlying pumiceous fall and terrace deposits of the 70a Kaharoa eruption. Eruptive destruction of vegetation, together with deposition of these relatively impermeable layers, caused major readjustment of the local erosion and sedimentation regime. Pre-1886 gullies were deepened and locally extended following the eruption, and new gullies formed in places. Small alluvial fans have formed at the mouths ofthese gullies, where eroded 1886 and pre-1886 tephra has been redeposited overlying 1886 fall deposits on t~e upper flood-plain of the current Tarawera River. Facies analysis reveals that a wide spectrum of transport and depositional mechanisms, from debris flows through hyperconcentrated flow to dilute streamflow, was involved in construction of the fans. Volume calculations indicate that 8.55x106m3 of material has been removed from the gullies, ofwhich only 1.81x106m3 can be accounted for within the fans. Only 15-20% of the eroded material was newly deposited 1886 scoria, the remainder being derived from enlargement of the pre-1886 gullies by renewed erosion of pumiceous terrace deposits. These results indicate that much of the tephra eroded from the gullies occurred either prior to 1886, or has been carried downstream along the Tarawera River, where it forms conspicuous low terraces along the present· river channel. Field data indicates that initial remobilisation occurred relatively soon after deposition of the fall deposits. There is no apparent record in the field area of the flood reported to have resulted from sudden drainage of approximately 3.35m from Lake Tarawera in 1904.
Named Localities:
Thesis description:
v. 80 p. ill. Diagms. Photos. Map folded in pocket, 30 cm.
Department:
OU geology Identifier:
1995Drieberg
OURArchive handle:
OURArchive access level:
Location (WKT, WGS84):
POLYGON ((176.670521912932628 -38.161039197808925,176.553000777798275 -38.165373184585356,176.550522918020391 -38.114321777686698,176.667076903598513 -38.110379576514546,176.670521912932628 -38.161039197808925))
Collection
Citation
Drieberg, Bede, “Post Eruption Deposition from the 10 June 1886 Mt Tarawera Eruption,” Otago Geology Theses, accessed February 7, 2025, https://theses.otagogeology.org.nz/items/show/307.