Research Commons
      • Browse 
        • Communities & Collections
        • Titles
        • Authors
        • By Issue Date
        • Subjects
        • Types
        • Series
      • Help 
        • About
        • Collection Policy
        • OA Mandate Guidelines
        • Guidelines FAQ
        • Contact Us
      • My Account 
        • Sign In
        • Register
      View Item 
      •   Research Commons
      • University of Waikato Theses
      • Masters Degree Theses
      • View Item
      •   Research Commons
      • University of Waikato Theses
      • Masters Degree Theses
      • View Item
      JavaScript is disabled for your browser. Some features of this site may not work without it.

      Products and Processes of Cone-Building Eruptions at North Crater, Tongariro

      Griffin, Anna Marie
      Thumbnail
      Files
      thesis.pdf
      74.60Mb
      Citation
      Export citation
      Griffin, A. M. (2007). Products and Processes of Cone-Building Eruptions at North Crater, Tongariro (Thesis, Master of Science (MSc)). The University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/2235
      Permanent Research Commons link: https://hdl.handle.net/10289/2235
      Abstract
      North Crater occupies the north-western quadrant of the Tongariro Volcanic Centre

      and represents one of at least eleven vents which have been active on Tongariro since

      the last glacial maximum. The most recent cone-forming activity at North Crater is

      thought to have occurred between 14-12 ka ago to produce the distinct, wide, flattopped

      andesite cone. This project focused mainly on the cone-building eruptions at

      North Crater, including stratigraphic correlations with distal tephra, interpreting

      eruptive processes, and establishing the sequence of events during cone construction.

      Detailed field work identified key stratigraphic sections and facies in the proximal,

      medial and distal environments. These sections allowed stratigraphic correlations to

      be made between proximal cone-building facies and distal sheet-forming facies at

      North Crater, and established a complete North Crater eruption stratigraphy. In the

      proximal environment, welded and non to poorly welded facies formed from fallout

      of a lava-fountain, pyroclastic flow or as fallout from a convecting plume. In the

      medial and distal environment, the lithofacies consist of fallout from a convecting

      plume and minor pyroclastic flow. Convective fall and non to poorly welded

      pyroclastic flow deposits dominate the lower eruption stratigraphy suggesting

      explosive eruptions involving a gas-rich magma. A change to welded deposits

      produced from lava-fountaining occurs later in the cone-building sequence and

      suggest a change to lower explosively and eruption of gas-poor magma.

      Grain size, componentry data, density, petrography and SEM analysis were carried

      out on representative samples to characterise the different facies, and reveal

      information about eruption processes. The non to poorly welded deposits are typically

      made up of vesicular pumice, scoria and mingled clasts of sub-rounded bombs and

      lapilli. The welded facies are relatively dense and clast outlines are often difficult to

      distinguish. The eruptives are porphyritic with abundant plagioclase gt clinopyroxene gt

      orthopyroxene gt opaques. Quartzofeldspathic crustal xenoliths are common and

      indicate crustal assimilation. Mingled clasts of light and dark glass were found to

      have microlites present in the dark glass, but were absent in the light glass. Electron

      microprobe analyses found that the dark and light glass components in a single clast

      had similar compositions, showing that the contrasting physical appearance of the

      glass is not due to a different chemical composition.

      Forty three whole rock XRF analyses showed that the magmas ranged from basaltic

      andesite to andesite, and Harker variation plots display linear trends typical of magma

      mixing. Magma mixing as the most important magmatic process is supported by

      disequilibrium of phenocryst compositions and phenocryst textures. Magma

      viscosity, bulk density and temperature was determined using MAGMA (Kware), and

      indicate that they fall into the range of typical andesites.

      Eruptive activity involved vigorous lava-fountaining, minor convecting eruption

      plumes and dominant collapsing eruption plumes. This activity has produced welded

      and non-welded pyroclastic flow and fall deposits to form the large cone seen today.

      There are significant volcanic hazards associated with this style of activity at North

      Crater, characterised by lava-fountaining, eruption plume fallout, and widespread

      pyroclastic flows and lahars extending beyond the ring plain. These could all be

      potentially devastating to the central North Island of New Zealand.
      Date
      2007
      Type
      Thesis
      Degree Name
      Master of Science (MSc)
      Publisher
      The University of Waikato
      Rights
      All items in Research Commons are provided for private study and research purposes and are protected by copyright with all rights reserved unless otherwise indicated.
      Collections
      • Masters Degree Theses [2381]
      Show full item record  

      Usage

      Downloads, last 12 months
      33
       
       

      Usage Statistics

      For this itemFor all of Research Commons

      The University of Waikato - Te Whare Wānanga o WaikatoFeedback and RequestsCopyright and Legal Statement