title: Volcanology of the basaltic lava succession within the Auckland pit of the Bombay Quarry, Bombay Volcanic Complex, South Auckland Volcanic Field

authors: Kapasi, Aliasgar

subjects: Volcanology

abstract: The South Auckland Volcanic Field (SAVF), which was active 1.59 – 0.51 million years ago and comprises around 82 volcanic centres, represents a complete history of a monogenetic field preserved in the geological record. The Auckland pit in the Bombay Quarry was recently exposed, revealing an infilled palaeovalley of volcanic and sedimentary deposits possibly associated with the nearby Bombay Volcanic Complex. A set of vertical drill cores from across the quarry were available for this study.
 
The stratigraphy of the volcanic and sedimentary deposits and the facies architecture were examined and described from the drill cores available, and a set of stratigraphic logs were produced. Volcanic and sedimentary units identified were: basement Waitemata and Tauranga group sediments, three individual ponded basalt lavas with intercalated scoria and Quaternary alluvium and/or Kauroa ash deposits. Facies identified include: moderately vesicular basalt (A.1), vesicular basalt with vesicle trails (A.2), non-vesicular basalt (A.3), poorly vesicular basalt (A.4), scoria deposit (B), scoriaceous basalt (C) and intercalated silt/clay (D).

Petrographic characteristics were analysed by optical microscopy, which show that all three basalt lavas have minerals comprising: olivine and clinopyroxene phenocrysts, and a groundmass of plagioclase, opaques and mafic minerals, however, the proportions of each mineral vary between samples. Olivine, clinopyroxene and plagioclase elemental compositions for each of the three basalt units were determined by electron microprobe analysis and revealed that the middle basalt had relatively lower proportion of Mg- and Ca-rich minerals compared to the upper and lower basalts. Furthermore, mineral compositions were consistent with the broad group B rock type of the SAVF lavas.
  
Bulk-rock geochemical characteristics were analysed by X-ray fluorescence spectrometry where the basalt samples were classified as basanites and ne-hawaiites. The lower and upper basalts have a relatively wide range of major and trace element compositions; whereas, the middle basalt has less variation.

The three basalt lava flows represent pahoehoe and/or transitional lava flows, which occurred during magmatic eruptions separated by periods of volcanic quiescence represented by Quaternary alluvium and/or Kauroa ash deposits. The magma source beneath the Bombay area reveals that it consists of dominantly a garnet-bearing peridotite source where only group B type lavas were erupted over time. This process indicates a polygenetic-like eruption history within a monogenetic field, which may be an ideal analogue for understanding the future of shield volcanism in the South Auckland and Auckland Volcanic Field.

text: Volcanology of the basaltic lava succession within the Auckland pit of the Bombay Quarry, Bombay Volcanic Complex, South Auckland Volcanic Field The South Auckland Volcanic Field (SAVF), which was active 1.59 – 0.51 million years ago and comprises around 82 volcanic centres, represents a complete history of a monogenetic field preserved in the geological record. The Auckland pit in the Bombay Quarry was recently exposed, revealing an infilled palaeovalley of volcanic and sedimentary deposits possibly associated with the nearby Bombay Volcanic Complex. A set of vertical drill cores from across the quarry were available for this study.
 
The stratigraphy of the volcanic and sedimentary deposits and the facies architecture were examined and described from the drill cores available, and a set of stratigraphic logs were produced. Volcanic and sedimentary units identified were: basement Waitemata and Tauranga group sediments, three individual ponded basalt lavas with intercalated scoria and Quaternary alluvium and/or Kauroa ash deposits. Facies identified include: moderately vesicular basalt (A.1), vesicular basalt with vesicle trails (A.2), non-vesicular basalt (A.3), poorly vesicular basalt (A.4), scoria deposit (B), scoriaceous basalt (C) and intercalated silt/clay (D).

Petrographic characteristics were analysed by optical microscopy, which show that all three basalt lavas have minerals comprising: olivine and clinopyroxene phenocrysts, and a groundmass of plagioclase, opaques and mafic minerals, however, the proportions of each mineral vary between samples. Olivine, clinopyroxene and plagioclase elemental compositions for each of the three basalt units were determined by electron microprobe analysis and revealed that the middle basalt had relatively lower proportion of Mg- and Ca-rich minerals compared to the upper and lower basalts. Furthermore, mineral compositions were consistent with the broad group B rock type of the SAVF lavas.
  
Bulk-rock geochemical characteristics were analysed by X-ray fluorescence spectrometry where the basalt samples were classified as basanites and ne-hawaiites. The lower and upper basalts have a relatively wide range of major and trace element compositions; whereas, the middle basalt has less variation.

The three basalt lava flows represent pahoehoe and/or transitional lava flows, which occurred during magmatic eruptions separated by periods of volcanic quiescence represented by Quaternary alluvium and/or Kauroa ash deposits. The magma source beneath the Bombay area reveals that it consists of dominantly a garnet-bearing peridotite source where only group B type lavas were erupted over time. This process indicates a polygenetic-like eruption history within a monogenetic field, which may be an ideal analogue for understanding the future of shield volcanism in the South Auckland and Auckland Volcanic Field.

year: 2016

title: A question of scale: How turbulence around aerial roots shapes the seabed morphology in mangrove forests of the Mekong Delta

authors: Mullarney, Julia C.

abstract: Mangrove forests are highly productive ecosystems that provide many physical, societal, and ecological services in tropical and subtropical regions. Accurate prediction of the morphological evolution for these areas, in the face of global sea level rise and changes in sediment supply, requires understanding of interactions between vegetation growth, water flows, and sediment transport. Data presented from a wave-exposed mangrove forest in the Mekong Delta, Vietnam, include unique measurements that resolved water flows in and around the aerial mangrove roots (known as pneumatophores) over scales from a few millimeters to hundreds of meters. Flows were highly turbulent, with turbulence values sometimes as large as those measured in surf zones. These energetic processes appear to stir up sediments, with small scour troughs observed around individual pneumatophores, and larger-scale scour around clusters of pneumatophores. The vegetation fringe (the boundary between forest and mudflat) was a particularly dynamic area, with elevated turbulence levels, greater vegetation densities, coarser sediments, and occasional wave breaking. Intense turbulent dissipation at the fringe then reduces the energy of shoreward-propagating waves, sheltering the forest interior. The small-scale processes appear to be linked with forest-wide patterns of sediment transport and deposition. We discuss these links in the context of the biophysical interactions that control the changing shapes of deltas worldwide.

text: A question of scale: How turbulence around aerial roots shapes the seabed morphology in mangrove forests of the Mekong Delta Mangrove forests are highly productive ecosystems that provide many physical, societal, and ecological services in tropical and subtropical regions. Accurate prediction of the morphological evolution for these areas, in the face of global sea level rise and changes in sediment supply, requires understanding of interactions between vegetation growth, water flows, and sediment transport. Data presented from a wave-exposed mangrove forest in the Mekong Delta, Vietnam, include unique measurements that resolved water flows in and around the aerial mangrove roots (known as pneumatophores) over scales from a few millimeters to hundreds of meters. Flows were highly turbulent, with turbulence values sometimes as large as those measured in surf zones. These energetic processes appear to stir up sediments, with small scour troughs observed around individual pneumatophores, and larger-scale scour around clusters of pneumatophores. The vegetation fringe (the boundary between forest and mudflat) was a particularly dynamic area, with elevated turbulence levels, greater vegetation densities, coarser sediments, and occasional wave breaking. Intense turbulent dissipation at the fringe then reduces the energy of shoreward-propagating waves, sheltering the forest interior. The small-scale processes appear to be linked with forest-wide patterns of sediment transport and deposition. We discuss these links in the context of the biophysical interactions that control the changing shapes of deltas worldwide.

year: 2017

title: How Maui captured the sun: using a MUD for educational simulation

authors: Cunningham, Sally Jo

subjects: computer science

abstract: MUDs (Multi-User Dungeons) are text-based, multi-user communication and modelling programs. This paper investigates the potential of a popular extensible MUD, the LambdaMOO system, as a tool for second language training and for educational simulation gaming.

text: How Maui captured the sun: using a MUD for educational simulation MUDs (Multi-User Dungeons) are text-based, multi-user communication and modelling programs. This paper investigates the potential of a popular extensible MUD, the LambdaMOO system, as a tool for second language training and for educational simulation gaming.

year: 1995-12