Anja Moebis

Anja Moebis
Massey University · Institute of Agriculture and Environment

PhD

About

26
Publications
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451
Citations

Publications

Publications (26)
Article
Holocene volcanism at the Tongariro Volcanic Centre (TgVC), at the south-western end of the Taupo Volcanic Zone (TVZ), New Zealand, involved eruptions from at least three centres and was dominated by numerous “small” eruptions of VEI 1–4. These produced very thin, grey to black, fine to coarse ash deposits of basaltic andesite to andesitic composit...
Article
The 6 August 2012 Te Maari eruption produced violent and widespread “cold” Pyroclastic Density Currents (PDCs) following unroofing of the pressurized hydrothermal system. Despite an erupted volume of only ~ 5 x105 m3, and lacking any juvenile component, the 340,000 m3 of PDCs spread over an area of 6.1 km2 and had mobilities that were on the order...
Article
Full-text available
The weak geophysical precursors of the 6 August 2012 Te Maari eruption of Mt. Tongariro and a lack of obvious juvenile components in its proximal ballistic deposits imply that the eruption was caused by the sudden decompression of a sealed, hot hydrothermal system. Strong magmatic signals in pre- and post-eruption gas emissions indicate that fresh...
Article
Full-text available
The ballistic ejection of blocks during explosive eruptions constitutes a major hazard near active volcanoes. Fields of ballistic clasts can provide important clues towards quantifying the energy, dynamics and directionality of explosive events, but detailed datasets are rare. During the 6 August 2012 hydrothermal eruption of Upper Te Maari (Tongar...
Article
Full-text available
Arc magmas typically contain phenocrysts with complex zoning and diverse growth histories. Microlites highlight the same level of intracrystalline variations but require nanoscale resolution which is globally less available. The southern Taupo Volcanic Zone (TVZ), New Zealand, has produced a wide range of explosive eruptions yielding glassy microli...
Article
Pyroxene crystals from recent Central Plateau tephras are used to deduce their formation conditions through two-pyroxene thermobarometry. Crystals return pseudo-pressures and pseudo-temperatures that are artefacts of uptake of antecrysts formed at a range of crustal levels by isobaric cooling of previously intruded magmas. MELTS modelling of tephra...
Article
Full-text available
To assess whether magma ascent rates control the style of volcanic eruption, we have studied the petrography, geochemistry and size distribution of microlites of plagioclase and pyroxene from historical eruptions from Tongariro, Ruapehu and Ngauruhoe volcanoes located in the southern Taupo Volcanic Zone, New Zealand. The studied deposits represent...
Article
Low to moderate-intensity eruptions (VEI ≤ 3) constitute the most frequent eruptions on historical time scales and can last from days to years. Direct observations of historical eruptions (e.g. Ruapehu 1995–1996, Nakadake 2003–2005, Etna 2002–2003) have highlighted the complexity of these eruptions, which often involve multiple phases and sudden ch...
Conference Paper
The Tongariro Volcanic Centre (TgVC), located at the southern end of the Taupo Volcanic Zone in New Zealand, has produced historical explosive eruptions of different eruptive styles. To understand magma ascent processes and their associated timescales, the textures and compositions of microlites and micro-phenocrysts from glass shards (c. 12 ka BP...
Conference Paper
Full-text available
To assess how magma ascent rates control the style of volcanic eruption, we have studied microlites from historical eruptions from the Tongariro Volcanic Centre, New Zealand, ranging in age from 11,000 years BP to 1996, and covering a range of eruption styles from Strombolian to Plinian. Petrographic analysis shows that larger microlites display co...
Article
Full-text available
Crystals within volcanic rocks record geochemical and textural signatures during magmatic evolution before eruption. Clues to this magmatic history can be examined using crystal size distribution (CSD) studies. The analysis of CSDs is a standard petrological tool, but laborious due to manual hand-drawing of crystal margins. The trainable Weka segme...
Conference Paper
Full-text available
Crystals within erupted volcanic rocks record geochemical and textural signatures during magmatic evolution prior to the onset of eruptions. Growth times of microlites can be derived through Crystal Size Distribution (CSD) analysis combined with well-constrained microlite growth rates, yielding petrologically-determined magma ascent timescales. Our...
Article
Volcanic eruptions are at their most deadly when pyroclastic density currents sweep across landscapes to devastate everything in their path1, 2. The internal dynamics underpinning these hazards cannot be directly observed3. Here we present a quantitative view inside pyroclastic density currents by synthesizing their natural flow behaviour in large-...
Article
Full-text available
Crystal nucleation and growth are first order processes captured in volcanic rocks and record important information about the rates of magmatic processes and chemical evolution of magmas during their ascent and eruption. We have studied glass-rich andesitic tephras from the Central Plateau of the Southern Taupo Volcanic Zone by electron- and ion-mi...
Article
Using a high resolution ion microprobe with SCAPS imaging, the peritectic reaction of forsterite + silica to enstatite was studied down to submicron level in natural andesitic tephras from the Central Plateau of North Island, New Zealand. The fayalitic component of natural olivines is stable in high-silica melts, and therefore the reaction is in fa...
Article
For active or dormant andesite volcanoes, detailed, stratigraphically controlled, geochemical and petrological information enables an understanding of the magma supply and plumbing system feeding eruptions at the surface. This can establish a basis for predictive eruption models and thus for hazard prediction and management. The potential for petro...
Article
Volcanic ice-slurry flows constitute a significant hazard at snow-capped volcanoes. These four-phase flows of ice, volcanic particles, water and air exhibit extreme rates of volumetric bulking and unusually high mobility. Thus far, the rapid melting and relocation of ice-slurry deposits have retarded detailed studies towards a better understanding...
Article
The andesitic volcano Ngauruhoe, which is located within the Tongariro Volcanic Complex at the southern end of the Taupo Volcanic Zone in North Island, New Zealand, has been constructed over the past 5 ka and last erupted in 1975. Nearby Ruapehu volcano has a much longer eruptive history extending back beyond 230 ka B.P. The magmas erupted at both...
Article
Conference title - Geological Society of New Zealand, New Zealand Geophysical Society, New Zealand Geochemical and Mineralogical Society joint conference, Copyright - GeoRef, Copyright 2012, American Geosciences Institute. Reference includes data supplied by Institute of Geological and Nuclear Sciences Limited (GNS Science), Lower Hutt, New Zealand...
Article
Conference title - Geological Society of New Zealand and New Zealand Geophysical Society joint annual conference; launching International Year of Planet Earth, Copyright - GeoRef, Copyright 2012, American Geosciences Institute. Reference includes data supplied by Institute of Geological and Nuclear Sciences Limited (GNS Science), Lower Hutt, New Ze...
Article
Conference title - IUGG XXIV general assembly, Copyright - GeoRef, Copyright 2012, American Geosciences Institute., Date revised - 2011-01-01, Language of summary - English, Pages - Abstract 6978, ProQuest ID - 840344052, SubjectsTermNotLitGenreText - Australasia; dams; debris flows; deposition; geologic hazards; lahars; mass movements; New Zealand...
Conference Paper
Ruapehu lahars are typically derived from eruptions or outbursts from the hydrothermally heated Crater Lake. Hence the chemical contrast of this pulse of acidic brine into normal streamflow can be used, alongside sediment concentration and flow stage/discharge to understand the interaction of lahars and river water in their path. Observations of er...

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Projects (2)
Project
Validation of multiphase models (MFIX) against large-scale experiments of pyroclastic density currents