Products of magmatic systems feature in work by members of the department with interests in New Zealand's crustal evolution (xenoliths in volcanic ejecta), in evolution of plutonic rocks, and in physical volcanology.
James White has supervised most physical volcanology projects at Otago in recent years, the majority at PhD level. The projects have been geographically and topically diverse, ranging from submersible-based studies of modern seamounts, through analysis of intrusion and eruption processes in the Ferrar Province of today's Antarctica, to experimental work addressing interaction of magma with water, explosions in unconsolidated substrates, and submarine eruption-fed density currents.
Subglacially emplaced sequences in Iceland, tuff cones and submarine deposits of pumice in Korea and Japan are under study, as are roots of an intracontinental volcanic field in the western USA and modern submarine deposits drilled in the Caribbean and Philippine seas. The best way to undertake a self-directed survey of this research is through the list of publications and supervised PhD students at James' staff page.
The uniting theme for this research is a focus on physical interactions of magma with its environment during and in-transit to eruption. At most sites on Earth magma encounters water or groundwater on the way to the surface, and interactions of various sorts between magma and water are a topic of sustained research interest at Otago, as during New Zealand's 1886 Rotomahana/Tarawera eruption.
This may be Otago's largest small volcano; it is the eroded remnant of a large multi-vent volcanic centre in the Waipiata Volcanic Field of monogenetic volcanoes. Research at Swinburn will address differential distribution of magma within volcanic fields, magmatic evolution, the nature of the original volcano, emplacement processes for a variety of lavas and pyroclastic rocks, and the relationship of the volcano with its tectonic setting. It formed on substantial paleotopography in an area evolving from an extensional to a compressional setting; it is now cut by a fault bounding a probably still-growing monoclinal fold.
Eruptions of basaltic magma at shelfal water depths produce volcanoes that commonly grow to the water surface to become emergent. Two surtseyan volcanoes in the western USA have been the topic of a recent Otago PhD, and are now ready for a new suite of largely laboratory-based study to make them THE type examples for subaqueously formed basaltic volcanoes. A small amount of fieldwork will extend sampling from the volcanoes to more distal ash sheets, and laboratory work will build on 2-dimensional quantitative vesicularity analysis by subjecting the same samples to micro-Computed Tomography (uCT) and FTIR analysis, to assess magma permeability and retained volatile content, respectively. Arrangements are in place to couple this work with new analyses of tephra from Surtsey and its unique drill core. Current projects are working with outcrops of many surtseyan volcanoes in Oligocene sequences near Dunedin, focusing both on the pyroclastic rocks themselves and on the sedimentary/oceanographic setting into which they erupted.
Submarine pumice-forming eruptions
Silicic eruptions are different in many and obvious ways from basaltic ones. Submarine volcanoes span most if not all of the range in scale and composition exhibited subaerially, but erupt into a very different environment where location relative to sea level really matters. Work from Otago on this topic is in early stages, but builds on previous work with how pumice saturates with water, with magma-water heat exchange, and with deep-marine (>1 km) basaltic eruptions at Loihi seamount (and Seamount Six). Projects on the topic would probably involve seafloor samples +/- the cruise collecting them, or/and fieldwork in Japan or elsewhere.
Recent work by GNS scientists, university colleagues and PhD students will soon be presented in the first detailed geological map of Tongariro National Park, containing Ruapehu and Tongariro volcanoes.
Dating of lavas and surface-dating of moraine deposits shows that many eruptions that built the volcanoes occurred during repeated episodes of glaciation. Their work and related dissertations establishes a framework that will support a focused analysis of subglacial eruptive processes and the effects of eruptions at these two andesitic arc volcanoes that stand high above the surrounding landscapes.
Goals of this project are: (1) Establish eruption and emplacement processes of individual subglacially formed lavas and pyroclastic deposits of Tongariro and Ruapehu volcanoes; (2) Model melting from eruptions; (3) Infer and field-test downstream effects of on-volcano icemelt; (4) Distinguish features of subglacial products that are shared with products of subaqueous eruptions from those unique to subglacial settings.
- More information about the Project: Ice-contact volcanism in the Tongariro National Park, New Zealand
Ideas for projects that might be undertaken in future years include those listed below.
Dunedin Volcano is an intraplate volcanic complex with rocks dated from 16 Ma to 10 Ma, and it developed during a time of varying sea level, erupting compositionally diverse magmas in a range of styles. The rocks are alkaline, and early works on Dunedin Volcano are keystone publications that will ensure widespread attention to new work on the volcano's magma lineage(s). Its physical evolution reflects both shallow eruption processes and environmental controls, and the development of crustal magma storage and distribution pathways
A new collaboration with the experimental petrology group at INGV in Rome will provide new opportunities to investigate the parameters controlling magmatic processes. The Dunedin volcano consists of lavas with very varied compositions, from basalt to trachyte/phonolite. Some of these later rock types also contain inclusions from the mantle and hence provide a means to testing hypotheses of magma generation, evolution and ascent.
Contact Marco Brenna
Magma ascent dynamics
How does a body of magma leave its source and ascend? This question is addressed through the study of mantle-derived crystal inclusions (xenocrysts/xenoliths) by a variety of microanalytical techniques, including laser-ablation ICP, electron microprobe and the Australian Synchrotron. The ultimate goal is to determine magma ascent rates and incorporate these in models of magmatic behaviour in volcanic systems such as the Auckland Volcanic Field or the older volcanoes of Eastern Otago.
Contact Marco Brenna
This one is broad and will probably involve multiple projects. An area of special interest is Hopi Buttes volcanic field, in northeastern Arizona, USA, where remnants of hundreds of volcanoes are exposed at a range of erosional levels. Current work is providing some fascinating advances on work done in the late 1980s', and will challenge many explanations for how such volcanoes operate. The next phase of work will relate experiments (below) and fieldwork on the dike/conduit transition, some examples of which are spectacularly exposed in the field.
Work with experimental groups in Germany and the USA is expected to continue. In Buffalo, New York, field-scale experiments on excavation of craters and diatremes began this year with one Otago student involved. The experiments relate to maar-diatreme volcanism, and may lead to new field studies or supplement ongoing ones. Similarly, work with colleagues in Wuerzburg, Germany has included experimental magma-water interactions of interest for both submarine eruptions and maar-diatreme explosions, and lab-scale gas-decompression explosions that produce craters and related depositional features in granular substrates.
Opportunities to work on interesting volcanic questions arise in many ways. If you're a student interested in postgraduate volcanology at Otago, contact James.