The general properties of micropulsations are reviewed, together with some theories of their origin. A particular study is made of the hydromagnetic wave theory and of the probability of these waves being produced by gyrating charged particles in the magnetosphere. The conditions are discussed under which gyration-induced hydromagnetic waves have frequencies within the micropulsation range. Assuming the production of Alfvén waves by some process in the magnetosphere, a layer model is developed to investigate the transmission of these waves down along the Earth’s magnetic field lines to the ionosphere. One feature of this model is a realistic ionospheric termination, in which a phase shift and amplitude reduction may be introduced into back reflected waves. Calculations using the model indicate a definite harmonic structure associated with micropulsations and only a small variation of frequency with geomagnetic latitude; they also provide a good explanation of the frequency structure and diurnal variation of ‘pearls’.

The most common hazards for communities surrounding mountain‐forming stratovolcanoes are mass flows of a range of types. Determining their frequency,characteristics and distribution is a major focus of hazard mapping efforts. Recent improvements in computer power and numerical models have meant that simulation of mass flow scenarios is a new tool available for hazard analysis. Its application to hazard mapping, land use planning and emergency management awaits robust evaluation of the conditions under which simulation tools are effective. This study focuses on this question in attempting to improve mass‐flow hazard assessments at the typical stratovolcanoes of Mts. Taranaki and Ruapehu in New Zealand. On Mt. Ruapehu, Titan2D modelling was applied to forecast behaviour of non‐cohesive lahars in the Whangaehu River, primarily produced by Crater Lake break‐outs, such as on 18 March 2007. The simulations were accurate in predicting inundation area, bifurcation, super‐elevation, hydraulic ponding, velocity and travel times of the lahar to 9‐10 km. A 6 x 10[exponent 6] m³ simulated granular flow had a minimum discharge of 1800‐2100 m³/s at the apex of the Whangaehu Fan, 9‐10 km from source, comparable to all historic information. The modelling implied that it was highly unlikely for a flow of this nature to overtop a lahar training dyke (bund) at the fan‐apex location and avulse northward into a more vulnerable catchment. Beyond this point, the model could not cope with the rapid and complex changes in rheology of these non‐cohesive lahars. At Mt. Taranaki chronostratigraphic grouping of mapped past lahar deposits often clouds the actual series of landscape forming processes and hence variations in hazard that occurred over time. Here, patterns of mass flows following emplacement of a 7 km³ debris avalanche deposit were examined from field geology and Titan2D modelling to define a three‐stage recovery process, where lahars of different types and sources were focused initially beside and later on top of the debris avalanche deposit for up to 10 000 years. Results from Titan2D were used to identify source areas of mass flows at different stages and their probable rheologies. Debris avalanche emplacement at Mt. Taranaki was investigated on the c. 7 ka B.P. Opua Formation with the help of Titan2D simulations to identify initial collapse parameters and major flow paths. Once again, the simulations were reliable in proximal reaches, but could not reproduce the rheological transformations from an initial collapsing/sliding pile through to a cohesive clay‐rich flow with long runout. In a further example, past block‐and‐ash flows (BAFs) and dense pyroclastic flow deposits northwest of the current crater were analysed to define the range of realistic model parameters for Titan2D simulations. These could be incorporated inside aGeographic Information System to produce a gradational map of relative probabilities of inundation by future BAF events that took both modelling and geological variability into account. This study highlights that computational models are now reaching the stage where a holistic approach can be taken to hazard analysis that combines both geological mapping and simulation of mass flow scenarios in a probabilistic framework to provide better tools for decision makers and land‐use planners.

The Karikari Plutonics are Early Miocene in age and consist of two plutonic bodies, with age relations delineated by cross- cutting relationships, and associated later stage dykes. The older pluton is a complex body exhibiting textural variability, cumulate-style crystallisation, varied enclaves (indicating complex magma chamber processes including convection and crystallisation along steeply-dipping northwest oriented fronts) and a multi-phase structural and dyke intrusion history. Modal analysis shows this body to be diorite to quartz monzodiorite, and geochemically calc-alkaline and medium-K in nature. In contrast the younger pluton is extremely homogeneous and intruded by a single, volumetrically sparse, dyke phase. Modally quartz monzonite to granite (adamellite), and high-K calc- alkaline, this body has higher Si, K-group + Na, REE group and HFSE group elements than the older pluton. Mineral differences are confined to An contents in plagioclase, En values in orthopyroxenes and a wider range of Al in younger pluton hornblendes. Igneous differentiation can be modelled within the older pluton and between the older and younger bodies, by fractional crystallisation dominated by plagioclase, with subordinate ortho- and clino- pyroxene and oxide phases. The dykes show a compositional range from basaltic andesite to dacite, with andesite volumetrically dominant. A temporal trend can be seen with younger dykes becoming more felsic and of greater volume, and changing orientation from northeast to northwest. Two subdivisions can be made based on the presence or absence of hornblende. Pyroxene only dykes are mostly medium-K and dominantly andesitic, whereas hornblende-bearing lithologies are both medium-K and high-K, are andesite and dacite, and appear to be more evolved chemically. The rock envelope into which the Karikari Plutonics was intruded consists of Cretaceousage basalts, rhyolites and sedimentary lithologies. Although a regular contact aureole is not exposed, the lowest grade of contact metamorphism is delineated by the first occurrence of biotite. Rocks equivalent to the hornblende hornfels facies are widespread and rare pyroxene hornfels are found adjacent to contacts. Alteration and veining, particularly prevalent in fault/shear zones, and the presence of a magmatic-hydrothermal type breccia are evidence for a hydrothermal system associated with the waning stages of Lower Miocene-age igneous activity on the Karikari Peninsula. Fluid inclusion and stable isotope data indicates the presence of fluids of both magmatic and meteoric origin. The Karikari Plutonics are correlated with the arc-type regional association of Northland and the Coromandel Peninsula. The source of these rocks is broadly M-type, hydrous and involving subduction zone, and modified mantle wedge components, but with some unspecified crustal involvement indicated by Sr isotopes. Specifically this source is modelled, for the Karikari Plutonics, as having LREE enriched 2x relative to HREE and partially melting (< 15% of the source) at the base of the crust (≥30 km). These melts gave rise to the arc-type association either erupting at the surface, or ponding in upper crustal (≤10 km) magma chambers.

The Karikari Plutonics are Early Miocene in age and consist of two plutonic bodies, with age relations delineated by cross- cutting relationships, and associated later stage dykes. The older pluton is a complex body exhibiting textural variability, cumulate-style crystallisation, varied enclaves (indicating complex magma chamber processes including convection and crystallisation along steeply-dipping northwest oriented fronts) and a multi-phase structural and dyke intrusion history. Modal analysis shows this body to be diorite to quartz monzodiorite, and geochemically calc-alkaline and medium-K in nature. In contrast the younger pluton is extremely homogeneous and intruded by a single, volumetrically sparse, dyke phase. Modally quartz monzonite to granite (adamellite), and high-K calc- alkaline, this body has higher Si, K-group + Na, REE group and HFSE group elements than the older pluton. Mineral differences are confined to An contents in plagioclase, En values in orthopyroxenes and a wider range of Al in younger pluton hornblendes. Igneous differentiation can be modelled within the older pluton and between the older and younger bodies, by fractional crystallisation dominated by plagioclase, with subordinate ortho- and clino- pyroxene and oxide phases. The dykes show a compositional range from basaltic andesite to dacite, with andesite volumetrically dominant. A temporal trend can be seen with younger dykes becoming more felsic and of greater volume, and changing orientation from northeast to northwest. Two subdivisions can be made based on the presence or absence of hornblende. Pyroxene only dykes are mostly medium-K and dominantly andesitic, whereas hornblende-bearing lithologies are both medium-K and high-K, are andesite and dacite, and appear to be more evolved chemically. The rock envelope into which the Karikari Plutonics was intruded consists of Cretaceousage basalts, rhyolites and sedimentary lithologies. Although a regular contact aureole is not exposed, the lowest grade of contact metamorphism is delineated by the first occurrence of biotite. Rocks equivalent to the hornblende hornfels facies are widespread and rare pyroxene hornfels are found adjacent to contacts. Alteration and veining, particularly prevalent in fault/shear zones, and the presence of a magmatic-hydrothermal type breccia are evidence for a hydrothermal system associated with the waning stages of Lower Miocene-age igneous activity on the Karikari Peninsula. Fluid inclusion and stable isotope data indicates the presence of fluids of both magmatic and meteoric origin. The Karikari Plutonics are correlated with the arc-type regional association of Northland and the Coromandel Peninsula. The source of these rocks is broadly M-type, hydrous and involving subduction zone, and modified mantle wedge components, but with some unspecified crustal involvement indicated by Sr isotopes. Specifically this source is modelled, for the Karikari Plutonics, as having LREE enriched 2x relative to HREE and partially melting (< 15% of the source) at the base of the crust (≥30 km). These melts gave rise to the arc-type association either erupting at the surface, or ponding in upper crustal (≤10 km) magma chambers.

The Karikari Plutonics are Early Miocene in age and consist of two plutonic bodies, with age relations delineated by cross- cutting relationships, and associated later stage dykes. The older pluton is a complex body exhibiting textural variability, cumulate-style crystallisation, varied enclaves (indicating complex magma chamber processes including convection and crystallisation along steeply-dipping northwest oriented fronts) and a multi-phase structural and dyke intrusion history. Modal analysis shows this body to be diorite to quartz monzodiorite, and geochemically calc-alkaline and medium-K in nature. In contrast the younger pluton is extremely homogeneous and intruded by a single, volumetrically sparse, dyke phase. Modally quartz monzonite to granite (adamellite), and high-K calc- alkaline, this body has higher Si, K-group + Na, REE group and HFSE group elements than the older pluton. Mineral differences are confined to An contents in plagioclase, En values in orthopyroxenes and a wider range of Al in younger pluton hornblendes. Igneous differentiation can be modelled within the older pluton and between the older and younger bodies, by fractional crystallisation dominated by plagioclase, with subordinate ortho- and clino- pyroxene and oxide phases. The dykes show a compositional range from basaltic andesite to dacite, with andesite volumetrically dominant. A temporal trend can be seen with younger dykes becoming more felsic and of greater volume, and changing orientation from northeast to northwest. Two subdivisions can be made based on the presence or absence of hornblende. Pyroxene only dykes are mostly medium-K and dominantly andesitic, whereas hornblende-bearing lithologies are both medium-K and high-K, are andesite and dacite, and appear to be more evolved chemically. The rock envelope into which the Karikari Plutonics was intruded consists of Cretaceousage basalts, rhyolites and sedimentary lithologies. Although a regular contact aureole is not exposed, the lowest grade of contact metamorphism is delineated by the first occurrence of biotite. Rocks equivalent to the hornblende hornfels facies are widespread and rare pyroxene hornfels are found adjacent to contacts. Alteration and veining, particularly prevalent in fault/shear zones, and the presence of a magmatic-hydrothermal type breccia are evidence for a hydrothermal system associated with the waning stages of Lower Miocene-age igneous activity on the Karikari Peninsula. Fluid inclusion and stable isotope data indicates the presence of fluids of both magmatic and meteoric origin. The Karikari Plutonics are correlated with the arc-type regional association of Northland and the Coromandel Peninsula. The source of these rocks is broadly M-type, hydrous and involving subduction zone, and modified mantle wedge components, but with some unspecified crustal involvement indicated by Sr isotopes. Specifically this source is modelled, for the Karikari Plutonics, as having LREE enriched 2x relative to HREE and partially melting (< 15% of the source) at the base of the crust (≥30 km). These melts gave rise to the arc-type association either erupting at the surface, or ponding in upper crustal (≤10 km) magma chambers.

The Karikari Plutonics are Early Miocene in age and consist of two plutonic bodies, with age relations delineated by cross- cutting relationships, and associated later stage dykes. The older pluton is a complex body exhibiting textural variability, cumulate-style crystallisation, varied enclaves (indicating complex magma chamber processes including convection and crystallisation along steeply-dipping northwest oriented fronts) and a multi-phase structural and dyke intrusion history. Modal analysis shows this body to be diorite to quartz monzodiorite, and geochemically calc-alkaline and medium-K in nature. In contrast the younger pluton is extremely homogeneous and intruded by a single, volumetrically sparse, dyke phase. Modally quartz monzonite to granite (adamellite), and high-K calc- alkaline, this body has higher Si, K-group + Na, REE group and HFSE group elements than the older pluton. Mineral differences are confined to An contents in plagioclase, En values in orthopyroxenes and a wider range of Al in younger pluton hornblendes. Igneous differentiation can be modelled within the older pluton and between the older and younger bodies, by fractional crystallisation dominated by plagioclase, with subordinate ortho- and clino- pyroxene and oxide phases. The dykes show a compositional range from basaltic andesite to dacite, with andesite volumetrically dominant. A temporal trend can be seen with younger dykes becoming more felsic and of greater volume, and changing orientation from northeast to northwest. Two subdivisions can be made based on the presence or absence of hornblende. Pyroxene only dykes are mostly medium-K and dominantly andesitic, whereas hornblende-bearing lithologies are both medium-K and high-K, are andesite and dacite, and appear to be more evolved chemically. The rock envelope into which the Karikari Plutonics was intruded consists of Cretaceousage basalts, rhyolites and sedimentary lithologies. Although a regular contact aureole is not exposed, the lowest grade of contact metamorphism is delineated by the first occurrence of biotite. Rocks equivalent to the hornblende hornfels facies are widespread and rare pyroxene hornfels are found adjacent to contacts. Alteration and veining, particularly prevalent in fault/shear zones, and the presence of a magmatic-hydrothermal type breccia are evidence for a hydrothermal system associated with the waning stages of Lower Miocene-age igneous activity on the Karikari Peninsula. Fluid inclusion and stable isotope data indicates the presence of fluids of both magmatic and meteoric origin. The Karikari Plutonics are correlated with the arc-type regional association of Northland and the Coromandel Peninsula. The source of these rocks is broadly M-type, hydrous and involving subduction zone, and modified mantle wedge components, but with some unspecified crustal involvement indicated by Sr isotopes. Specifically this source is modelled, for the Karikari Plutonics, as having LREE enriched 2x relative to HREE and partially melting (< 15% of the source) at the base of the crust (≥30 km). These melts gave rise to the arc-type association either erupting at the surface, or ponding in upper crustal (≤10 km) magma chambers.

No description available.

The Quaternary geology of Chatham Island has been investigated using several different techniques, including: tephrochronology, mineralogy, palynology and stratigraphy; in an attempt to draw together a Quaternary history for the Island. The Quaternary record of Chatham Island comprises mainly deposits from terrestrial environments, predominantly thick blanket peats and aeolian sand, all of which range from latest Castlecliffian to Haweran/Recent in age. Quaternary deposits that demonstratably predate this age range (i.e. > Oxygen Isotope Stage 12) have not been recognised anywhere on the Island. Their absence is, at this stage, attributed to a major marine transgression across much of the northern and central portions of the Island during Oxygen Isotope Stage 11. Two rhyolitic tephra produced during two of the largest eruptions from the Taupo Volcanic Zone are present on Chatham Island. The 27.1 ka Kawakawa Tephra is well preserved across most of the Island, occurring within most pre-Holocene sequences. The 345 ka Rangitawa Tephra, not previously recognised on Chatham Island, is found in a few scattered coastal locations where older, late Castlecliffian sediments are preserved. In the absence of any other forms of radiometric age control these two tephras have provided the principal means for time control within and between stratigraphic sequences on the Island. Palynology has been used predominantly to determine climatic conditions at the time of sediment accumulation. Palynological investigations of seven sections of peat deposits have also demonstrated that cyclic changes in vegetation patterns have occurred throughout the Quaternary on Chatham Island. However these changes have not been as significant as those that occurred on mainland New Zealand over the Quaternary. It is concluded that this indicates climatic deterioration during glacials may not have been as pronounced on Chatham Island as on the mainland. Marine terraces created during former high sea level stands are preserved in several areas on Chatham Island. Quaternary terrace surfaces ranging in age from Last Interglacial (OIS 5e) to OIS 11 occur at heights of 3-5 m, 9 – 10 m, 16 m, 20 m and 30 - 40 m above sea level. An exhumed surface of Late Pliocene age occurs at 7 – 14 m a.s.l.. Terrace ages have been determined using cover-bed stratigraphy, and in particular the presence or absence of tephra marker beds. Height-age relationships of marine terraces have been used to develop preliminary rates of tectonic uplift on Chatham Island. The resulting values range between 0.01 – 0.13 mm/yr and are very low compared with more tectonically active areas of mainland New Zealand. However, there is considerable variation in these rates across Chatham Island, indicating that the tectonic history of the Island over the Quaternary may be complex. This thesis has also demonstrated that considerably more work is required to fully understand the Quaternary history of Chatham Island. In particular, better numerical age control on key deposits; more detailed, high-resolution pollen records from key locations; and obtaining stratigraphic records from a greater range of locations. This is particularly so for the southern uplands where older records are virtually inaccessible due to a thick blanketing of post-glacial peat deposits.

This study attempts to determine a relative age of the Wahianoa moraines, Mt Ruapehu using three relative age dating techniques: Lichenometry, Schmidt hammer and Boulder roundness. There were three study areas used, termed the Wahianoa ‘A’, ‘B’ and ‘C’ moraines. Upon determining a relative age for these moraines, their timing of their formation was placed within New Zealand’s glacial timescale. This is the first study of its kind conducted on Mt Ruapehu and has left the door open for more research in this field. The species of lichens measured on the Wahianoa moraines were Rhizocarpon subgenus, which the largest diameters were measured using callipers. A total of 606 lichens were measured in the Wahianoa Valley and were processed using the growth curve and size frequency methods. A lichenometric growth curve was constructed from lichens growing in the Ohakune cemetery. The dates derived from both methods placed the formation of the Wahianoa moraines during the Little Ice Age. An L-type Schmidt hammer was used on the boulders in the Wahianoa Valley. A total of 280 measurements were taken off the boulders on the Wahianoa moraines. The results of this method, when compared to Winkler’s (2005) study in the South Island placed the formation of the Wahianoa moraines pre-Little Ice Age. Although no definitive ages could be derived from this comparison due to differences in lithology between the two studies, it provided an idea as to where the formation of these moraines could belong. This is the first time that the Boulder roundness method has been used in New Zealand, having only been developed by Kirkbride (2005). This method was used to determine which of the ridges in the Wahianoa Valley were older. It was found that the Wahianoa ‘A’ moraines were the oldest in the valley followed by Wahianoa ‘B’ and ‘C’ respectively. A climate reconstruction was also conducted for the Wahianoa Valley to see what conditions may have been in existence during the formation of the Wahianoa moraines. The paleo-ELA for the Wahianoa Glacier was estimated using the Accumulation-Area Ratio (AAR), Terminus to Headwall Ratio (THAR), Maximum Elevation of the Lateral Moraines (MELM) and Extrapolation methods. The current ELA was estimated using the AAR, THAR and Extrapolation methods. The difference between these estimates was used to determine what temperature decrease would have caused the formation of the Wahianoa moraines. The average paleo-ELA was found to be c. 1715m, while the current ELA was found to be 2475m which lead to a 4.5°C decrease. This temperature decrease correlates well with that of the Last Glacial Maximum. This study found significant differences in relative age of the Wahianoa moraines. There are a number of factors that can affect the growth of lichens such as micro-environmentalconditions and the fact that a growth curve was constructed off site. Factors such aspetrography can affect the Schmidt hammer results and the Boulder roundness measurements. In addition, precipitation can affect the ELA values which can then cause the wrong placement within a glacial event. Further research lies in the use of the Schmidt hammer on a known age surface such as the Mangatepopo moraines which will aide in a better correlation of relative age. Also, further research using climate reconstructions on Mt Ruapehu and the effect of precipitation will also aide in a better correlation with a glacial event.

Andesitic volcanoes are notorious for their rapid and unpredictable changes in eruptive style between and during volcanic events, a feature normally attributed to shallow crustal and intra-edifice magmatic processes. Using the example of eruptions during the last 1000 yrs at Mt. Taranaki (the Maero Eruptive Period), deposit sequences were studied to (1) understand lava dome formation and destruction, (2) interpret the causes of rapid shifts from extrusive to explosive eruption styles, and (3) to build a model of crustal magmatic processes that impact on eruption style. A new detailed reconstruction of this period identifies at least 10 eruptive episodes characterised by extrusive, lava dome- and lava flow-producing events and one sub- Plinian eruption. To achieve this, a new evaluation procedure was developed to purge glass datasets of contaminated mineral-glass analyses by using compositional diagrams of mineral incompatible-compatible elements. Along with careful examination of particle textures, this procedure can be broadly applied to build a higher degree of resolution in any tephrostratigraphic record. Geochemical contrasts show that the products of the latest Mt. Taranaki eruption, the remnant summit dome (Pyramid Dome) was not formed during the Tahurangi eruptive episode but extruded post-AD1755. Its inferred original maximum volume of 4.9×106 m3 (DRE) was formed by simultaneous endogenous and exogenous dome growth within days. Magma ascent and extrusion rates are estimated at =0.012 ms-1 and =6 m3s-1, respectively, based on hornblende textures. Some of the Maero-Period dome effusions were preceded by a vent-clearing phase producing layers of scattered lithic lapilli around the edifice [Newall Ash (a), Mangahume Lapilli, Pyramid Lapilli]. The type of dome failure controlled successive eruptive phases in most instances. The destruction of a pressurised dome either caused instantaneous but short-lived magmatic fragmentation (Newall and Puniho episodes), or triggered a directed blast-explosion (Newall episode), or initiated sustained magmatic fragmentation (Burrell Episode). The transition from dome effusion to a sustained, sub- Plinian eruption during the Burrell Lapilli (AD1655) episode was caused by unroofing a conduit of stalled magma, vertically segregated into three layers with different degrees of vesiculation and crystallisation. The resultant ejecta range from brown, grey and black coloured vesicular clasts to dense grey lithics. Bulk compositional variation of erupted clasts can be modelled by fractionation of hornblende, plagioclase, clinopyroxene, and Fe-Ti oxides. Pre-eruption magma ascent for the Maero Period events is assumed to begin at depths of c.9.5 km.