The stratigraphic record of lahars in the Whangaehu River reveals that in the past 180,000 years this route has been one of the main conduits for lahars from Mount Ruapehu, the highest active andesitic stratovolcano in the Central North Island of New Zealand. Both debris flows and hyperconcentrated flows have engulfed surfaces up to 160 km distance from the Volcano. Eight episodes of laharic activity are recognized by the distinctive lithology and similar age of their deposits. The newly defined upper Pleistocene Whangaehu Formation provides evidence for the earliest lahar event in the Valley, c. 180,000- 140,000 years ago. There is only meagre evidence for laharic activity following this event until the Ohakean and Holocene, although two new informally named deposits - the Mangatipona pumice sand (c. 37,000 years B.P.) and Apitian lahars (c. 32,000-25,500 years B.P) - are recognized, of minor extent. The formerly defined late Quaternary Te Heuheu (c. 25,500- 14,700 years B.P.), Tangatu (c. 14,700-5,370 years B.P.), Manutahi (c. 5 ,370-3,4600 years B.P.), Mangaio (c. 4,600 years B.P.) and Onetapu (< c. 1,850 years B.P.) Formations are here described and interpreted. Triggering mechanisms for lahar deposits are distinguished based on lithological criteria. (a) Bouldery deposits in the Whangaehu Formation are interpreted to have been emplaced by a single highly competent debris flow triggered by a southerly-directed flank collapse at Mount Ruapehu. This debris flow was competent enough to transport boulders up to 2 m in diameter over 140 km from the Volcano. Bouldery deposits are also recognized in the Onetapu Formation, but are restricted to higher gradient surfaces on the Mount Ruapehu ring plain. The Onetapu Formation deposits are interpreted to have been emplaced by lahars resulting from catastrophic drainage of Crater Lake, which occupies the active crater on Mount Ruapehu. (b) Pebbly and sandy deposits are interpreted to have been emplaced by low competence debris flows and hyperconcentrated flows. These lahar deposits are recognized in all formations described. The lithology in these deposits is commonly pumice and they are interpreted to have been triggered by eruptions and/or high rainfall events at the Volcano. Formations, and individual members within Formations, were dated by radiocarbon dating of organic material found below, within or above lahar deposits, or by coverbed stratigraphy. Both rhyolitic and andesitic tephras provided recognizable time planes in the late Quaternary coverbeds overlying lahar deposits. In this study quantitative analysis of quartz abundance, which is shown to vary between loesses and palaeosols, is used as an indirect means of establishing a surrogate for past climate changes which have been correlated to the deep sea oxygen isotope curve. A minimum age for the newly defined Whangaehu Formation is established by this method. The accumulation rate for lahars in the Whangaehu River has accelerated from 1 km3 every c. 23,000 years in the past c. 160,000 years to 1 km3 in 589 years in the past c. 2,000 years. This acceleration probably results from the increased frequency of lahars in the River following the development of Crater Lake c. 2,000 years B.P. According to this pattern an estimated 0.17 km3 volume of lahars could be anticipated over the next 100 years. If the 2,000 year accumulation rate were to be met over the next 100 years there would be 170 lahars of l0[superscript]6 m3 in this time interval , or 17 lahars of 10[superscript]7 m3 (or 1.7 lahars of 10[superscript]8 m3). The largest reported volume for an historic lahar is 10[superscript]6 m3 and these have occurred on average once every 30 years. The accumulation rate for historic lahars is 0.0054 km3 in 100 years. Therefore, although the accumulation rate appears to have slowed down, further large lahars with magnitudes 10 or 100 times greater than those witnessed could be expected.

The stratigraphic record of lahars in the Whangaehu River reveals that in the past 180,000 years this route has been one of the main conduits for lahars from Mount Ruapehu, the highest active andesitic stratovolcano in the Central North Island of New Zealand. Both debris flows and hyperconcentrated flows have engulfed surfaces up to 160 km distance from the Volcano. Eight episodes of laharic activity are recognized by the distinctive lithology and similar age of their deposits. The newly defined upper Pleistocene Whangaehu Formation provides evidence for the earliest lahar event in the Valley, c. 180,000- 140,000 years ago. There is only meagre evidence for laharic activity following this event until the Ohakean and Holocene, although two new informally named deposits - the Mangatipona pumice sand (c. 37,000 years B.P.) and Apitian lahars (c. 32,000-25,500 years B.P) - are recognized, of minor extent. The formerly defined late Quaternary Te Heuheu (c. 25,500- 14,700 years B.P.), Tangatu (c. 14,700-5,370 years B.P.), Manutahi (c. 5 ,370-3,4600 years B.P.), Mangaio (c. 4,600 years B.P.) and Onetapu (< c. 1,850 years B.P.) Formations are here described and interpreted. Triggering mechanisms for lahar deposits are distinguished based on lithological criteria. (a) Bouldery deposits in the Whangaehu Formation are interpreted to have been emplaced by a single highly competent debris flow triggered by a southerly-directed flank collapse at Mount Ruapehu. This debris flow was competent enough to transport boulders up to 2 m in diameter over 140 km from the Volcano. Bouldery deposits are also recognized in the Onetapu Formation, but are restricted to higher gradient surfaces on the Mount Ruapehu ring plain. The Onetapu Formation deposits are interpreted to have been emplaced by lahars resulting from catastrophic drainage of Crater Lake, which occupies the active crater on Mount Ruapehu. (b) Pebbly and sandy deposits are interpreted to have been emplaced by low competence debris flows and hyperconcentrated flows. These lahar deposits are recognized in all formations described. The lithology in these deposits is commonly pumice and they are interpreted to have been triggered by eruptions and/or high rainfall events at the Volcano. Formations, and individual members within Formations, were dated by radiocarbon dating of organic material found below, within or above lahar deposits, or by coverbed stratigraphy. Both rhyolitic and andesitic tephras provided recognizable time planes in the late Quaternary coverbeds overlying lahar deposits. In this study quantitative analysis of quartz abundance, which is shown to vary between loesses and palaeosols, is used as an indirect means of establishing a surrogate for past climate changes which have been correlated to the deep sea oxygen isotope curve. A minimum age for the newly defined Whangaehu Formation is established by this method. The accumulation rate for lahars in the Whangaehu River has accelerated from 1 km3 every c. 23,000 years in the past c. 160,000 years to 1 km3 in 589 years in the past c. 2,000 years. This acceleration probably results from the increased frequency of lahars in the River following the development of Crater Lake c. 2,000 years B.P. According to this pattern an estimated 0.17 km3 volume of lahars could be anticipated over the next 100 years. If the 2,000 year accumulation rate were to be met over the next 100 years there would be 170 lahars of l0[superscript]6 m3 in this time interval , or 17 lahars of 10[superscript]7 m3 (or 1.7 lahars of 10[superscript]8 m3). The largest reported volume for an historic lahar is 10[superscript]6 m3 and these have occurred on average once every 30 years. The accumulation rate for historic lahars is 0.0054 km3 in 100 years. Therefore, although the accumulation rate appears to have slowed down, further large lahars with magnitudes 10 or 100 times greater than those witnessed could be expected.

The Oligocene Te Kuiti Group in Waitomo County, North Island, New Zealand, is divided into two subgroups, six formations and seven limestone members; six of the members are new. The stratigraphic definition, distribution, thickness, lithology and contacts of major rock units, and the three dimensional relationships between them, are described and figured in detail. Rapid lateral and vertical lithologic variation in strata is accomodated by recognition of 31 lithofacies. Te Kuiti sediments, which include mainly bioclastic lutites, bioclastic arenites and biocalcarenites, were deposited in sublittoral waters, from a few to about 100 metres depth, as seas transgressed south over a topoqraphically subdued, but locally varied landscape cut in Mesozoic lutites and arenites. Distribution of major paleotectonic elements indicates the gross sedimentary environment was one of a north-facing, partly enclosed basin with a prominent north-trending median basement ridge (Piopio High) in the south. Deposition continued until this ridge was almost completely buried, at which time the Te Kuiti embayment expanded rapidly and linked with more southerly basins. The contact with the overlying Mahoenui Group is generally conformable in Waitomo County. Formations and members are commonly bounded by unconformities, mainly disconformities, some of which preserve features consistent with their interpretation as submarine hardgrounds. The unconformities record periods of erosion or non-deposition during major downward shifts in base level controlled partly by eustatic sea level changes. Comprehensive paleontological charts are prepared for each formation and age relationships established. Macrofossils are generally scarce, and dominated by thick-shelled, epifaunal bivalves. Foraminifera are more abundant and are mainly benthonic forms. Formations may straddle New Zealand stage boundaries and, within Waitomo County, are not strongly diachronous. Primary sedimentary structures in arenites and calcarenites include mainly thinly bedded wavy-, lenticular-, and cross-stratification formed by the spreading and interfering of sand sheets, sand ribbons and sand waves across extensive areas of flat shallow sea floor, possibly under the influence of tidal currents. Lutites and muddy arenites are massive and bioturbated. A new classification for mixed terrigenous-allochemical rocks is proposed and an X-ray technique developed for modal analyses of lutites. The petrography of individual lithofacies is described and illustrated in detail and summarised on pie diagrams. Variations in the kind, quantity, size, sorting and abrasion of bioclasts, in the king and quantity of matrix add/or cement, and in the content of glauconite and terrigenous sand and mud serve to distinguish the various lithofacies. Bioclasts are derived principally from bryozoans, echinoids and benthonic foraminifers and, to a lesser extent, from coralline algae, planktonic foraminifers, molluscs and brachiopods. Siliciclasts include mainly quartz, oligoclase – andesine plagioclase, potash feldspar, montmorillonitic clays and glauconite. Quartz and feldspar were detritally inherited from Mesozoic basement rocks; montmorillonite formed from the marine diagenetic transformation of vermiculite and degraded chlorite and illite derived from Oligocene soils; glauconite developed from mont-morillonitic clays under specific environmental conditions. Complete chemical analyses of seven glauconite concentrates are presented and compared with published analyses. The principal non-opaque heavy minerals in the group are zircon, epidote and apatite. Sediment pores are infilled with granular and rim ortho-sparite cement, or by a variety of matrix materials, including micrite, calcilutite and lutite. Petrologs display the vertical variation in petrographic properties through the group and, in conjunction with grain size analyses of insoluble residues, are used to interpret the energy level of the environment of deposition of individual rock units. Te Kuiti sediments accumulated under a spectrum of environmental energy conditions, ranging from quiet to strongly agitated waters. The primary Te Kuiti sediment was dominated by metastable magnesium calcite and, less abundant, aragonite skeletons. These skeletons underwent syndiagenetic stablisation reactions at, or close below, the sea floor. Large quantities of skeletal aragonite were dissolved from the sediment before lithification. Aragonite was preserved only where anaerobic conditions were maintained in the sediment. Stabilisation of magnesium calcite grains involved the texturally non-destructive process of incongruent dissolution, which yielded a replacement product of calcite. Sources of CaCO3 for cement included (a) solution of aragonite grains, (b) intergranular solution of bioclasts and, most important, (c) pervasive solution of bioclasts, under shallow burial loads, at those levels in the sediment relatively enrichment in siliciclastic, and especially muddy, material. Dissolved CaCO3 was precipitated as calcite cement in adjacent or nearby sediment layers. A paragenetic sequence of diagenetic events is established for the group. Finally, Oligocene paleogeography and paleoclimate are outlined and a synthesis of the environment of formation and depositional history of sediments of the Te Kuiti Group in Waitomo Country is established.

The Oligocene Te Kuiti Group in Waitomo County, North Island, New Zealand, is divided into two subgroups, six formations and seven limestone members; six of the members are new. The stratigraphic definition, distribution, thickness, lithology and contacts of major rock units, and the three dimensional relationships between them, are described and figured in detail. Rapid lateral and vertical lithologic variation in strata is accomodated by recognition of 31 lithofacies. Te Kuiti sediments, which include mainly bioclastic lutites, bioclastic arenites and biocalcarenites, were deposited in sublittoral waters, from a few to about 100 metres depth, as seas transgressed south over a topoqraphically subdued, but locally varied landscape cut in Mesozoic lutites and arenites. Distribution of major paleotectonic elements indicates the gross sedimentary environment was one of a north-facing, partly enclosed basin with a prominent north-trending median basement ridge (Piopio High) in the south. Deposition continued until this ridge was almost completely buried, at which time the Te Kuiti embayment expanded rapidly and linked with more southerly basins. The contact with the overlying Mahoenui Group is generally conformable in Waitomo County. Formations and members are commonly bounded by unconformities, mainly disconformities, some of which preserve features consistent with their interpretation as submarine hardgrounds. The unconformities record periods of erosion or non-deposition during major downward shifts in base level controlled partly by eustatic sea level changes. Comprehensive paleontological charts are prepared for each formation and age relationships established. Macrofossils are generally scarce, and dominated by thick-shelled, epifaunal bivalves. Foraminifera are more abundant and are mainly benthonic forms. Formations may straddle New Zealand stage boundaries and, within Waitomo County, are not strongly diachronous. Primary sedimentary structures in arenites and calcarenites include mainly thinly bedded wavy-, lenticular-, and cross-stratification formed by the spreading and interfering of sand sheets, sand ribbons and sand waves across extensive areas of flat shallow sea floor, possibly under the influence of tidal currents. Lutites and muddy arenites are massive and bioturbated. A new classification for mixed terrigenous-allochemical rocks is proposed and an X-ray technique developed for modal analyses of lutites. The petrography of individual lithofacies is described and illustrated in detail and summarised on pie diagrams. Variations in the kind, quantity, size, sorting and abrasion of bioclasts, in the king and quantity of matrix add/or cement, and in the content of glauconite and terrigenous sand and mud serve to distinguish the various lithofacies. Bioclasts are derived principally from bryozoans, echinoids and benthonic foraminifers and, to a lesser extent, from coralline algae, planktonic foraminifers, molluscs and brachiopods. Siliciclasts include mainly quartz, oligoclase – andesine plagioclase, potash feldspar, montmorillonitic clays and glauconite. Quartz and feldspar were detritally inherited from Mesozoic basement rocks; montmorillonite formed from the marine diagenetic transformation of vermiculite and degraded chlorite and illite derived from Oligocene soils; glauconite developed from mont-morillonitic clays under specific environmental conditions. Complete chemical analyses of seven glauconite concentrates are presented and compared with published analyses. The principal non-opaque heavy minerals in the group are zircon, epidote and apatite. Sediment pores are infilled with granular and rim ortho-sparite cement, or by a variety of matrix materials, including micrite, calcilutite and lutite. Petrologs display the vertical variation in petrographic properties through the group and, in conjunction with grain size analyses of insoluble residues, are used to interpret the energy level of the environment of deposition of individual rock units. Te Kuiti sediments accumulated under a spectrum of environmental energy conditions, ranging from quiet to strongly agitated waters. The primary Te Kuiti sediment was dominated by metastable magnesium calcite and, less abundant, aragonite skeletons. These skeletons underwent syndiagenetic stablisation reactions at, or close below, the sea floor. Large quantities of skeletal aragonite were dissolved from the sediment before lithification. Aragonite was preserved only where anaerobic conditions were maintained in the sediment. Stabilisation of magnesium calcite grains involved the texturally non-destructive process of incongruent dissolution, which yielded a replacement product of calcite. Sources of CaCO3 for cement included (a) solution of aragonite grains, (b) intergranular solution of bioclasts and, most important, (c) pervasive solution of bioclasts, under shallow burial loads, at those levels in the sediment relatively enrichment in siliciclastic, and especially muddy, material. Dissolved CaCO3 was precipitated as calcite cement in adjacent or nearby sediment layers. A paragenetic sequence of diagenetic events is established for the group. Finally, Oligocene paleogeography and paleoclimate are outlined and a synthesis of the environment of formation and depositional history of sediments of the Te Kuiti Group in Waitomo Country is established.

The Oligocene Te Kuiti Group in Waitomo County, North Island, New Zealand, is divided into two subgroups, six formations and seven limestone members; six of the members are new. The stratigraphic definition, distribution, thickness, lithology and contacts of major rock units, and the three dimensional relationships between them, are described and figured in detail. Rapid lateral and vertical lithologic variation in strata is accomodated by recognition of 31 lithofacies. Te Kuiti sediments, which include mainly bioclastic lutites, bioclastic arenites and biocalcarenites, were deposited in sublittoral waters, from a few to about 100 metres depth, as seas transgressed south over a topoqraphically subdued, but locally varied landscape cut in Mesozoic lutites and arenites. Distribution of major paleotectonic elements indicates the gross sedimentary environment was one of a north-facing, partly enclosed basin with a prominent north-trending median basement ridge (Piopio High) in the south. Deposition continued until this ridge was almost completely buried, at which time the Te Kuiti embayment expanded rapidly and linked with more southerly basins. The contact with the overlying Mahoenui Group is generally conformable in Waitomo County. Formations and members are commonly bounded by unconformities, mainly disconformities, some of which preserve features consistent with their interpretation as submarine hardgrounds. The unconformities record periods of erosion or non-deposition during major downward shifts in base level controlled partly by eustatic sea level changes. Comprehensive paleontological charts are prepared for each formation and age relationships established. Macrofossils are generally scarce, and dominated by thick-shelled, epifaunal bivalves. Foraminifera are more abundant and are mainly benthonic forms. Formations may straddle New Zealand stage boundaries and, within Waitomo County, are not strongly diachronous. Primary sedimentary structures in arenites and calcarenites include mainly thinly bedded wavy-, lenticular-, and cross-stratification formed by the spreading and interfering of sand sheets, sand ribbons and sand waves across extensive areas of flat shallow sea floor, possibly under the influence of tidal currents. Lutites and muddy arenites are massive and bioturbated. A new classification for mixed terrigenous-allochemical rocks is proposed and an X-ray technique developed for modal analyses of lutites. The petrography of individual lithofacies is described and illustrated in detail and summarised on pie diagrams. Variations in the kind, quantity, size, sorting and abrasion of bioclasts, in the king and quantity of matrix add/or cement, and in the content of glauconite and terrigenous sand and mud serve to distinguish the various lithofacies. Bioclasts are derived principally from bryozoans, echinoids and benthonic foraminifers and, to a lesser extent, from coralline algae, planktonic foraminifers, molluscs and brachiopods. Siliciclasts include mainly quartz, oligoclase – andesine plagioclase, potash feldspar, montmorillonitic clays and glauconite. Quartz and feldspar were detritally inherited from Mesozoic basement rocks; montmorillonite formed from the marine diagenetic transformation of vermiculite and degraded chlorite and illite derived from Oligocene soils; glauconite developed from mont-morillonitic clays under specific environmental conditions. Complete chemical analyses of seven glauconite concentrates are presented and compared with published analyses. The principal non-opaque heavy minerals in the group are zircon, epidote and apatite. Sediment pores are infilled with granular and rim ortho-sparite cement, or by a variety of matrix materials, including micrite, calcilutite and lutite. Petrologs display the vertical variation in petrographic properties through the group and, in conjunction with grain size analyses of insoluble residues, are used to interpret the energy level of the environment of deposition of individual rock units. Te Kuiti sediments accumulated under a spectrum of environmental energy conditions, ranging from quiet to strongly agitated waters. The primary Te Kuiti sediment was dominated by metastable magnesium calcite and, less abundant, aragonite skeletons. These skeletons underwent syndiagenetic stablisation reactions at, or close below, the sea floor. Large quantities of skeletal aragonite were dissolved from the sediment before lithification. Aragonite was preserved only where anaerobic conditions were maintained in the sediment. Stabilisation of magnesium calcite grains involved the texturally non-destructive process of incongruent dissolution, which yielded a replacement product of calcite. Sources of CaCO3 for cement included (a) solution of aragonite grains, (b) intergranular solution of bioclasts and, most important, (c) pervasive solution of bioclasts, under shallow burial loads, at those levels in the sediment relatively enrichment in siliciclastic, and especially muddy, material. Dissolved CaCO3 was precipitated as calcite cement in adjacent or nearby sediment layers. A paragenetic sequence of diagenetic events is established for the group. Finally, Oligocene paleogeography and paleoclimate are outlined and a synthesis of the environment of formation and depositional history of sediments of the Te Kuiti Group in Waitomo Country is established.

The long-term behaviour of andesitic stratovolcanoes is characterised by a repetition of edifice growth and collapse phases. This cyclic pattern may represent a natural frequency at varying timescales in the growth dynamics of stratovolcanoes, but is often difficult to identify because of long cycle-timescales, coupled with incomplete stratigraphic records. The volcaniclastic ring-plain succession surrounding the 2 518 m Mt. Taranaki, New Zealand, comprises a wide variety of distinctive volcanic mass-flow lithofacies with sedimentary and lithology characteristics that can be related to recurring volcanic cycles over >190 ka. Debrisflow and monolithologic hyperconcentrated-flow deposits record edifice growth phases while polylithologic debris-avalanche and associated cohesive debris-flow units were emplaced by collapse. Major edifice failures at Mt. Taranaki occurred on-average every 10 ka, with five events recognised over the last 30 ka, a time interval for which stratigraphic records are more complete. The unstable nature of Mt. Taranaki mainly results from its weak internal composite structure including abundant saturated pyroclastic deposits and breccia layers, along with its growth on a weakly indurated and tectonically fractured basement of Tertiary mudstones and sandstones. As the edifice repeatedly grew beyond a critical stable height or profile, large-scale collapses were triggered by intrusions preceding magmatic activity, major eruptions, or significant regional tectonic fault movements. Clasts within debris-avalanche deposits were used as a series of windows into the composition of previous successive proto-Mt Taranaki edifices in order to examine magmatic controls on their failure. The diversity of lithologies and their geochemical characteristics are similar throughout the history of the volcano, with the oldest sample suites displaying a slightly broader range of compositions including more primitive rock types. The evolution to a narrower range and higher-silica compositions was accompanied by an increase in K2O. This shows that later melts progressively interacted with underplated amphibolitic material at the base of the crust. These gradual changes imply a long-term stability of the magmatic system. The preservation of similar internal conditions during the volcano’s evolution, hence suggests that external processes were the main driving force behind its cyclic growth and collapse behaviour and resulting sedimentation pattern.

This thesis presents a detailed late Tertiary and early Quaternary pollen record from two c. 40 m long sedimentary cores (the Patiki cores) from west Auckland. The cores consist of slightly to highly carbonaceous clays, with a thick sand incursion at mid-depth. The sediments below the sand incursion are aged through palynostratigraphy as mid-late Pliocene (Hautawan). The sediments above the sand incursion have numerous interbedded tephras, and are aged through a combination of Isothermal Plateau Fission Track dating, palaeomagnetism and orbital tuning to the marine oxygen isotope record as 1.0 – 1.4 Ma (MIS 28 - 45, Marahauan substage). The Tertiary pollen record portrays regional vegetation assemblages of extinct Nothofagus brassii-type species and modern-day podocarps, with local modern-day oligotrophic mire assemblages. A cool climatic phase is indicated by a period of dominance of an extinct member of the Proteaceae. However, the duration of this interval cannot be determined due to a lack of numerical age control for the record. The Quaternary pollen record consists of mostly extant pollen types. It shows multiple compositional shifts from Nothofagus-dominated to conifer-dominated regional vegetation, with local oligotrophic mire vegetation except for a fully aquatic phase at mid-depth (MIS 35). The primary axis score curve of a detrended correspondence analysis (DCA) of the pollen record was correlated to the marine isotope record, and shows that the Nothofagus-dominated intervals correspond to cool climate stages, while the conifer-dominated intervals correspond to warm stages. The strongest cool stage maximum is indicated at 12 - 13 m depth (MIS 34), where the vegetation consists of Fuscospora, Prumnopitys taxifolia and heath shrubs. The strongest warm stage maximum is indicated at c. 9 m depth (MIS 31) where the vegetation consists of Dacrydium forest. Astronomically forced climate change is an important driving force behind vegetation composition changes portrayed in the Quaternary pollen record. The majority of warm stage maxima inferred in the pollen record (conifer-dominated intervals) coincide with periods of maximum obliquity, and vice versa for inferred cool stage maxima (Nothofagus-dominated intervals). The modulating effect of eccentricity on precession is influential on the pollen record during MIS 31 and 34. The relationship between selected climate indicator taxa and calculated insolation values indicates that reduced seasonality in Auckland during warm climate stages favours Agathis, Dacrydium, Phyllocladus and Halocarpus, while increased seasonality during cool climate stages favours Nothofagus ‘fusca'-type, Nothofagus menziesii, and Prumnopitys taxifolia. In both situations the trees are probably responding to a combination of changes in mean global temperatures and seasonality, and reacting according to their own adaptive responses to astronomically driven climate change. The Quaternary pollen record contains plant mixtures that do not occur in New Zealand today, for example Agathis australis with Nothofagus menziesii, and Halocarpus bidwillii / biformis. The climate was probably cooler than it is in Auckland today, but never as cold as the last glacial maximum in Auckland when grasslands were present. Under more equable climatic conditions, with less extreme glacial and interglacial cycles, populations of comparably 'warm' and 'cool' climate taxa were probably able to shift throughout the region and mixed to a greater extent than is currently observed. The overall vegetation response to climate change (particularly above MIS 36) is analogous to that recorded in northern New Zealand in the late Pleistocene, and supports a negligible change in climatic preference of the main canopy species since the early Quaternary. The phytosociological idiosynchracies in the pollen record are not inconsistent with the known tolerance limits of the taxa involved, or with the individualistic nature of vegetation composition.

This thesis presents a detailed late Tertiary and early Quaternary pollen record from two c. 40 m long sedimentary cores (the Patiki cores) from west Auckland. The cores consist of slightly to highly carbonaceous clays, with a thick sand incursion at mid-depth. The sediments below the sand incursion are aged through palynostratigraphy as mid-late Pliocene (Hautawan). The sediments above the sand incursion have numerous interbedded tephras, and are aged through a combination of Isothermal Plateau Fission Track dating, palaeomagnetism and orbital tuning to the marine oxygen isotope record as 1.0 – 1.4 Ma (MIS 28 - 45, Marahauan substage). The Tertiary pollen record portrays regional vegetation assemblages of extinct Nothofagus brassii-type species and modern-day podocarps, with local modern-day oligotrophic mire assemblages. A cool climatic phase is indicated by a period of dominance of an extinct member of the Proteaceae. However, the duration of this interval cannot be determined due to a lack of numerical age control for the record. The Quaternary pollen record consists of mostly extant pollen types. It shows multiple compositional shifts from Nothofagus-dominated to conifer-dominated regional vegetation, with local oligotrophic mire vegetation except for a fully aquatic phase at mid-depth (MIS 35). The primary axis score curve of a detrended correspondence analysis (DCA) of the pollen record was correlated to the marine isotope record, and shows that the Nothofagus-dominated intervals correspond to cool climate stages, while the conifer-dominated intervals correspond to warm stages. The strongest cool stage maximum is indicated at 12 - 13 m depth (MIS 34), where the vegetation consists of Fuscospora, Prumnopitys taxifolia and heath shrubs. The strongest warm stage maximum is indicated at c. 9 m depth (MIS 31) where the vegetation consists of Dacrydium forest. Astronomically forced climate change is an important driving force behind vegetation composition changes portrayed in the Quaternary pollen record. The majority of warm stage maxima inferred in the pollen record (conifer-dominated intervals) coincide with periods of maximum obliquity, and vice versa for inferred cool stage maxima (Nothofagus-dominated intervals). The modulating effect of eccentricity on precession is influential on the pollen record during MIS 31 and 34. The relationship between selected climate indicator taxa and calculated insolation values indicates that reduced seasonality in Auckland during warm climate stages favours Agathis, Dacrydium, Phyllocladus and Halocarpus, while increased seasonality during cool climate stages favours Nothofagus ‘fusca'-type, Nothofagus menziesii, and Prumnopitys taxifolia. In both situations the trees are probably responding to a combination of changes in mean global temperatures and seasonality, and reacting according to their own adaptive responses to astronomically driven climate change. The Quaternary pollen record contains plant mixtures that do not occur in New Zealand today, for example Agathis australis with Nothofagus menziesii, and Halocarpus bidwillii / biformis. The climate was probably cooler than it is in Auckland today, but never as cold as the last glacial maximum in Auckland when grasslands were present. Under more equable climatic conditions, with less extreme glacial and interglacial cycles, populations of comparably 'warm' and 'cool' climate taxa were probably able to shift throughout the region and mixed to a greater extent than is currently observed. The overall vegetation response to climate change (particularly above MIS 36) is analogous to that recorded in northern New Zealand in the late Pleistocene, and supports a negligible change in climatic preference of the main canopy species since the early Quaternary. The phytosociological idiosynchracies in the pollen record are not inconsistent with the known tolerance limits of the taxa involved, or with the individualistic nature of vegetation composition.

The long-term behaviour of andesitic stratovolcanoes is characterised by a repetition of edifice growth and collapse phases. This cyclic pattern may represent a natural frequency at varying timescales in the growth dynamics of stratovolcanoes, but is often difficult to identify because of long cycle-timescales, coupled with incomplete stratigraphic records. The volcaniclastic ring-plain succession surrounding the 2 518 m Mt. Taranaki, New Zealand, comprises a wide variety of distinctive volcanic mass-flow lithofacies with sedimentary and lithology characteristics that can be related to recurring volcanic cycles over >190 ka. Debrisflow and monolithologic hyperconcentrated-flow deposits record edifice growth phases while polylithologic debris-avalanche and associated cohesive debris-flow units were emplaced by collapse. Major edifice failures at Mt. Taranaki occurred on-average every 10 ka, with five events recognised over the last 30 ka, a time interval for which stratigraphic records are more complete. The unstable nature of Mt. Taranaki mainly results from its weak internal composite structure including abundant saturated pyroclastic deposits and breccia layers, along with its growth on a weakly indurated and tectonically fractured basement of Tertiary mudstones and sandstones. As the edifice repeatedly grew beyond a critical stable height or profile, large-scale collapses were triggered by intrusions preceding magmatic activity, major eruptions, or significant regional tectonic fault movements. Clasts within debris-avalanche deposits were used as a series of windows into the composition of previous successive proto-Mt Taranaki edifices in order to examine magmatic controls on their failure. The diversity of lithologies and their geochemical characteristics are similar throughout the history of the volcano, with the oldest sample suites displaying a slightly broader range of compositions including more primitive rock types. The evolution to a narrower range and higher-silica compositions was accompanied by an increase in K2O. This shows that later melts progressively interacted with underplated amphibolitic material at the base of the crust. These gradual changes imply a long-term stability of the magmatic system. The preservation of similar internal conditions during the volcano’s evolution, hence suggests that external processes were the main driving force behind its cyclic growth and collapse behaviour and resulting sedimentation pattern.

The long-term behaviour of andesitic stratovolcanoes is characterised by a repetition of edifice growth and collapse phases. This cyclic pattern may represent a natural frequency at varying timescales in the growth dynamics of stratovolcanoes, but is often difficult to identify because of long cycle-timescales, coupled with incomplete stratigraphic records. The volcaniclastic ring-plain succession surrounding the 2 518 m Mt. Taranaki, New Zealand, comprises a wide variety of distinctive volcanic mass-flow lithofacies with sedimentary and lithology characteristics that can be related to recurring volcanic cycles over >190 ka. Debrisflow and monolithologic hyperconcentrated-flow deposits record edifice growth phases while polylithologic debris-avalanche and associated cohesive debris-flow units were emplaced by collapse. Major edifice failures at Mt. Taranaki occurred on-average every 10 ka, with five events recognised over the last 30 ka, a time interval for which stratigraphic records are more complete. The unstable nature of Mt. Taranaki mainly results from its weak internal composite structure including abundant saturated pyroclastic deposits and breccia layers, along with its growth on a weakly indurated and tectonically fractured basement of Tertiary mudstones and sandstones. As the edifice repeatedly grew beyond a critical stable height or profile, large-scale collapses were triggered by intrusions preceding magmatic activity, major eruptions, or significant regional tectonic fault movements. Clasts within debris-avalanche deposits were used as a series of windows into the composition of previous successive proto-Mt Taranaki edifices in order to examine magmatic controls on their failure. The diversity of lithologies and their geochemical characteristics are similar throughout the history of the volcano, with the oldest sample suites displaying a slightly broader range of compositions including more primitive rock types. The evolution to a narrower range and higher-silica compositions was accompanied by an increase in K2O. This shows that later melts progressively interacted with underplated amphibolitic material at the base of the crust. These gradual changes imply a long-term stability of the magmatic system. The preservation of similar internal conditions during the volcano’s evolution, hence suggests that external processes were the main driving force behind its cyclic growth and collapse behaviour and resulting sedimentation pattern.