stratigraphy and dispersal of the mangaone subgroup pyroclastic deposits okataina volcanic centre new zealand abstract the mangaone subgroup from the okataina volcanic centre consists of silicic plinian pyroclastic units that lie between the oruanui deposit from the taupo volcanic centre corrected 14 c calendar age 26 5 ka and the rotoiti flow rotoehu fall deposits from okataina volcanic centre k ar age 64 ka in this study we present a new stratigraphy for the subgroup that is significantly revised from the earlier work and was developed after extensive field mapping and laboratory study we now recognize and describe a total of 12 rhyolitic units as opposed to the 8 that had been recognized previously with a total bulk eruptive volume of approximately 81 km 3 the vents for all the mangaone subgroup units were within the haroharo caldera and possibly migrated through time first within a roughly north south trending zone in the central part of the caldera and then toward the eastern part of the caldera we present new radiometric ages suggesting that the whole sequence was erupted in a relatively short time span possibly 10 15 ka our findings of more eruptions in a shorter time span than in previous work underscores the utility of detailed field studies particularly when volcanic hazards are being assessed all the fall units have plinian dispersals but show various degrees of magma water interaction the majority of the eruptions were large and intense enough to generate pyroclastic flows yet flows were observed in only 2 units and is volumetrically small

implications for intraplate volcanism and back arc deformation in northwestern new zealand from joint inversion of receiver functions and surface waves summary we employ a joint inversion of teleseismic receiver functions and surface wave phase velocities to determine the shear wave velocity structure in the crust and upper mantle beneath northwestern new zealand receiver functions primarily contain information on velocity contrasts while surface waves are sensitive to the average shear velocity with depth by performing a joint inversion we reduce the limitations of each method resulting in a more robust shear wave model inversion results reveal regions of low shear wave velocity of 2 8 km s 1 in the mid crust 10 19 km depth and 4 0 km s 1 in the upper mantle 70 90 km depth beneath quaternary intraplate basalt fields we infer that the mid crustal low velocity zones lvzs are bodies of partial melt most likely rhyolite intrusions we suggest that the upper mantle lvz is caused by the melt producing regions of the upper mantle and is a source for the basalts of the auckland volcanic field this is in agreement with models for a shallow upper mantle source rather than a deep seated mantle plume for the auckland volcanism average shear velocities for the upper crust are 3 4 3 6 km s 1 increasing to 3 6 4 0 km s 1 in the lower crust the moho is interpreted to be 29 1 km deep in the southern end of the array shallowing to 26 1 km towards the edge of the continental shelf of northern new zealand low upper mantle shear velocities of 4 2 0 1 km s 1 are observed and are thought to represent a small percentage of partial melt in the upper mantle beneath this back arc region these low velocities extend to greater depth 90 km beneath the southern stations indicating that mantle deformation associated with the mantle wedge to the south may extend as far north as the southern end of our array near surface low velocity layers extend to 6 km depth beneath a station at the northern tip of new zealand likely representing the expression of a thick sequence of sediments from the northland allochthon and the more recent northland basin

tephra beds in deep sea cores off northern new zealand implications for the history of taupo volcanic zone mayor island and white island volcanoes twenty piston cores were collected from water depths of 650 3300 m from offshore bay of plenty north island new zealand they contain tephra from 11 okataina volcanic centre and 4 taupo volcanic centre rhyolite eruptions during the last 50 kyr that produce a tephrostratigraphic framework across the tectonically and volcanically complex region of southern havre trough alderman trough and the bay of plenty continental shelf this allows correlation between offshore and onshore sequences up to 200 km from source volcanoes covering much of marine isotope stages 3 and 2 the framework temporally constrains poorly dated and newly recognised volcanic events macroscopic tephra layers from the peralkaline mayor island volcano are documented for the first time at pre 50 post 50 40 5 37 4 22 2 and 14 2 ka in addition to the well known 7 ka tuhua event these macroscopic layers represent some of the most explosive events from this volcano and provide new marker horizons they are dispersed up to 90 km north east to east of the edifice minor tephra dispersal is also recorded at 17 8 25 5 35 and pre 50 ka the tephra contain high sio2 73 75 5 wt glass and subordinate basaltic components and each tephra represents a distinct magma batch that can be fingerprinted the mayor island tephra form two temporal trends toward less evolved magma compositions punctuated by a large caldera forming event at 36 ka the historically active andesitic white island volcano does not have widely dispersed tephra and the oldest primary deposit found is 21 ka five pre 50 ka rhyolite eruptions from an unknown taupo volcanic zone source provide evidence for explosive activity in a time interval poorly documented on land the cores demonstrate the patchy and uneven preservation of large magnitude tephra falls caused by local faulting bioturbation and ponding in bathymetrically complex regions reworked tephra layers are common and often lack indicative lithological features such units could easily be misinterpreted as primary events without micro beam geochemical analyses of glass shards

a multi proxy record of changing environments from ca 30 000 to 9000 cal a bp onepoto maar palaeolake auckland new zealand we present a high resolution record of lacustrine sedimentation spanning ca 30 000 to 9000 cal a bp from onepoto maar northern north island new zealand the multi proxy record of environmental change is constrained by tephrochronology and accelerator mass spectrometric 14c ages and provides evidence for episodes of rapid environmental change during the last glacial coldest period lgcp and last glacial interglacial transition lgit from northern new zealand the multi proxy palaeoenvironmental record from onepoto indicates that the lgcp was cold dry and windy in the auckland region with vegetation dominated by herb and grass in a beech forest mosaic between ca 28 500 and 18 000 cal a bp the lgcp was accompanied by more frequent fires and influx of clastic sediment indicating increased erosion during the lgcp with a mid lgcp interstadial identified between ca 25 000 and 23 000 cal a bp rapid climate amelioration at ca 18 000 cal a bp was accompanied by increased terrestrial biomass exemplified by the expansion of lowland podocarp forest especially dacrydium cupressinum increasing biomass production is reversed briefly by lgit perturbations which are apparent in many of the proxies that span ca 14 000 10 500 cal a bp suggesting generally increased wetness and higher in situ aquatic plant productivity with reduced terrestrial organic matter and terrigenous detrital influx furthermore conditions at that time were probably warmer and frosts rare based on the increasing importance of ascarina the subsequent early holocene is characterised by podocarp conifer forest and moist mild conditions postglacial sea level rise breached the crater rim and deposited 36 m of estuarine mud after ca 9000 cal a bp copyright 2011 john wiley sons ltd

the role of external environmental factors in changing eruption styles of monogenetic volcanoes in a mio pleistocene continental volcanic field in western hungary abstract the occurrence shape structure and eruption style of monogenetic volcanoes such as maars tuff rings tuff cones and scoria cones are generally governed by several internal composition of the magma magmatic flux ascent rate viscosity volatile contents and external conditions regional and local tectonics topography and the presence of surfacial ground and meteoric water these controlling factors are together responsible for the eruption style distribution pattern volcanic facies architecture and morphology of the monogenetic volcanic landforms the late miocene to pleistocene bakony balaton highland volcanic field bbhvf in western hungary is a typical small sized at least 6 volcanic cycles have been identified by cluster analysis time gap between the cycles were vary from 1 66 up to 0 06 ma while the average eruption recurrence rate was 0 1078 ma event the time volume diagram of the volcanism of bbhvf have shown time predictive behavior combined with low magma flux total preserved volume 2 867 km3 and output rates 0 53 km3 ma for the entire volcanic field and 0 90 km3 ma for the last 5 cycles suggesting that volcanism was largely tectonically controlled and not magmatically controlled furthermore the topographic differences between the northern elevated and southern basin like parts of the volcanic field are also important in local differences in dominant fragmentation style because the elevated part of the field was prone to host large more magmatically evolved volcanoes than on the lower water saturated unconsolidated sediments which favored to the magma water interaction driven phreatomagmatic fragmentation the third controlling parameter which seems to play an important role in controlling the eruptive style of monogenetic volcanism at bbhvf was the paleoclimate fluctuation especially during the time interval of 3 0 to 2 5 ma thus mainly the long term environmental changes e g aridification have been response the shifting fragmentation style from phreatomagmatic to more magmatic ones

radiocarbon ages of holocene pelado guespalapa and chichinautzin scoria cones south of mexico city implications for archaeology and future hazards pelado guespalapa and chichinautzin monogenetic scoria cones located within the sierra del chichinautzin volcanic field scvf at the southern margin of mexico city were dated by the radiocarbon method at 10 000 2 800 4 700 and 1 835 years b p respectively most previous research in this area was concentrated on xitle scoria cone whose lavas destroyed and buried the pre hispanic town of cuicuilco around 1 665 35 years b p the new dates indicate that the recurrence interval for monogenetic eruptions in the central part of the scvf and close to the vicinity of mexico city is 2 500 years if the entire scvf is considered the recurrence interval is 1 700 years based on fieldwork and landsat imagery interpretation a geologic map was produced morphometric parameters characterizing the cones and lava flows determined and the areal extent and volumes of erupted products estimated the longest lava flow was produced by guespalapa and reached 24 km from its source total areas covered by lava flows from each eruption range between 54 chichinautzin and 80 km2 pelado and total erupted volumes range between 1 and 2 km3 cone an average eruption rate for the entire scvf was estimated at 0 6 km3 1 000 years these findings are of importance for archaeological as well as volcanic hazards studies in this heavily populated region

ages of 24 widespread tephras erupted since 30 000 years ago in new zealand with re evaluation of the timing and palaeoclimatic implications of the lateglacial cool episode recorded at kaipo bog abstract tephras are important for the nz intimate project because they link all three records comprising the composite inter regional stratotype developed for the new zealand climate event stratigraphy nz ces here we firstly report new calendar ages for 24 widespread marker tephras erupted since 30 000 calendar cal years ago in new zealand to help facilitate their use as chronostratigraphic dating tools for the nz ces and for other palaeoenvironmental and geological applications the selected tephras comprise 12 rhyolitic tephras from taupo nine rhyolitic tephras from okataina one peralkaline rhyolitic tephra from tuhua and one andesitic tephra each from tongariro and egmont taranaki volcanic centres age models for the tephras were obtained using three methods i 14 c based wiggle match dating of wood from trees killed by volcanic eruptions these dates published previously ii flexible depositional modelling of a high resolution 14 c dated age depth sequence at kaipo bog using two bayesian based modelling programs bacon and oxcal s p sequence function and the intcal09 data set with sh offset correction 44 17 yr and iii calibration of 14 c ages using oxcal s tau boundary function and the shcal04 and intcal09 data sets our preferred dates or calibrated ages for the 24 tephras are as follows youngest to oldest all mid point or mean ages of 95 probability ranges kaharoa ad 1314 12 taupo unit y ad 232 10 mapara unit x 2059 118 cal yr bp whakaipo unit v 2800 60 cal yr bp waimihia unit s 3401 108 cal yr bp stent unit q 4322 112 cal yr bp unit k 5111 210 cal yr bp whakatane 5526 145 cal yr bp tuhua 6577 547 cal yr bp mamaku 7940 257 cal yr bp rotoma 9423 120 cal yr bp opepe unit e 9991 160 cal yr bp poronui unit c 11 170 115 cal yr bp karapiti unit b 11 460 172 cal yr bp okupata 11 767 192 cal yr bp konini bed b 11 880 183 cal yr bp waiohau 14 009 155 cal yr bp rotorua 15 635 412 cal yr bp rerewhakaaitu 17 496 462 cal yr bp okareka 21 858 290 cal yr bp te rere 25 171 964 cal yr bp kawakawa oruanui 25 358 162 cal yr bp poihipi 28 446 670 cal yr bp and okaia 28 621 1428 cal yr bp secondly we have re dated the start and end of the lateglacial cool episode climate event nzce 3 in the nz ces previously referred to as the lateglacial climate reversal as defined at kaipo bog in eastern north island new zealand using both bacon and oxcal p sequence modelling with the intcal09 data set the ca 1200 yr long cool episode indicated by a lithostratigraphic change in the kaipo peat sequence to grey mud with lowered carbon content and a high resolution pollen derived cooling signal began 13 739 125 cal yr bp and ended 12 550 140 cal yr bp mid point ages of the 95 highest posterior density regions bacon modelling the oxcal modelling generating almost identical ages confirmed these ages the lateglacial cool episode ca 13 8 12 6 cal ka bp thus overlaps a large part of the entire antarctic cold reversal chronozone ca 14 1 12 4 cal ka bp or ca 14 6 12 8 cal ka bp and an early part of the greenland stadial 1 younger dryas chronozone ca 12 9 11 7 cal ka bp the timing of the lateglacial cool episode at kaipo is broadly consistent with the latitudinal patterns in the antarctic cold reversal signal suggested for the new zealand archipelago from marine and terrestrial records and with records from southern south america

fingerprints and age models for widespread new zealand tephra marker beds erupted since 30 000 years ago a framework for nz intimate abstract the role of tephras in the nz intimate project is a critical one because most high resolution palaeoclimatic records are linked and dated by one or more tephra layers in this review first we document eruptive distributional and compositional fingerprinting data both mineralogical and geochemical for 22 key marker tephras erupted since 30 000 years ago to facilitate their identification and correlation we include new glass compositional data the selected marker tephras comprise 10 from taupo and nine from okataina volcanoes rhyolitic one from tuhua volcano peralkaline rhyolitic and one each from tongariro and egmont volcanoes andesitic second we use four approaches to develop 2 age models for the tephras youngest to oldest 1 calendar ages for kaharoa and taupo y were obtained by wiggle matching log derived tree ring sequences dated by 14c 2 whakaipo v was dated using an age depth model from peat 3 14 tephras in the montane kaipo peat sequence waimihia s unit k whakatane tuhua mamaku rotoma opepe e poronui c karapiti b okupata konini waiohau rotorua rerewhakaaitu were dated by simultaneously wiggle matching stratigraphic position and 51 independent 14c age points against intcal04 using bayesian probability methods via both oxcal and bpeat and 4 the five oldest tephras erupted before ca 18 000 cal yr bp were dated by calibrating limited numbers of 14c ages using intcal04 okareka or comparison curves of the expanded cariaco basin sequence te rere kawakawa oruanui poihipi okaia kawakawa oruanui tephra the most widely distributed marker tephra was erupted probably ca 27 097 957 cal yr bp potential dating approaches for the older tephras include their identification in antarctic ice cores if present or annually laminated sediments for which robust calendar age models have been constructed high precision ams 14c dating on appropriate material from environmentally stable sites systematic luminescence dating or new radiometric techniques e g u th he if suitable minerals are available and errors markedly reduced further application of bayesian age modelling to stratigraphic sequences of 14c ages possibly augmented with luminescence ages may help refine age models for pre holocene tephras with the largest errors finally we discuss the critical role these marker tephras play in the ongoing construction of an event stratigraphy for the new zealand region which is a key objective of australasian and southern hemisphere intimate projects

tectonically controlled vent migration during maar diatreme formation an example from a miocene half graben basin in se korea abstract understanding the roles of external controls such as hydrology and tectonics is crucial for interpreting the evolution of a phreatomagmatic volcano and its subsurface structure called the diatreme the yangpori diatreme in a miocene terrestrial half graben basin of korea provides an opportunity to assess the roles of synvolcanic fault movement in forming a maar diatreme volcano the exposed part of the diatreme fill consists of two offset stacked sequences with contrasting lithofacies characteristics a lower sequence early diatreme fill of locally stratified or bedded basaltic lapilli tuff and tuff in the northeastern part and an upper sequence later diatreme fill of dacite clast rich and disorganized tuff breccia in the southwestern part the boundary between these sequences is abrupt suggesting eruption of the volcano in two distinct phases the first phase of eruption was driven by phreatomagmatic explosions mainly within the basin fill some of the diatreme fill was deposited in a local pond by debris flows and suspension settling of fines whereas the rest by fallout from eruption plumes and jets the second phase of eruption was driven by phreatomagmatic explosions at a fracture aquifer within the basement accompanying sudden lowering of the explosion locus the later diatreme fill therefore contains abundant basement derived dacite clasts its deposition was accomplished by en masse fallout of volcanic debris from dense collapsing columns a number of faults and shear fractures were generated within and in the vicinity of the diatreme together with penecontemporaneous basaltic intrusions structural and geochemical analyses show that many of these structures are genetically related with the formation of the diatreme the early diatreme fill was also tilted toward the southwest suggesting southwestward shift of the locus of explosion and diatreme excavation the explosion locus of the yangpori volcano is therefore interpreted to have migrated both vertically and laterally the abrupt lithofacies boundary between the early and later diatreme fills and the proximity of the diatreme to the basin margin suggests that the migration was caused by an abrupt tectonic activity near the basin margin most probably the feeder dike was dislocated by movement along the basin margin fault which created abundant fractures deep within the basement that redirected ascending magma and opened a new hydraulically active zone in the basement synvolcanic faulting is therefore interpreted to have played a crucial role in forming the offset stacked architecture of the yangpori diatreme sequences the faulting is also inferred to have influenced significantly the morphology and internal facies architecture of unpreserved ejecta rimbeds

holocene vegetation and volcanic activity auckland isthmus new zealand a 12 000 to 4000 yr bp pollen and tephra bearing profile from auckland new zealand provides insights into the vegetation history and evidence for early holocene volcanic activity in this area centred on the mount wellington basaltic volcano possibly 500 yr separated initial scoriaceous ash deposition ca 9500 yr ago and subsequent major lava flows ca 9000 yr ago from mount wellington the local vegelation topography and drainage patterns were substantially modified during this time and damming by the lava flows resulted in the formation of lake waiatarua in a shallow valley head ca 9000 yr ago diatom evidence indicates that this lake was initially deep 5 m but was shallowing around 4000 yr ago in contrast to the mount wellington eruptions tephra deposition resulting from distant rhyolitic volcanic activity of the central north island and mayor island has had little effect on the auckland vegetation during this time interval 12 000 4000 yr ago between ca 12 000 and 10 000 yr ago conifer angiosperm forest was the predominant vegetation cover on auckland isthmus but during the early holocene forest dominated by metrosideros expanded probably on to fresh volcanic surfaces resulting from the mount wellington eruptions at this time swamp forest communities developed in waiatarua valley basin and included species indicative of moist mild relatively frost free climates some taxa show histories consistent with other records from the northern new zealand region including the rise of ascarina lucida ca 11 000 to 9000 yr ago and its subsequent decline and the expansion of agathis australis kauri forest communities from ca 6000 yr ago taken together the history of local and regional vegetation points to a mild moist and weakly seasonal early holocene climate which subsequently became drier with greater seasonal temperature extremes

lidar based quantification of lava flow susceptibility in the city of auckland new zealand abstract lava flows represent one of the most significant volcanic hazards from basaltic monogenetic volcanoes such as spatter cones scoria cones maars and tuff rings they are common features emanating from parasitic vents on the flanks of polygenetic volcanoes and in dominantly flat lying intraplate volcanic fields the auckland volcanic field avf is a volcanic field that has been active for the last ca 250 ka hosting at least 50 monogenetic volcanoes morphometric parameters of lava flows such as volume length thickness and area were used to quantify the potential lava flow inundation susceptibility to new zealand s most densely populated area the city of auckland based on an airborne light detection and ranging lidar digital surface model dsm the morphometric parameters of fifteen studied flows included average length of 2 5 km range 0 7 6 5 km overall average thickness of 14 8 m range 3 4 43 8 m average of maximum thicknesses of 48 2 m range 18 3 180 5 m average area occupied of 5 1 km 2 range 0 4 25 1 km 2 and average volume of 0 12 km 3 range 0 005 1 km 3 based on these parameters and a lidar derived dsm the present topography was classified into sea topographic depressions low lying areas prone to inundation by an average lava flow buffer zones prone to inundation only by extremely thick lava flows and peaks or ridges which are unlikely to be overtopped in monogenetic fields each new vent occurs in a new location creating uncertainty around the spatial location of the volcanic hazard thus this research provides a general vent location independent approach to describe the lava flow susceptibility for a potentially active monogenetic volcanic field what this analysis reveals is that the city of auckland can be divided into two distinct areas with strongly different susceptibility to lava flow inundation the southern part of the city is predominantly flat without hindrance to lava flow whereas the hilly northern and central part has many ridges that can limit or channelise lavas these contrasting properties must be accounted for in scenario based or probabilistic hazard and risk models developed for the avf

from sink to volcanic source unravelling missing terrestrial eruption records by characterization and high resolution chronology of lacustrine volcanic density flow deposits lake inawashiro ko fukushima japan

the spatial and temporal cost of volcanic eruptions assessing economic impact business inoperability and spatial distribution of risk in the auckland region new zealand volcanic risk assessment has historically concentrated on quantifying the frequency magnitude and potential diversity of physical processes of eruptions and their consequent impacts on life and property a realistic socio economic assessment of volcanic impact must however take into account dynamic properties of businesses and extend beyond only measuring direct infrastructure property loss the inoperability input output model heralded as one of the 10 most important accomplishments in risk analysis over the last 30 years kujawaski syst eng 9 281 295 2006 has become prominent over the last decade in the economic impact assessment of business disruptions we develop a dynamic inoperability input output model to assess the economic impacts of a hypothetical volcanic event occurring at each of 7270 unique spatial locations throughout the auckland volcanic field new zealand this field of at least 53 volcanoes underlies the country s largest urban area the auckland region which is home to 1 4 million people and responsible for 35 3 nz 201481 2 billion of the nation s gdp statistics new zealand 2015 we apply volcanic event characteristics for a small medium scale volcanic eruption scenario and assess the economic impacts of an average eruption in the auckland region economic losses are quantified both with and without business mitigation and intervention responses in place we combine this information with a recent spatial hazard probability map bebbington and cronin bull volcanol 73 1 55 72 2011 to produce novel spatial economic activity at risk maps our approach demonstrates how business inoperability losses sit alongside potential life and property damage assessment in enhancing our understanding of volcanic risk mitigation

a composite pollen based stratotype for inter regional evaluation of climatic events in new zealand over the past 30 000 years nz intimate project abstract our review of paleoclimate information for new zealand pertaining to the past 30 000 years has identified a general sequence of climatic events spanning the onset of cold conditions marking the final phase of the last glaciation through to the emergence to full interglacial conditions in the early holocene in order to facilitate more detailed assessments of climate variability and any leads or lags in the timing of climate changes across the region a composite stratotype is proposed for new zealand the stratotype is based on terrestrial stratigraphic records and is intended to provide a standard reference for the intercomparison and evaluation of climate proxy records we nominate a specific stratigraphic type record for each climatic event using either natural exposure or drill core stratigraphic sections type records were selected on the basis of having very good numerical age control and a clear proxy record in all cases the main proxy of the type record is subfossil pollen the type record for the period from ca 30 to ca 18 calendar kiloyears bp cal ka bp is designated in lake bed sediments from a small morainic kettle lake galway tarn in western south island the galway tarn type record spans a period of full glacial conditions last glacial coldest period lgcp within the otira glaciation and includes three cold stadials separated by two cool interstadials the type record for the emergence from glacial conditions following the termination of the last glaciation post termination amelioration is in a core of lake sediments from a maar pukaki volcanic crater in auckland northern north island and spans from ca 18 to 15 64 0 41 cal ka bp the type record for the lateglacial period is an exposure of interbedded peat and mud at montane kaipo bog eastern north island in this high resolution type record an initial mild period was succeeded at 13 74 0 13 cal ka bp by a cooler period which after 12 55 0 14 cal ka bp gave way to a progressive ascent to full interglacial conditions that were achieved by 11 88 0 18 cal ka bp although a type section is not formally designated for the holocene interglacial 11 88 0 18 cal ka bp to the present day the sedimentary record of lake maratoto on the waikato lowlands northwestern north island is identified as a prospective type section pending the integration and updating of existing stratigraphic and proxy datasets and age models the type records are interconnected by one or more dated tephra layers the ages of which are derived from bayesian depositional modelling and oxcal based calibrations using the intcal09 dataset along with the type sections and the lake maratoto record important well dated terrestrial reference records are provided for each climate event climate proxies from these reference records include pollen flora stable isotopes from speleothems beetle and chironomid fauna and glacier moraines the regional composite stratotype provides a benchmark against which to compare other records and proxies based on the composite stratotype we provide an updated climate event stratigraphic classification for the new zealand region the stratotype and event classification are not intended to act as definitive statements of paleoclimate history for the new zealand region but rather provide a firm baseline against which to compare other records including those from the marine realm

sub millennial eruptive recurrence in the silicic mangaone subgroup tephra sequence new zealand from bayesian modelling of zircon double dating and radiocarbon ages abstract accurate dating of young 38 4 1 4 1 7 ka bp and constrains the beginning of the msg eruption period to 42 7 3 5 3 7 ka bp unit a and the end to 30 6 1 5 0 6 ka bp unit l thus the entire msg sequence was emplaced in 12 100 years representing an eruption frequency of one event per 930 years on average our study demonstrates the efficacy of zdd to yield accurate eruption ages on pyroclastic deposits highlighting its potential for dating young

sedimentology eruptive mechanism and facies architecture of basaltic scoria cones from the auckland volcanic field new zealand abstract scoria cones are a common type of basaltic to andesitic small volume volcanoes e g 10 1 10 5 km 3 that results from gas bubble driven explosive eruptive styles although they are small in volume they can produce complex eruptions involving multiple eruptive styles eight scoria cones from the quaternary auckland volcanic field in new zealand were selected to define the eruptive style variability from their volcanic facies architecture the reconstruction of their eruptive and pyroclastic transport mechanisms was established on the basis of study of their volcanic sedimentology stratigraphy and measurement of their pyroclast density porosity scanning electron microscopy 2d particle morphology analysis and visible and near visible infrared spectroscopy collection of these data allowed defining three end member types of scoria cones inferred to be constructed from lava fountaining transitional fountaining and strombolian type and explosive strombolian type using the physical and field based characteristics of scoriaceous samples a simple generalised facies model of basaltic scoria cones for the avf is developed that can be extended to other scoria cones elsewhere the typical avf scoria cone has an initial phreatomagmatic phases that might reduce the volume of magma available for subsequent scoria cone forming eruptions this inferred to have the main reason to have decreased cone volumes recognised from auckland in comparison to other volcanic fields evolved dominantly in dry eruptive condition e g no external water influence it suggests that such subtle eruptive style variations through a scoria cone evolution need to be integrated into the hazard assessment of a potentially active volcanic field such as that in auckland

the huguang maar lake a high resolution record of palaeoenvironmental and palaeoclimatic changes over the last 78 000 years from south china abstract a series of seven piston cores from the huguang maar lake situated near the south china sea coastline provides insight into regional palaeoenvironmental and palaeoclimatic changes in southern china over the last 78 000 years the data set comprises a high resolution record of magnetic susceptibility dry density and water content total organic carbon and inorganic carbon total nitrogen biogenic silica bsio2 and palynological results the time scale was developed by ams 14c dating of 17 terrestrial plant macro fossils during the last glacial the huguang record is characterised by an alternation of more temperate and humid periods from 78 to 58 and 48 to 40 5 ka bp and periods with predominance of grassland vegetation and possibly lowered lake level from 58 to 48 and ca 40 5 to 15 ka bp the huguang data have been compared to regional marine and terrestrial records in order to discuss variability of the south east asian monsoon system for most of the last glacial period the huguang proxies do not exhibit marked millennial scale variability as known from some long se asian and many north atlantic records this picture changes at about 15 cal ka bp when the huguang and greenland records appear to correlate well a short climatic reversal which is assumed to reflect a younger dryas type event is well recorded in the huguang record during the holocene the huguang multi proxy data show a much higher variability than during the last glacial stage probably reflecting at least for the early mid holocene fluctuations in monsoon activity however the last 4000 years of the sediment record are clearly influenced by enhanced human activity and thus difficult to interpret in terms of palaeoclimate change

late quaternary paleolimnology of onepoto maar auckland new zealand implications for the drivers of regional paleoclimate abstract a high resolution record of lacustrine environments spanning ca 30 9 cal ka bp was obtained from onepoto maar northern north island new zealand the multi proxy record of environmental change is constrained by tephrochronology and ams 14 c ages and provides evidence for episodes of rapid environmental change during the last glacial coldest period lgcp 28 5 18 cal ka bp and late glacial interglacial transition lgit from northern new zealand the onepoto pollen record indicates that the lgcp was cold dry and windy in the auckland region with vegetation dominated by herbs and grasses in a beech forest mosaic at the same time the diatom record indicates oligotrophic conditions with low lakes levels and turbulence whilst cladocerans indicate low water temperatures the inference of cold dry and windy conditions during the lgcp is supported by geochemical evidence for increased sediment influx charcoal and co 2 limiting conditions for terrestrial macrophytes rapid climate amelioration and forest expansion after ca 18 cal ka bp corresponds with reduced sediment influx diatom and cladoceran inferred higher lake levels indicating increasing moisture availability and temperature diatom flora indicates that an oligotrophic circumneutral lake was becoming established during the lgit but conditions were still variable between ca 13 8 and 12 5 cal ka bp two brief drier and possibly cooler episodes are apparent ca 13 8 13 2 and 13 12 5 cal ka bp followed by a warm phase combined with generally stable high lake levels between ca 12 5 and 10 5 cal ka bp subsequently the lake water chemistry became more alkaline and eutrophic possibly because sea level had risen high enough by this time to influence ground water chemistry

laschamp and mono lake geomagnetic excursions recorded in new zealand eight basaltic lavas from the auckland volcanic field new zealand record three distinct sets of excursional geomagnetic field directions and low paleointensities however the timing and therefore paleomagnetic significance of these records have been poorly understood radiocarbon k ar and thermoluminescence dating constrain these lavas to have erupted during the last 75 ka a period during which as many as three excursions have been recorded differentially at several northern and fewer southern hemisphere sites forty 40ar 39ar incremental heating experiments conducted on groundmass from seven of these excursional lavas indicate that they erupted during at least two periods at 39 1 4 1 and 31 6 1 8 ka coincident with 40ar 39ar astrochronologic and 14c ages determined for the laschamp and mono lake excursions respectively samples from a lava flow associated with a third cluster of virtual geomagnetic poles vgps are complicated by low concentrations of radiogenic argon in the presence of excess argon and thus yield discordant age spectra and an imprecise age of 26 6 8 1 ka our findings indicate that the laschamp and mono lake excursions until recently identified unequivocally and isotopically dated only in the northern hemisphere were globally synchronized at 40 1 and 32 1 ka however the vgps of lavas that record the laschamp excursion in new zealand and france are inconsistent with a simple clockwise looping geometry inferred from vgp paths obtained in eight marine sediment cores spanning the laschamp excursion we suggest that the differences in vgps recorded at the various sites are significant and may point to non axial dipole components and lower mantle control on transitional fields during short lived excursions

late middle miocene volcanism in northwest borneo southeast asia implications for tectonics paleoclimate and stratigraphic marker abstract explosive volcanic events often produce pyroclastic materials that can be recognized from the geological record these discrete pyroclastics form regional marker beds here we report the occurrence of a tephra layer interbedded within very thick coal beds near mukah sarawak borneo traceable for tens of kilometers in the mukah area of sarawak this tephra layer can be considered as regional stratigraphic marker with precise chronostratigraphic control systematic sedimentological mineralogical geochemical and zircon u pb geochronological studies have revealed a major effusive volcanic event during the latest middle miocene presumably contemporaneous and or related to a magmatic event of an earlier phase of the mt kinabalu pluton or magmatism in west sarawak or east sabah the volcanic event had promoted catastrophic flooding of coastal swamps and fall out from the ash clouds that formed a regionally monotonous tephra layer across the serravallian tortonian boundary in conjunction with the regional occurrences of trap rocks structural trends and known tectonic events we constrained the regional depositional environments and climate the tephra layer was deposited in a coastal plain swamp seasonal shallow high moderate energy fluvial channel lacustrine environmental setting wherein atmospheric fallout and eroded material from regoliths formed over older basement and volcanic rocks of the hinterland which were mixed to produce the tephra layer this tephra layer is sandwiched between the very thick coal beds a pre existent volcanic chamber that was active for a long time also experienced periodic explosive activity from probably the same magma chamber and conduit and including a major explosive activity that recycled early formed crystals and felsic magma rhyolite dacite during the major effusive event are also recognized our findings provide robust evidence for the prevalence of intensive chemical weathering under a wet humid climate and relative tectonic quiescence before the major effusive event and the existence of vast monotonously gently sloping coastal plains and luxuriant vegetation akin to the present

deposition of the 2011 2012 cordon caulle tephra chile 40 s in lake sediments implications for tephrochronology and volcanology tephras preserved in lake sediments are commonly used to synchronize sedimentary archives of climate and environmental change and to correlate them with terrestrial environments they also provide opportunities to reconstruct volcanic explosive activity e g eruption frequency and tephra dispersal although sedimentary processes may affect the record of tephras in lakes lake sediments are generally considered as one of the best archives of tephra stratigraphy the 2011 2012 eruption of cordon caulle volcano chile 40 degrees s offered an ideal opportunity to study the processes affecting tephra deposition in lakes although the prevailing westerlies transported the erupted pyroclastic material away from nearby puyehue lake the tephra was identified within this relatively large lake with a thickness ranging from 1 to 10cm this is in contrast with smaller lakes where tephra thickness was in agreement with ashfall distribution maps geomorphological observations and sedimentological analyses provide evidence that the tephra deposited in puyehue lake entirely consists of material reworked from the upper watershed transported by rivers and distributed by lake currents according to particle size and density our results have important implications for tephrochronology and volcanology they suggest that 1 lakes do not act as passive tephra traps 2 lakes with large watersheds record more eruptions than smaller lakes which only register direct ashfalls affecting conclusions regarding the recurrence of volcanic eruptions and 3 using lakes with large watersheds for isopach mapping systematically leads to an overestimation of erupted tephra volumes smaller lakes with limited drainage basins are generally better suited for volcanological studies

basaltic magmatic mapping a suggested methodology and the resulting petrologic and volcanic hazard implications from the springerville volcanic field east central arizona abstract the magmatic mapping methods we describe from the recently completed map of the pleistocene springerville volcanic field svf provide a robust organizational model for detailed mapping of similar monogenetic continental fields results from this work offer a unique temporal and physical assessment of the lavas and their volcanic hazards from this field for comparison with other similar volcanic occurrences on all terrestrial like planets magmatic mapping focuses on recognizing each individual magmatic event or unit it involves delineating contacts between units characterizing the units placing them into a stratigraphically controlled temporal framework and organizing the data for analysis based on these recognized units the 3000 km2 svf contains 501 units comprised of lava flows and cinder scoria cones of the 12 lithologic classes we defined olivine phyric lavas are most abundant 244 units comprising nearly 45 of the mapped areal extent of volcanic outcrop the next most extensive are diktytaxitic 7 units and olivine plagioclase 48 units units each making up approximately 15 of the outcrop area younger units trend towards more evolved lithologies ranging from aphyric to feldspathic basalts these 5 lithologic classes 106 total units 16 7 areal extent have smaller average areas similarly lava geochemistry trends towards more alkalic products in younger units the largest geochemical class is basalt with tholeiitic affinities 24 areal extent followed by transitional basalts 23 7 alkali olivine basalts 20 5 and hawaiites 12 9 with lesser amounts of the five more evolved classes 15 5 combined and basanites 3 7 eruptions progressed from large volumes of tholeiites 21 6 observed 36 interpreted early in its lifespan 2 1 5 ma to an intermediate period 1 5 1 0 ma characterized by aob 11 3 and transitional basalts 8 9 with increasing evolved alkali rocks ear 12 5 its most recent phase 1 0 to 0 3 ma was dominated by more alkalic eruptions ear comprising 12 3 with aob and transitional basalt totaling 7 4 a field wide trend mimicked locally by seven temporal vent clusters defined by condit and connor 1996 this pattern from early high volume tholeiitic to lower volume alkalic eruptions provides some predictability as to the types of volcanic hazards inherent in these fields in terms of lava flow hazards the most destructive events of this field come from eruptions of fluid high volume lavas with tholeiitic affinities which are the least predictable because they initiate volcanism both field wide and within spatial temporal vent clusters and they affect the largest areal extent of any magma type the later stage lower volume alkalic eruptions pose a greater explosive threat although their timing in the chemo temporal patterns observed in the svf suggest a higher degree of predictability

proximal tephra hazards recent eruption studies applied to volcanic risk in the auckland volcanic field new zealand abstract auckland new zealand is unique in being a metropolitan area built on an active volcanic field despite the small size and intensity of auckland eruptions the risk from tephra fall is high because of the high density of buildings and lifelines the nature of this threat can be evaluated by comparisons with historical strombolian and hawaiian eruptions which have occurred in non populated areas cone building phases of such eruptions are typically protracted i e weeks to months in duration prolonging the period during which emergency managers will have to fine tune mitigation for numerous parameters such as fluctuations in intensity and wind shifts rapid cone growth during future eruptions will define a region of some 30 to 100 ha where complete destruction will occur on a time scale of hours the cost of this destruction is likely to range between nz 200m and nz 1 4b ca us 130m to us 900m beyond this we have modeled the cumulative long term effect of the build up of a downwind blanket of lapilli and ash by estimating accumulation rates for three phases of the 1959 k lauea iki eruption in hawai i the effect of changing wind direction was evaluated using low level wind data from auckland these results show that intervals between 4 and 100 h will lapse before onset of significant damage to buildings

construction of the north head maungauika tuff cone a product of surtseyan volcanism rare in the auckland volcanic field new zealand the auckland volcanic field avf comprises at least 52 monogenetic eruption centres dispersed over 360 km2 eruptions have occurred sporadically since 250 ka predominantly when glacio eustatic sea levels were lower than today now that around 35 of the field is covered by shallow water up to 30 m depth any eruption occurring in the present or near future within this area may display surtseyan dynamics the north head tuff cone evidences eruptive dynamics caused by magma interaction with seawater the first stages of the eruption comprise a phreatomagmatic phase that built a 48 m high tuff cone north head tuff deposits contain few lithic fragments 10 vol and are characterized by deposits from collapsing tephra jets and fall from relatively wet tephra columns the conditions needed for this eruption existed between 128 and 116 ka when the sea level in the auckland area was at least 10 12 m above the pre eruptive surface the hazards associated with this type of eruption pose a risk to the densely populated coastal residential zones and the activities of one of the busiest harbours in new zealand

towards characterising rhyolitic tephra layers from new zealand with rapid non destructive μ xrf core scanning abstract tephra layers are of importance for the construction of reliable age control in late quaternary paleoenvironmental and volcanic hazard studies especially in volcanically active settings such as the north island of new zealand however their identification involves time consuming and destructive processing steps making the application of non destructive xrf core scanners potentially advantageous for tephra identification here we investigate the potential of the itrax xrf core scanner to differentiate between rhyolitic tephra layers sourced from various northern new zealand rhyolitic volcanic centres deposited in maar lakes of the auckland volcanic field in their macroscopic form these tephra layers are usually visibly distinct when surrounded by a dark organic rich sediment matrix although their attribution to source volcanic centre and eruption typically requires examination of their mineral assemblages combined with chemical fingerprinting of the rhyolite glass shards we demonstrate that xrf core scanning of rhyolitic tephra layers from the taupo volcanic zone and tuhua volcanic centre can also allow identification and sometimes differentiation of the tephra using xrf derived elemental counts especially high si k ca and very low br and ti different rhyolite tephra layers vary in their relative abundances of major minor and trace elements as is evident from electron microprobe and la icp ms analyses of their glass shards mo tube based xrf cannot detect na nor mg and is of lower reliability for the lighter elements ca al which play an important role in traditional tephra fingerprinting nevertheless we are able to demonstrate that xrf core scanning data can distinguish between previously identified tephra layers using multivariate statistics furthermore the study emphasises the need for a standard protocol for xrf core scanning of tephra layers for this approach to be more widely applicable especially to aid or be a substitute for conventional geochemical approaches used for tephra fingerprinting

impacts of the 1945 and 1995 1996 ruapehu eruptions new zealand an example of increasing societal vulnerability over the past 50 yr the risk to society from volcanic eruptions has increased sharply due to an increased population more developed and diversified economies and a more technologically advanced infrastructure this fact is demonstrated vividly by the impacts from the two largest eruptions of the twentieth century from the cone volcano of ruapehu which suggest that the vulnerability of key sectors in new zealand society has increased by one to two orders of magnitude over this period both the 1945 and 1995 1996 eruptions included explosive phases that dispersed ash over a wide area of the north island for a period of several months individual ash falls were only a few millimeters thick in communities within 150 km of the volcano and only trace amounts were found in communities farther away the 1995 1996 eruption caused similar physical effects to the 1945 eruption but had considerably greater social and economic impacts the greatest contribution to the cost of the 1995 1996 eruption estimated in excess of 130 million new zealand dollars was the impact on the alpine tourist industry in the central north island essentially nonexistent in 1945 other significant impacts were felt by the rapidly growing aviation and electricity generation sectors the cost of any future eruption of the same magnitude is likely to grow as the vulnerability of our society increases at a rapid rate

oxygen and carbon isotope patterns archived in shells of the aquatic gastropod radix hydrologic and climatic signals across the tibetan plateau in sub monthly resolution abstract the tibetan plateau tp including its surrounding mountain ranges represents the largest store of ice outside the polar regions it hosts numerous lakes as well as the head waters of major asian rivers on which billions of people depend and it is particularly sensitive to climate change the moisture transport to the tp is controlled by the indian and pacific monsoon and the westerlies understanding the evolution of the interaction of these circulation systems requires studies on climate archives in different spatial and temporal contexts the objective of this study is to learn more about the interannual variability of precipitation patterns across the tp and how different hydrologic systems react to different climatic factors aragonite shells of the aquatic gastropod radix which is widely distributed in the region may represent suitable archives for inferring hydrologic and climatic signals in particularly high resolution therefore sclerochronological studies of 18 o and 13 c ratios in radix shells from seven lakes were conducted each representing a different hydrologic and climatic setting on a transect from the pamirs across the tp the shell patterns exhibit an increasing influence of precipitation and a decreasing influence of evaporation on the isotope compositions from west to east 18 o values of shells from lakes on the eastern and central tp donggi cona yamdrok yumco tarab co mirror monsoon signals indicated by more negative values and higher variabilities compared to the more western lakes karakul bangong nyak manasarovar in yadang co located on the central southern tp the monsoon rains did not reach the lake in the sampling year although it is located in a region which is usually affected by monsoon circulation the 18 o values are used to differentiate the annual hydrological cycle into ice cover period melt water period precipitation period and evaporation period 13 c compositions in the shells particularly depend on specific habitats which vary in biological productivity and in carbon sources 18 o and 13 c patterns show a positive covariance in shells originating from large closed basins the results show that radix shells mirror general climatic differences between the seven lake regions these differences reflect both regional and local climate signals in sub seasonal resolution without noticeable dependence on the particular lake system

contrasting magma types and steady state volume predictable basaltic volcanism along the great rift idaho the great rift is an 85 km long 2 to 8 km wide volcanic rift zone in the snake river plain idaho three latest pleistocene to holocene basaltic lava fields craters of the moon kings bowl and wapi are located along the great rift the craters of the moon lava field is a composite of more than 60 lava flows 25 cinder cones and at least 8 eruptive fissure systems it covers 1 600 km2 and contains 30 km3 of lava flows and associated pyroclastic deposits field radiocarbon and paleomagnetic data show that the craters of the moon lava field formed in eight eruptive periods each of which was typically several hundred years or less in duration and was separated from others before and after by intervals of several hundred to several thousand years the first eruptive period began 15 000 yr b p and the latest eruptive period ended 2100 yr b p the small kings bowl lava field 3 3 km2 0 01 km3 and the larger wapi lava field 330 km2 6 km3 both formed 2250 yr b p three magma types have fed flows along the great rift the types are 1 a contaminated type that has a sio2 range of 49 64 and commonly shows petrographic evidence of contamination 2 a fractionated type that has a sio2 range of 44 54 and shows no evidence of contamination and whose chemical and mineralogical variation can be accounted for mainly by crystal fractionation and 3 a snake river plain type that has a sio2 range of 45 48 shows little evidence of fractionation and is represented by kings bowl wapi flows and olivine basalts of the snake river plain the contaminated and fractionated magma types were erupted at the craters of the moon lava field and the snake river plain magma type was erupted at the kings bowl and wapi lava fields these relations imply that the magma reservoirs are spatially isolated the magma output rate for the craters of the moon segment of the great rift was constant at 1 5 km3 1 000 yr for the period from 15 000 to 7000 yr b p the rate increased to 2 8 km3 1 000 yr from 7000 to 2000 yr b p mainly as a result of the addition of contaminated magma to the nearly constant output rate of fractionated magma the craters of the moon segment of the great rift has experienced quasi steady state volume predictable volcanism for the last 15 000 yr the recurrence interval of eruptive activity for the craters of the moon lava field ranges from several hundred to 3 000 yr because the present interval has lasted 2 100 yr another eruptive period seems likely to occur within the next 1 000 yr the steady state volume predictable relationship suggests that 5 6 km3 of lava will be erupted in the next eruptive period

last glacial pollen climate reconstructions from northland new zealand despite wide ranging interest in the vegetation and climate of northland new zealand during the last glacial cycle the region and timeframe lack quantitative climate reconstructions while land based pollen records have tended to be poorly dated and fragmentary the region is also important for geochronology due to the co occurrence of the rotoehu tephra a widely dispersed isochron near the current limits of radiocarbon dating and extensive subfossil wood remains of agathis australis with strong dendrochronological and dendroclimatological potential we present new pollen records and temperature reconstructions from three sites set in coastal dune belts from western mid northland 35 s all containing rotoehu tephra that collectively span the last 70 ka the phases and amplitude of temperature changes broadly align with those reported from elsewhere in new zealand and with marine isotope climate stratigraphic records including maximum temperature depression of 6 8 c during the last glacial maximum we argue that these climatic patterns are intimately linked to shifts in the southern westerly wind belt the northern margins of which extend to the region today correspondence between the northland temperature shifts and atmospheric co2 supports the model of ocean atmosphere co2 flux modulated by latitudinal migration of the southern westerlies copyright 2017 john wiley sons ltd

re anchoring the late pleistocene tephrochronology of new zealand based on concordant radiocarbon ages and combined 238u 230th disequilibrium and u th he zircon ages abstract the caldera forming rotoiti eruption from okataina volcano was one of the largest rhyolite events of the last 100 ka in the taupo volcanic zone new zealand its associated widespread tephra layer rotoehu tephra is a significant time marker in terrestrial marine paleoclimate correlation studies in the sw pacific however the accurate and precise age of this eruption and of the subsequent smaller volume earthquake flat eqf eruption has been the subject of controversy despite numerous studies we have applied combined 238u 230th disequilibrium and u th he dating of zircon from rotoiti and eqf deposits and obtained overlapping ages of 45 1 7 3 3 ka and 45 1 6 2 9 ka respectively these results are supported by new and published high precision radiocarbon data bracketing the age of the rotoiti eruption between 44 8 0 3 and 47 5 2 1 ka cal bp these age data are also in good agreement with a range of previously published estimates based on paleoclimate palynology luminescence dating of enclosing sediment and sedimentation rates in terrestrial and marine settings however these results are at variance with a commonly quoted age of 60 ka largely constrained by a single 40ar 39ar age of an overlying glassy lava flow at a distal tephra site this study demonstrates the potential for combined 238u 230th disequilibrium and u th he dating of zircon in tephra and other volcanic deposits to provide age control in the 40 100 ka time interval a period difficult to constrain using more traditional radiocarbon k ar and 40ar 39ar methods

climatic and topographic controls on the style and timing of late quaternary glaciation throughout tibet and the himalaya defined by 10be cosmogenic radionuclide surface exposure dating abstract temporal and spatial changes in glacier cover throughout the late quaternary in tibet and the bordering mountains are poorly defined because of the inaccessibility and vastness of the region and the lack of numerical dating to help reconstruct the timing and extent of glaciation throughout tibet and the bordering mountains we use geomorphic mapping and 10 be cosmogenic radionuclide crn surface dating in study areas in southeastern gonga shan southern karola pass and central western nyainqentanggulha shan and tanggula shan tibet and we compare these with recently determined numerical chronologies in other parts of the plateau and its borderlands each of the study regions receives its precipitation mainly during the south asian summer monsoon when it falls as snow at high altitudes gonga shan receives the most precipitation 2000 mm a 1 while near the margins of monsoon influence the karola pass receives moderate amounts of precipitation 500 600 mm a 1 and in the interior of the plateau little precipitation falls on the western nyainqentanggulha shan 300 mm a 1 and the tanggula shan 400 700 mm a 1 the higher precipitation values for the tanggula shan are due to strong orographic effects in each region at least three sets of moraines and associated landforms are preserved providing evidence for multiple glaciations the 10 be crn surface exposure dating shows that the formation of moraines in gonga shan occurred during the early mid holocene neoglacial and little ice age on the karola pass during the lateglacial early holocene and neoglacial in the nyainqentanggulha shan date during the early part of the last glacial cycle global last glacial maximum and lateglacial and on the tanggula shan during the penultimate glacial cycle and the early part of the last glacial cycle the oldest moraine succession in each of these regions varies from the early holocene gonga shan lateglacial karola pass early last glacial western nyainqentanggulha shan and penultimate glacial cycle tanggula shan we believe that the regional patterns and timing of glaciation reflect temporal and spatial variability in the south asian monsoon and in particular in regional precipitation gradients in zones of greater aridity the extent of glaciation has become increasingly restricted throughout the late quaternary leading to the preservation of old 100 ka glacial landforms in contrast in regions that are very strongly influenced by the monsoon 1600 mm a 1 the preservation potential of pre lateglacial moraine successions is generally extremely poor this is possibly because lateglacial and holocene glacial advances may have been more extensive than early glaciations and hence may have destroyed any landform or sedimentary evidence of earlier glaciations furthermore the intense denudation mainly by fluvial and mass movement processes which characterize these wetter environments results in rapid erosion and re sedimentation of glacial and associated landforms which also contributes to their poor preservation potential

high precision 40 ar 39 ar dating of quaternary basalts from auckland volcanic field new zealand with implications for eruption rates and paleomagnetic correlations abstract the auckland volcanic field avf which last erupted ca 550 years ago is a late quaternary monogenetic basaltic volcanic field ca 500 km 2 in the northern north island of new zealand prior to this study only 12 out of the 53 identified eruptive centres of the avf had been reliably dated careful sample preparation and 40 ar 39 ar analysis has increased the number of well dated centres in the avf to 35 the high precision of the results is attributed to selection of fresh non vesicular non glassy samples from lava flow interiors sample selection was coupled with separation techniques that targeted only the groundmass of samples with 10 m wide coupled with ten increment furnace step heating of large quantities up to 200 mg of material the overall avf age data indicate an onset at 193 2 2 8 ka an apparent six eruption flare up from 30 to 34 ka and a 10 kyr hiatus between the latest and second to latest eruptions such non uniformity shows that averaging the number of eruptions over the life span of the avf to yield a mean eruption rate is overly simplistic together with large variations in eruption volumes and the large sizes and unusual chemistry within the latest eruptions rangitoto 1 and rangitoto 2 our results illuminate a complex episodic eruption history in particular the rate of volcanism in avf has increased since 60 ka suggesting that the field is still in its infancy multiple centres with unusual paleomagnetic inclination and declination orientations are confirmed to fit into a number of geomagnetic excursions with five identified in the mono lake two within the laschamp one within the post blake or blake and two possibly within the hilina pali

using paleoseismology and tephrochronology to reconstruct fault rupturing and hydrothermal activity since c 40 ka in taupo rift new zealand abstract the taupo volcanic zone tvz in north island new zealand is the on land continuation of the tonga kermadec arc formed in the quaternary at the obliquely convergent boundary of the pacific and australian tectonic plates the central tvz is a region of intense silicic volcanism and active rifting with a very high heat flux within this zone is a dynamic landscape affected by a dense active fault network the taupo rift in this rift the ngakuru graben hosts fossil hydrothermal systems in an area parallel to numerous active faults including the east strand of whirinaki fault that forms a major structure using various geoscientific techniques including mapping stratigraphy paleoseismic trenching and tephrostratigraphy in conjunction with lidar derived dems we reconstruct and date the fault s rupture history along with hydrothermal activity including silica sinter development since c 40 000 calendar years ago 40 cal ka at a site near hossack road called meade ages for kawakawa c 25 4 cal ka okareka c 21 8 cal ka rotorua c 15 6 cal ka rotoma c 9 4 cal ka and taupo c 1 7 cal ka tephras enabled us to date five identified fault rupture events using the meade trench excavation slip rates of 2 66 0 77 mm yr pre kawakawa tephra 0 28 0 04 mm yr between c 25 4 ka and taupo and 0 51 0 19 mm yr post taupo and the recurrence interval of 5500 cal yr during the last c 25 4 cal kyr all correlate with events of similar ages determined from studies on other trenches on whirinaki fault intercalated with tahuna tephra c 39 3 cal ka and additionally dated at c 38 9 cal ka using radiocarbon the hydrothermal sinter began developing at the meade site at c 39 cal ka and ceased by c 21 8 cal ka marked by okareka tephra we examine the causative relationship between fault activity and the development of sinter by comparing the chronology of volcanic eruptions and fault rupturing events with that of sinter formation as recorded in three neighbouring sites mangatete matthews and fitzpatrick the findings improve understanding of the complex rupture behaviour of faulting and provide evidence for relationships between tectonic and hydrothermal activities which were additionally influenced by the impacts of climatic change and geomorphic processes on landscape evolution within the late quaternary period the study also exemplifies the unique value of tephrochronology in helping to disentangle complex geological deposits and events in an extremely dynamic part of the earth s surface the taupo rift

sub seasonal oxygen and carbon isotope variations in shells of modern radix sp gastropoda from the tibetan plateau potential of a new archive for palaeoclimatic studies carbon and oxygen isotope ratios have been measured for nine aragonite shells of the gastropod genus radix from the lake bangda co 30 29 n 97 04 e 4450 m a s l at the south eastern edge and from two characteristic sites at the lake kyaring co 31 09 n 88 17 e 4650 m a s l on the central tibetan plateau radix shells were sampled for isotope ratio analysis with high spatial resolution along the ontogenetic spiral of growth providing the basis of isotope records with a sub seasonal time resolution 18o values of shells from bangda co are on average 15 0 relative to pdb and the pattern exhibits a clear onset and progression of the summer monsoon precipitation indicated by a strong amount effect this pattern mirrors the precipitation pattern in the respective year and region as expected for a small surface area ca 0 3 km2 and shallow 5 m lake or habitat with short water residence times and little evaporative 18o enrichment of the lake water in contrast 18o values of radix shells from kyaring co habitat a which is connected to the deep several tens of metres and big surface area ca 660 km2 lake average at 13 0 consistent with a higher evaporation rate and longer water residence time the latter is supported by more 18o enriched water in this habitat the 18o values of radix shells from kyaring co habitat b are nearly as low as shells from bangda co due to the similar habitat characteristic but isotopic patterns of these shells exhibit a weaker amount effect in both lake systems 13c values of the shells are coupled with oxygen isotopes because a large amount of isotopically light carbon is washed from mountain slopes into the lake during the rainy season although other processes influence the isotopic patterns e g biological productivity 13c or temperature 18o these influences are minor compared with the monsoon signal or the effect of evaporation in the radix shell records the overall weaker amount effect in radix shells from kyaring co habitat b compared with shells from bangda co are consistent with a current decreasing monsoon influence from the south eastern edge towards the central tibetan plateau thus fossil shells of the gastropod genus radix are a valuable archive for reconstructing climatic and environmental changes on the tibetan plateau and provide information about former habitat sizes and depths

contrasting punctuated zircon growth in two syn erupted rhyolite magmas from tarawera volcano insights to crystal diversity in magmatic systems abstract two mineralogically and chemically distinct rhyolite magmas t1 and t3 were syn erupted from the same conduit system during the 21 9 ka basalt intrusion triggered okareka eruption from tarawera volcano new zealand high spatial resolution u th disequilibrium dating of zircon crystals at the 3 5 m scale reveals a protracted yet discontinuous zircon crystallization history within the magmatic system both magma types contain zircon whose interiors predate the eruption by up to 200 ka the dominant age peak in the t1 magma is 30 ka with subordinate peaks at 45 75 and 100 ka whereas the t3 magma has a dominant zircon interior age peak at 90 ka with smaller modes at 35 and 150 ka these patterns are consistent with isolated pockets of crystallization throughout the evolution of the system crystal rim analyses yield ages ranging from within error of the eruption age to at least 90 ka prior to eruption highlighting that zircon crystallization frequently stalled long before the eruption continuous depth profiling from crystal rims inward demonstrates protracted growth histories for individual crystals up to 100 ka that were punctuated by asynchronous hiatuses of up to 30 ka in duration disparate zircon growth histories can result from localized thermal perturbations caused by mafic intrusions into a silicic reservoir the crystal age heterogeneity at hand sample scale requires considerable crystal transport and mixing we propose that crystal mixing was achieved through buoyancy instabilities caused by mafic magma flow through crystal mush a terminal pre eruptive rejuvenation event was capable of mobilizing voluminous melts that erupted but was too short

the auckland volcanic field new zealand geophysical evidence for structural and spatio temporal relationships abstract geophysical data from the monogenetic auckland volcanic field reveal complex structural and spatio temporal relationships at different scales the volcanic field is coincident with regional magnetic and gravity anomalies that mark a major crustal suture and with a discontinuity marking a significant structural asperity here the linear regional magnetic anomaly splays into a wide band of nnw trending lineaments arising from serpentinised shear zones in the upper crust that matches the extent of the volcanic field and that may reflect a region of crustal weakness creating preferential permeability however there appears to be no simple correlation between the locations of individual vents and these lineaments that might delineate more shallow structural controls with this orientation probably as a consequence of other structural influences high resolution aeromagnetic data over the volcanic field show that the volcanoes have a wide range of magnetic signatures indicating a variability of subsurface structure scoria cone volcanoes typically have strong anomalies up to several 100 nt whilst tuff ring volcanoes typically have weak anomalies less than 50 nt though the surface geology is not always an indicator of the nature and extent of the subsurface deposits both cone and tuff ring volcanoes in the auckland field appear to be underlain by subsurface bowl shaped bodies of basalt implying that their eruption histories commonly involve lava ponding into early excavated craters the present geophysical data give no evidence for subsurface dyke like structures or for substantial near surface volumes of basaltic rocks where there are no known eruption centres or buried flows aeromagnetic and palaeomagnetic data suggest that a number of adjacent vents with an implied structural linkage may be contemporaneous though other examples occur where vents of clearly different ages exploit the same apparent structure a unique feature of the auckland field is that at least 5 widely separated and structurally unrelated volcanoes are contemporaneous these observations highlight the spatial and temporal heterogeneities that can occur in monogenetic fields and have an important bearing on recurrence rates and temporally linked eruptions which are probably more common than is generally supposed and are key factors in statistically based hazard assessments

migration of volcanism in the san francisco volcanic field arizona the remanent magnetization of volcanic rocks has been determined at 650 sites in the san francisco volcanic field in the southern part of the colorado plateau the polarity of remanent magnetization combined with k ar age determinations spatial and petrographic associations stratigraphic relations and state of preservation of the cinder cones provides a basis for assignment to known magnetic polarity epochs of 610 mafic vents and 100 intermediate to silicic flows flow sequences and vents the age assignments for basaltic rocks include 243 brunhes 0 73 ma vents 220 matuyama 0 73 to 2 48 ma vents and 147 pre matuyama 2 48 to about 5 0 ma vents basaltic volcanism migrated northeastward before matuyama time at a rate of 1 2 cm yr and eastward s87 5 e over the past 2 5 m y at a rate of 2 9 0 3 cm yr concomitant acceleration in total magma production from 75 to 1 400 10 6 km3 yr and frequency of basaltic eruptions from 1 per 17 000 yr to 1 per 3 000 yr occurred between 5 and 0 25 ma for the past 0 25 m y magma production 180 10 6 km3 yr and perhaps eruption frequency have decreased this evolutionary sequence coupled with the lead and strontium isotopic composition of the rocks can be explained by magmatism caused by shear heating at the base of the lithosphere we propose that this eastward drift of volcanic activity represents absolute westward motion of the north american plate our model is in agreement with a model in which the african plate is fixed to the deep mantle

tools and techniques for developing tephra stratigraphies in lake cores a case study from the basaltic auckland volcanic field new zealand abstract probabilistic hazard forecasting for a volcanic region relies on understanding and reconstructing the eruptive record derived potentially from proximal as well as distal volcanoes tephrostratigraphy is commonly used as a reconstructive tool by cross correlating tephra deposits to create a stratigraphic framework that can be used to assess magnitude frequency relationships for eruptive histories when applied to widespread rhyolitic deposits tephra identifications and correlations have been successful however the identification and correlation of basaltic tephras are more problematic here using tephras in drill cores from six maars in the auckland volcanic field avf new zealand we show how x ray density scanning coupled with magnetic susceptibility analysis can be used to accurately and reliably identify basaltic glass shard bearing horizons in lacustrine sediments and which when combined with the major and trace element signatures of the tephras can be used to distinguish primary from reworked layers after reliably identifying primary vs reworked basaltic horizons within the cores we detail an improved method for cross core correlation based on stratigraphy and geochemical fingerprinting we present major and trace element data for individual glass shards from 57 separate basaltic horizons identified within the cores our results suggest that in cases where major element compositions sio2 cao al2o3 feo mgo do not provide unambiguous correlations trace elements e g la gd yb zr nb nd and trace element ratios e g la yb n gd yb n zr yb n are successful in improving the compositional distinction between the avf basaltic tephra horizons thereby allowing an improved eruptive history of the avf to be reconstructed

distal record of multi sourced tephra in onepoto basin auckland new zealand implications for volcanic chronology frequency and hazards we have documented 80 tephra beds dating from ca 9 5 to 50 ka contained within continuously deposited palaeolake sediments from onepoto basin a volcanic explosion crater in auckland new zealand the known sources for distal 190 km from vent tephra include the rhyolitic taupo volcanic centre 4 and okataina volcanic centre 14 and the andesitic taranaki volcano 40 and tongariro volcanic centre 3 the record provides evidence for four new events between ca 50 and 28 ka mangaone subgroup suggesting okataina was more active than previously known the tephra record also greatly extends the known northern dispersal of other mangaone subgroup tephra ten rhyolitic tephra pre date the rotoehu eruption ca 50 ka and some are chemically dissimilar to post 50 ka rhyolites some of these older tephra were produced by large magnitude events however their source remains uncertain eight tephra from the local basaltic auckland volcanic field avf are also identified interpolation of sedimentation rates allow us to estimate the timing of 12 major explosive eruptions from taranaki volcano in the 27 5 9 5 ka period in addition 28 older events are recognised the tephra are trachytic to rhyolitic in composition all have high k2o contents 3 wt and there are no temporal trends this contrasts with the proximal lava record that shows a trend of increasing k2o with time by combining the onepoto tephra record with that of the previously documented pukaki crater 15 avf basaltic fall events are constrained at 34 6 30 9 29 6 29 6 25 7 25 2 24 2 23 8 19 4 19 4 15 8 and 14 5 ka and three pre 50 ka events this provides some of the best age constraints for the avf and the only reliable data for hazard recurrence calculations the minimum event frequency of both distal and local fall events can be estimated and demonstrates the auckland city region is frequently impacted by ash fall from many volcanoes

mid holocene palaeohydrochemistry and palaeohydrology of yamdrok yumtso southern tibetan plateau reconstructed from δ18o and δ13c of fossil shells of the gastropod radix auricularia palaeohydrochemical and palaeohydrological changes of lakes have seldom been reconstructed from the fossil shells of the gasropod radix auricularia which is a new and potentially high resolution

a model for calculating eruptive volumes for monogenetic volcanoes implication for the quaternary auckland volcanic field new zealand abstract monogenetic basaltic volcanism is characterised by a complex array of behaviours in the spatial distribution of magma output and also temporal variability in magma flux and eruptive frequency investigating this in detail is hindered by the difficulty in evaluating ages of volcanic events as well as volumes erupted in each volcano eruptive volumes are an important input parameter for volcanic hazard assessment and may control eruptive scenarios especially transitions between explosive and effusive behaviour and the length of eruptions erosion superposition and lack of exposure limit the accuracy of volume determination even for very young volcanoes in this study a systematic volume estimation model is developed and applied to the auckland volcanic field in new zealand in this model a basaltic monogenetic volcano is categorised in six parts subsurface portions of volcanoes such as diatremes beneath phreatomagmatic volcanoes or crater infills are approximated by geometrical considerations based on exposed analogue volcanoes positive volcanic landforms such as scoria spatter cones tephras rings and lava flow were defined by using a light detection and ranging lidar survey based digital surface model dsm finally the distal tephra associated with explosive eruptions was approximated using published relationships that relate original crater size to ejecta volumes considering only those parts with high reliability the overall magma output converted to dense rock equivalent for the post 250 ka active auckland volcanic field in new zealand is a minimum of 1 704 km3 this is made up of 1 329 km3 in lava flows 0 067 km3 in phreatomagmatic crater lava infills 0 090 km3 within tephra tuff rings 0 112 km3 inside crater lava infills and 0 104 km3 within scoria cones using the minimum eruptive volumes the spatial and temporal magma fluxes are estimated at 0 005 km3 km2 and 0 007 km3 ka the temporal volumetric evolution of auckland is characterised by an increasing magma flux in the last 40 ky which is inferred to be triggered by plate tectonics processes e g increased asthenospheric shearing and backarc spreading of underneath the auckland region

rapid change in early holocene environments inferred from lake pupuke auckland city new zealand sediment cores from lake pupuke in auckland city new zealand contain a high resolution millennial to centennial scale record of changing climate and catchment hydrology spanning the past ca 10 000 years here we focus on the period between 9500 25 and 7000 155 cal yr bp during which grain size diatom palaeoecology biogenic silica concentrations sediment elemental and carbon isotope geochemistry reflect changes in sediment sources and lake conditions with a significant event commencing at ca 8240 cal yr bp commensurate with a lowering of lake level faster erosion rates and increased sediment influx with a duration of ca 360 yrs however the changes in the lake are not reflected in the terrestrial vegetation where the pollen record indicates that podocarp forest dominated the auckland region with apparent environmental stability during this part of the early holocene the synchronous change in most of the proxies between ca 8240 and 7880 cal yr bp at lake pupuke indicates the presence of a sustained episode of relatively low lake level and concomitant increased rate of erosion in the early holocene that appears to be at least partly coeval with the 8200 cal yr bp meltwater event proposed for the north atlantic region copyright 2008 john wiley sons ltd

lake level variations of qinghai lake in northeastern qinghai tibetan plateau since 3 7 ka based on osl dating abstract qinghai lake is the largest internally drained lake in china and its unique location makes it sensitive to climate changes late glacial climate changes associated with variation in qinghai lake levels have been intensively investigated for the past 40 years with particular attention paid to lake level fluctuation histories between the last interglacial and the holocene however the details of lake level fluctuations during the holocene are still unclear using both optically stimulated luminescence osl dating of quartz for 22 samples and infra red stimulated luminescence irsl of feldspars only for sample hyw1 whose irsl age is 37 15 years a total of 23 samples are dated from paleoshoreline deposits fluvial sediments and aeolian sands a total of 13 sections near the modern lake shore with ages from 37 15 to 3710 350 years these ages are used to reconstruct the lake level fluctuation history spanning the last 3700 years the results indicate that 1 the youngest irsl age of 37 15 years is in agreement with the independent age of 39 29 years suggesting that luminescence dating is able to date decadal samples for sediments from the study area 2 the lake experienced several oscillations imposed on an overall regressive trend during the past 3700 years 3 the dated paleoshoreline deposits are generally related to warm and wet periods suggesting that those shoreline deposits formed during cold and dry periods if any may have been modified by later transgressions 4 lake level fluctuations during the period of 3700 240 years ago are generally consistent with the climate conditions identified in other proxies with the highest lake level occurring about 1770 years ago and 5 after 240 years ago the lake level dropped more rapidly which is inconsistent with the proxy records showing a warmer and wetter phase

last glacial maximum and holocene lake levels of owens lake eastern california usa abstract stratigraphic investigations of fluvio deltaic and lacustrine sediments exposed in stream cuts quarry walls and deep trenches east of the sierra nevada in owens valley near lone pine california have enabled the reconstruction of pluvial owens lake level oscillations age control for these sediments is from 22 radiocarbon 14 c dates and the identification and stratigraphic correlation of a tephra which when plotted as a function of age versus altitude define numerous oscillations in the level of pluvial owens lake during the latest pleistocene and early holocene we have constructed a lake level altitude curve for the time interval 27 000 cal yr bp to present that is based on the integration of this new stratigraphic analysis with published surface stratigraphic data and subsurface core data pluvial owens lake regressed from its latest pleistocene highstands from 27 000 to 15 300 cal yr bp as recorded by 15 m of down cutting of the sill from the altitudes of 1160 to 1145 m by 11 600 cal yr bp the lake had dropped 45 m from the 1145 m sill this lowstand was followed by an early holocene transgression that attained a highstand near 1135 m before dropping to 1120 m at 7860 7650 cal yr bp that had not been recognized in earlier studies the lake then lowered another 30 m to shallow and near desiccation levels between 6850 and 4300 cal yr bp fluvial cut and fill relations north of lone pine and well preserved shoreline features at 1108 m indicate a minor lake level rise after 4300 cal yr bp followed by alkaline and shallow conditions during the latest holocene the new latest quaternary lake level record of pluvial owens lake offers insight to the hydrologic balance along the east side of the southern sierra nevada and will assist regional paleoclimatic models for the western basin and range

extracting a primary holocene crytoptephra record from pupuke maar sediments auckland new zealand post depositional reworking of volcanic glass shards is a common problem in tephrochronological studies distinguishing between primary and reworked tephra is challenging particularly in cryptotephra investigations that depend on identifying peaks of glass shard concentrations in sediment sequences rather than discrete macroscopic tephra layers here we investigated macro and cryptotephra in sediments of lake pupuke new zealand to identify primary from reworked tephra and thus refine the record of tephra fall events in the region over the last ca 9 cal ka geochemical fingerprinting stratigraphic correlation 14c ages and x ray fluorescence and magnetic susceptibility core scanning were employed to filter out reworked tephra and thus establish a new holocene tephrochronological framework for the region five primary macrotephra layers and 18 primary cryptotephra were identified confidence levels are attached to the newly identified cryptotephra and geochemical characterization of well dated rhyolite tephra was used to establish an associated age model our results suggest that holocene tephra fall from both local and distal volcanoes affected auckland more frequently than previously documented with a possible average frequency of at least once every 424 years furthermore the study demonstrates the importance of identifying the extent of post depositional reworking to establish the veracity of the cryptotephra record

amplified hazard of small volume monogenetic eruptions due to environmental controls orakei basin auckland volcanic field new zealand orakei maar and tuff ring in the auckland volcanic field is an example of a basaltic volcano in which the style and impacts of the eruption of a small volume of magma were modulated by a fine balance between magma flux and groundwater availability these conditions were optimised by the pre 85 ka eruption being hosted in a zone of fractured and variably permeable plio pleistocene mudstones and sandstones orakei maar represents an end member in the spectrum of short lived basaltic volcanoes where substrate conditions rather than the magmatic volatile content was the dominant factor controlling explosivity and eruption styles the eruption excavated a crater 80 m deep that was subsequently filled by slumped crater wall material followed by lacustrine and marine sediments the explosion crater may have been less than 800 m in diameter but wall collapse and wave erosion has left a 1 000 m diameter roughly circular basin a tuff ring around part of the maar comprises dominantly base surge deposits along with subordinate fall units grain size texture and shape characteristics indicate a strong influence of magma water and magma mud interactions that controlled explosivity throughout the eruption but also an ongoing secondary role of magmatic gas driven expansion and fragmentation the tuff contains 70 of material recycled from the underlying plio pliestocene sediments which is strongly predominant in the 2 fraction the magmatic clasts are evolved alkali basalt consistent with the eruption of a very small batch of magma the environmental impact of this eruption was disproportionally large when considering the low volume of magma involved dre 0 003 km3 hence this eruption exemplifies one of the worst case scenarios for an eruption within the densely populated auckland city destroying an area of 3 km2 by crater formation and base surge impact an equivalent scenario for the same magma conditions without groundwater interaction would yield a scoria spatter cone with a diameter of 400 550 m destroying less than a tenth of the area affected by the orakei event

environmental magnetism past present and future environmental magnetism involves the application of rock and mineral magnetic techniques to situations in which the transport deposition or transformation of magnetic grains is influenced by environmental processes in the atmosphere hydrosphere and lithosphere the first explicit description of environmental magnetism as a distinct field was in 1980 since that time environmental magnetism has become a broad field that is finding application in an ever increasing array of scientific disciplines in this review of the present state of environmental magnetic studies we divide the field into three broad but arbitrary categories the first involves the use of mineral magnetic assemblages in the geological record to study physical processes in depositional environments this category includes the correlation of sediment cores using magnetic susceptibility measurements studies of geomagnetic field behavior the analysis of depositional and postdepositional mechanical processes that affect sediments and the examination of magnetic parameters that might represent proxies for paleoclimatic variation the second category encompasses studies of the processes responsible for variations in the magnetic minerals brought into a sedimentary environment these provenance investigations include studies of changes in catchment derived sediment in lakes fluctuations in contributions from terrigenous aeolian and glaciogenic components in deep sea sediments and the origin of atmospheric particulates the final category addresses in situ changes and transformations of magnetic minerals in sedimentary environments including pedogenesis authigenetic diagenetic formation of ferrimagnetic phases dissolution of magnetic minerals due to reductive diagenesis and contributions of biomagnetism to sedimentary magnetism because environmental magnetism can address problems in so many disciplines and because many of these problems may be inaccessible to other techniques it is likely that the scope of environmental magnetism will continue to expand rapidly environmental magnetism is capable of providing important data for studies of global environmental change climatic processes and the impact of humans on the environment all of which are major research initiatives in the international scientific community these factors suggest that environmental magnetism has a bright and diverse future

late holocene climate variability from lake pupuke maar auckland new zealand abstract spectral analyses of quasi annual organo diatomaceous laminae couplets in an auckland maar lake indicate brief sub decadal scale episodes with strong spectral power and long periods of weak to no spectral power between c 1700 to c 550 cal yr bp laminae couplet thickness appears to be a function of changes in wind flow over the basin with enhanced wind flow deepening the mixing zone and providing additional nutrients for laminae formation aeolian dust from australia amplifies the wind signal spectral signals in the high power episodes are focused in

reconstruction of the volcanic history of the tacambaro puruaran area michoacan mexico reveals high frequency of holocene monogenetic eruptions the 690 km2 tacambaro puruaran area located at the arc front part of the michoacan guanajuato volcanic field in the trans mexican volcanic belt tmvb records a protracted history of volcanism that culminated with intense monogenetic activity in the holocene geologic mapping 40ar 39ar and 14c radiometric dating and whole rock chemical analyses of volcanic products provide insights to that history eocene volcanics 55 40 ma exposed at uplifted blocks are related to a magmatic arc that preceded the tmvb early tmvb products are represented by poorly exposed pliocene silicic domes 5 2 ma quaternary 30 km may be related to high rates of magma production at depth and a favorable tectonic setting

tephra evidence for the most recent eruption of laoheishan volcano wudalianchi volcanic field northeast china abstract wudalianchi volcanic field wdlc is one of the youngest intracontinental monogenetic volcanic fields in china the 1719 1721 ce laoheishan huoshaoshan eruption and the 1776 ce laoheishan eruption are the latest eruptions in wdlc based on the local historical records however most of the recent explosive eruptive products around wdlc are attributed to the 1719 1721 ce laoheishan huoshaoshan eruption while less attentions were paid on the 1776 ce laoheishan eruption there are two types of scoria fall deposits around laoheishan volcano i e the upper light grey high vesicular scoria deposit us and below dark low vesicular scoria deposit bs most of the glass shards from us exhibit 4 na2o while bs show 5 content with trachyandesitic to tephriphonolitic in composition that can be clearly distinguished from those from other nearby volcanic regions such as nuomin 150 km to nangelaqiushan lake nglq arxan chaihe 450 km to nglq longgang 700 km to nglq and jingbohu 550 km to nglq a cryptotephra layer is clearly revealed as a distinct peak in magnetic susceptibility measurements from nglq 8 km northwest to laoheishan volcano glass composition of the cryptotephra layer recorded in nglq is similar to the proximal us around laoheishan volcano on basis of historical records and field observations we ascribed us to the 1776 ce laoheishan eruption and bs to the 1719 1721 ce laoheishan huoshaoshan eruption consequently historical records assigned a precise age 1776 ce for the tephra recorded in nglq and thus can be used to refine the age model of these lacustrine sediments

a multiple approach radiometric age estimate for the rotoiti and earthquake flat eruptions new zealand with implications for the mis 4 3 boundary abstract pyroclastic fall deposits of the paired rotoiti and earthquake flat eruptions from the taupo volcanic zone new zealand combine to form a widespread isochronous horizon over much of northern new zealand and the southwest pacific this horizon is important for correlating climatic and environmental changes during the last glacial period but has been the subject of numerous disparate age estimates between 35 1 2 8 and 71 6 ka all errors are 1 s d obtained by a variety of techniques a potassium argon k ar age of 64 4 ka was previously determined on bracketing lavas at mayor island volcano offshore from the taupo volcanic zone we present a new more precise 40ar 39ar age determination on a lava flow on mayor island that shortly post dates the rotoiti earthquake flat fall deposits of 58 5 1 1 ka this value coupled with existing ages from underlying lavas yield a new estimate for the age of the combined eruptions of 61 0 1 4 ka which is consistent with u th disequilibrium model age data for zircons from the rotoiti deposits direct 40ar 39ar age determinations of plagioclase and biotite from the rotoiti and earthquake flat eruption products yield variable values between 49 6 2 8 and 125 3 10 0 ka with the scatter attributed to low radiogenic ar yields and or alteration and or inheritance of xenocrystic material with inherited ar rotoiti earthquake flat fall deposits occur in new zealand in association with palynological indicators of mild climate attributed to marine isotope stage mis 3 and thus used to suggest an age that is post 59 ka the natures of the criteria used to define the mis 4 3 boundary in the northern and southern hemispheres however imply that the new 61 ka age for the rotoiti earthquake flat eruption deposits will provide the inverse namely a more accurate isochronous marker for correlating diverse changes across the mis 4 3 boundary in the southwest pacific

shallow seated explosions in the construction of the motukorea tuff ring auckland new zealand evidence from lithic and sedimentary characteristics at least 52 eruption centres are scattered within the 360 km2 auckland volcanic field avf motukorea now an island in the waitemata harbour is one of 39 avf volcanoes that experienced a phreatomagmatic explosive phase before a magmatic phase the volcano erupted through a 200 300 m thick consolidated mudstone sandstone sequence of the miocene waitemata group which overlies the waipapa terrane greywacke basement detailed field descriptions of the sedimentary characteristics of the early phreatomagmatic deposits were carried out along with examination of lithics the ejecta ring deposit comprises 55 to 60 vol lithics of which waitemata group fragments constitute approximately 90 vol whereas 10 vol are waipapa fragments suggesting a dominance of shallow fragmentation the sedimentary characteristics of the stratigraphic sequence at motukorea suggest a dominance of wet surges at the beginning of the eruption with progression into drier sequences upwards this is reflected in increasing inter bedded juvenile pyroclast dominated fall deposits up sequence these characteristics are attributed to the changing hydrogeological conditions within the diatreme and the host rocks these findings shed light on the eruption dynamics of phreatomagmatic eruptions through consolidated rocks in the avf and enable the depiction of a scenario of future eruptions within the field in similar substrates

paleovegetation of marine isotope stages 4 and 3 in northern new zealand and the age of the widespread rotoehu tephra abstract paleolake sediment constrained by tephrochronology from onepoto basin volcanic crater in auckland northern new zealand 36 48 s provides one of the few uninterrupted records of paleovegetation for marine oxygen isotope stages mis 4 and 3 76 000 26 000 yr b p in the region this period was characterized by cool temperate conifer hardwood forest that lacked some of the warmer taxa typical of the holocene the period 64 400 60 500 yr b p was marked by opening of forest canopy and expansion of small trees and shrubs and correlates to the thermal minima of mis 4 however the landscape was never as open as the forest shrubland mosaic of the mis 2 the beginning of mis 3 60 500 50 500 yr b p was marked by the dramatic expansion and then decline of conifer hardwood forest dominated by dacrydium cupressinum a species that prefers wetter conditions this forest was succeeded by the typically montane nothofagus at 50 500 yr b p corresponding to a thermal decline thus mis 3 began with an abrupt change to moist cool conditions that lasted about 5000 yr followed by gradual cooling and dryer conditions this supports some interpretations from other parts of the southwest pacific region that mis 3 was a period of increased precipitation the widespread and stratigraphically important rotoehu tephra erupted from okataina volcanic centre has been variously dated at 45 000 65 000 yr b p at onepoto sedimentation rate and paleovegetation reconstruction imply an age of c 44 300 yr b p the tephra provides a correlation horizon in the marine and terrestrial realms during a period mis 3 difficult to date by radiometric methods

phreatomagmatic eruptions through unconsolidated coastal plain sequences maungataketake auckland volcanic field new zealand abstract maungataketake is a monogenetic basaltic volcano formed at 85 89 ka in the southern part of the auckland volcanic field avf new zealand it comprises a basal 1100 m diameter tuff ring with a central scoria spatter cone and lava flows the tuff ring was formed under hydrogeological and geographic conditions very similar to the present the tuff records numerous density stratified wet base surges that radiated outward up to 1 km decelerating rapidly and becoming less turbulent with distance the pyroclastic units dominantly comprise fine grained expelled grains from various sedimentary deposits beneath the volcano mixed with a minor component of juvenile pyroclasts 35 vol subtle lateral changes relate to deceleration with distance and vertical transformations are minor pointing to stable explosion depths and conditions with gradual transitions between units and no evidence for eruptive pauses this volcano formed within and on 60 m thick plio pleistocene poorly consolidated highly permeable shelly sands and silts kaawa formation capped by near impermeable water saturated muds tauranga group these sediments rest on moderately consolidated miocene aged permeable turbiditic sandstones and siltstones waitemata group magma water fuelled thermohydraulic explosions remained in the shallow sedimentary layers excavating fine grained sediments without brittle fragmentation required on the whole the resulting cool wet pyroclastic density currents were of low energy the unconsolidated shallow sediments deformed to accommodate rapidly rising magma leading to development of complex sill like bodies and a range of magma water contact conditions at any time the weak saturated sediments were also readily liquefied to provide an enduring supply of water and fine sediment to the explosion loci changes in magma flux and or subsequent stabilisation of the conduit area by a lava ring barrier led to ensuing strombolian and fire fountaining eruption phases future eruptions in littoral environments around auckland are likely to be of this type producing base surges that rapidly decrease in energy over short runout distances 1 km

decoupled crystallization and eruption histories of the rhyolite magmatic system at tarawera volcano revealed by zircon ages and growth rates we obtained u th disequilibrium age data on zircons from each of the four rhyolite eruptions that built tarawera volcano in the last 22 ka within the okataina volcanic center ovc caldera new zealand secondary ion mass spectrometry analyses on unpolished euhedral crystal faces that lack resorption features show that crystal growth variously terminated from near eruption age to 100 ka prior to eruption age depth profiling of crystals reveals long periods of continuous 34 ka and discontinuous growth 90 ka growth hiatuses of up to 40 ka duration occur but do not all relate to obvious resorption surfaces age differences up to similar magnitude are found on opposing faces of some crystals suggesting episodes of partial exposure to melts these features are best explained by periodic complete or partial sub solidus storage and or inclusion in larger crystal phases followed by rapid liberation prior to eruption this is supported by high abundances of u and th 500 2 000 ppm in some zircons consistent with periods of high crystallinity 70 in the magmatic system based on crystal melt partitioning contemporaneous but contrasting rim ward trends of these elements within crystals even in the same lava hand sample require synchronous growth in separate melt bodies and little connectivity within the system but also significant crystal transport and mixing prior to eruption many crystals record continuity of growth through the preceding 60 ka ovc caldera collapse and subsequent eruptions from tarawera this demonstrates a decoupling between eruption triggers such as shallow crustal extension and mafic intrusion and the crystallization state of the ovc silicic magmatic system the data highlights the need to distinguish between the time for accumulation of eruptible magma and the long term magma residence time based on the age of crystals with high closure temperatures when assessing the potential for catastrophic eruptions

longevity of a small shield volcano revealed by crypto tephra studies rangitoto volcano new zealand change in eruptive behavior of a basaltic field abstract the life span of small volcanoes in terrestrial basaltic fields commonly considered monogenetic can be difficult to assess due to a paucity of datable materials capable of providing a 102 103 year age resolution we have used microscopic tephra layers crypto tephra in lake sediments to determine the longevity of rangitoto volcano a small shield that represents the most recent volcanism in the auckland volcanic field avf new zealand previous studies suggested construction in a relatively short interval at 550 500 cal yrs bp in contrast the tephra record shows evidence of intermittent activity from 1498 140 to at least 504 6 cal yrs bp a longevity of 1000 years rangitoto volcano is thought to represent about half the magma erupted in the 250 ka history of avf thus the avf has experienced a dramatic shift to prolonged and voluminous central vent volcanism in its most recent history this demonstrates the difficulty in determining time erupted volume relationships in such fields previous avf hazard risk modeling based on isolated short lived

late quaternary transition from lacustrine to a fluvio lacustrine environment in the north western nam co tibetan plateau china abstract holocene sediments from a 9 m high outcrop at the gangyasang qu s entry into lake nam co on the south eastern tibetan plateau were studied in a multiproxy approach the lowermost part of the section is of early holocene age and consists of varved sediments deposited in a proglacial lake geomorphological investigations of fossil beach ridges and fossil cliff lines in the littoral zone of nam co indicate a late pleistocene lake level high of 29 m above the present level a warming is visible in ostracode rich silts deposited after 9 6 ka bp an ostracode based transfer function estimates a lake level 28 m higher than today from this time until about 5 2 ka bp a late pleistocene lake level high was accompanied by an increase in lake size causing nam co to overflow into the lower course of gangyasang qu where a bay with slack water conditions formed between 4 2 and 1 3 ka bp the lake level was approximately 10 m higher than today the progradation of the gangyasang qu delta into nam co and the decreasing lake level shifted the study site into a fluvio lacustrine environment the sandy character and relatively low numbers of ostracode valves in the topmost sediments indicate increased fluvial activity possibly due to a temporary increase in flood frequency this facies lasted at least until 1 3 ka bp when the lake level of nam co dropped again and the river incised more than 10 m into the underlying fluvio lacustrine and lacustrine sediments

in situ cosmogenic 3he and 36cl and radiocarbon dating of volcanic deposits refine the pleistocene and holocene eruption chronology of sw peru constraining the age of young lavas which generally fall outside the effective range of traditional geochronology methods remains a key challenge in volcanology limiting the development of high resolution eruption chronologies we present an in situ cosmogenic 3he and 36cl surface exposure chronology alongside new minimum limiting 14c ages documenting young eruptions at five sites in the western cordillera southern peru four 3he dated lavas on the nevado coropuna volcanic complex hitherto thought to be dormant indicate that the central dome cluster is young and potentially active two holocene lavas on the easternmost dome are the youngest directly dated lavas in peru to date east of coropuna lava domes and block lava flows represent the most extensive output to date of nevado sabancaya one of peru s most active volcanoes two 3he measurements confirm the holocene age of these deposits and expand the chronology for one of the youngest major lava fields in peru 36cl surface exposure ages from the purupurini dome cluster and nevado casiri document middle late holocene episodes of effusive activity while basal 14c ages from a lava dammed wetland constrain an effusive eruption at mina arcata north of coropuna to the late glacial period these new data advance the recent western cordillera volcanic record whilst demonstrating both the considerable potential and fundamental limitations of cosmogenic surface exposure methods for such applications

the 26 5 ka oruanui eruption new zealand an introduction and overview abstract the 26 5 ka oruanui eruption from taupo volcano in the central north island of new zealand is the largest known wet eruption generating 430 km3 of fall deposits 320 km3 of pyroclastic density current pdc deposits mostly ignimbrite and 420 km3 of primary intracaldera material equivalent to 530 km3 of magma erupted magma is 99 rhyolite and 90 pdc deposits range from mm to cm thick ultra thin veneers enclosed within fall material to 200 m thick ignimbrite in proximal areas the farthest travelled 90 km most energetic pdcs velocities 100 m s 1 occurred during phase 8 but the most voluminous pdc deposits were emplaced during phase 10 grain size variations in the pdc deposits are complex with changes seen vertically in thick proximal accumulations being greater than those seen laterally from near source to most distal deposits modern lake taupo partly infills the caldera generated during this eruption a 140 km2 structural collapse area is concealed beneath the lake while the lake outline reflects coeval peripheral and volcano tectonic collapse early eruption phases saw shifting vent positions development of the caldera to its maximum extent indicated by lithic lag breccias occurred during phase 10 the oruanui eruption shows many unusual features its episodic nature wide range of depositional conditions in fall deposits of very wide dispersal and complex interplay of fall and pdc activity

early syn rift evolution in the west cameros basin upper jurassic nw iberian range spain and pedogenetic calcretes in early syn rift alluvial systems upper jurassic west cameros basin northern spain reply first we would like to highlight our appreciation of dr platt s and dr wright s comments and the opportunity they give us to discuss some aspects of our papers sacristan horcajada et al 2015 2016 improving the final state of our work knowledge about sedimentology of alluvial systems has had an important development in recent years with new proposals for models in rift basins where tectonics play a predominant role nichols and fisher 2007 hartley et al 2010 weismann et al 2010 fielding et al 2012 the differential behavior of the extensional structures during the earliest syn rift stage tithonian in the west cameros basin played a key role in the architecture of the various alluvial systems sacristan horcajada et al 2015 as well as the distribution of various calcrete sequences sacristan hocajada et al 2016 we discuss the points raised drs platt and wright in the same order they established with respect to this section of the discussion we consider it important to emphasize several points 1 the types of early syn rift alluvial systems studied from our point of view in the case of the nuestra senora de brezales formation it would be an oversimplification to refer only to alluvial fans the brezales fm abbreviation of nuestra senora de brezales fm see below has been interpreted as the result of clastic sedimentation in alluvial systems alluvial and fluvial fans developed in generally small halfgrabens specifically in our recent studies detailed facies analysis stratigraphic framework and paleogeographic reconstructions have proved that the arrangement of the depositional system was complex and heterogeneous due to the differential behavior of the extensional structures that controlled each halfgraben sacristan horcajada et al 2012b sacristan horcajada et al 2013 sacristan horcajada et al 2015 this different tectonic activity produced that each halfgraben basin displayed different sedimentary architectures and alluvial records although they were developed under similar climatic conditions

eruption recurrence rates in a basaltic volcanic field based on tephra layers in maar sediments implications for hazards in the auckland volcanic field long term eruption recurrence rates in monogenetic basaltic volcanic fields are difficult to assess because of low eruption frequencies but they are important because of the spread of human infrastructure into such fields auckland city new zealand is built on the auckland volcanic field a young 250 ka basaltic volcanic field in the absence of abundant material for radiocarbon and isotopic dating an eruptive chronology based on basalt tephra layers deposited in maar lakes was developed interbedded well dated tephra layers from silicic volcanoes some 220 270 km to the south were used as age constraints the basalt tephra layers reveal a pattern of activity not evident from the temporal spatial distribution of volcanic landforms twenty four basalt tephra layers over the last 80 k y represent an average frequency of one per 3 5 k y recurrence times vary from 0 5 k y to 20 k y and show no temporal trend the tephra record shows a major flare up in explosive activity at 32 2 ka during heightened activity at 34 24 ka this was related to a period of simultaneous eruptions from several volcanoes across the field revealed by paleomagnetic and isotopic ages in contrast the field has been relative quiet during the last 20 k y punctuated by the construction of a shield volcano at 0 7 ka thus the surface manifestation of magmatism varies greatly with time complicating long term volcanic hazard forecasting despite the high risk from future basalt activity because of proximity ash fall from distant andesite volcanoes is the most frequently occurring volcanic hazard in auckland city

spatial distribution and alignments of volcanic centers clues to the formation of monogenetic volcanic fields monogenetic basaltic volcanic fields occur worldwide in tectonic environments ranging from extensional to convergent understanding similarities and differences between these fields may help to characterize key controls on their generation such volcanic fields consist of numerous volcanic centers each of which represents a pathway of magma from its source to the surface we analyzed the spatial distribution of volcanic centers in 37 monogenetic volcanic fields and assuming that the distribution of volcanic centers relative to each other is matched by a similar source pattern within the mantle applied the following methods for each 1 the poisson nearest neighbor pnn analysis representing the degree to which the distribution of the volcanic centers departs from a predicted poisson distribution and 2 a volcanic alignment analysis to ascertain the preferential pathways if any used by the magma to reach the surface this is the first comprehensive global comparison of such analyses magma pathways within the brittle upper crust are influenced to various degrees by two end member situations 1 formation of new extension fractures perpendicular to the least compressive stress 3 and 2 re activation of pre existing fractures that are near parallel to the maximum principal stress 1 the results of the pnn analysis show that independently of the tectonic environment most volcanic fields display a clustered distribution of their volcanic centers alignment analysis shows that either the ambient tectonic environment exerts a strong influence on the preferential orientations of the volcanic alignments or that it is in competition with other factors e g pre existing structures local stress changes due to older intrusions overall these results indicate that the propagation of the magma and therefore the spatial distribution of the volcanic centers within volcanic fields is the product of an interplay between deep level influences i e nature of the magma source and shallow level influences i e stress field pre existing crustal structures of the lithosphere

correlation of basaltic tephra from mt wellington volcano implications for the penultimate eruption from the auckland volcanic field abstract mt wellington volcano in the auckland volcanic field is a basaltic complex comprising several vents tuff rings cones and lava flows interstitial glass in shard and lapilli groundmass displays considerable variability 41 48 wt sio 2 anhydrous but within sample variation is relatively narrow mostly 2 allowing two broad compositional affinities to be recognised that relate to the eruptive sequence the tuff ring contains lower sio 2 glasses whereas the main cinder cone comprises higher sio 2 glasses fe ti oxides also display a moderate compositional range ulvospinel usp 40 55 although within sample variation is generally narrower 5 usp allowing tuff ring deposits usp 50 compositional outliers are evident amongst the fe ti oxide crystals in many samples and probably result from slow post depositional cooling and or variable oxidation conditions during syn eruption recycling at the vent although abundant microlites restrict the deposits that can be geochemically fingerprinted randomly selected analyses of glass shards show only limited variation within samples 1 wt sio 2 suggesting that variable microlite formation had little effect on the residue melt the larger compositional differences such as that between the tuff ring and cinder cone also do not appear to be related to microlite formation because both deposits display a similar range in microlite content correlations between the edifice and distal deposits in maar sediments provide insights to the eruption episode they demonstrate that the main cinder cone was a late stage event there was no significant hiatus months to decades within the entire sequence and that the cinder cone was responsible for the wide dispersal of ejecta in the region by placing the mt wellington event within a stratigraphic framework of well dated tephra from other volcanoes it is possible to evaluate radiocarbon chronologies and constrain the eruption age to 10 000 bp

volcanic risk ranking for auckland new zealand ii hazard consequences and risk calculation in a companion paper a methodology for ranking volcanic hazards and events in terms of risk was presented and the likelihood and extent of potential hazards in the auckland region new zealand investigated in this paper the effects of each hazard are considered and the risk ranking completed values for effect are proportions of total loss and as with likelihood and extent are based on order of magnitude

shallow seated controls on styles of explosive basaltic volcanism a case study from new zealand abstract the pyroclastic deposits of many basaltic volcanic centres show abrupt transitions between contrasting eruptive styles e g hawaiian versus strombolian or dry magmatic versus wet phreatomagmatic these transitions are controlled dominantly by variations in degassing patterns magma ascent rates and degrees of interaction with external water we use crater hill a 29 ka explosive effusive monogenetic centre in the auckland volcanic field new zealand as a case study of the transitions between these end member eruptive styles the crater hill eruption took place from at least 4 vents spaced along a nne trending 600 m long fissure that is contained entirely within a tuff ring generated during the earliest eruption phases early explosive phases at crater hill were characterised by eruption from multiple unstable and short lived vents later dominantly extrusive volcanism took place from a more stable point source most of the crater hill pyroclastic deposits were formed in 3 phreatomagmatic p and 4 dry magmatic m episodes forming in turn the outer tuff ring and maar crater p1 m1 p2 and scoria cone 1 m2 m4 this activity was followed by formation of a lava shield and scoria cone 2 purely wet activity is represented by the bulk of p1 and p2 and purely dry activity by much of m2 m4 however m1 and parts of m2 and m4 show evidence for simultaneous eruptions of differing style from adjacent vents and rapid variations in the extent and timing of magma water interaction at each vent the nature of the wall rock lithics and these rapid variations in inferred water magma ratios imply interaction was occurring mostly at depths of 80 m and the vesicularity patterns in juvenile clasts from these and the p beds imply that rapid degassing occurred at these shallow levels we suggest that abrupt transitions between eruptive styles in time and space at crater hill were linked to changes in the local magma supply rate and patterns and vigour of degassing during the final metres of ascent

geomagnetic excursion captured by multiple volcanoes in a monogenetic field 1 five monogenetic volcanoes within the quaternary auckland volcanic field are shown to have recorded a virtually identical but anomalous paleomagnetic direction mean inclination and declination of 61 7 and 351 0 respectively consistent with the capture of a geomagnetic excursion based on documented rates of change of paleomagnetic field direction during excursions this implies that the volcanoes may have all formed within a period of only 50 100 years or less these temporally linked volcanoes are widespread throughout the field and appear not to be structurally related however the general paradigm for the reawakening of monogenetic fields is that only a single new volcano or group of closely spaced vents is created typically at intervals of several hundred years or more therefore the results presented show that for any monogenetic field the impact of renewed eruptive activity may be significantly under estimated especially for potentially affected population centres and the siting of sensitive facilities