revised calendar date for the taupo eruption derived by 14c wiggle matching using a new zealand kauri 14c calibration data set taupo volcano in central north island new zealand is the most frequently active and productive rhyolite volcano on earth its latest explosive activity about 1800 years ago generated the spectacu

characteristics of three recent earthquake sequences in the taupo volcanic zone new zealand abstract we have analysed three recent earthquake sequences in the northern part of the taupo volcanic zone a 1998 sequence at haroharo with a largest event of ml 4 8 and a 2004 sequence near lake rotoehu largest event ml 5 4 had normal b values and displayed an aftershock decay pattern with most of the activity within the first few days in contrast a 2005 sequence a few tens of kilometres away at matata largest event ml 4 1 had very different characteristics with a slow development and decay no tendency for enhanced seismicity after the larger events and a very high b value the focal mechanisms of the rotoehu and matata events are normal and have stress patterns consistent with the geodetically observed extension of the taupo volcanic zone in a northwest southeast direction the extensive recent volcanism in the okataina volcanic centre does not seem to have affected the stress pattern in this area the rotoehu sequence showed a strong resemblance particularly in the time distribution of events to the well known swarm activity in the vogtland region on the german czech border in which larger events were followed by a burst of seismicity as in a normal aftershock sequence some of the arguments that have been advanced to explain the vogtland swarm as seismicity induced by fluid injection apply to rotoehu but there is no direct evidence of fluid involvement the matata sequence appears to have a continuing trigger mechanism either a slow injection of fluid or a slow slip event in an environment in which opening pore spaces prevent high overpressures developing the matata sequence occurred close to the area of the 1987 ml 6 3 edgecumbe earthquake so exhibiting two extremes of seismic temporal pattern namely mainshock aftershock and a swarm with many events of similar magnitude within a small area

discussion on the concepts in paleoenvironmental reconstruction from coal macerals and petrographic indices abstract organic facies analyses quantify the coal constituents and plot various associations to discriminate the paleoenvironment for coal bearing successions this allows the relation of coal composition to mire ecosystems or environments coal petrographic models are used extensively to reconstruct the nature of ancient peat forming environments many authors proposed relations between specific maceral assemblages and or micro lithotypes and peat forming environments the key controlling factors which affect peat environment include hydrogeology redox ph vegetation type clastic influx sedimentation and peat accumulation rate etc recent advancements in coal maceral study and organic petrology reveal the pros and cons of the available indices and models the main reasons for the failure of the petrographic models are oversimplification of the effects of humification on tissue preservation vs destruction the use of post diagenetic processes e g geochemical gelification in determining depositional environments changes in petrographic composition related to floral evolution geological age rank increase and compaction lack of distinction between different inertinite maceral in some models here the widely used petrographic indices and models are reviewed based on the observations of several workers and the applicability and concepts of paleo environmental reconstruction are discussed a multi disciplinary approach including petrography palynology chemistry etc has been recommended which is more logical and scientific than the exclusive use of petrographic composition for paleoenvironmental interpretation

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

the intav intercomparison of electron beam microanalysis of glass by tephrochronology laboratories results and recommendations abstract the international focus group on tephrochronology and volcanism intav of the international union for quaternary research inqua has conducted an intercomparison of tephrochronology laboratories with electron beam microanalytical data on volcanic glasses submitted from 27 instruments at 24 institutions in 9 countries this assessment includes most active tephrochronology laboratories and represents the largest intercomparison exercise yet conducted by the tephrochronology community the intercomparison was motivated by the desire to assess the quality of data currently being produced and to stimulate improvements in analytical protocols and data reporting that will increase the efficacy of tephra fingerprinting and correlation participating laboratories were each supplied with a mount containing three samples for analysis 1 rhyolitic lipari obsidian id3506 2 phonolitic sheep track tephra from mt edziza british columbia canada and 3 basaltic laki 1783 a d tephra a fourth sample rhyolitic old crow tephra was also distributed most laboratories submitted extensive details of their analytical procedures in addition to their analytical results most used some combination of defocused or rastered beam and modest beam current to reduce alkali element migration approximately two thirds reported that they routinely analyze one or more secondary standards to evaluate data quality and instrument performance despite substantial variety in procedures and calibration standards most mean concentrations compare favorably between laboratories and with other data typically four or fewer data contributions had means for a given element on a given sample that differed by more than 2 standard deviations from the overall means obtaining accurate na 2 o concentrations for the phonolitic tephra proved to be a challenge for many laboratories only one half of the data sets had means within 1 standard deviation of the 8 2 wt na 2 o value obtained by other methods one mean is higher and 14 are lower three of the data set means fall below 7 wt na 2 o most submissions had relative precision better than 1 5 for the major elements for low abundance elements the precision varied substantially with relative standard deviations as small as 10 and as large as 110 because of the strong response to this project the tephrochronology community now has a large comparative data set derived from common reference materials that will facilitate improvements in accuracy and precision and which can enable improved use of published data produced by the participating laboratories finally recommendations are provided for improving accuracy precision and reporting of electron beam microanalytical data from glasses

earthquake histories and holocene acceleration of fault displacement rates displacement rates for normal and reverse faults n 57 are generally higher when averaged for the holocene 10 ka than for the late quaternary 300 ka and longer time scales holocene acceleration of displacement rates could be attributed to geological processes that produce increases of tectonic tempo we propose an alternative model in which the observed rate changes arise from variability in earthquake slip and or recurrence coupled with a sampling bias toward those faults that are best represented at the earth s surface and that accrued displacement fastest during the holocene this model is consistent with displacement rates measured over time intervals of as long as 300 ka for 129 faults from the taupo rift new zealand departures of earthquake parameters and associated displacement rates from their long term 300 ka averages are attributed to fault interactions and occur on time intervals inversely related to these long term displacement rates and to regional strain rates

morphometry of scoria cones and their relation to geodynamic setting a dem based analysis abstract the morphometry of a great number of scoria cones belonging to volcanic fields of various geodynamic settings has been measured and analyzed addressing the question whether there is a relation between the prevalent cone shape in a given field and the geodynamic setting of the field itself morphometric analysis was carried out on freely downloadable digital elevation models dems the accuracy of the used dems and the associated error in scoria cone morphometry were determined by cross comparing high resolution lidar derived dems usgs ned tinitaly dem and aster gdem the 10 m tinitaly 01 and usgs ned dems are proven to be suitable for scoria cone morphometry whereas aster gdem can be used reliably for cones with volume greater than 30 10 6 m 3 according to a detailed morphometry of all scoria cones we propose that the cones related to subductional setting show relatively higher values of h c o w co and lower values of w cr w co than the cones related to extensional setting the detected differences can be imputable to peculiar eruption dynamics resulting in slight but systematic changes in shape and differences in lithological and sedimentological characteristics that govern post eruptive erosion to constrain the pathway of scoria cone erosion the detected morphometric changes were also interpreted using a simple linear degradation model utilizing the obtained simulation results the inferred initial cone base and the age of scoria cones we calculated a diffusion coefficient k for several dated cones which are related to the prevalent climate our results despite the high error associated allow to assess the median k for all volcanic fields due to the complexity of the factors behind it is not easy to understand if the prevalent shape characterizing a certain volcanic field is due mainly to sin eruptive or post eruptive mechanisms however our distinction between the two main geodynamic settings may be the first step to decipher these factors

developing sub 5 m lidar dems for forested sections of the alpine and hope faults south island new zealand implications for structural interpretations abstract kilometre wide airborne light detection and ranging lidar surveys were collected along portions of the alpine and hope faults in new zealand to assess the potential for generating sub 5 m bare earth digital elevation models dems from ground return data in areas of dense rainforest bush cover as an aid to mapping these faults the 34 km long franz whataroa lidar survey was flown along the densely vegetated central most portion of the transpressive alpine fault six closely spaced flight lines 200 m apart yielded survey coverage with double overlap of swath collection which was considered necessary due to the low density of ground returns 0 16 m 2 or a point every 6 m2 under mature west coast podocarp broadleaf rainforest this average point spacing 2 5 m allowed for the generation of a robust high quality 3 m bare earth dem the dem confirmed the zigzagged form of the surface trace of the alpine fault in this area originally recognised by norris and cooper 1995 norris and cooper 1997 and highlights that the surface strike variations are more variant than previously mapped the 29 km long hurunui hope lidar survey was flown east of the main divide of the southern alps along the dextral slip hope fault where the terrain is characterised by lower rainfall and more open beech forest flight line spacings of 275 m were used to generate a dem from the ground return data the average ground return values under beech forest were 0 27 m 2 and yielded an estimated cell size suitable for a 2 m dem in both cases the lidar revealed unprecedented views of the surface geomorphology of these active faults lessons learned from our survey methodologies can be employed to plan cost effective high gain airborne surveys to yield bare earth dems underneath vegetated terrain and multi storeyed canopies from densely forested environments across new zealand and worldwide

palaeocirculation across new zealand during the last glacial maximum at 21 ka abstract what circulation pattern drove southern alps glacial advances at 21 ka late 20th century glacial advances in new zealand are commonly attributed to a dual precipitation increase and cooler than normal temperatures associated with enhanced westerly flow that occur under synoptic pressure patterns termed zonal regimes kidson 2000 but was the circulation pattern that supported major southern alps glacial advances during the global lgm similar to the modern analog here a regional climate regime classification rcrc time slice was used to infer past circulation for new zealand during the lgm at 21 ka palaeoclimate information that supported the construction of the 21 ka time slice was derived from the nz intimate climate event stratigraphy ces one new auckland maar proxy record and additional low resolution data sourced from the literature the terrestrial evidence at 21 ka implicates several possibilities for past circulation depending on how interpretations for some proxies are made the interpretation considered most tenable for the lgm based on the agreement between terrestrial evidence marine reconstructions and palaeoclimate model results is an anticyclonic zonal circulation regime characterized by increased influences from blocking highs over the south island during winter and an increase in zonal and trough synoptic types with southerly to westerly quarter wind flow during summer these seasonal circulation traits would have generated lower mean annual temperatures cooler than normal summer temperatures and overall lower mean annual precipitation for new zealand particularly in the western south island at 21 ka the anticyclonic zonal time slice reconstruction presented in this study has different spatial traits than the late 20th century and the early little ice age signatures suggesting more than one type of regional circulation pattern can drive southern alps glacial activity this finding lends support to the hypothesis that temperature over precipitation change is more important as the primary modulator of southern alps ice advances the rcrc approach also demonstrates some subtle advantages of integrating multi proxy data within a palaeocirculation context for new zealand notably because this reconstruction technique enables direct comparisons to coarsely resolved palaeoclimate model outputs that do not have downscaled information

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

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

interdependence of fault displacement rates and paleoearthquakes in an active rift paleoearthquakes at earth s surface often generate faults with variable displacement rates over short time intervals e g 18 k y the nature and origin of these variations and the extent to which they result from systematic and therefore predictable earthquake processes is unresolved we examine the processes underlying fluctuations in displacement rates by charting the accumulation of displacement over the last 60 k y on 25 normal fault traces distributed across the taupo rift new zealand displacement rates become more stable with increasing fault size and are uniform when aggregated across the entire rift the increased stability of fault displacement rates at greater spatial scales suggests that each fault is a component of a kinematically coherent system in which all faults interact and their earthquake histories are interdependent fault interdependencies generate short term complex 18 k y fluctuations in the timing and magnitude of earthquakes but also ultimately result in the stability of displacement rates on million year time scales

the geological history of geysir iceland a tephrochronological approach to the dating of sinter the vertical succession through the discharge apron of geysir up to 3 5 m thick is formed of five lithological units a e units a b c and e are formed of siliceous sinters whereas unit d is a brown ash bed tephra grains in units c d and e came from katla hekla and vei ivotn katla tephra in unit d has been largely altered to palagonite integration of tephrochronological ages historical records and geological and geomorphological relationships shows that the geysir succession developed in four main phases during phase i c 10 000 4000 years ago laminated sinters formed from hot spring waters phase ii initiated c 3300 years ago saw the termination of sinter formation and blanketing of the area with tephra from katla and hekla phase iii c 3000 900 years ago represented by the boundary between units d and e was characterized by weathering and little sinter deposition phase iv was initiated with the re birth of geysir 800 900 years ago sinter deposited from the discharged waters has however been largely confined to the southern part of the discharge apron only limited opal a precipitation has occurred since 1916 because of a decline in geysir9s eruptions

environmental impact of the 1 8 ka taupo eruption new zealand landscape responses to a large scale explosive rhyolite eruption abstract large scale ignimbrite eruptions from rhyolitic caldera volcanoes can trigger geologically instantaneous changes in sedimentary systems over huge areas by either burying existing environments or overloading them with vast quantities of unconsolidated particulate material the post eruption readjustment of the landscape to such perturbations is one of the most dramatic processes in physical sedimentology exemplified here by the 1 8 ka taupo eruption in the central north island of new zealand this eruption generated voluminous fall deposits then climaxed with emplacement of a c 30 km 3 non welded ignimbrite over a near circular area of c 20 000 km 2 approximately 90 of the area but the headwaters of many of the north island s largest rivers were impacted by both the primary pyroclastic fall and flow material large scale post eruption remobilisation of this material coupled with the re establishment of fluvial systems occurred in a distinct sequence as recorded by the evolution of sedimentary facies in different sub environments following an initial period dominated by mass flows re establishment of fluvial systems began with the headward erosion of box canyons through the ponded ignimbrite deposits a process often associated with the break out of temporary lakes aggradational streams developed in these channels rapidly evolved from shallow ephemeral sediment laden outbursts associated with flash flood events to deeper permanent braided rivers before declining sediment yields led to retrenchment of single thread rivers and a return to pre eruption gradients and bedloads years to decades later typically the modern profile of many streams and rivers follow closely their pre eruption profiles and incision and erosion is overwhelmingly confined to the deposits of the eruption itself although the general remobilisation pattern is similar for all impacted river systems detailed studies of the waikato rangitaiki mohaka ngaruroro and whanganui catchments show that the relative timing and scale of each eruption response phase differs between each catchment these reflect differences in catchment physiography and hydrology and the volume and type of pyroclastic material deposited in each ultimately the landscape response reflects the relative spatial distributions of and the volumetric ratios between the volumes of pyroclastic debris water and accommodation space in the basin cf kataoka and manville this volume

a revised age for the kawakawa oruanui tephra a key marker for the last glacial maximum in new zealand abstract the kawakawa oruanui tephra kot is a key chronostratigraphic marker in terrestrial and marine deposits of the new zealand nz sector of the southwest pacific erupted early during the last glacial maximum lgm the wide distribution of the kot enables inter regional alignment of proxy records and facilitates comparison between nz climatic variations and those from well dated records elsewhere we present 22 new radiocarbon ages for the kot from sites and materials considered optimal for dating and apply bayesian statistical methods via oxcal4 1 7 that incorporate stratigraphic information to develop a new age probability model for kot the revised calibrated age 2 standard deviations for the eruption of the kot is 25 360 160 cal yr bp the age revision provides a basis for refining marine reservoir ages for the lgm in the southwest pacific

geothermal mineralization i the mechanism of formation of the beowawe nevada siliceous sinter deposit the siliceous sinter deposit at beowawe nev has a volume of 7 71 x 10 sup 7 m sup 3 and contains 1 28 x 10 sup 11 kg silica this silica precipitated from geothermal solutions that welled up along the malpais fault a graben bounding fault sinter formation involved three steps 1 geothermal solutions saturated with quartz in the reservoir moved to the surface where they cooled and became supersaturated with amorphous silica 2 amorphous silica particles nucleated heterogeneously to produce a colloidal suspension 3 the amorphous silica particles agglomerated and were cemented together by amorphous silica precipitating in the embayments between the particles at least 5 58 x 10 sup 14 kg of geothermal solution must have been produced over time to account for the mass of silica in the beowawe deposit this fluid would have carried at least 4 95 x 10 sup 17 kj of heat to the surface 21 references 6 figures 1 table

volcanic and structural evolution of the okataina volcanic centre dominantly silicic volcanism associated with the taupo rift new zealand article the okataina volcanic centre ovc contains the northeasternmost caldera complex in onshore taupo volcanic zone tvz new zealand sited largely within the taupo rift pyroclastic fall deposits and ignimbrites deposited in the bay of plenty coast area between 420 and 625 ka were probably erupted from ovc and these provide a maximum age for the centre the earliest ignimbrite for which there is good evidence for eruption from ovc is the c 550 ka quartz biotite ignimbrite exposed to the west of lake okataina and to se of ovc this ignimbrite probably correlates with one of the early ignimbrites found in the kawerau geothermal wells and is large enough to have been accompanied by caldera collapse it was followed by extensive rhyolitic explosive eruptions of the murupara subgroup culminating with eruption of the matahina ignimbrite at c 325 ka this c 160 km 3 magma volume eruption was accompanied by caldera collapse to form the southern part of the present day okataina caldera complex a long duration sequence of rhyolite lavas and pyroclastics was then erupted on the southern and western sides of ovc before eruption of the 100 km

stratigraphy chronology styles and dynamics of late quaternary eruptions from taupo volcano new zealand taupo volcano is the southerly of two dormant caldera volcanoes in the rhyolite dominated central portion of the taupo volcanic zone in the north island of new zealand taupo has an average magma output rate of 0 2 m 3 s 1 over the past 65 000 years and is one of the most frequently active and productive rhyolite volcanoes known the structure of the modern inverse volcano was formed largely by caldera collapse associated with the voluminous 22 600 14 c years bp oruanui eruption and has been little modified since except for collapse following the 1850 14 c years bp eruption the products of 28 eruptions labelled psi omega a ldots z all of which post date the oruanui eruption are defined and described here twenty seven of these eruptions are represented by pyroclastic deposits of which three were accompanied by a mappable lava extrusion and one eruption z solely by evidence for a lava extrusion the deposits of seven eruptions b c e s v x and y largely correspond to previously defined tephra formations karapiti poronui opepe waimihia whakaipo mapara and taupo respectively the previously defined motutere and hinemaiaia tephras are reinterpreted to represent the products of 12 eruptions g to r while the remaining eight deposits and one eruption are newly recognized eruption psi occurred at ca 17 200 14 c or 20 500 calibrated years bp and eruption z about 1740 calibrated years bp eruption volumes vary by more than three orders of magnitude between 0 01 and more than 44 km 3 and repose periods by more than two orders of magnitude from ca 20 to 6000 years the eruption deposits reflect great variations in parameters such as volume the dispersal characteristics of the fall deposits the presence or absence of intraeruptive time breaks the formation of pyroclastic flows the degree of magma water interaction the vesiculation state of the magma on fragmentation and the relative proportions of juvenile obsidian versus foreign lithologies in the lithic fractions all but seven fall deposits are plinian in dispersal two y1 and probably w are sub plinian one y5 has been termed ultraplinian while psi and a are too poorly preserved for their dispersal to be assessed the lengths of repose periods in the post oruanui sequence range are not randomly distributed but show self similar properties fractal dimensionality repose intervals r in years of not more than 350 years follow n 53 5r 0 21 and those of not less than 350 years follow n 2096r 0 83 where n is the number of eruptions the shorter repose periods may reflect triggering processes such as regional extension affecting magma bodies during their viable lifetimes while longer repose intervals i e not less than 350 years may reflect an episodicity of major rifting events or the production of magma bodies below the volcano bulk volumes v in km 3 of the eruption products also show self similar properties fractal dimensionality with n 6 17v 0 46 however there are then apparently random relationships between eruption volumes and the preceding or succeeding repose period such that prediction of the time and size of the next eruption is impossible the post oruanui activity at taupo represents noise superimposed on the more uniform longer term activity in the central taupo volcanic zone where large greater than 100 km 3 eruptions such as the oruanui occur at more evenly spaced intervals of one per 40 60 000 years

the role of fluids in lower crustal earthquakes near continental rifts earthquakes in the lower continental crust of the earth are rare as the lower crust is thought to be too hot to allow brittle failure so it is surprising that they occasionally occur where continental crust is rifting apart a study of three dimensional crustal structure and seismicity in the taupo volcanic zone an active continental rift in new zealand has now provided insight into how these earthquakes arise the crustal earthquakes form a continuous band along the rift and often occur in swarms suggesting fluid movement in critically loaded fault zones seismic velocities within the band are consistent with the presence of fluids and the linking of upper and lower crust seismicity to crustal structure point to a common explanation for all of the seismicity probably the weakening of faults on the periphery of an otherwise dry crust by hot fluids a report on three dimensional tomographic imaging of seismic velocities and attenuation in the taupo volcanic zone an active continental rift where earthquakes are known to occur in the lower crust finds that crustal earthquakes form a continuous band along the rift and often occur in swarms suggesting fluid movement in critically loaded fault zones the occurrence of earthquakes in the lower crust near continental rifts has long been puzzling as the lower crust is generally thought to be too hot for brittle failure to occur1 2 such anomalous events have usually been explained in terms of the lower crust being cooler than normal3 4 but if the lower crust is indeed cold enough to produce earthquakes then the uppermost mantle beneath it should also be cold enough2 and yet uppermost mantle earthquakes are not observed5 numerous lower crustal earthquakes occur near the southwestern termination of the taupo volcanic zone tvz an active continental rift in new zealand6 here we present three dimensional tomographic imaging of seismic velocities and seismic attenuation in this region using data from a dense seismograph deployment7 we find that crustal earthquakes accurately relocated with our three dimensional seismic velocity model form a continuous band along the rift deepening from mostly less than 10 km in the central tvz to depths of 30 40 km in the lower crust 30 km southwest of the termination of the volcanic zone these earthquakes often occur in swarms suggesting fluid movement in critically loaded fault zones8 seismic velocities within the band are also consistent with the presence of fluids and the deepening seismicity parallels the boundary between high seismic attenuation interpreted as partial melt within the central tvz and low seismic attenuation in the crust to the southwest this linking of upper and lower crustal seismicity and crustal structure allows us to propose a common explanation for all the seismicity involving the weakening of faults on the periphery of an otherwise dry mafic crust by hot fluids including those exsolved from underlying melt such fluids may generally be an important driver of lower crustal seismicity near continental rifts

irreversible change of the rotomahana waimangu hydrothermal system new zealand as a consequence of a volcanic eruption the hydrology of the long lived rotomabana waimangu hydrothermal system of new zealand was changed irreversibly by the brief 1886 tarawera rift basalt eruption the nature of the pre 1886 surface thermal activity indicates that boiling conditions prevailed in the upflow zone beneath the vicinity of the then existing shallow lake rotomahana on june 10 1886 magma erupted through this part of the system triggering violent volcanic and hydrothermal explosions that led to the formation of new fluid conduits and a large crater that filled to form the present lake rotomahana several years after the eruption hot springs broke out along the line of 1886 craters southwest of lake rotomahana the evolution of these features has been punctuated by spectacular geysers from 1900 to 1904 and a substantial hydrothermal eruption in 1917 the main effect of the 1886 volcanic eruption on the hydrothermal system was the perturbation of pressure gradients causing abrupt near surface cooling followed by gradual reheating 23 refs 4 figs

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