the taupo eruption new zealand i general aspects the ca a d 186 taupo eruption was the latest eruption at the taupo volcanic centre occurring from a vent at horomatangi reefs now submerged beneath lake taupo in the central north island of new zealand minor initial phreatomagmatic activity was followed by the dry vent 6 km 3 hatepe plinian outburst large amounts of water then entered the vent during the 2 5 km 3 hatepe phreatoplinian ash phase eventually stopping the eruption though large amounts of water continued to be ejected from the vent area causing gullying of the ash deposits after a break of several hours to weeks phreatoplinian activity resumed generating the 1 3 km 3 rotongaio ash notable for its fine grainsize and for containing significant quantities of non or poorly vesicular juvenile material the vent area then became dry again and eruption rates and power markedly increased into the 23 km 3 taupo ultraplinian phase which is the most powerful plinian outburst yet documented synchronous with this ultraplinian activity lesser volumes of non to partially welded ignimbrite were generated by diversion of ejecta from or partial collapse of the eruption column the rapid rate of magma withdraw al during this phase removed support from the vent area to trigger local vent collapse and initiate the catastrophic eruption of the ca 30 km 3 taupo ignimbrite finally after some years lava was extruded on to the floor of the reformed lake taupo and floating fragments derived from the lava carapace were driven ashore the known eruption volume is more than 65 km 3 while additional volumes are represented by primary material now beneath lake taupo and layer 3 to the ignim brite phases a total volume of more than 105 km 3 is likely equivalent to more than 35 km 3 of magma plus more than 3 km 3 of lithic debris airfall deposits more than 10 cm thick blanketed 30000 km 2 of land east of the vent while ignimbrite covers a near circular area of 20000 km 2 widespread and locally severe ground shaking occurred during but mostly after the eruption associated with subsidence in the lake taupo basin secondary deposits are abundant above and extending beyond the taupo ignimbrite consisting of the products of surface water interacting with the still hot ignimbrite and subsequent water reworking of the light pumiceous materials the complexity and size of this eruption preclude accurate forecasting of the size nature and return period of the inevitable next eruption from the taupo volcanic centre

modeling suspended sediment discharge from the waipaoa river system new zealand the last 3000 years hydrotrend a hydrologic transport model is used to simulate the water and suspended sediment discharge of the waipaoa river system over the last 3 kyr a time period in which a well documented sequence of natural events and anthropogenic activities that profoundly impacted drainage basin processes occurred comparisons between observed and simulated data show that the model output replicates the frequency and distribution of flow events and the suspended sediment concentration discharge relationship and the long term trends in suspended sediment discharge are consistent with the sediment record preserved on the middle shelf water discharge tracks precipitation and average annual discharge may have been up to 20 higher and 6 lower at different times in the past suspended sediment discharge changed from 2 3 4 5 to 14 9 8 7 mt yr 1 during the anthropocene increasing by 140 after polynesian arrival by 350 after european colonization and by 660 after the catchment headwaters were deforested

effects of earthquake induced landslides on sediment budget and transport over a 50 yr period landsliding during a magnitude 7 7 earthquake in 1929 in northwestern south island new zealand delivered up to 400 000 m 3 km 2 of sediment to stream channels first to third order channels were buried to depths of as much as 10 m with sedimentary rock debris for distances ranging from 2 of the 92 km 2 study area because of the coarse grain size of the sedimentary rock debris and trapping of sediment in numerous landslide dammed lakes sand and pebble sized debris originating from landslides on a 6 6 km 2 area of granite has been transported downstream no more than 10 km at least 50 to 75 of this granitic debris is retained in the fourth order 92 km 2 catchment 50 yr after the earthquake the long retention times of sediment and the volume of debris supplied by landslides during a large earthquake suggest that earthquake induced landsliding is the principal sediment supply mechanism in the region

sediment characteristics of an extreme flood 1993 upper mississippi river valley the 1993 mississippi river flood was notable for its high magnitude long duration summer occurrence and low sediment discharge a field survey of a 70 km long reach in the vicinity of quincy illinois revealed that the event was characterized by 100 yr flood had remarkably little sedimentological or geomorphological impact on the flood plain within the study reach because the transport effectiveness of floods in large drainage basins is influenced by event sequencing in the same manner as floods in small watersheds and the cohesive flood plain soils were not susceptible to erosion

magnitude and frequency of landsliding in a large new zealand catchment knowledge of long term average rates of erosion is necessary if factors affecting sediment yields from catchments are to be understood without such information it is not possible to assess the potential influence of extreme storms and therefore to evaluate the relative importance of various components of a sediment budget a study of the sediment budget for the waipaoa catchment north island new zealand included evaluation of long term rates of landsliding for six landslide prone land systems in the catchment the number of landslides per unit area generated by each of several storms was counted on sequential aerial photographs and correlated with the magnitude of the corresponding storm the resulting relationships were combined with magnitude frequency relationships derived for storms from 70 to 100 year rainfall records in the area to estimate a long term magnitude frequency relationship for landsliding for each land system the long term average values of the areal landslide frequency number of slides per unit area per unit time were then calculated from these relationships the volumes of a sample of landslide scars were measured in the field and the proportion of slides that deliver sediment to channels was determined from aerial photographs these measurements then allowed calculation of the long term average rate of sediment production to streams from landslides for different land systems and types of vegetation results suggest that shallow landslides currently contribute about 15 5 of the suspended sediment load in the waipaoa river above the kanakanaia gauging station and that 75 of the sediment production from the landslides occurs during storms with recurrence intervals of less than 27 years reforestation of 6 3 93 km2 of the slide prone lands in the catchment between 1990 and 1995 resulted in a calculated decrease in slide derived sediment of 10 calculations suggest that reforestation of an additional 3 66 km2 of the catchment in areas with the most sensitive combinations of land system and storm regime could decrease the total sediment inputs from landsliding by about 20

supply and removal of sediment in a landslide dominated mountain belt central range taiwan abstract a strong coupling between hillslope and valley systems is often inferred for mountain landscapes dominated by bedrock landsliding we reveal the nature of this link using data sets on landsliding and sediment transport from two montane catchments draining the eastern central range of taiwan here the magnitude frequency distribution of landslides can be modeled by a robust power law but this scale invariance is not mirrored in the sediment discharge at the mountain front instead downstream sediment loads reflect a complex response to both sediment supply and ambient hydraulic conditions the rivers do not transport significant amounts of sediment unless it is provided by hillslope mass wasting in the catchment removal of landslide debris is a function of the transport capacity of the stream at the site of entry thus there is a dual supply and transport control on sediment loads in bedrock floored streams over a monitoring period of 25 yr the bulk of the sediment leaving the mountain bel

holocene shoreline depositional processes at poverty bay a tectonically active area northeastern north island new zealand abstract holocene depositional processes at poverty bay have been affected by 1 tectonism 2 sea level response to climate change 3 fluvial processes responding to 1 and 2 severe storms and volcanic eruptions the height distribution of radiocarbon dated beach and estuarine shells and wood show that during the holocene relative uplift of the land has occurred at the northeastern margin of the poverty bay flats while subsidence has occurred at the southwestern margin three holocene tectonic subregions are distinguished at the poverty bay flats coast a northern gisborne wainui uplift area a central makaraka awapuni static pivotal area and a southern patutahi muriwai downdrop area periods of significant fluvial upstream degradation into gravel terrace deposits and downstream gravel aggradation are dated at ca late last glaciation 12 000 9000 and 7000 5000 bp the 12 000 9000 bp gravel deposits show tilting to the southwest major erosion and infilling events also occurred at ca 1700 and 300 bp holocene marine transgression and progradation shoreline locations are mapped and the coastal processes are reviewed in terms of the tectonic fluvial and eustatic sea level influences

shallow subduction tectonics in the raukumara peninsula new zealand as illuminated by earthquake focal mechanisms the raukumara peninsula affords an excellent opportunity to study the subduction process as subduction of the buoyant hikurangi plateau on the pacific plate has resulted in exposure of the forearc above the shallow part of the subduction thrust here we report on the focal mechanisms of 117 earthquakes of m l 2 4 4 9 and shallower than 80 km recorded during a 5 month deployment of 36 portable seismographs on the peninsula mechanisms have been constrained using both first motion polarity data and amplitudes of seismogram envelopes downdip tensional strain predominates in the subducted plate with taxes of events in both the upper and lower planes of the dipping seismic zone generally paralleling the local dip of the zone trenchward extensional strain is seen in the uppermost part of the overlying australian plate in line with geodetic and geological results this can be related to extension and gravity sliding of surficial rocks due to uplift of the raukumara range resulting from underplating of subducted sediment there is a marked change in earthquake mechanisms along strike in the lower part of the overlying plate and at the plate interface a concentration of low angle thrust events at the plate interface in the northeastern half of the peninsula suggests that the plate interface is less coupled there than to the southwest this along strike change in plate coupling corresponds closely to a change in the crustal structure of the overlying plate and also to a change in tectonic rotation domain determined paleomagnetically

forest disturbance in the central north island new zealand following the 1850 bp taupo eruption the 1850 bp taupo eruption covered c 30 000 km2 of the central north island with airfall deposits and c 20 000 km2 with ignimbrite this paper reviews pollen and charcoal analyses of lake and peat sediment cores from sites at various distances and directions from the taupo vent to establish the effects of this eruption on the surrounding forests forests within range of the ignimbrite were destroyed and forests located up to 170 km east of the vent suffered variable degrees of damage from ashfall stands of pteridium esculentum and other seral taxa flourished immediately after the eruption fires occurred during the eruption and continued for several decades after the degree and nature of vegetation disturbance above the taupo tephra varied according to the thickness of ashfall local topographical features and probably the vigour of the forest revegetation was complete within 200 years of the eruption even at sites overwhelmed by the taupo ignimbrite post eruption forests were similar to those exi

self organized criticality in layered lacustrine sediments formed by landsliding landsliding is the dominant mass wasting process in humid temperate uplands and an important regulator of sediment yield from steep land drainage basins information about the magnitude and frequency distribution of landslides has been derived from aerial photography but it has proved difficult to set limits on the long term scaling behavior of landsliding because the requirements of spatial and temporal coherence and the large number of observations necessary to undertake magnitude versus frequency analyses are not easy to fulfill we use a 2250 yr long record of hillslope erosion associated with extreme hydrologic events preserved in sediments from lake tutira new zealand to investigate scaling in landslide deposits both the magnitude versus frequency distribution of sediment layers attributed to landsliding and the distribution of time intervals between landsliding events take the form of power laws the former with an exponent b 2 06 and the latter with an exponent b 1 4 these results suggest that the erosional events originate from a self organized critical process and are in agreement with observations of scaling in turbidite deposits and grain flows in controlled laboratory experiments the implications are that the aggregate behavior of landsliding at the catchment scale is orderly and that the stratigraphic record preserves a unique long term perspective on a fundamental geomorphic process and the extreme hydrologic events that trigger it

coseismic uplift of holocene marine terraces in the pakarae river area eastern north island new zealand abstract holocene marine terraces along 15 km of the northeastern coast of north island record episodic tectonic uplift a maximum of seven terraces are arranged in staircase fashion and lie about 20 km above the subduction interface between the pacific and australian plates the highest t1 corresponds with the maximum of the holocene marine transgression about 6700 14 c yr b p younger terraces are marine abrasion platforms overlain by thin beach deposits radiocarbon ages of marine shells from beach deposits indicate that uplift above marine conditions occurred ca 6700 t1 5500 t2 3900 t3 2500 4 1600 t5 1000 t6 and slightly younger than 600 t7 yr b p uplift probably occurred coseismically the maximum late holocene uplift rate in the study area is 8 mm yr altitudinal distribution of terraces suggests deformation exists as a ca 20 km elongate dome broken at the southern end by the pakarae fault which trends across the dome rupture on this fault has accompanied the growth of the dome but is not responsible for it bathymetric profiling suggests that an active fault parallel to and about 5 km offshore is probably responsible for the episodic coastal uplift

the formation and failure of natural dams of the numerous kinds of dams that form by natural processes dams formed from landslides glacial ice and late neoglacial moraines present the greatest threat to people and property landslide dams form in a wide range of physiographic settings the most common types of mass movements that form landslide dams are rock and debris avalanches rock and soil slumps and slides and mud debris and earth flows the most common initiation mechanisms for dam forming landslides are excessive rainfall and snowmelt and earthquakes landslide dams can be classified into six categories based on their relation with the valley floor type i dams 11 of 184 landslide dams from around the world that we were able to classify do not reach from one valley side to the other type ii dams 44 span the entire valley floor in some cases depositing material high on opposite valley sides type iii dams 41 move considerable distances both upstream and downstream from the landslide failure type iv dams 1 are rare and involve the contemporaneous failure of material from both sides of a valley type v dams 1 also are rare and are created when a single landslide sends multiple tongues of debris into a valley and forms two or more landslide dams in the same reach of river type vi dams 3 involve one or more failure surfaces that extend under the stream or valley and emerge on the opposite valley side many landslide dams fail shortly after formation in our sample of 73 documented landslide dam failures 27 of the landslide dams failed less than 1 day after formation and about 50 failed within 10 days over topping is by far the most common cause of failure the timing of failure and the magnitude of the resulting floods are controlled by dam size and geometry material characteristics of the blockage rate of inflow to the impoundment size and depth of the impoundment bedrock control of flow and engineering controls such as artificial spill ways diversions tunnels and planned breaching by blasting or conventional excavation glacial ice dams can produce at least nine kinds of ice dammed lakes the most dangerous are lakes formed in main valleys dammed by tributary glaciers failure can occur by erosion of a drainage tunnel under or through the ice dam or by a channel over the ice dam cold polar ice dams generally drain supraglacially or marginally by downmelting of an outlet channel warmer temperate ice dams tend to fail by sudden englacial or subglacial breaching and drainage late neoglacial moraine dammed lakes are located in steep mountain areas affected by the advances and retreats of valley glaciers in the last several centuries these late neoglacial dams pose hazards because 1 they are sufficiently young that vegetation has not stabilized their slopes 2 many dam faces are steeper than the angle of repose 3 these dams and lakes are immediately downslope from steep crevassed glaciers and near vertical rock slopes and 4 downstream from these dams are steep canyons with easily erodible materials that can be incorporated in the flow and increase flood peaks the most common reported failure mechanism is overtopping and breaching by a wave or series of waves in the lake generated by icefalls rockfalls or snow or rock avalanches melting of ice cores or frozen ground and piping and seepage are other possible failure mechanisms natural dams may cause upstream flooding as the lake rises and downstream flooding as a result of failure of the dam although data are few for the same potential energy at the dam site ownstream flood peaks from the failure of glacier ice dams are smaller than those from landslide moraine and structed earth fill and rock fill dam failures moraine dam failures appear to produce some of the largest downstream flood peaks for potential energy at the dam site greater than 1011 1012 joules differences in flood peaks natural dam failures appear to be controlled by dam characteristics and failure mechanisms

erosion of tephra from the 1980 eruption of mount st helens erosion of tephra on hillslopes north of mount st helens was measured at intervals of several months between 1980 and 1983 using large arrays of stakes rill erosion was initially greater than sheetwash but its importance decreased comparatively quickly both rill erosion and sheetwash decreased by one to two orders of magnitude over the three year period because a stable rill network developed and more permeable and less erodible substrates were created or exposed the decrease occurred prior to recovery of plants the causes for the rapid decline in erosion at mount st helens explain patterns of erosion following several other recent tephra eruptions basin wide annual rates of erosion were computed by mapping the surface cover the hillslope gradient and the texture and thickness of tephra and by using statistical relations developed between them and erosion rates annual erosion decreased from 26 mm between may 1980 and may 1981 to 1 8 mm between may 1982 and may 1983 projecting this rate of decline into the future indicated that only about one sixth of the tephra on hillslopes will be removed by water erosion before soil creep and other forms of mass wasting again dominate hillslope evolution

el nino southern oscillation signal associated with middle holocene climate change in intercorrelated terrestrial and marine sediment cores north island new zealand a synchronous textural variation in intercorrelated high resolution sediment records from floodplain continental shelf and continental slope settings of the eastern north island new zealand provides evidence of increased storminess after ca 4 ka an upcore change in sediment texture reflects the transition to landsliding which supplanted fluvial incision as the dominant mode of sediment production in the middle holocene this signal which appears in all three records indicates a regional response to external forcing and records the impact of an intensified atmospheric circulation marking the establishment of the contemporary climate that is strongly influenced by the el nino southern oscillation the change in climate was a hemispheric event and in the southern hemisphere its timing is confirmed by independent proxy records from elsewhere in new zealand and the circum south pacific region

dynamics of an unusual cone building trachyte eruption at pu u wa awa a hualālai volcano hawai i the pu u wa awa a pyroclastic cone and pu u anahulu lava flow are two prominent monogenetic eruptive features assumed to result from a single eruption during the trachyte dominated early post shield stage of hual lai volcano hawai i pu u wa awa a is composed of complex repetitions of crudely cross stratified units rich in dark dense clasts which reversely grade into coarser pumice rich units pyroclasts from the cone are extremely diverse texturally ranging from glassy obsidian to vesicular scoria or pumice in addition to fully crystalline end members the 100 m thick pu u anahulu flow is in contrast entirely holocrystalline using field observations coupled with whole rock analyses this study aimed to test whether the pu u wa awa a tephra and pu u anahulu lava flows originated from the same eruption as had been previously assumed crystal and vesicle textures are characterized along with the volatile contents of interstitial glasses to determine the origin of textural variability within pu u wa awa a trachytes e g magma mixing vs degassing origin we find that 1 the two eruptions likely originated from distinct vents and magma reservoirs despite their proximity and similar age 2 the textural diversity of pyroclasts forming pu u wa awa a can be fully explained by variable magma degassing and outgassing within the conduit 3 the pu u wa awa a cone was constructed during explosions transitional in style between violent strombolian and vulcanian involving the formation of a large cone and with repeated disruption of conduit plugs but without production of large pyroclastic density currents pdcs and 4 the contrasting eruption styles of hawaiian trachytes flow cone and pdc forming are probably related to differences in the outgassing capacity of the magmas prior to reaching the surface and not in intrinsic compositional or temperature properties these results further highlight that trachytes are kinetically faster magmas compared to dacites or rhyolites likely degassing and crystallizing more rapidly

viscosity of hydrous etna basalt implications for plinian style basaltic eruptions water dissolved in a silicate melt can strongly influence its physical properties and thus magma behavior during crystallization degassing foaming and fragmentation etna is a basaltic volcano whose activity is dominated by effusive eruptions which have long represented a threat to the densely populated surrounding area recently recognition of the products of a plinian eruption 122 b c has raised further issues for hazard assessment at etna and other basaltic volcanoes constraining the behavior of etna magma under conditions relevant to both effusive and explosive hazards requires viscosity data under conditions near the glass transition here we have investigated the viscosity of hydrous etna lava in order to better understand eruptive processes which characterize this volcano the experimental methods which have been used include piston cylinder synthesis of the hydrated melts micropenetration viscometry for low temperature viscosity measurements and near infrared spectroscopy for the evaluation of sample homogeneity and measurements of water content additionally scanning calorimetric determinations were performed to check whether incipient crystallization had occurred sample compositions were determined using electron microprobe analysis and 57fe mossbauer spectroscopy results from this study are compared with previous reports of trachytic phonolitic and model calc alkaline rhyolite hpg8 compositions the viscosity of the basaltic melt dry and wet has been parameterized in terms of temperature and water content via the non arrhenian equation log10 4 643 5 812 44 427 04 h2o t k 499 31 28 74 ln h2o where is the viscosity in pa s h2o is the water content in wt and t is the temperature in kelvin we observe that the viscosity of alkali basalt at more than 0 5 wt h2o is similar to that of an alkaline trachyte agnano monte spina eruption phlegrean fields and much higher than that of a peralkaline phonolite teide tenerife at similar silica contents and nbo t for water contents above 1 5 wt the viscosity of the basalt is similar to that of rhyolitic melts with similar water contents at temperatures ranging from 1 050 to 1 150 c and with water contents between 0 5 and 2 3 wt eruptive conditions the viscosities calculated using the equation defined in this study are 1 in reasonable agreement with those calculated using shaw s model and 2 much lower than those experimentally determined in a previous study however outside these temperature and water content ranges the agreement with shaw s model 1972 breaks down

signals of watershed change preserved in organic carbon buried on the continental margin seaward of the waipaoa river new zealand abstract holocene sediments buried on the continental shelf seaward of the waipaoa river northeastern new zealand preserve a stratigraphic record of terrestrial environmental change the well characterized long term record of storms volcanism and human disturbance in this region provides an opportunity to examine how such changes are reflected in the character of organic carbon oc buried on the continental margin complimentary evidence obtained from analyses of the 14 c content and the elemental and stable carbon isotopic composition of different sedimentary fractions including charcoal wood and clay sized isolates indicates that these perturbations led to mobilization of oc components with variable storage histories in the watershed charcoal transported in the modern waipaoa river and buried in offshore depocenters includes a highly aged component that has apparently been slowly released from storage in soil or alluvial terraces the charcoal fraction ages become dramatically younger in sediments deposited after the taupo volcanic eruption 1717 cal yr bp and then polynesian settlement ca 700 cal yr bp both signaling biomass burning the mean age of woody plant fragments and clay bound oc deposited on the shelf also varies over time with older material having accumulated in the middle holocene and since human occupation deposition of older than average wood fragments and clay bound oc between about 5 and 3 6 kyr bp correlates with evidence for a period of increased storm frequency in the region and may reflect the enhanced delivery of aged soil and sedimentary rock mobilized from hill slopes via earthflows and or deep seated landslides similarly the deposition of older wood and clay bound oc commensurate with the first anthropogenic disturbance ca 700 years ago is consistent with accelerated mass wasting due to deforestation at the same time a change in the elemental and stable isotopic composition of bulk and clay bound oc buried on the shelf may reflect increased marine primary productivity and or mobilization of oc from deep levels in soil profiles deforestation of the waipaoa headwaters by european settlers beginning in the middle 19th century is evinced by a sharper rise in the age of clay associated oc buried offshore today deep gully incision into fractured sedimentary bedrock is a major source of sediment and kerogen to the river and this process has left its mark on the age of sedimentary oc delivered to the adjacent margin

redox state microstructure and viscosity of a partially crystallized basalt melt abstract as measured in air above the glass transition range the viscosity of an alkali basalt increases markedly with time by about two orders of magnitude in 12 h this effect is essentially physical and due to the presence of microcrystals although partial crystallization of the melt into spinel and an sio2 poor pyroxene leads to a considerable enrichment in silica of the residual liquid partial crystallization depends strongly on the initial redox state of samples in that the presence of ferrous iron is required for spinel crystals to form and for pyroxene to nucleate and grow around them other measurements show that the viscosity of the crystal free liquid decreases slightly with increasing ratios r fe2 fe because the differences between samples with r 0 16 and 0 83 amount to about 1 5 and 0 3 log units at 950 and 1400 k respectively comparisons of the viscosities of the residual liquid matrix and of the initially crystal free basalt show that physical effects caused by the presence of microcrystals begin to be observed at a low crystal fraction of 5 vol finally a model of viscosity calculation is developed for the melts which reproduces all data obtained in this work to better than 10

rapid and widespread dispersal of flood sediment on the northern california margin the dispersal of flood sediment from small river systems is a poorly studied yet potentially important aspect of active continental margin sedimentation in january 1995 during a flood with a 30 yr return period the eel river northern california delivered an estimated 25 3 106 t metric tons of fine grained 62 m sediment to the ocean the flood formed a distinct layer on the sea bed that was centered on the 70 m isobath extended for 30 km along shelf and 8 km across shelf and was as thick as 8 5 cm but contained only 6 106 t of sediment thus 75 of the flood derived sediment did not form a recognizable deposit but was instead rapidly and widely dispersed over the continental margin stratigraphic models of and compilations of sediment flux to active continental margins need to take the dispersive nature of small river systems into account

structural environment of iron in hydrous aluminosilicate glass and melt evidence from x ray absorption spectroscopy abstract the iron speciation in hydrous haplotonalitic and haplogranitic silicate glasses was studied using xafs spectroscopy and transmission electron microscopy tem spectral features occurring at the main crest of the xanes at the iron k edge of hydrous glasses indicate contributions to the spectra by iron moieties present in a more ordered structural environment than found in the dry glass these differences are also suggested by analysis of the exafs these effects are not completely suppressed even for those samples that were quenched with a higher cooling rate strongest differences to the dry glass are observed for a sample that was quenched slowly through the temperature of glass transformation crystals 60 to 1500 nm in size of magnetite maghemite and another unidentified phase were observed in this sample by tem whereas no crystals were found in samples quenched with regular or high cooling rates in situ xanes measurements up to 700 c and 500 mpa were performed to reveal the origin i e during synthesis or quench of the structural differences for those hydrous glasses that do not display any detectable crystallization the comparison of xanes spectra collected on fe 2 in water saturated haplogranitic melt at 700 c and 500 mpa and on fe 2 in dry melt at 1150 c shows that the local structural environment of fe 2 in both systems is similar this indicates that there is no detectable and direct influence of water on the local structure around iron in this type of melt hence the differences observed between hydrous and dry glasses can only be related to artefacts formed during the quench process

measuring the degree of nanotilization of volcanic glasses understanding syn eruptive processes recorded in melt inclusions iron and water content substantially affect the physical properties of natural silicate melts and may therefore influence magmatic and volcanic processes such as crystallization degassing flow behaviour and eruptive style here we present raman spectroscopic data for a set of synthetic and natural multicomponent glasses with varying iron oxidation state and water content we systematically study the effect of different raman excitation sources on the spectral response of both crystal free and magnetite nanolite bearing glasses spanning basaltic to calc and per alkaline rhyolitic compositions based on these data we document changes in raman spectra resulting from the formation of nano scale crystals we show that the peak located at similar to 970 cm 1 is directly related to the presence of fe2o3 dissolved in the quenched melt structure and that this feature is present regardless of the chemical composition of the sample and the raman excitation source we further show that a peak between 670 and 690 cm 1 which is not related to any other spectral feature of the glass structure reveals the presence of nanolites based on systematic spectral investigations of this feature we present a new index that allows to identify if iron is present in the nanocrystalline state and or bound in the glass structure since the melt structural and physical effects of the formation of nanolites can heavily affect the flow behaviour of melts and the eruptive style of volcanoes the results presented in this study significantly broaden the application of raman spectroscopy for investigations of nano heterogeneity in synthetic and natural glasses we apply this method to study both the degree of nanolitization as well as the h2o content and iron oxidation state of groundmass glasses as well as melt inclusions and glass embayments in explosive products from pantelleria island italy we observe that the process of nanotilization is not purely restricted to magnetite nanolites but that raman spectroscopy may also identify the incipient crystalization of pyroxene and feldspar at sub micron scale the data document that nanolite formation correlates well with the observed intensity of the respective eruptions suggesting that structural changes in the melt caused by incipient crystallization play an important role in defining the eruptive style of relatively low viscosity magmas

using rat gnawed seeds to independently date the arrival of pacific rats and humans in new zealand the pacific rat rattus exulans was transported throughout the south pacific with voyaging humans thus the earliest dated evidence of pacific rat can be used to infer first human contact until recently it was considered that rats arrived in new zealand with humans in the thirteenth century ad however controversial radiocarbon dates on pacific rat bones now suggest that rats reached the remote islands of new zealand with people c ad 50 150 these dates are anomalous because they imply human contact with new zealand more than 1000 years before any archaeological evidence for human presence and precede settlement of tropical eastern polynesia the ancestral homeland of maori the first new zealanders the early rat bone dates are controversial for other technical reasons which have been debated in the literature here distinctive rat gnawed seed cases preserved in sediments are used as a proxy to independently date the arrival of the pacific rat and humans in new zealand this method effectively b

reaction and relaxation in a coarse grained fluvial system following catchment wide disturbance abstract the waiapu river catchment drainage area of 1734 km2 is one of the most prolific conveyors of sediment in the world annually delivering roughly 35 mt of fine material to the ocean from eroding gullies hillslopes and reworked sediment on valley floors tectonic and geologic influences in combination with a dynamic climate influenced by tropical cyclones and clearance of vegetation from steep hillslopes predisposes this region to high rates of erosion the bedload sediment regime of the river is strongly influenced by several exceptionally large gullies and gully complexes that produce a coarse grained poorly sorted sediment mixture rapid abrasion and breakdown leads to high rates of suspended sediment yield a wave of bedload material manifesting as elevated bed levels and significant widening of active alluvial fills has been triggered by large inputs of hillslope material from a few key tributary catchments following cyclone bola in 1988 we review the evidence for the relaxation process of the sedimentary system in the subsequent 29 years appraising some of the legacy effects that may endure as associated with reworking of the considerable alluvial stores within the waiapu system we use structure from motion sfm techniques and archival aerial photos to quantify changes in sediment storage at the base of two major gully systems in recent decades a record of over 850 cross section surveys at 62 sites on 10 rivers throughout the catchment 1958 2017 indicates recent transition from a trend of continuous accumulation to downcutting and remobilisation of valley bottom deposits the channel cross sections provide a minimum estimate of sediment flux from source areas to the lower reaches of the river giving a rudimentary but spatially extensive picture of the wave of material cascading through the drainage network the largest impacts occur in the upper steepland rivers closest to the landslide derived sediment supply transport rates here as inferred from cross section change are at a maximum during an aggradational phase following cyclone bola then taper off despite the large sediment accumulations remaining in the system as of 2017 the river is in the process of incising the upper extents of this deposit on a trajectory of recovery toward pre bola conditions the compilation of cross section data provides us with new insights into the sensitivity of particular sites in the landscape as well as the changing relationship between reach sediment storage and transport rates during the response and relaxation phase of a major disturbance in a large catchment

fluvial sediment transport and deposition following the 1991 eruption of mount pinatubo the 1991 eruption of mount pinatubo generated extreme sediment yields from watersheds heavily impacted by pyroclastic flows bedload sampling in the pasig potrero river one of the most heavily impacted rivers revealed negligible critical shear stress and very high transport rates that reflected an essentially unlimited sediment supply and the enhanced mobility of particles moving over a smooth fine grained bed dimensionless bedload transport rates in the pasig potrero river differed substantially from those previously reported for rivers in temperate regions for the same dimensionless shear stress but were similar to rates identified in rivers on other volcanoes and ephemeral streams in arid environments the similarity between volcanically disturbed and arid rivers appears to arise from the lack of an armored bed surface due to very high relative sediment supply in arid rivers this is attributed to a flashy hydrograph whereas volcanically disturbed rivers lack armoring due to sustained high rates of sediment delivery this work suggests that the increases in sediment supply accompanying massive disturbance induce morphologic and hydrologic changes that temporarily enhance transport efficiency until the watershed recovers and sediment supply is reduced d 2002 elsevier science b v all rights reserved

twentieth century floods recorded in the deep mediterranean sediments flood generated turbidity currents represent an important process of marine sedimentation however no deposit related to this process has yet been described at sea turbiditic sequences cored at 2000 m water depth in the mediterranean show tractive structures and superposition of reverse and normal grading they are related to floods triggered during the twentieth century deposits from flood generated turbidity currents have a great impact on the interpretation of deep ocean paleoclimate records obtained near continental margins by linking deep marine sedimentary records to continental climatic changes through flood frequency and magnitude implications of this study should help redefine the reservoir character of oil fields in fine grained turbidites

depositional processes on an ancient and modern muddy shelf northern california the modern eel river shelf and analogous pleistocene rio dell formation in northern california provide an ideal opportunity to combine the advantages of studying a modern environment with those of studying an ancient sequence and thereby enables further understanding of muddy shelf processes the modern shelf is the site of accumulation of a thick deposit of holocene mud both large scale sediment distribution patterns and small scale stratigraphy on the shelf indicate that river floods play an important role in sediment accumulation even on a high energy storm dominated coast the major factors in preservation of this flood signature are the cohesive behaviour of fine grained sediments and episodically rapid rates of sediment input the rio dell formation includes approximately 400 m of mostly fine grained shelf deposits that accumulated offshore from a palaeo eel river mouth the shelf sediments comprise four depositional sequences sequence 1 records progradation from outer to inner shelf depths facies trends closely resemble across shelf trends on the modern shelf suggesting that processes were similar detailed examination of these deposits provides insight into the nature and role of various processes on both the ancient and modern shelf muddy facies of the rio dell sequence are characterized by bioturbated clayey silts interbedded with event layers of several types clay rich silt layers are interpreted as flood deposits and physically stratified coarse silt layers are interpreted to record transport and deposition of coarse silt on the midshelf during storms sediment transport calculations and consideration of grain size distributions of bioturbated sediments which form the bulk of the rio dell sequence suggest that these sediments are the result of biological homogenization of the fine grained flood deposits and of the coarser grained storm deposits the results of this study in general indicate that fine grained shelf deposits do preserve a distinguishable if subtle record of depositional processes

knickpoint initiation and distribution within fluvial networks 236 waterfalls in the waipaoa river north island new zealand if knickpoints transmit signals of base level fall in river networks then improvements in our understanding of their retreat rate and basin wide distribution helps constrain the transient response following perturbation many studies of knickpoint retreat focus on the response of trunk streams to base level fall here we examine the response of an entire fluvial network as recorded by 236 active knickpoints distributed within the waipaoa river on the north island of new zealand base level fall within the waipaoa catchment initiated 18 000 years ago in response to a climatically triggered and tectonically exacerbated pulse of incision using observations from field work aerial photo analysis and a digital elevation model dem we study the knickpoint positions within the network we find that 70 of the knickpoints are located at drainage areas between 1 10 5 m 2 and 1 10 6 m 2 and more than half are b1 km upstream of a large change in drainage area for the knickpoints b1 km upstream of large tributary junctions we find that the retreat distances were well correlated with the tributaries drainage areas in order to determine how a pulse of incision distributes itself throughout a fluvial network we develop two simple end member models and compare their behavior to the observed knickpoint distribution in the waipaoa in the first model we propose that a knickpoint initiated at the basin outlet retreats upstream and distributes the signal throughout the network at a rate that is a power law function of drainage area in the second model we propose that knickpoints form near a threshold drainage area below which channels cannot incise with the same efficiency as possible in downstream reaches though neither model addresses the along stream variability in substrate or knickpoint form the misfit between the modeled and the observed knickpoints along stream positions are surprisingly low b1 km 1 25 of the total stream length for knickpoints with drainage areas b1 10 6 m 2 large misfits up to 3 5 km are observed for knickpoints with present day drainage areas greater than 1 10 6 m 2 the large single step in channel elevation that characterizes knickpoints presently observed in tributaries of the waipaoa river may not characterize the base level fall signal that propagated through the trunk streams evidence for progressive rather than instantaneous incision in the trunk streams the knickpoints vicinities to tributary junctions and the equivalent success of the two end member models lead us to conclude that the present positions of the 236 observed knickpoints are largely a consequence of thresholds in channel incision at low drainage areas

electron probe microanalysis of fe2 σfe ratios in calcic and sodic calcic amphibole and biotite using the flank method abstract we present an analytical approach to determine the fe2 fe ratio in amphiboles and biotites using electron probe microanalysis epma the flank method applied in this study is based on the fact that fel line spectra show different peak position and intensity for fe2 and fe3 which is associated with a resonant process involving both x ray absorption and emission the flank positions for l and l which correspond to sites with minimal fe3 l3 absorption and maximal fe2 l2 absorption respectively are determined based on the l line spectra difference of two fe rich ferric and ferrous garnet endmembers i e andradite and almandine spectra intensities measured at the l and l flank positions for selected amphibole and biotite references can be quantitatively correlated with their fe2 weight contents by a linear relation l l a b fe2 in which a and b are constants calibrated upon reference materials it is emphasized that the constants a and b may vary significantly for different mineral groups and analytical conditions thus a calibration is necessary for each analytical session our tests show that the potential beam damage during epma that may induce oxidation of the measured material can be minimized by using a large beam size e g 20 m the fe2 fe ratios determined using the epma flank method in collected natural calcic and sodic calcic amphiboles feot 2 4 12 7 wt fe2 fe 0 45 75 and biotites feot 4 3 28 2 wt fe2 fe 0 67 0 87 are consistent within an error of 0 1 with the data obtained from the colorimetric wet chemistry method the epma flank method has the potential to be widely applied for accurate in situ determination of fe oxidation states in a wide range of minerals provided that references are available

organic carbon in floodplain alluvium signature of historic variations in erosion processes associated with deforestation waipaoa river basin new zealand 1 we use c org and 13c to trace the origin of the alluvium deposited on the waipaoa river floodplain at mcphail s bend between 1853 and 2002 the overbank deposits exhibit a more positive range of 13c values 26 3 0 6 than contemporary suspended sediment in transport at intermediate flows 27 8 0 2 when gully erosion releases most material to stream channels reflecting the greater contribution made by shallow landsliding in the headwaters during large precipitation events overbank sediment associated with recent floods contains a higher 50 amount of organic carbon than alluvium deposited by pre 1927 floods which was derived from outcrops of weathered bedrock on steep riparian hillslopes that were the primary sediment source before the soil mantled hillslopes elsewhere in the headwaters of the basin were destabilized by deforestation the recent alluvium resembles the bw horizon of soils present on these hillslopes sediment deposited during floods generated by localized storms and an overbank event that did not feature widespread shallow landsliding also has a distinctive signature that provides an indication of its provenance the organic carbon associated with the alluvium appears to be old 4031 40 b p in the case of the carbon associated with sediment deposited in 2002 and to be derived from weathered cretaceous and tertiary sedimentary rocks

oceanic export of relict carbon by small mountainous rivers small mountainous rivers smr export globally significant quantities of particulate organic carbon poc to the oceans the composition of which may be distinct from poc delivered by major world rivers to better constrain the controls on the 14c signatures of poc suspended in smr we examined the temporal variability of 14c and 13c of poc suspended in the santa clara river a smr in california usa our data suggest mixing of bedrock and contemporary soil which can be applied to other smr in contrasting climate zones and with varying land cover the data also suggest that chemical denudation is incomplete but effective to the point that only the most recalcitrant moieties of the parent poc are exported we further propose sediment yield as a potentially useful proxy for the 14c of riverine poc a preliminary analysis of the existing data for a spectrum of rivers supports this hypothesis

modern accumulation rates and a sediment budget for the eel shelf a flood dominated depositional environment the northern california continental margin is periodically impacted by geologically significant storms which have a marked influence on terrigenous sediment supply flood deposition and long term accumulation of fine grained sediment on the eel shelf accumulation of eel river muds on the adjacent shelf was investigated using 210pb and 137cs geochronologies in order to understand the fate of sediment discharged by the eel river and to relate patterns of net sediment accumulation 100 yr time scale to sediment dynamics 210pb data demonstrate that modern accumulation of river mud occurs from the 50 m isobath seaward across shelf accumulation rates decrease from maximum mid shelf values of 0 6 1 7 g cm 2 yr 1 to values of 0 2 0 4 g cm 2 yr 1 at the shelf break with a spatially weighted mean of 0 5 g cm 2 yr 1 0 4 cm yr for the entire shelf 210pbxs sediment depth profiles from the region of highest accumulation rate are characterized by subsurface intervals of low and uniform activity which are produced by flood deposition in some cores particular 210pbxs activity intervals may be associated with major eel river floods of 1955 1964 and 1974 it is postulated that because of the coincidence of high river flow events and southerly winds during cyclonic winter storms net northward transport allows for preferential deposition of fine grained sediment north of the river mouth over the past 100 years fluvial sediment input combined with marine dispersal processes have produced a mid shelf depocenter evident by both the spatial distribution of 210pb accumulation rates and by clay rich flood layers partially preserved in shelf deposits a fine grained sediment budget for the dispersal system based on hydrological data and 210pb geochronologies demonstrates that a maximum of 20 3 109 kg yr of the mean annual supply of fluvial mud 14 109 kg yr is trapped on the shelf the results of this study demonstrate that 1 short term sedimentation processes associated with floods can influence sediment accumulation on longer time scales and 2 a major fraction of fine grained sediment supplied to tectonically active margins by flood prone mountainous rivers bypasses narrow continental shelves

geochemistry of large river suspended sediments silicate weathering or recycling tracer this study focuses on the major and trace element composition of suspended sediments transported by the world s largest rivers its main purpose is to answer the following question is the degree of weathering of modern river borne particles consistent with the estimated river dissolved loads derived from silicate weathering in agreement with the well known mobility of elements during weathering of continental rocks we confirm that river sediments are systematically depleted in na k ba with respect to the upper continental crust for each of these mobile elements a systematics of weathering indexes of river borne solids is attempted a global consistency is found between all these indexes important variations in weathering intensities exist a clear dependence of weathering intensities with climate is observed for the rivers draining mostly lowlands however no global correlation exists between weathering intensities and climatic or relief parameters because the trend observed for lowlands is obscured by rivers draining orogenic zones an inverse correlation between weathering intensities and suspended sediment concentrations is observed showing that the regions having the highest rates of physical denudation produce the least weathered sediments finally chemical and physical weathering are compared through the use of a simple steady state model we show that the weathering intensities of large river suspended sediments can only be reconciled with the silicate derived dissolved load of rivers by admitting that most of the continental rocks submitted to weathering in large river basins have already suffered previous weathering cycles a simple graphical method is proposed for calculating the proportion of sedimentary recycling in large river basins finally even if orogenic zones produce weakly weathered sediments we emphasize the fact that silicate chemical weathering rates and hence co2 consumption rates by silicate weathering are greatly enhanced in mountains simply because the sediment yields in orogenic drainage basins are higher hence the parameters that control chemical weathering rates would be those that control physical denudation rates

sediment yield following severe volcanic disturbance a two decade perspective from mount st helens explosive volcanic eruptions perturb water and sediment fluxes in watersheds consequently posteruption sediment yields can exceed preeruption yields by several orders of magnitude annual suspended sediment yields following the catastrophic 1980 mount st helens eruption were as much as 500 times greater than typical background level and they generally declined nonlinearly for more than a decade although sediment yields responded primarily to type and degree of disturbance streamflow fluctuations significantly affected sediment yield trends consecutive years 1995 1999 of above average discharge reversed the nonlinear decline and rejuvenated yields to average values measured within a few years of the eruption after 20 yr the average annual suspended sediment yield from the 1980 debris avalanche deposit remains 100 times 10 4 mg megagrams km 2 above typical background level 10 2 mg km 2 within five years of the eruption annual yields from valleys coated by lahar deposits roughly plateaued and average yields remain about 10 times 10 3 mg km 2 above background level yield from a basin devastated solely by a blast pyroclastic current diminished to background level within five years these data demonstrate longterm instability of eruption generated detritus and show that effective mitigation measures must remain functional for decades

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

a chronology of natural and anthropogenic influences on coastal sedimentation new zealand 14c and 137cs chronologies of sediment accumulation were obtained from five sediment cores taken from wellington harbour new zealand a 10 000 year chronology records the holocene transgression european colonisation and variations in the general sediment accumulation rate caused by earthquake uplift and anthropogenic activity rates vary from a high of 60 to a low of 0 1 mm a 1 in general rates increased at the beginning of the holocene marine transgression but by 5000 yr bp they reached a stable level harbour wide these rates remained stable until the second half of the 19th century when deforestation by european settlers caused order of magnitude increases in sediment accumulation in the past 40 80 years rates have increased again as a result of urban growth and river channel management although the effects are less pervasive harbour wide influences can be placed in two categories natural and anthropogenic the latter being recent contributions to a sedimentary regime dominated by the holocene marine transgression sediment accumulation rates indicate that two major earthquake uplift events had only a local effect on harbour sediments anthropogenic influences are considered to be more significant sedimentologically than earthquake activity

influence of composition and thermal history of volcanic glasses on water content as determined by micro raman spectrometry development of raman spectrometry for quantification of water content in natural glasses requires the assessment of the dependence of the technique on glass composition and thermal history in the low frequency domain raman spectra topology varies due to glass depolymerization and substitution in the framework of si4 iv by alkali balanced al3 iv and fe3 iv in calcalkaline rhyolite to basaltic andesite and alkaline trachyte phonolite to alkali basalt glasses these processes result in strong dependence of previous analytical procedure internal calibration on glass composition here we show that an analytical procedure based on calibration to an external standard is only faintly composition dependent for si rich alkaline glasses trachytes phonolites for a given glass composition thermal history also plays a fundamental role in the choice of raman procedure for water analysis repeated cycles of thermal annealing induce microcrystallization of hydrous trachyte glasses and modify cation distribution in the glass structure application of these concepts to analysis of banded obsidians suggests that small scale heterogeneities in glasses are not simply related to magma degassing but could depend on thermal history and consequent relaxation paths in the melt

the effect of water and fo2 on the ferric ferrous ratio of silicic melts new experiments on the effect of dissolved water on the ferric ferrous ratio of silicic melts have been performed at 200 mpa between 800 c and 1000 c and for fo2 between nno 1 35 and nno 6 6 water saturated conditions were investigated compositions studied include six metaluminous synthetic melts with feotot progressively increasing from 0 47 to 4 25 wt two natural obsidian glasses one peraluminous and the other peralkaline and a synthetic rhyolitic glass having the composition of the matrix glass of the june 15 1991 pinatubo dacite ferrous iron was analyzed by titration and feotot by electron microprobe variation of quench rate was found to have no detectable effect on the ferric ferrous ratio of the hydrous silicic melts investigated at nno no dependence of the ferric ferrous ratio with temperature is observed at fo2 nno 1 the experimental ferric ferrous ratios are equal or lower than calculated the peralkaline samples show the same type of behaviour a non linear relationship between xfe2o3 xfeo and fo2 implies that a term for dissolved water must be added to the kc equation if it is to be applied to the calculation of ferric ferrous ratios of hydrous silicic melts above nno 1 the ferric ferrous ratio is essentially controlled by the anhydrous melt composition and fo2 however differences exist between measured and calculated ferric ferrous ratios of silicic melts that are not all attributable to the effect of dissolved water additional work is needed to describe more precisely the dependence of the ferric ferrous ratio on anhydrous melt composition the oxidizing effect of water is restricted to relatively reduced magmatic liquids in oxidized calk alkaline magma series the presence of dissolved water will not largely influence melt ferric ferrous ratios

fire and alluvial chronology in yellowstone national park climatic and intrinsic controls on holocene geomorphic processes we employed a systemwide approach a large and robust set of radiocarbon ages and modern process analogs to interpret the holocene history of forest fire related sedimentation and overall alluvial activity in northeastern yellowstone national park debris flow and flood events following the 1988 fires provided facies models for interpreting the stratigraphic record of fire related sedimentation within valley side alluvial fans of soda butte creek fire related deposits make up approximately 30 of the late holocene fan alluvium fifty 14 c ages on fire related events cluster within the intervals of 3300 2900 2600 2400 2200 1800 and 1400 800 yr b p and suggest earlier episodes of large fires and fan aggradation around 7500 5500 and 4600 4000 yr b p a major pulse of fire related debris flow activity between 950 and 800 yr b p coincided with the height of the widely recognized medieval warm period ca a d 1050 1200 instrumental climate records over the last 100 yr in yellowstone imply that the intensity and interannual variability of summer precipitation are greater during warmer periods enhancing the potential for severe short term drought major forest fires and storm generated fan deposition along lower soda butte creek fill cut terrace treads were created by lateral migration of channels and accumulation of overbank sediments ca 8000 yr b p terrace level t1a 7000 5600 t1b 3100 2600 t2 2000 1300 t3 and post 800 yr b p t4 these periods coincide with overbank sedimentation on slough creek and the lamar river but alternate with intervals of fire related fan deposition implying a strong climatic control local paleoclimatic data suggest cooler effectively wetter conditions during terrace tread formation in warmer drier intervals reduced average runoff in axial streams results in meander belt narrowing concurrent channel incision may be caused by infrequent large floods greater resistance to downcutting however allowed fewer terraces to be formed along slough creek and the lamar river alluvial systems in northeastern yellowstone show a clear response to millennial scale climatic cycles wherein alluvial fans aggrade and prograde over flood plains in drier periods axial streams widen their flood plains and trim back the fans during wetter periods small scale climatic fluctuations of the holocene thus had substantial impact on postglacial landscapes in northeastern yellowstone

erosion thresholds and suspended sediment yields waipaoa river basin new zealand characteristics of the suspended sediment load in the waipaoa river new zealand and in two of its tributaries mangatu and te arai rivers are examined for evidence of different dominant erosion processes in the basins upstream different shapes of the suspended sediment concentration water discharge relations lead to differences in long term average yield event yield magnitude frequency relations and relative importance of large flows and rare events in the mangatu river frequent runoff events 2 1 are relatively more important to the long term yield 11 540 t km yr half of the long term average load is transported by events with return periods less than 1 year and there is little evidence of an erosion threshold limitation on sediment supply this is consistent with the predominance in the mangatu basin of hillslope erosion processes that involve scour by surface and channelized runoff particularly gully erosion this contrasts with the te arai river where sediment concentration tends to be much lower at low and moderate flows frequent runoff events transport less of the long term yield 4600 t km 2 yr than do rarer large magnitude flood events event sediment yields are an order of magnitude lower during events with subannual return periods and half of the long term average load is transported during events with a return period of 2 years some of these characteristics appear to result in part from two populations of runoff events in the te arai basin nonetheless they are consistent with field evidence that most of the sediment supplied to the te arai stream network is generated by shallow landslides which are activated once a rainfall threshold is exceeded

a 2400 yr record of natural events and anthropogenic impacts in intercorrelated terrestrial and marine sediment cores waipaoa sedimentary system new zealand the waipaoa sedimentary system spans 100 km from terrestrial upland to continental rise alluvial buffering has little effect on sediment flux at the outlet of this mesoscale dispersal system and hinterland to margin transport is accomplished rapidly because of this synergy the floodplain and shelf depocenters are sensitive to changes in sediment production in the hinterland and natural and anthropogenically forced changes in sediment source dynamics that occur at several temporal and spatial scales leave distinctive signals in the stratigraphic record manifested as variations in sediment properties these signals appear in intercorrelated sediment cores from a headwater riparian storage area and the major terrestrial and marine repositories for sediment discharged during the past 2 4 k y the signals represent the landscape response to vegetation and land use change short term fluctuations in climate that affect surface properties and processes and extreme storms and subduction thrust earthquakes extreme storms are the minimum geomorphologically effective event preserved in the sediment records lower magnitude storms that are integral components of the prevailing hydrometeorological regime create high frequency fluctuations in sediment properties and collectively contribute to event sequences of 100 yr duration events and event sequences comprise a hierarchy of temporally sensitive phenomena the impacts of which are conditioned by frequency and magnitude by contrast vegetation disturbance is a spatially sensitive phenomenon that directly impacts sediment source areas and lowers the threshold of landscape sensitivity to erosion for this reason the taupo eruption of 1 718 ka and the piecemeal vegetation changes that occurred after the arrival of polynesian settlers also generated strong depositional signals after european colonization deforestation of the hinterland altered landscape sensitivity and precipitated the transition to an erosional regime that impacted sediment production and dispersal across the entire magnitude frequency spectrum of events regulating sediment delivery to and transport in stream channels no other perturbation had such a profound impact on the late holocene depositional record

watershed control on the carbon loading of marine sedimentary particles abstract previous investigations of the factors governing organic carbon burial on continental margins have pointed toward the important apparently protective association of carbon with mineral particles these studies have also revealed dramatic transformations of carbon particle relationships at the land sea interface riverine particles in some settings lose a large portion of their loads of sorbed terrestrial carbon upon discharge to the ocean and gradually reload to similar levels with marine carbon the eel river in northern california and the adjacent continental shelf were selected as an ideal system to investigate the rates of these processes the river is episodically subject to large floods and the shelf stratigraphy preserves a record of the resultant large pulses of sediment and carbon input to the marine environment carbon isotopic carbon to nitrogen and carbon to surface area ratios of particles in flood deposits were expected to reflect the rapid unloading of terrestrial carbon from discharged particles whereas nonflood sediments that have accumulated at slower rates on the shelf were expected to carry higher loads of marine carbon our results indicate however that particles on the eel shelf have retained their loads of terrigenous carbon and that a significant portion of the particle sorbed carbon buried on the shelf is kerogen derived from the mesozoic tertiary franciscan complex we hypothesize that rates of uplift and mass wasting in the eel watershed and rates of particle delivery to and burial on the continental shelf are so rapid that kerogen is not completely oxidized and is recycled instead the loading of carbon on clay sized particles delivered to the shelf moreover is dependent on river discharge and may reflect the relative importance of different mass wasting processes during precipitation events of varying intensity the eel river system is likely to be representative of other small mountainous rivers and indicates that processes on land may play an important role in governing the amount and character of carbon being buried on the continental margins

terrigenous input and paleoproductivity in the southern ocean the geochemistry of several sites along the polar front zone of the southern ocean revealed significant changes in terrigenous input and productivity on glacial timescales our records indicate concentrations and fluxes of terrigenous elements i e fe al and ti are low during interglacials and increase tenfold to twentyfold during glacials phosphorus accumulation reactive p concentrations and p ti ratios exhibit similar trends as the terrigenous components suggesting increased export production during glacials in all cores elemental ratios remain relatively constant indicating terrigenous sources at each site have not likely varied over the past 250 kyr iron accumulation rates for these sites are 10 times higher during glacials than interglacials and exceed the estimated regional eolian fluxes by 50 times the source of this terrigenous material is thus likely to be hemipelagic rather than direct eolian input or ice rafting and we speculate fe upwelled from this source may have stimulated glacial productivity in the southern ocean

micro raman determination of iron redox state in dry natural glasses application to peralkaline rhyolites and basalts abstract the position scaled intensity and topology of the raman stretching envelope at 1000 cm 1 hf have been established in complex anhydrous glasses having variable fe 3 fe ratios and contrasting compositions of peralkaline rhyolite pantellerite feo t 7 8 wt iron poor and iron rich basalts feo t 7 6 and 10 1 wt sensitivity of glass structure to iron redox decreases with increasing glass basicity raman spectra of pantellerite glasses fe 3 fe 0 04 0 97 evidence the sharp increase of a band at 970 cm 1 with the progressive entry of 4 fold fe 3 in alkali bonded q 3 units the spectral evolution of basalts with increasing iron oxidation fe 3 fe 0 05 0 87 is more subtle and is likely determined by formation of less polymerized units the moderate to low influence of redox state changes on the structure of natural basalt glass compared with the high sensitivity of their synthetic analogues can be attributed to strong competition between network forming cations al fe in the absence of an excess of alkalis we demonstrate that raman calibration against reference glasses allows precise determination of fe 2 fe 3 ratio but is highly composition dependent as a consequence of the variable link existing between fe 2 fe 3 and glass polymerization specific calibration procedures based on deconvolution shift or intensity of hf band are required for compositions with high acid glasses moderate or poor basic glasses sensitivity to iron redox changes respectively

holocene paleoseismicity in the fold and thrust belt of the hikurangi subduction zone eastern north island new zealand abstract along the 500 km long eastern coastline of the north island new zealand there are at most seven distinct holocene marine terraces aged 7 ka b p or less the highest of the terraces is 27 m above present day mean sea level the coastal region is subdivided into fourteen distinct subregions based on radiocarbon ages of marine deposits overlying wave cut shore platforms and geographic distribution of similarly aged terraces holocene marine terraces are the result of uplift associated with large earthquakes co seismic deformation this conclusion is based on characteristic stepped terrace morphology clustering of ages of terrace deposits within subrogions and the occurrence of co seismic uplift in historic time differential uplift across structures and distinct age variations at subregion boundaries are also characteristic recurrence intervals of uplift in any one terrace sequence vary from 0 4 ka to 2 0 ka and individual amounts of uplift vary from 1 0 m to 4 0 m in the past 2 5 ka ages from all terraces within subrogions indicate at least 21 paleoseismic events affecting coastal areas of eastern north island in that period these events cluster in time and in separate parts of eastern north island several earthquakes occurred 0 3 0 6 1 0 1 5 2 1 and 2 3 ka b p our data strongly support the concept of segmentation of deformation along the subduction margin the likely cause of coastal uplift is movement on steep reverse faults local structures rather than the subduction thrust that propagate from or near the subduction thrust some 20 25 km below the region earthquakes of moment magnitude 7 3 8 0 are estimated to be associated with these fault movements

the formation of sedimentary strata in an allochthonous shelf environment the washington continental shelf nittrouer c a and sternberg r w 1981 the formation of sedimentary strata in an allochthonous shelf environment the washington continental shelf mar geol 42 201 232 models of fine scale 120 m shelf regions the inner shelf sand and mid shelf sandy silt are the predominant accretionary deposits on the shelf important sedimento logical observations obtained by boxcoring the upper 1 2 m of these deposits are a progressive decrease in grain size with distance from the columbia b downward coarsening within the seabed c loss of distinct sedimentary structure homogenization of sediment with distance from the columbia non dimensional parameters based on sediment transport and benthic biological studies can be used to relate rates of sediment mixing re working to rates of accumulation these parameters have the potential for quantitative prediction of strata formation from measurements of active processes physical and biological mixing can be assumed to remain relatively constant in an alongshelf direction on the washington shelf and accumulation rate is known from pb 210 geochronology to decrease away from the columbia together these factors tend to increase the ratio of mixing to accumulation with distance from the columbia and predict the sedimentological observations listed above

holocene sediment deposition on the poverty slope margin by the muddy waipaoa river east coast new zealand the margin off the raukumara peninsula east coast north island of new zealand is characterised by high terrigenous sediment flux the dramatic effects of historic land use change the rapid uplift of mesozoic and soft tertiary sediments and by complex sediment tectonic interactions on a steep and unstable continental slope the poverty bay shelf and slope indentation are adjacent to the waipaoa river which delivers 15 mt year 1 of mud this study presents new data from the poverty slope the seaward extension of the waipaoa dispersal system a 3 km3 lobe of postglacial sediment emerges from the poverty gap and feathers down onto the upper slope downslope the poverty indentation has received a significant holocene flux of terrigenous sediment accumulating in two mid slope basins the paritu trough and a smaller lower slope basin below the south paritu ridge hemipelagic sediment has accumulated on the mid slope at around 0 05 g cm 2 year 1 0 06 cm year 1 since the mid late holocene seismic reflection echo type and backscatter imagery indicate mud deposits on the mid slope debris at the base of regularly spaced upper slope gullies and a large avalanche deposit in the upper paritu trough the consistency of the tephrostratigraphy indicates that despite slope instability hemipelagic sedimentation is the dominant background process operating at millennial time scales at least since the mid holocene the poverty slope should be included in any budget calculation of post colonisation increased sediment yield for the margin the poverty canyon has probably been largely inactive during the holocene highstand

late cenozoic evolution and earthquake potential of an active listric thrust complex above the hikurangi subduction zone new zealand in the center of the frontal wedge of the hikurangi subduction zone new zealand mahia peninsula and its submarine continuation lachlan ridge are being uplifted and folded above an active landward dipping thrust fault complex that is 80 km long high quality marine seismic reflection profiles reveal complex deformation of a cretaceous to holocene sedimentary section and enable a detailed analysis of the stratigraphy structural evolution deformation rates and future earthquake potential the structural analysis is facilitated by uplifted marine terraces on mahia peninsula and by 14 submarine unconformities in the hanging wall sequence five of which are correlated across the eroded crest of lachlan ridge and into the footwall basin the ages of the unconformities are determined by seismic ties to an offshore exploration well onshore outcrops on the peninsula and seabed samples dated by pollen coccolith nannoflora and foraminifera biostratigraphy nine regional quaternary unconformities which developed in response to eustatic fluctuations in sea level and are not older than ca 1 ma are correlated with oxygen isotope stages in equatorial pacific ocean drilling project core 677 the ages of fault growth strata and progressive restorations of deformed stratigraphy indicate that lachlan ridge developed during three phases of deformation since subduction of the pacific plate commenced beneath the australian plate in the early miocene these include an initial phase of thrust faulting a subsequent phase dominated by extensional faulting and the current mainly pleistocene to holocene phase of structural inversion reactivated listric thrust faulting and folding early to middle miocene thrusts in the deeper core of the complex developed out of sequence by sequentially stepping up into the hanging wall section creating an imbricate fan with emerging thrust tips now buried within the forelimb basin in the middle miocene early pliocene listric extensional faults developed in the active thrust wedge possibly as a result of substantial relief on the subducted pacific plate and controlled the development of lachlan basin to the west of the ridge the principal active thrust is the lachlan fault a listric extensional detachment reactivated to accommodate thrust movement and consisting of at least three right stepping segments depth converted seismic profiles indicate that the fault dips westward at 15 20 6 8 km beneath the western flank of lachlan ridge and steepens to 55 70 or even steeper in the upper 1 2 km of section beneath the eastern flank syninversion pleistocene fault growth strata on both flanks of the associated anticline provide an exceptional record of progressive fold limb rotation resulting from the listric fault geometry a geometric analysis of the fault growth strata and deformed terraces was used to derive a maximum dip slip displacement rate of as fast as 3 0 6 5 mm yr the implied shortening rate of 2 6 6 3 mm yr represents 8 20 of the total 31 mm yr of orthogonal plate convergence across this part of the upper plate of the hikurangi subduction zone the top of the pre fault growth paleogene section reveals as much as 5 8 1 5 km of vertical separation in the north decreasing to 30 50 of this value in the south temporal 10 3 10 6 yr and spatial 10 3 10 4 m of strike length variations in vertical deformation rate have occurred during the past 1 m y maximum rates occurred in the holocene and middle quaternary a long term increase in vertical separation rate on all segments during the pleistocene largely reflects a change in thrust kinematics associated with structural inversion the relatively greater increase in uplift rate on the northern part of the fault during the past 1 m y could be related to the possibility that a subducted seamount lies 10 km beneath the peninsula estimates of earthquake source parameters incorporating paleoseismic uplift data from mahia peninsula indicate a potential moment magnitude of up to m w 7 6 8 0 for an earthquake that ruptures all three segments of the lachlan fault the average recurrence interval for such events is estimated to be 615 2333 yr which is consistent with a mean recurrence interval of 1062 yr for four late holocene earthquakes thus the uplift and folding of mahia peninsula and lachlan ridge results from coseismic displacements on a major listric thrust fault that ruptures the upper plate frequently in association with large magnitude earthquakes

a decadal record of underflows from a coastal river into the deep sea four periods of extreme turbidity were measured in monterey submarine canyon over the past 12 yr these turbid events occurred simultaneously with the four largest flood events of the nearby salinas river they filled the canyon with fresher warmer and apparently buoyant water that extended to depths below 1 km the low salinity signature must reflect underflow of the salinas river plume that was driven to depth by negative buoyancy contributed from the suspended sediment a flux estimate for the 1995 event suggests that one half or more of the river s suspended sediment load was carried down the canyon in the underflow underflows may contribute significantly to the carbon budget of the continental slope

a tale of two deltas seismic mapping of near surface sediments on the mississippi alabama outer shelf and implications for recent sea level fluctuations abstract high frequency seismic reflection profiles showing near surface sediments of the mississippi alabama outer shelf define two shelf margin deltas and three unconformities the deepest unconformity lies below the westernmost delta the middle unconformity separates the two deltas and the shallowest unconformity is atop the easternmost delta the deeper two unconformities are extensive and erosional to the shelf edge implying type 1 sequence boundaries the shallowest is restricted in its depth range and extent suggesting a type 2 boundary both delta wedges contain sigmoid reflectors representing foreset beds and have apparent transgressive layers at their bases thus these two sediment wedges and their bounding unconformities represent parts of three sea level cycles although we lack good age constraints the middle unconformity appears to represent the last glacial maximum so the western delta must have been deposited before and the eastern delta afterwards internal reflector geometries suggest the eastern delta was deposited during an episode of falling sea level implying a relative sea level regression within the overall deglacial transgression

towards a structural model for the viscosity of geological melts abstract the viscosity of silicate melts is the most important physical property governing magma transport and eruption dynamics this macroscopic property is controlled by composition and temperature but ultimately reflects the structural organization of the melt operating at the microscale at present there is no explicit relationship connecting viscosity to silicate melt structure and vice versa here we use a single raman spectroscopic parameter indicative of melt structure to accurately forecast the viscosity of natural multicomponent silicate melts from spectroscopic measurements on glasses preserved on earth and other planets the raman parameter is taken as the ratio of low and high frequency vibrational bands from the silicate glass by employing a green source laser wavelength of 514 5 nm r514 5 our model is based on an empirical linkage between r514 5 and coefficients in the vogel fulcher tammann function for the temperature dependence of melt viscosity the calibration of the raman based model for melt viscosity is based on 413 high temperature measurements of viscosity on 23 melt compositions for which published raman spectra are available the empirical model obviates the need for chemical measurement of glass compositions thereby providing new opportunities for tracking physical and thermochemical properties of melts during igneous processes e g differentiation mixing assimilation furthermore our model serves as a milepost for the future use of raman spectral data for predicting transport and calorimetric properties of natural melts at geological conditions e g volatiles and pressure and production

palaeoclimatic implications of a storm erosion record from late holocene lake sediments north island new zealand abstract a ca 2250 year storm history has been identified from a high resolution lake sediment record from the east coast of the north island new zealand this event based chronology identifies 340 storms in the pre european record the record is largely one of natural variability without human impacts layers of minerogenic sediment representing the products of individual storm events are clearly visible in lake cores these storm sediment pulses derived mainly from landslides record the frequency and magnitude of storms clusters of pulses identify six periods of high sedimentation and associated erosion before european settlement a d 1878 at least five of these are interpreted as periods of higher rainfall and probably warmer temperatures since historic records show that most large storms are derived from the subtropics tropics most of the storm periods correspond to warm climate intervals previously identified from new zealand and from southern hemisphere palaeoclimatic evidence the mapara 2 period ca 2090 1855 cal yr b p was the stormiest other periods were of shorter duration the mapara 2 period occurred at times of sustained warmth in the tasmanian and chilean tree ring records which might suggest hemispheric warming at this time one storm period burrell which occurred during the historical enso record was at a time of moderately high enso activity three earlier periods also appear to show responses to enso two storm periods correspond to previously proposed new zealand wide periods of increased erosion and sedimentation estimates of palaeo storm rainfalls from relationships between storm rainfall and sediment thickness of historical events suggest that storm pulses ca 12 mm thick represent palaeo storms of ca 450 mm rainfall

element partitioning in sediment soil and vegetation in an alluvial terrace chronosequence limagne rift valley france a landscape geochemical study abstract the geochemical behaviour of specific elements in fluvial sediments topsoils soil profiles and plant material on a sequence of quaternary alluvial terraces was reconstructed semi quantitatively using indices of accumulation or depletion with respect to abundance in the lithosphere local soils and sediments topsoils of different ages and soil profiles are most clearly differentiated by the degree of leaching of ca mg and some minor elements with respect to less mobile si and ti clay translocation within soil profiles of older terraces leads to accumulation of al and associated elements in deeper horizons and accumulation of fe and mn in pseudogley horizons in the upper part of the clay accumulation layers p k ca mn and zn are strongly concentrated in plant materials relative to the topsoils ca is accumulated more strongly in oak bark than in grasses and the relative accumulation is greater on the older terraces due to the low ca content in their topsoils mn contents of both grasses and oak bark are greater on the older terraces than the younger for most elements topsoil and plant material contents show little correlation probably because plant requirements exert a greater control on element uptake than does availability the results illustrate that landscape geochemical analysis is useful for rapid appraisal of long term landscape processes such as erosion sedimentation weathering and preferential plant uptake

modern sediment dispersal and accumulation on the outer poverty continental margin abstract the poverty margin was sampled in 2005 and 2006 as part of an international initiative to examine the terrestrial and marine sedimentary response to natural and human impacts on dispersal systems at mud dominated coasts the nsf margins source to sink initiative 210pb accumulation rates generally decrease from 1 g cm2 y in the mid shelf depocenter on the outer shelf to 0 1 g cm2 y on the mid slope plateau range 0 04 2 53 g cm2 y higher accumulation rates are observed all along the outer poverty shelf extending over the shelf break onto the upper poverty slope in canyons and gullies rates are fast in gullies that incise into the shelf edge 0 75 1 g cm2 y particularly in the area between waipaoa canyon and poverty canyon and in the axis of poverty canyon 1 29 1 89 g cm2 y below 1200 m water depth rates in the axis of poverty canyon are no more rapid than those found at open slope cores in similar water depths 0 12 0 15 g cm2 y excess 210pb profiles generally exhibit steady state characteristics except in the axis of poverty canyon where non steady state 210pb profiles are observed 137cs was not found above minimum detection limits or above statistical background levels in any cores from the poverty margin 7be was found distributed widely along and across the margin during both summer and winter periods observed to depths of up to 4 cm widespread presence of 7be on the margin in both winter and summer suggests that terrestrially derived sediment is reaching the outer shelf and upper slope throughout the year a sediment budget based on 210pb accumulation rate data shows that approximately 13 18 of the waipaoa annual discharge is accumulating on the outer poverty margin as a whole and approximately 11 15 of the annual discharge is accumulating on the continental slope alone notably approximately 28 of the sediment annually accumulating in the outer margin is being sequestered in slope gullies and canyons although they represent only 6 of the area of the outer margin

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

shelf record of climatic changes in flood magnitude and frequency north coastal california continental shelf deposits off the eel river north coastal california document a recent increase in the magnitude and frequency of major hydrologic floods 10 yr recurrence interval the shelf record reveals a sudden three fold increase in sedimentation rate ca 1954 and a concomitant increase in the frequency of preserved flood beds comparison of sedimentary and river discharge records reveals that major floods after ca 1950 had a more pronounced effect on coastal sediment delivery and accumulation offshore than previous recorded events of similar magnitude and that stratigraphic preservation of flood events is highly dependent on flood frequency and net sedimentation rate we contend that this change in marine sedimentation is a response to documented climatic phenomena that have increased the frequency of major floods throughout the western united states during the past half century together with intrabasinal impacts of extreme floods in 1955 and 1964 anthropogenic increase in watershed sediment production is a probable secondary factor

effects of climate and landscape development on the terrestrial phosphorus cycle past variations in the terrestrial cycle of phosphorus p a biolimiting nutrient are poorly understood detailed geochemical analysis of p in lake sediment cores spanning the late pleistocene to the present from the western appalachian plateau the coast mountains of british columbia and the san bernardino mountains of southern california reveal large changes in terrestrial p cycling p is transformed from a mineralized form to more bioavailable forms with increased soil development and landscape stability in the catchments this process occurs relatively rapidly i e within 3 000 5 000 yr and can be reset quickly the degree of transformation depends on local climate and the starting point of the soil system the release of solid phase p from these landscapes follows modeled patterns of high rates during the initial stages of soil development and low rates upon soil and landscape stabilization changes in weathering style were confirmed for the southern california catchment by analysis of ge si ratios of lake diatoms which revealed substantially higher values during an interval of high p release and low values at present these records point to significant variability in the terrestrial p mass balance on glacial time scales a feature that needs to be incorporated into models of nutrient andmore carbon cycling in the past less

geomorphologic controls on the age of particulate organic carbon from small mountainous and upland rivers 1 to assess the role that erosion processes play in governing the character of particulate organic carbon poc discharged from small mountainous and upland rivers a suite of watersheds from oregon california and new zealand was investigated the rivers share similar geology tectonic setting and climate but have sediment yields that range over 3 orders of magnitude the 14c age of the poc loads is highly correlated with sediment yield carbon isotope mass balances reveal that the rivers carry bimodal mixtures of modern plant and ancient rock derived oc at lower yields modern plant oc dominates the material delivered to the river by sheetwash and shallow landsliding with increasing yield a progressively larger part of the poc is contributed directly from bedrock erosion via deep gully incision our results support the inference that active margin watersheds are important sources of aged poc to the ocean

residence time of alluvium in an aggrading fluvial system relationships between the surface area and age of alluvial deposits were used to estimate the residence time of alluvium in the 2205 km2 waipaoa river basin new zealand the contemporary waipaoa river is an efficient transporter of sediment to the continental shelf but the basin has been characterized by rapid channel and valley aggradation in the historic period and by extensive mid to late holocene alluvial storage in the lower reaches the area weighted mean age of alluvial deposits in the lower part of the river basin is 4400 yr these deposits comprise terrace remnants isolated by downcutting and holocene to recent sediments that are potentially remobilizable by the modern river even though the amount of storage is small relative to downstream transport the majority of the potentially remobilizable alluvium is likely to remain in storage for 100 yr and its half life time for 50 per cent removal is 2000 yr within the confines of the flfloodplain the apparent loss of older deposits is due primarily to burial but losses of the most recent deposits are due almost entirely to remobilization 30 40 per cent with the remainder preserved in the alluvial record for at least 104 yr most of this sediment is likely to remain in storage until there is a shift to a degradational state copyright 2006 john wiley sons ltd

spatial and temporal patterns in fluvial recovery following volcanic eruptions channel response to basin wide sediment loading at mount pinatubo philippines the june 1991 eruption of mount pinatubo philippines was one of the largest volcanic eruptions of the twentieth century emplacing 5 6 km 3 of pyroclastic fl ow material on the fl anks of the volcano the combination of abundant relatively fi ne grained easily erodible material and intense tropical rainfall led to numerous lahars immediately following the eruption even after major lahars ended sediment yields in some basins remained orders of magnitude above pre eruption levels using data collected from 1996 through 2003 we investigated fi ve basins that experienced varying amounts of sediment loading in the 1991 eruption from 1 to 33 of the basin area covered by valley fi lling pyroclasticfl ow deposits from measurements of fl ow and bed characteristics made through time we developed a general conceptual model for channel recovery following basin wide sediment loading initially fi ner grained sediment and pumice are mobilized preferentially through selective transport once the bed is coarse enough for gravel size clasts to interact with one another clast structures develop increasing form roughness and critical shear stress and inhibiting initial clast mobility as sediment inputs continue to decline the channel incises into valley bottom sediments progressively armoring through winnowing at pinatubo incision and armoring occur fi rst as dry season phenomena due to reduced sediment inputs eventually moving to year round low fl ow bed stability observed timing of the onset of in channel biological recovery suggests that reestablishment of channel stability helps catalyze aquatic ecosystem recovery

the southern hemisphere westerlies in the australasian sector over the last glacial cycle a synthesis abstract the southern hemisphere westerlies in the southwest pacific are known to have waxed and waned numerous times during the last two glacial cycles though even semi continuous histories of the westerlies extend back no more than about 20 000 years we have good evidence for at least three scales of events a westerly maximum occurs at the last glacial maximum there is less conclusive evidence for another westerly maximum in the late holocene and for a minimum at ca 11 ka it is too early to ascribe even a cycle to these data but there are grounds to suggest that milankovitch precessional forcing may underlie the observed pattern there is also a quasi 2600 year cycle present in antarctic ice cores that appears to correlate to variation in westerly flow there is strong centennial scale variability in historical times the little ice age lia ca 1400 1850 was associated with a poleward shift in the circumpolar trough in the southern ocean strengthened westerly circulation over tasmania and a strengthening of southwesterly circulation and neoglaciation in southern new zealand while the preceding period 800 1400 ad was less certainly marked by reduced westerly flow from modern records we know that decadal and inter annual variability is important e g pacific decadal oscillation high latitude mode also known as the antarctic oscillation el nino southern oscillation only a minority of the proxies examined can identify changes on these temporal scales but data from tree rings ice cores and laminated lake sediments do indicate systematic changes in these phenomena through time rossby wave patterns are shown to play a critical role in long duration events as well as at the synoptic scale we conclude that westerly circulation is as strong now as at any time in the last glacial cycle in addition changes in latitudinal boundaries in the westerlies may be nearly as large in inter annual zonal shifts ca 2 maximum as in glaciation interglaciation movements ca 3 4 there is however reasonable evidence of strengthening weakening across much of the westerly belt at westerly maxima minima such as the lia early holocene

speleothem master chronologies combined holocene 18o and 13c records from the north island of new zealand and their palaeoenvironmental interpretation the stable isotope records of four stalagmites dated by 19 tims uranium series ages are combined to produce master chronologies for delta 18 o and delta 13 c the delta 18 o records display good overall coherence but considerable variation in detail variability in the delta 13 c records is greater but general trends can still be discerned this implies that too fine an interpretation of the structure of individual isotopic records can be unreliable speleothem delta 18 o values are demonstrated to show a positive relationship with temperature by comparing trends with other proxy records but also to respond negatively to rainfall amount speleothem delta 13 c is considered to be most influenced by rainfall the postglacial thermal optimum occur red around 10 8 ka bp which is similar in timing to antarctica but up to 2000 years earlier than most northern hemisphere sites increasingly negative delta 18 o values after 7 5 ka bp indicate that temperatures declined to a late mid holocene minimum centred around 3 ka bp but more positive values followed to mark a warm peak about 750 years ago which coincided with the mediaeval warm period of europe low 5110 values at 325 years bp suggest cooling coincident with the little ice age a marked feature of the delta 13 c record is an asymmetric periodicity averaging c 2250 years and amplitude of c 1 9parts per thousand it is concluded that this is mainly driven by waterbalance variations with negative swings representing particularly wet intervals the 5110 record shows a higher frequency cyclicity with a period of c 500 years and an amplitude of c 0 25 parts per thousand this is most likely to be temperature driven but some swings may have been amplified by precipitation

radiocarbon age of the kaharoa tephra a key marker for late holocene stratigraphy and archaeology in new zealand the kaharoa eruption the most recent rhyolitic volcanic event in new zealand resulted in the deposition of the compositionally distinctive kaharoa tephra over at least 30 000 km2 of northern and eastern north island the tephra forms an isochronous marker bed for various late holocene stratigraphic and palaeoen vironmental studies but is particularly important for evaluating the chronology of new zealand s notably short prehistory because it was erupted within the last millennium close to the time of first polynesian colonization we derive a definitive radiocarbon age previously ambiguous for the kaharoa tephra of 665615 bp using cluster analysis of 22 radiocarbon ages relevant to the kaharoa eruptive episode the error weighted mean age obtained on unscreened ages minus outliers is supported by statistically identical ages obtained from three sets of screened ages selected to minimize the effects of inbuilt age or contamination based on the intercepts method and 1 sigma range of northern hemisph

input of river derived sediment to the new zealand continental shelf ii mineralogy and composition abstract clay mineralogies and elemental compositions of river borne sediments from new zealand were examined as indicators of likely sources of the lithogenous component of sediments on the continental shelf relative occurrences of kaolin and smectite enabled the rivers to be fitted into three main groups these correspond closely with geography as follows 1 most of the rivers from north island 2 all the rivers from the north east coast of south island 3 most of the rivers from the remainder of south island elemental analyses of their sediments also led to a geographical grouping of rivers six main groups resulted from a q mode cluster analysis of elemental compositions these were the northernmost river wairoa river the east coast of north island the west coast of north island the east coast of south island the south east and west coasts of south island the west coast of south island there is substantial overlap between the groupings by clay mineralogy and by composition the results can be interpreted mainly in terms of the geologies of source areas exceptions to regional trends reflect either an unusual geology in the source areas or low sediment loads where soils contribute significantly to the sediments the terrigenous component of offshore sediments and new zealand riverine sediments have similar compositions suggesting that the former are derived in a relatively unmodified form from riverine sediments

terrestrial palynology from marine cores as an indicator of environmental change for the waipaoa sedimentary system and north eastern new zealand diverse terrestrial palynomorph assemblages of pleistocene to recent age have been recovered from mainly marine sediment cores along the eastern new zealand margin these assemblages record a range of environmental changes including climate deforestation reforestation rates of erosion sediment provenance and age volcanic activity polynesian and european settlement strength and direction of ocean currents astronomical cyclicity and other major events many of which can be correlated with shorter onshore terrestrial sequences as such pollen yields valuable information on the dynamic new zealand landscape which is of particular relevance to a source to sink approach this paper provides an integrated summary of published and unpublished late pleistocene palynological studies off eastern north island new zealand that gives context for an analysis of cores within and marginal to the waipaoa sedimentary system pollen assemblages faithfully reflect the last glacial vegetation dominated by grass and shrub land species together with elevated tertiary pollen from enhanced erosion of the regolith the glacial termination and holocene were marked by establishment of podocarp forest a mid holocene disappearance of sediment trapping mangroves and introduction of distal pollen with establishment of coastal current systems under rising sea level these natural signals are overprinted by abrupt changes in pollen species caused by volcanic eruptions finally endemic forest and shrub pollen were markedly reduced with human colonisation associated land use changes and introduction of exotic species

earthquake triggered increase in sediment delivery from an active mountain belt in tectonically active mountain belts earthquake triggered landslides deliver large amounts of sediment to rivers we quantify the geomorphic impact of the 1999 mw 7 6 chi chi earthquake in taiwan which triggered 20 000 landslides coseismic weakening of substrate material caused increased landsliding during subsequent typhoons most coseismic landslides remained confined to hillslopes downslope transport of sediment into the channel network occurred during later storms the sequential processes have led to a factor of four increase in unit sediment concentration in rivers draining the epicentral area and increased the magnitude and frequency of hyperpycnal sediment delivery to the ocean four years after the earthquake rates of hillslope mass wasting remain elevated in the epicentral area

a late medieval warm period in the southern ocean as a delayed response to external forcing on the basis of long simulations performed with a three dimensional climate model we propose an interhemispheric climate lag mechanism involving the long term memory of deepwater masses warm anomalies formed in the north atlantic when warm conditions prevail at surface are transported by the deep ocean circulation towards the southern ocean there the heat is released because of large scale upwelling maintaining warm conditions and inducing a lagged response of about 150 years compared to the northern hemisphere model results and observations covering the first half of the second millenium suggest a delay between the temperature evolution in the northern hemisphere and in the southern ocean the mechanism described here provides a reasonable hypothesis to explain such an interhemipsheric lag

event suspended sediment characteristics and the generation of hyperpycnal plumes at river mouths east coast continental margin north island new zealand abstract steepland rivers draining small coastal watersheds often have very high suspended sediment loads but the event characteristics of suspended sediment concentration and yield in this class of river is not well documented continuous monitoring at four sites in the waipaoa river basin new zealand demonstrates that during individual and composite events suspended sediment concentration versus water discharge relations typically show clockwise hysteresis and that event maximum concentration is poorly related to event peak discharge the signature of different erosion processes is also imprinted on the event yield magnitude frequency distributions gully dominated tributary basins produce relatively high yields at all frequencies reflecting greater sediment availability whereas in tributary basins where shallow landsliding is the dominant erosion process there is a steep increase in yields in relation to return period we estimate that flood discharges from the waipaoa river approach or exceed

the influence of sea level and tectonics on late pleistocene through holocene sediment storage along the high sediment supply waipaoa continental shelf abstract we present geophysical and core evidence showing how subsidence caused by forearc shortening has accommodated late pleistocene and holocene sediments supplied to the tectonically active waipaoa shelf nz limiting off shelf export during the early sea level highstand the last glacioeustatic fall and subsequent rise exposed and then flooded a shelf segmented into subbasins separated by zones of uplift leaving key stratigraphic markers of shoreline regression and transgression that vary strongly in character across the shelf highstand sediment isopachs tied to piston cores dated using tephra correlation and a radiocarbon age model provide a sediment budget at 2000 yr intervals from the mid holocene 5500 cal yr bp to present sediment load estimates from our shelf budget are in agreement with published model estimates for suspended sediment discharge from the waipaoa river for the past 3000 yr but importantly do not show the 6 fold increase in the waipaoa s sediment output that began with human settlement 700 yr ago and accelerated with deforestation over the last century bypassing of waipaoa sediment to the slope may therefore be a recent phenomenon caused by unnaturally high sediment loads a conclusion supported by data reported elsewhere in this volume our study also reveals evidence for 1 a relatively thick mid shelf transgressive section deposited during the last eustatic rise that may correlate to estuarine sequences reported from numerous sites on the modern coastline of the north island 2 a slight decrease in total basin filling rates during the highstand and 3 variability in the partitioning of highstand sediments between individual subbasins that may reflect differing degrees of tectonic accommodation

coastal uplift mechanisms at pakarae river mouth constraints from a combined holocene fluvial and marine terrace dataset abstract one of the major environmental controls on sedimentary systems is tectonics and thus in order to make quantitative explanations and predictions of the behaviour of sedimentary systems it is important to quantify tectonic rates and mechanisms in this study we show how a combined holocene fluvial and marine terrace dataset can be used to place constraints on coastal uplift mechanisms at pakarae river mouth to the east of the waipaoa sedimentary system mapping and surveying of fluvial terraces shows that the terraces can be divided into three sets i pgt a fill terrace formed during post glacial sea level rise 10000 7000 cal yr bp ii a sequence of post 7000 cal yr bp degradation terraces and iii historical post ad 1880 flood terraces a conceptual model of terrace evolution proposes that coseismic uplift has resulted in the observed back tilting downstream divergence and successive abandonment of tectonic terraces coastal uplift mechanisms are then examined by comparing the fluvial and marine terrace uplift distribution and the uplift per event from the marine terraces with those predicted by forward elastic dislocation models the models agree with the interpretation that the terrace uplift can be explained by coseismic slip on a steeply west dipping reverse fault located close to the shore possibly in combination with rupture of the hikurangi margin subduction interface 10 24 km below this study also provides insights into the tectonic drivers and impacts on the adjacent waipaoa sedimentary system including the possible role of subduction earthquakes growth of structures on the shelf and upper slope and the role that the interplay between sea level and tectonic controls has on sediment dispersal

dating initial maori environmental impact in new zealand abstract over the last decade there has been an intense debate as to whether new zealand prehistory is long 1500 yr short

posteruption suspended sediment transport at mount st helens decadal scale relationships with landscape adjustments and river discharges received 11 december 2002 revised 30 september 2003 accepted 18 november 2003 published 17 january 2004 1 widespread landscape disturbance by the cataclysmic 1980 eruption of mount st helens abruptly increased sediment supply in surrounding watersheds the magnitude and duration of the redistribution of sediment deposited by the eruption as well as decades to centuries old sediment remobilized from storage have varied chiefly with the style of disturbance posteruption suspended sediment transport has been greater and more persistent from zones of channel disturbance than from zones of hillslope disturbance despite the severe landscape disturbances caused by the eruption relationships between discharge magnitudes and frequencies and suspended sediment transport have been remarkably consistent discharges smaller than mean annual flows generally have transported 5 but locally 15 of the annual suspended sediment loads and infrequent p 0 01 large floods have transported as much as 50 of the annual suspended sediment loads in a single day however moderate magnitude discharges those greater than mean annual flows but less than 2 year floods have transported the greatest amounts of sediment from all disturbance zones such discharges have transported on average 60 to 95 of the annual suspended sediment loads usually within cumulative periods of 1 3 weeks each year although small magnitude and largemagnitude discharges have locally and episodically transported considerable amounts of suspended sediment there has not been any notable change in the overall nature of the effective discharges moderate magnitude flows have been the predominant discharges responsible for transporting the majority of suspended sediment during 20 years of posteruption landscape adjustment index terms 1824 hydrology geomorphology 1625 1815 hydrology erosion and sedimentation 1860 hydrology runoff and streamflow keywords sediment yield suspended sediment transport mount st helens erosion volcano geomorphology

use of the geochemical record preserved in floodplain deposits to reconstruct recent changes in river basin sediment sources abstract the geochemical record preserved in overbank floodplain deposits is used in combination with a composite fingerprinting technique and the chronology provided by 137 cs dateable horizons to reconstruct recent changes in sediment sources in the exe and severn basins uk composite fingerprints for discriminating potential source materials are identified from a suite of properties including heavy metals trace metals and cation bases these fingerprints are then compared with those of historical floodplain deposits using a numerical sediment mixing model relative contributions from distinct spatial sources characterised in terms of the devonian carboniferous and permian geological sub areas of the exe and the ordovician silurian devonian carboniferous permian and triassic jurassic sub areas of the severn are shown to fluctuate over the recent past in response to intrinsic e g the occurrence of extreme hydrologic events and extrinsic e g anthropogenic disturbance associated with land use change controls the potential for fingerprint property transformation in association with floodplain storage is assessed and the scope for further research using fingerprinting to reconstruct longer term sediment sources is discussed

the river it goes right on post glacial landscape evolution in the upper waipaoa river basin eastern north island new zealand abstract post glacial incision created 50 to 120 m of relief in the headwaters of the waipaoa river basin but it is not known how the signal of incision propagated along the trunk streams we addressed this issue by imposing previously determined long term rates of rock uplift that vary between 0 6 and 4 mm year 1 on the preaggradation longitudinal profile acting over the past 27 1 2 cal ka bp these rates are sufficient to passively elevate the waipaoa 1 terrace to its present level but during the last glacial maximum rates of vertical incision failed to match those of the uplifting rocks thus by the time favorable conditions for incision were reestablished after the antarctic cold new zealand late glacial reversal we estimate that the channel would have been elevated 55 m above the datum the river should otherwise have maintained the channel incised rapidly after the transition from glacial to interglacial conditions and reacquired its steady state form in the mid holocene 5 5 2 cal ka bp thereafter we suggest rates of incision matched rates of uplift no knickpoints are found on the upper waipaoa and mangatu rivers because incision commenced simultaneously along the entire length of the trunk streams and the pattern of incision is consistent with the downstream decline in the rate of rock uplift we also used hypsometric analysis to show how post glacial incision affected the surface morphology of low order 0 1 4 3 km 2 drainages in the headwaters of the waipaoa river basin values of the hypsometric integral are higher for proximal basins which the incision signal did not permeate than for low order basins bordering the upper waipaoa river and the lower reaches of tributaries that possessed enough erosive capacity to keep pace with incision along the mainstem hillslope adjustments were focused on the lower and mid sections of these basins so that the most pronounced changes to the hypsometric curve occur in the vicinity of the toe whereas the entire form of the hypsometric curve changes once mass wasting processes encroach onto hillslopes in the middle and upper sections of a basin

the heat capacity of hydrous multicomponent natural melts and glasses abstract the thermophysical properties of silicate melts and glasses are of fundamental importance for the characterization of the dynamics and energetics of silicate melts on earth and terrestrial planets the heat capacity of silicate melts is of particular importance because of its implications for the temperature dependencies of melt enthalpy and entropy and for the potential relationship to melt structure and transport properties currently there are reliable models for predicting the heat capacity of simple and multicomponent silicate glasses c p glass as a function of composition and temperature recent differential scanning calorimetry dsc measurements of heat capacity for multicomponent silicate liquid c p liquid however have shown that published models do not accurately reproduce heat capacity measurements on some silicate melts here we have compiled a database of heat capacity values for hydrous and anhydrous multicomponent natural samples the measurements are on pairs of glasses and melts over the compositional range wt of sio 2 44 79 al 2 o 3 5 35 tio 2 0 3 feo tot 0 11 na 2 o k 2 o 0 27 cao mgo 0 39 h 2 o 0 6 3 and minor oxides the compiled data show strong correlations between silica content x sio2 and the configurational heat capacity c p config defined as c p liquid cp glass measured across the glass transition temperature t g this correlation is used to establish an empirical model for predicting c p liquid as a function of melt composition i e sio 2 content and values of c p glass measured at the onset of the glass transition c p liquid 52 6 55 88 x sio 2 c p glass the model reproduces values of c p liquid to within an average relative error of 2 4 published models for the heat capacities of silicate melts e g stebbins 1984 richet and bottinga 1985 lange and navrotsky 1992 applied to the same dataset have average relative errors in excess of 5 5

estimating river sediment discharge to the ocean application to the eel margin northern california abstract hydrotrend a synthetic river discharge numerical model can simulate the natural variability daily annually and longer in the flux of water and sediment delivered to the coastal ocean the numerical model is designed to make discharge predictions based on climate even though field measurements of river flow are not available provided that appropriate assumptions are made regarding past climate the model can predict how a river may have behaved in the geological past sediment load is determined from a river s rating coefficients when applied to the flood dominated eel river northern california hydrotrend captures the intermonthly and interannual variability of discharge and loads over a century or more hydrotrend is applied to the ice age paleo eel river when sea level was lower and climate much cooler and wetter the paleo eel river at 18 000 year bp would see its hinterland runoff increase but not the magnitude of the peak discharges the post dicted sediment load of the paleo eel river was 25 greater than today s although basin precipitation was 45 greater and the hinterland area 4 greater through sea level lowering a method is provided to obtain sediment discharge rating coefficients for unmonitored modern rivers and paleo rivers the relationship q s g 1 2 h 3 2 a 1 2 provides for an estimate of a river s sediment load q s to within a factor of 3 over 7 orders of magnitude from knowledge of basin relief h and basin area a rating coefficients are determined from this estimate of q s and the power law rating curve q s aq b 1 where q is discharge