a seismic reflection study of northern baffin bay implication for tectonic evolution reflection profiles offshore of baffin island south of lancaster sound reveal coast parallel half grabens containing flat lying sedimentary sections typical of a rifted margin in northernmost baffin bay adjacent to devon and southern ellesmere islands four sedimentary basins are identified in these basins the sedimentary sections are faulted folded and laterally discontinuous the basement shows linear trends steep faults and abrupt variations in depth in one basin a 50 km long and 10 km wide flower structure is observed a transpressive tectonic regime is suggested to explain the uplifted sedimentary and basement section and the change in depth to basement across it a 150 km long paleoshelf buried by a thickening sedimentary wedge is present offshore of devon island because strike slip and compressional features are observed on seismic profiles north of lancaster sound and extensional features are observed to the south differences in the plate tectonic development are inferred the inte

late stage groundmass differentiation as a record of magma stagnation fragmentation and rewelding in the 2011 eruption of shinmoedake of the kirishima volcano group sub plinian eruptions were followed by lava extrusion with intermittent vulcanian explosions the interstices of microlites and relatively large nanolites 0 4 nm width in the groundmass of pyroclasts groundmass interstices were studied to reveal shallow magmatic processes that lead to different eruption styles the pumice of the sub plinian eruption has the least differentiated groundmass interstices composition the groundmass interstices of the dense juvenile fragments of the vulcanian explosions are divided into two groups the first group is the most differentiated as expected from their lava like texture whereas the second group is less differentiated and covers the range of sub plinian pumice the vulcanian pumice overlaps the dense juvenile fragments despite their high vesicularity this seemingly contradictory relationship of composition in the interstitial groundmass indicates the clastogenic lava origin of the less differentiated group of dense juvenile fragments in contrast magmas stagnated in the shallow conduit maintained elevated temperature and water content allowing groundmass interstices to differentiate by microlite growth these magmas then erupted as pumice in the vulcanian explosions and were effused as lava that was fragmented by subsequent explosions to be later sampled as a dense juvenile fragment the groundmass crystallinity increased by 9 1 vol in 5 45 days between the sub plinian and vulcanian eruptions increasing initial melt and magma viscosity from 106 1 7 4 and 107 0 8 3 pa s to 106 9 8 4 and 108 2 9 7 pa s respectively this viscosity increase by nanolite crystallization could have facilitated the stress fragmentation of conduit magma leading to vulcanian explosions post fragmentation expansion of the sub plinian pumice could have been suppressed by this viscosity increase resulting in their low vesicularity late stage groundmass differentiation can thus control shallow magmatic processes

gully systems under undisturbed indigenous forest east coast region new zealand abstract gully erosion is commonly associated with agricultural landscapes where vegetation clearance and farming practices increase runoff leading to fluvial incision however gully erosion can also occur in forests that have undergone some form of disturbance either natural or resulting from human impacts this paper reports on recent gully development within areas of undisturbed indigenous forest as a result of a high magnitude rainfall event on the east coast of new zealand s north island this region through a combination of crushed and sheared rock types steep topography and tectonic and climatic setting has high natural rates of erosion exacerbated by european deforestation in the late 19th and early 20th centuries sequential air photographs spanning a 58 year period between 1939 and 1997 were used to classify and document the growth and recovery of gully systems in the 14 1 km 2 headwaters of the mangaoporo catchment following a severe cyclone in 1988 with a rainfall of 535 mm there were 21 active gully systems within the indigenous forest on photography prior to 1988 only four gully systems were present during this period there were 8 major rainfall events 150 250 mm despite further 5 rainfall events of 150 250 mm between 1988 and 1997 all gully systems showed signs of recovery with a combined reduction in active area of 37 the nature and location of these features is strongly influenced by lithology orientation of jointing and bedding and to a topographic threshold defined by catchment slope and catchment area

a method for stability analysis of vegetated hillslopes an energy approach stability analyses of vegetated hillslopes are usually carried out by the limit equilibrium le method where shear displacement is not taken into account experiments show that soil with roots pro

contemporary changes in sediment yield in an alpine mountain basin due to afforestation the upper drome in france abstract the baurieres plain within the upper drome river basin was used to reconstruct recent changes in sediment supply in relation to changes in land use within an alpine catchment a considerable body of archival information is available furthermore the plain acts as a natural sediment trap and the reach basin interaction has not been disrupted by human activity based on archival data channel geometry measurements dendrogeomorphological and radionuclide analysis cs137 and unsupported pb210 the trends in channel change and sediment supply over the past two centuries are assessed and their causes are interpreted dendrogeomorphology and radionuclide profiles show that the floodplain is characterised by a decrease in sedimentation rate in the 1960s the ex pb210 profiles also suggest a spatial modification of the relative contribution in sediment supply of the catchment bedload yields are estimated to be at least 26 m3 km 2 year 1 between 1928 and 1996 based on an estimate of storage over a channel length of 11 5 km archival data concerning bedload removal from traps yields an estimate of 25 6 m3 km 2 year 1 between 1993 and 2001 these two values are very comparable suggesting no major modification in bedload transport within the reach during the 20th century if the bedload supply has not strongly decreased in the studied reach during this period the bedload sources have changed the volume of sediment stored in the beaurieres area between 1928 and 1996 corresponds to at least 40 of the sediment delivered by channel degradation from an upstream alluvial reach both changes in floodplain sedimentation as well as changes in bedload and suspended contributions from catchment sources are interpreted as responses to land use but also flow regime hillslope sediment production strongly decreased due to planned hillslope afforestation and torrent regulation at the end of the 19th century and spontaneous hillslope afforestation resulting from grazing decline mainly in the two decades following world war ii the observed change in suspended sediment supply which occurred around 1960 1965 has a clear synchronicity with spontaneous catchment afforestation following world war ii after this period a decrease in sediment supply a change in source but also a decrease in peak flow were observed changes in run off are complex and cannot be caused with only land use change flood hydrographs underwent peak decreases and duration increases through the 20th century because of increase in water retention capacity of the forested catchment in addition flood seasonality has changed with september and october flood events being much less frequent in the last part of the 20th century

mid miocene propagation of the yellowstone mantle plume head beneath the columbia river basalt source region columbia river flood basalt volcanism is the product of mid miocene distortion of the yellowstone mantle plume head against the precambrian margin of north america the overall migration pattern of columbia river basalt vents reflects northward propagation of the plume head beneath the west southwest migrating north american plate thermal uplift mimics the vent migration over the 1 5 m y of grande ronde basalt extrusion the projected crest of the plume head migrated 105 km 7 cm yr from the chief joseph dike swarm east oortheast into the clearwater embayment where uplift occurred over the same period at a rate of 0 67 mm yr chemical variations reflect progressive melting of the plume and mantle lithosphere followed by the mixing of these components with an enriched source from the overriding craton rapid thickening of the plume head against the cratonic margin led to decompressional melting and magma rise beneath a thin oceanic lithosphere of accreted terranes

the changing nature of mantle hotspots through time implications for the chemical evolution of the mantle the melting products of mantle plumes can place constraints on the geochemical structure of the mantle and show how it has varied through time the highest temperature melts komatiites and picrites derived from each plume are assumed to represent the best available sample of the thermal boundary layer from which the plume originates a survey of the geochemistry of picrites and komatiites shows that they underwent a fundamental change at about the archean proterozoic boundary archean komatiites have depleted or neutral geochemistry whereas most protero zoic and younger picrites have originated from enriched oib type mantle although rare depleted plumes persist to the tertiary e g gorgona if plumes originate from a thermal boundary layer near the core mantle interface the composition of this layer must have changed from a mixture of depleted and neutral mantle during the archean to mainly enriched mantle in the proterozoic this change coincides with a drop in the maximum mgo content of the ma

continental flood basalts episodic magmatism above long lived hotspots abstract the eruption of continental flood basalt cfb may reflect episodic magmatism above long lived mantle plumes the iceland and yellowstone hotspots have generated successive cfb provinces large intrusive complexes anomalous uplift basin formation and rifting events and linear volcanic chains dating back 120 and 70 ma respectively amagmatic intervals occurred 1 when ascent of plumes to shallow levels was impeded by impenetrable lithosphere resulting in sub lithospheric ponding of plume mantle and 2 in response to dispersion by subducting oceanic lithosphere in convergent margin settings by comparison with the plume eruptive potential of typical oceanic hotspots it is apparent that preservation of only a small portion of plume mantle ponded during an amagmatic interval is necessary to account for large volume of cfbs thermal erosion lithospheric attenuation translation of ponded hotspot mantle to the base of thinner penetrable lithosphere and passage of plume mantle through slab windows in subducting oceanic lithosphere led to subsequent breakthrough and eruption of cfb since both mantle plume and plate tectonic processes have been operating since the archean it seems likely that the migration of continents over hotspots with attendant magmatic and tectonic consequences is a common occurrence in the geological record

a comparison of earthflow movement mechanisms on forested and grassed slopes raukumara peninsula north island new zealand abstract surface movement rates on forested earthflows are 2 3 orders of magnitude less than those on grassed earthflows subsurface deformation results largely from extension flow on grassed earthflows and from compression flow on forested earthflows a rafting mechanism in which blocks of roots from individual trees interact with those of neighbouring trees to retard surface movement is used to explain deformation profiles of forested earthflows the rheology of earthflow materials is changed by the presence of tree roots

geomorphic changes in a complex gully system measured from sequential digital elevation models and implications for management high resolution digital elevation models dems were derived from sequential aerial photography of an active uvio mass movement gully complex in new zealand s north island east coast region to measure geomorphic changes over approximately one year the gully showed a complex behaviour combining uvial and mass movement erosion deposition and reworking of materials stored in an active debris fan during the measurement period 5200 1700 m3 of material were eroded from the 8 7 ha gully complex and 670 180 m3 from the 0 8 ha depositional fan giving a total of 5870 1710 m3 for the entire gully complex fan system the results provide a high resolution description of gully behaviour over a short time period and also demonstrate that mass movement slumping and debris ows accounted for almost 90 per cent 4660 200 m3 of the sediment generated this erosional response is described in terms of gully evolution by comparing the gully complex to other systems in the region in various stages of development the effect of gully evolution on geomorphic coupling between the gully complex and channel system is described and coupling is also shown to vary with the magnitude and frequency of rainfall events from a land management perspective the success of strategies such as tree planting to mitigate against gully erosion depends on the stage of gully development particularly on whether or not mass movement erosion has begun in contrast to gully rehabilitation efforts elsewhere basin wide afforestation in the early stages of gully incision is favoured over riparian planting given that mass movement assisted by excessive groundwater pressure is the main process leading to uncontrollable gully expansion to protect land effectively against continuing gully erosion of headwater catchments and resulting downstream aggradation it is necessary for land managers to understand the spatial and temporal variability of gully development fully so that mitigation efforts can be targeted appropriately copyright 2003 john wiley sons ltd

landslide occurrence as a response to land use change a review of evidence from new zealand abstract vegetation cover is an important factor influencing the occurrence and movement of rainfall triggered landslides and changes to vegetation cover often result in modified landslide behaviour however it is difficult to relate the occurrence of landslides directly to variations in land use especially in some european countries in contrast new zealand provides a good opportunity to investigate geomorphic responses to anthropogenic land cover changes before european settlers first arrived in the 1840s hilly regions were only marginally influenced by human activity the maoris new zealand s first settlers lived largely on coastal plains or near lakes and rivers they influenced general vegetation cover only through localized burning practices in contrast european settlers moved into the back country and converted extensive hill areas from native forest and bush to pasture this reduced the strength of the regolith and rendered the slopes more susceptible to landslides pulses of natural sedimentation in the pre european period have been related to volcanic activity climatic variability including changes in frequency of cyclonic storms and wind erosion and fluvial erosion following forest fires initiated either by volcanic eruptions or lightning strikes since european deforestation began sediment production has largely been determined by landslide events on unstable slopes thousands of landslides were triggered by high magnitude low frequency climatic events during storms with estimated return periods in excess of 50 years in contrast low magnitude high frequency rainfall events have caused gully and channel erosion examples from different parts of new zealand indicate changes in sediment generating processes following land use modifications after deforestation landslides have contributed significantly to sediment sequences in depositional basins such as lakes swamps estuaries coastal wetlands and the nearshore and offshore zones of continental platforms

the baffin bay lavas and the value of picrites as analogues of primary magmas the baffin bay picrites have been the focal point of a controversy concerning the mgo content of primary magmas derived from the upper mantle a sample population of 48 lava chilled margins collected across the baffin bay volcanic succession at the northeastern tip of padloping island exhibits a prominent compositional mode between 14 and 16 weight percent mgo 19 22 mg cation units mg 100 cations the petrography of these samples however requires that the padloping magmas were mixtures of olivine crystals and liquid at their eruption olivine phenocrysts constituted 15 to 30 volume percent of these magmas and retain compositions requiring coexisting liquid compositions with only 10 to 13 5 weight percent mgo 14 18 5 mg however highly magnesian olivine xenocrysts up to fo 93 found in the most magnesian lavas require the former existence of liquids with at least 18 weight percent mgo 24 mg if these xenocrysts represent early cumulates then the primary liquids of the padloping suite must have been at least this mgo rich with temperatures greater than 1 425 c such primary liquids could have evolved by olivine crystallization to a steady state equilibrated crystal liquid mixtures in a shallow reservoir system prior to eruption the compositions of the liquids of these mixtures appear to have been perched at the point of plagioclase saturation at approximately 1 275 c

magnetic glasses in the azuki and at volcanic ashes in japan abstract magnetic properties of volcanic glass shards have been described on the widespread azuki and at ashes in japan thermomagnetic analysis and isothermal remanent magnetization irm acquisition experiments were performed on both bulk samples and separated glass samples of the azuki volcanic ash together with progressive thermal demagnetization of natural remanent magnetization nrm the results demonstrate that titanomagnetite contained in volcanic glass shards is the sole contributor to the stable nrm of the azuki ash the results of a lowrie fuller test suggest that the remanence carrier of the ash layer is single domain grains of titanomagnetite which can be seen as submicron particles using electron microscopy on the basis of progressive irm acquisition in samples with various contents of at volcanic glass it is also suggested that titanomagnetite in glass shards is a significant magnetic carrier of nrm for the at ash since most of the glass shards are tens of microns in size they are expected to acquire depositional remanent magnetization drm without experience of succeeding post depositional process under aqueous conditions a redeposition experiment with the azuki ash shows that stable drm whose intensity is comparable to that of the nrm of the water laid azuki ash is acquired during several hours

a gully complex model for assessing gully stabilisation strategies abstract the north island east coast region is one of the areas most seriously affected by gully erosion both in new zealand and globally despite extensive efforts to mitigate erosion within the last fifty years the overall area of actively eroding gullies has increased in this study we present a gully model and its application for assessing the effectiveness of several afforestation scenarios to mitigate gully erosion in the east coast region the model uses empirical relationships to represent the major physical processes and environmental factors governing gully sediment yield 1 vertical degradation incision 2 spatial extension growth 3 stabilisation closure 4 the influence of forest cover and 5 the influence of the underlying geologic terrain overall the model shows a good fit and deviates only 6 from the observed actively eroding gully area and 8 from the number of actively eroding gullies the application of the model to assess past and future afforestation schemes indicates that 1 past afforestation efforts were effective in reducing sediment yield by approximately 33 in the waipaoa catchment and by 16 in the waiapu catchment from what it would have been without afforestation 2 the most effective strategy to minimize gully erosion is to reforest all present and newly initiating gullies which would halve the annual sediment yield by 2050 and 3 the earlier the planting is completed the more effectively afforestation will minimise gully erosion

origin of the columbia plateau and snake river plain deflection of the yellowstone plume previous models relating the snake river plain and columbia river basalt northwest united states to the yellowstone plume have not taken into account the effects of the subducted farallon and juan de fuca plates not only did subduction shield the surface from mantle plume activity but it deflected the plume in the direction of plate motion a variety of geophysical and geologic evidence suggests that the plume penetrated the subducted slab at 17 5 ma causing eruption of the columbia river basalt the plate boundary then migrated over the plume and the yellowstone plume has recovered to a more nearly vertical conduit forming the snake river plain and yellowstone plateau

the impact of magnetic viscosity on time domain electromagnetic data from iron oxide minerals embedded in rocks at opemiska quebec canada abstractthe magnetic viscosity mv effects observed at time scales between 0 01 and 10 ms at opemiska are associated with magnetic grains of variable size in rocks recent observations made during a ground time domain electromagnetic tdem survey at opemiska are consistent with four aspects of the spatial and amplitude characteristics of a mv response 1 the bz t decay rate is roughly proportional to 1 t1 where 0 4 0 4 2 the anomalies are mainly visible on the z component when the em receiver sensor is located inside or just outside the transmitter loop 3 there is no obvious x or y component response and 4 the sites where mv effects are seen in the tdem data are coincident with an airborne magnetic anomaly previous studies have demonstrated that mv could be caused by 1 fine grained particles of maghemite or magnetite in the overburden regolith or soil that were formed through lateritic weathering processes 2 volcanic glass shards from tuff containing approximately 1 by weig

quantifying sediment connectivity in an actively eroding gully complex waipaoa catchment new zealand abstract using a combination of airborne lidar 2005 and terrestrial laser scanning 2007 2008 2010 2011 sediment delivery processes and sediment connectivity in an 20 ha gully complex which significantly contributes to the waipaoa sediment cascade are quantified over a 6 year period the acquisition of terrain data from high resolution surveys of the whole gully fan system provides new insights into slope processes and slope channel linkages operating in the complex raw terrain data from the airborne and ground based laser scans were converted into raster dems with a vertical accuracy between surveys of 3 of sediment annually with a standard deviation of 20 806 m 3 the volumes of debris eroded from those areas dominated by surface erosion processes were higher than in areas dominated by landslide processes over the six year study period sediment delivery from the source zones to the fan was a factor of 1 4 times larger than the volume of debris exported from the fan into te weraroa stream the average annual volume of sediment exported to te weraroa stream varies widely from 23 195 to 102 796 m 3 fluctuations in the volume of stored sediment within the fan rather than external forcing by rainstorms or earthquakes account for this annual variation no large rainfall events occurred during the monitoring period therefore sediment volumes and transfer processes captured by this study are representative of the background conditions that operate in this geomorphic system

scratching the surface estimating dimensions of large igneous provinces a study of five major basaltic provinces including oceanic plateaus volcanic passive margins and continental flood basalts shows that they are voluminous constructions of extrusive igneous rock underlain by intrusive rock crustal thickness ranges from 20 to 40 km and lower crust is characterized by high 7 0 7 6 km s seismic velocities volumes and emplacement rates derived for two oceanic plateaus the ontong java and kerguelen broken ridge reveal short lived pulses of increased global crustal production and suggest an origin involving the lower mantle the ontong java rate of emplacement may have exceeded the contemporaneous global production rate of the entire mid ocean ridge system despite the importance off large igneous provinces in studies of mantle dynamics and the global environment scarce age and deep crustal data necessitate intensified efforts in seismic imaging and scientific drilling in a range of such features

channel evolution controlled by valley configuration during 70 years in a severely erosive catchment mangaoporo river new zealand abstract we examined the channel evolution process in a 19 5 km course in the mangaoporo river catchment area 72 6 km2 in the east coast region of north island new zealand over 70 years using aerial photographs and cross sectional survey records the catchment experienced expansive deforestation during the late 19th and early 20th centuries which accelerated the growth of the gully complexes the manner of the evolution was controlled largely by the underlying lithology that determined the valley configuration in the upstream confined section where hillslope and channel processes were closely coupled continuous sediment supply from gully complexes gradually converted the channel course from a narrow single thread to wide braided reaches or from sediment transfer to storage zones this change was accompanied by a decrease in unit stream power usp in 1939 the usp was above 200 w m2 in most of the upstream section while 40 of the usp values were near or below 50 w m2 in 2012 2013 because a narrow reach situated at the end of the storage zone limited the amount of sediment travelling further the downstream reaches were gradually disconnected from the upstream section and the channel forms changed more moderately than in the upstream section this reduction in sediment travelling with distance transformed a once braided reach at the end of the course to development of a supply limited condition with time the overall channel evolution was accelerated by major rainfall events including prolonged rainfall in 1956 and cyclone bola in 1988 which activated gully complexes and contributed to subsequent channel widening particularly in the upstream section although reforestation starting in the 1980s contributed to deactivation of gully complexes after 1988 the difficulty in controlling their total remission together with the lower usp values of the river in 2012 2013 compared to those before the previous major wet events indicate that the river has been evolving in an irreversible direction triggered by land use changes of more than a century ago

the nature of magnetic single domains in volcanic glasses of the kbs tuff magnetic and optical variations in volcanic glasses of the east african rift have been investigated by means of experimental and analytical study the results add to the formal understanding of magnetism in volcanic glasses and give us new perspectives on the nature origin and significance of fine grained magnetic minerals and on the magnetic petrology of glassy rocks the samples that we have studied in detail glass shards from the kbs tuff of northern kenya contain a superparamagnetic precipitate of microcrystals 2 to 10 nm in size the precipitate is likely to have formed at elevated temperature during or subsequent to eruption about 1 9 m y ago we have studied these microcrystals by means of transmission electron microscopy tem ac and dc magnetic methods electron spin resonance esr mossbauer spectroscopy and optical spectroscopy our efforts have concentrated on determining the magnetic mineralogy and understanding the mechanism s responsible for the optical and magnetic behavior of these glasses the particle size determination for the larger of these microcrystals has been achieved using tem imaging and mossbauer spectroscopy the mineralogy is nonstoichiometric magnetite based on mossbauer x ray diffraction and electron diffraction results the ratio of saturation remanent magnetization to saturation magnetization for the larger microcrystals is very nearly that predicted by single domain theory for a uniaxial anisotropy the origin of which may lie with stress or surface effects we interpret magnetic and esr results to infer the possible existence of microcrystals or amorphous clusters of fe atoms 1 nm or smaller in kbs glasses that appear homogeneous in high resolution tem images results from optical absorption experiments show that the color variations in kbs shards arise due to optical absorption by the precipitate a result consistent with classical electromagnetic theory

the post glacial downcutting history in the waihuka tributary of waipaoa river gisborne district implications for tectonics and landscape evolution in the hikurangi subduction margin new zealand abstract determining the spatial and temporal deliveries of sediment from the waipaoa river catchment in the post glacial period is a major goal of integrated source to sink landscape evolution studies in the region in a 2 2 km long section of the waihuka tributary 217 km 2 of the waipaoa river 2150 km 2 in eastern north island new zealand a sequence of at least ten fluvial terraces and abandoned meanders up to 45 m above the present river records rates and times of post glacial downcutting dateable organic and tephra horizons in the terrace and meander infill stratigraphy indicate that downcutting at this location on the waihuka tributary was dominated by a short lived event in the early holocene from 10 8 ka bp when as much as half of the downcutting was accomplished in only 10 15 of post glacial time the large downcutting event is interpreted to record the passing of a succession of major knickpoints or a knickzone through this tributary the initiation of knickpoint retreat in the catchment was primarily a consequence of reduction in sediment supply at the end of mis 2 based on the timing of rapid downcutting in the waipaoa river mainstem we estimate that the rate of knickpoint retreat along the waihuka tributary was about 2 km kyr in the period before and after rapid downcutting in the waihuka tributary modest incision rates averaging 1 2 mm yr probably represent the regional tectonic uplift rate

magnetic grain size variations through an ash flow sheet influence on magnetic properties and implications for cooling history rock magnetic studies of tuffs are essential to the interpretation of paleomagnetic data derived from such rocks provide a basis for interpretation of aeromagnetic data over volcanic terranes and yield insights into the depositional and cooling histories of ash flow sheets a rhyolitic ash flow sheet the miocene aged tiva canyon member of the paintbrush tuff contains both titanomagnetite phenocrysts present in the magma prior to eruption and cubic fe oxide microcrystals that grew after emplacement systematic variations in the quantity and magnetic grain size of the microcrystals produce large variations in magnetic properties through a section of the ash flow sheet penetrated in a borehole on the nevada test site natural remanent magnetization varies from less than 1 10 4 to more than 8 10 4 a m3 kg 1 and in phase magnetic susceptibility varies from less than 1 10 6 to more than 10 10 6 m3 kg 1 the microcrystals which include both magnetite and maghemite have curie points and maximum unblocking temperatures between 580 c and 640 c rock magnetic data including in phase and quadrature magnetic susceptibilities as well as hysteresis parameters demonstrate that these microcrystals are of superparamagnetic and single domain sizes titanomagnetite phenocrysts are the dominant remanence carriers in the central 50 m of the section whereas microcrystals are important contributors to remanent magnetization and magnetic susceptibility in two 15 m thick zones at the top and bottom within these zones the size of microcrystals decreases both toward the quenched margins and toward the interior of the sheet the decrease in microcrystal size toward the interior of the sheet is interpreted to indicate the presence of a cooling break possibly represented by a concentration of pumice laboratory heating produces changes in magnetic properties which vary complexly from sample to sample such changes include 1 decrease in saturation magnetization 2 both increase and decrease in in phase and quadrature magnetic susceptibilities and 3 shifts in coercivity spectra the complex sample to sample variation in response to heating is attributed to differences in initial grain size distributions

subsurface flow velocities through selected forest soils south island new zealand subsurface flow through soils in tawhai big bush and craigieburn state forests has been studied by applying water at a line source 1 m upslope from a pit in the base of which an intercepting trough is located by measuring lag times between the centres of mass of input and outflow and between the start of input and start of outflow minimum estimates of mean and maximum flow velocity v and vmax at 51 locations were obtained mean values for the tawhai sites were for v 0 3 cm s and for vmax 0 42 cm s but a considerable degree of variability was present with coefficients of variation up to 90 a number of different pathways through the soil are followed by flowing water macropore networks root channels etc are effective transmitters of water and at some sites conveyed up to 40 of the input rapidly to the interception trough variability in flow velocity and the proportion of the input appearing as rapid outflow is a function of antecedent moisture conditions and of the relative importance of the various pathways at a given site which is in turn a function of the characteristics of the soil the macropore network and the parent material at the base of the soil at sites where the soil had an open structure and the parent material was shattered or permeable the macropore network was a less important control upon soil hydrological behavior than where the subsoil had a less open structure and was underlain by impermeable bedrock measurements of flow velocities on undisturbed logged and logged burned planted sites were made at tawhai sf but the spatial and temporal variability was such that no statistically significant differences could be discerned the time lapse since logging may be insufficient for changes in the root systems to be having a hydrological impact but the high variability would require a sample size of over 1000 to show a significant difference in velocity of even 10 for rapid flow through macropores to have a significant influence on streamflow saturation of the soil is necessary before water can enter the macropores soil topographic geologic and climatic conditions in tawhai sf are such that saturation of the lower layers of the soil regularly occurs so that rapid flow through macropores can contribute to storm period streamflow water may reach the channel system from a proportion of the catchment which varies with antecedent moisture conditions and storm duration and intensity but which may attain 100 in moderate to large rain events because of the drier climate and deeper soils subsurface flow contributions to stormperiod streamflow should be less important in the big bush area and particularly in the craigieburn area where the parent materials shattered sandstone or ancient scree deposits do not provide an impermeable layer which diverts flow laterally

geologic origin of magnetic volcanic glasses in the kbs tuff volcanic glass shards and banded pumice from the kbs tuff of northern kenya exhibit marked variations in magnetic susceptibility and color colorless to dark brown the darker glass shards exhibit superparamagnetism which they now know to be carried by a population of tiny microcrystals of fe rich cubic oxide approx 20 to approx 100 a in size thought to be magnetite a theory for their origin is one of nucleation and growth precipitation in quenched homogeneous glass colorless at temperatures of approx 700 1000 sup 0 c during and immediately subsequent to eruption results from high temperature heating experiments on kbs shards support this idea the precipitate appears in the kbs shards as a consequence of their cooling history and is the origin of their coloring the origin cannot lie in negligible compositional differences between the colorless and darkest shards on the other hand banded pumice from the kbs tuff has both dark and colorless glasses of differing compositions the pumice appears banded because precipitation occurred preferentially in the fe rich glass although magma mixing may have played a role in the eruption of these materials on the basis of their survey of distal eruptive products it would appear that the volumetric amount of the maficmore end member dark pumice was insubstantial less

thermotectonic evolution of a rifted continental margin fission track evidence from the kangerlussuaq area se greenland fission track analyses of apatites from sediments precambrian gneisses and caledonian to tertiary intrusive rocks from the kangerlussuaq region reveal its post caledonian thermotectonic history inland the history involves cooling to temperatures within the high temperature part of the apatite annealing interval and slow cooling or reheating continued in cretaceous times through this interval apatites from coastal areas between kangerlussuaq and tasiilaq reveal only tertiary cooling in tertiary times cooling accelerated after the main intrusive phase in the tertiary the evolution is taken as evidence for a general uplift erosion since caledonian times probably disturbed by basin formation and sedimentation and reheating due to magmatic activity thermal subsidence of the rift shoulders following the opening of the adjacent oceanic basin is not indicated annealing patterns inland of the plume centre in the kangerlussuaq provide no evidence for the earlier movement of the plume from a westerly direction

lateral flow and ponding of starting plume material many mantle plumes started with voluminous heads of hot material that ascended as diapirs through the mantle flood basalts radial dike swarms and frequently continental breakup are associated with the impingement of starting plume heads on the base of the lithosphere the buoyant plume head material ponds at the base of the lithosphere and then flows laterally relief on the base of the lithosphere acts as an upside down drainage pattern with enclosed catchments for this flow that is plume material preferentially collects beneath regions where the lithosphere is locally thin such as thermally subsiding sedimentary basins an example is uplift associated with the iceland starting plume which inverted the mesozoic irish sea basin additional relief at the base of the lithosphere is associated with rifting and seafloor spreading in the case of the northern north sea material from the iceland starting plume ponded beneath a basin with locally thin lithosphere rifting breached the enclosed catchment allowing the ponded plume material to drain across the new passive margin toward very thin lithosphere produced by seafloor spreading rifting also creates a conduit for the flow of plume material away from the region underlain by the starting plume head an example is the volcanic passive margin off nova scotia which is 2000 km from the center of the bahama starting plume head numerical and analytical calculations indicate that lateral flow of plume material consistent with this observation is expected if its viscosity is around 1018 pa s

anisotropy of magnetic susceptibility in relation to source vents of ignimbrites empirical observations the anisotropy of magnetic susceptibility ams of young undeformed ashflow deposits e g bishop tuff california bandlier tuff new mexico show alignment of the maximum axis of magnetic susceptibility kmax with inferred flow lines the sense of flow is deduced from the predominant plunge bias of kmax axes these principles are discussed in relation to four deformed settings of ashflow deposits in the great basin of the western united states the magnetic susceptibility data provide valuable but not always unambiguous insight into probable source areas various complications arise in interpreting the ams data in terms of flow directions but these can be reduced by integration with geologic observations

the big flush paleomagnetic signature of a 70 ma regional hydrothermal event in displaced rocks of the northern canadian cordillera the 70 ma carmacks group a subaerial volcanic succession which once covered much of central southwest yukon has a paleomagnetic remanent direction which passes the fold test and the reversal test a new collection of 13 sites combined with 13 sites from a previous study renders a pole 088 6 e 78 4 n a95 7 8 which is far sided with respect to the pole for cratonic north america and implies a displacement from the south of 1900 700 km late triassic mandanna member red beds and early jurassic nordenskild formation tuffs deformed in the late jurassic fail the fold test and conglomerate test but pass a contact test with eocene dykes the postdeformational remanent direction is identical to that isolated from the carmacks group the magnetic signature contained in these older formations is probably an overprint produced by an extensive hydrothermal system active during carmacks extrusion geological work indicates that the carmacks group is plume related given its paleomagnetic latitude and geological nature we hypothesize that the carmacks group is a displaced segment of the yellowstone hot spot track and the hydrothermal system which remagnetized the older rocks was established by mantle upwelling below the region resume le groupe de carmacks go de 70 ma est une succession volcanique subaorienne qui couvrait jadis la majeure partie du centre sud ouest du yukon il possde une direction paloomagnotique romanente certifioe par le test du pli et le test des inversions une nouveau groupe de 13 sites combino 13 sites diune otude antorieure fournit un pule 088 6 e 78 4 n a95 7 8 qui est considorablement oloigno par rapport au pule du craton de liamorique du nord et qui implique un doplacement partir du sud de 1900 700 km les couches rouges du membre de mandanna du trias tardif et les tufs du formation de nordenskild du jurassique prococe qui subirent une doformation durant le jurassique tardif ont ochouo le test du pli et le test de conglomorat mais ils ont passo avec succs le test de contact avec les dykes de li ocne la direction romanente post tectonique est identique celle isoloe du groupe de carmacks la signature magnotique qui caractorise ces formations plus anciennes est probablement une roaimantation produite par un systme hydrothermal otendu qui fut actif durant liextrusion de carmacks liotude goologique rovle que le groupe de carmacks est apparento un panache tant donno sa latitude paloomagnotique et sa nature goologique nous avanaons lihypothse que le groupe de carmacks reprosente un segment doplaco du traco du point chaud de yellowstone et que le systme hydrothermal qui a roaimanto les roches les plus anciennes est ds liascension du manteau sous la rogion otudioe

tempe fossae mars a planetary analogon to a terrestrial continental rift tempe terra the northeastern part of the tharsis region on mars is characterized by several extensional structures differing in style and age the tempe fossae a particularly well developed system of graben striking n45 e have been studied for the first time in detail on the basis of viking orbiter imagery and mars observer laser altimeter mola topographic data the graben system appears to be unique in the whole region because of its extent the remarkable width and depth of the graben the varying graben pattern and the associated volcanism single graben can be up to 35 km wide and 120 km long while their depth can reach nearly 3000 m they typically show an asymmetric architecture often in halfgraben or step fault style the graben system widens and changes its style along strike from ne to sw from a single very deep and narrow graben to a complex set of several shallower sinuous graben and halfgraben crustal extension was measured in the northeastern part from the observable throw and amounts to 2 5 3 1 km volcanic structures can be found at several locations along the graben in the sw the graben system seems to be connected with the tempe terra volcanic province marked by flood basalts and plains volcanism craters were counted on volcanic units unaffected by extensional tectonics crater statistics indicate an absolute crater model age for the upper end of the extensional deformation of 3 5 ga the dimensions and the characteristics of the mapped graben system resemble those of terrestrial continental rifts and a comparison between them and the kenya rift reveals striking similarities therefore the tempe fossae are interpreted as a martian analog to a continental rift associated with an underlying mantle plume this hypothesis seems to be supported by recent geophysical models based on topography and gravity data from mars global surveyor which indicate regional uplift for tempe terra

generation and polybaric differentiation of east greenland early tertiary flood basalts major element trace element isotope and petrographic studies of magma diverentiation mantle melting the basal volcanics in the kangerdlugssuaq fjord region of the east greenland margin provide constraints on the generation and subsequent diverentiation and contamination histories of magmas during the early stage of continental rifting creating the north atlantic ocean basin most primitive lavas of the succession are introduction shown to have accumulated olivine corrections for crystal ac the distinctive geochemical features of continental flood cumulation yield estimates for erupted primitive liquids with mgo basalts cfbs are strongly controlled by the composition contents between 9 and 13 wt the occurrence of suspended and structure of the continental lithosphere and underfo88 olivine phenocrysts further requires the existence of parental lying mantle significant controversy remains concerning magmas with mgo contents up to 17 wt and feo contents up the balance of contributions from the lithosphere and to 14 wt quantitative modeling of fractionation indicates the mantle and the mechanisms by which the various that kangerdlugssuaq magmas primarily diverentiated at moderate source components contribute to basalt petrogenesis pressures 8 kbar to form dunitic and wehrlitic cumulates at how are basalt compositions influenced by generation depths of 25 km evolved east greenland flood basalts from the in anomalous regions in the deep mantle plumes by scoresby sund region record a more complex fractionation history interaction between rising magmas and the continental involving olivine clinopyroxene fractionation in the lower crust lithospheric mantle and by contamination with conas found for the lower basalts followed by olivine plagioclase tinental crust how are the diverentiation con clinopyroxene fractionation at shallow crustal levels cor tamination magma mixing and storage histories of cfbs relations between sio2 incompatible elements and sr nd isotopic controlled by the structure of the continental lithosphere ratios for the lower basalts are consistent with bulk assimilation and how do the thermal and chemical features of the of up to 15 20 archean leucogneiss with unradiogenic sr and mantle and the extensional history of the continental nd isotopic ratios characteristic of lewisian type lower crust lithosphere avect mantle melting and compositions of comparisons between inferred magma types for lower basalts and primary liquids estimated primary liquids from elsewhere in the north atlantic these questions are best addressed in the context of show complex relationships among feo mgo tio2 contents a geologically and geochemically well constrained cfb and cao al2o3 ratios that relate to regional and temporal changes province such as the north atlantic tertiary province in mantle temperatures lithospheric thickness and involvement of separation of east greenland from northern europe in at least two end member mantle sources we postulate that the the early tertiary at 60 myr ago was accompanied by lower basalts of east greenland were derived from iron poor voluminous volcanic activity the blosseville coast of mantle depleted by prior melt extraction and distinct from morb east greenland extending from kangerdlugssuaq fjord source mantle that was enriched in tio2 and lrees by a to scoresby sund fig 1 contains spectacularly exposed metasomatic event shortly before early tertiary magmatism we sections of lavas these sections begin at the basal contact associate this depleted mantle source with the ancestral iceland of the lavas with underlying cretaceous tertiary sediments and archean basement and continue to the plume anomaly

high resolution temporal and stratigraphic record of siletzia s accretion and triple junction migration from nonmarine sedimentary basins in central and western washington the presence of early eocene near trench magmatism in western washington and southern british columbia has led to speculation that this area experienced ridge trench interaction during that time however the effects of this process as they are preserved in other parts of the geologic record are poorly known we present high precision u pb zircon geochronology from paleogene nonmarine sedimentary and volcanic sequences in central and western washington that preserve a record of tectonic events between ca 60 and 45 ma the data reveal that the swauk chuckanut and manastash formations formed a nonmarine sedimentary basin along the north american margin between 59 9 and 51 3 ma this basin experienced significant disruption that culminated in basinwide deformation uplift and partial erosion during accretion of the siletzia terrane between 51 3 and 49 9 ma immediately following accretion dextral strike slip faulting began or accelerated on the darrington devil s mountain entiat leavenworth eagle creek and straight creek fraser fault zones between 50 and 46 ma during this time the chumstick formation was deposited in a strike slip basin coeval with near trench magmatism faulting continued on the entiat eagle creek and leavenworth faults until a regional sedimentary basin was reestablished 45 9 ma and may have continued on the straight creek fraser fault until 35 30 ma this record of basin disruption volcanism and strike slip faulting is consistent with ridge trench interaction and supports the presence of an oceanic spreading ridge at this latitude along the north american margin during the early eocene

hotspot tracks and the early rifting of the atlantic abstract many hotspot tracks appear to become the locus of later rifting as though the heat of the hotspot weakens the lithosphere and tens of millions of years later the continents are split along these weakened lines examples are the west coast of greenland east coast of labrador madeira hotspot the south coast of mexico north coast of honduras guyana hotspot and the south coast of west africa north coast of brazil st helena hotspot a modern day analog of a possible future rift is the snake river plain where the north american continent is being pre weakened by the yellowstone hotspot track this conclusion is based on reconstructions of the motions of the continents over hotspots for the past 200 million years the relative motions of the plates are determined from magnetic anomaly isochrons in the oceans and the motion of one plate is chosen ad hoc to best fit the motions of the plates over the hotspots however once the motion of this one plate is chosen the motions of all the other plates are prescribed by the relative motion constraints in addition to the correlation between the predicted tracks and sites of later continental breakup exposed continental shields correlate with the tracks their exposure may be the result of hotspot induced uplift which has led to erosion of their former platform sediment cover

high resolution magnetic susceptibility imaging of geological thin sections pilot study of a pyroclastic sample from the bishop tuff california u s a high resolution magnetic susceptibility imaging is a new technique for studying the magnetic properties of geological thin sections the two dimensional distribution of both remanent and induced magnetization can be determined with a spatial resolution 1 0 mm that is similar to the size of phenocrysts in the sample amongst many problems in rock magnetism to which it could be applied the technique holds great potential for understanding the origin of the anisotropy of magnetic susceptibility in pyroclastic flows preliminary tests on a single sample of ignimbrite indicate that secondary iron titanium oxide particles deposited within vesicle walls prior to their collapse are responsible for the bulk susceptibility

yellowstone in yukon the late cretaceous carmacks group the late cretaceous carmacks group a thick subaerial volcanic succession that once covered much of southwest yukon was deposited on an uplifted terrane and is divisible into a lower fragmental unit and an upper flood basalt unit coeval hydrothermal activity resulted in widespread alteration and gold mineralization the lavas are shoshonites enriched in large ion lithophile and light rare earth elements but depleted in high field strength elements ankaramitic absarokite flows in the upper carmacks group range up to 15 wt mgo requiring a high liquidus temperature 1400 c at 1 bar dry high k 2 o contents 3 of these magnesian lavas indicate that the potassic character of the volcanic suite was established in the mantle although previously interpreted as subduction related the carmacks group was erupted during a cordilleran wide magmatic lull and lacks coeval calc alkalic batholiths the lavas are petrologically similar to plume related eocene to pliocene potassic lavas of the western united states new paleomagnetic collections combined with previous work place the carmacks group 17 2 6 5 1900 700 km south of its present position relative to the craton during deposition near the paleolocation of the yellowstone hotspot the spatial coincidence similarity of tectonic setting and lithologic similarity of the carmacks group and yellowstone volcanic successions suggest that the carmacks group is the 70 ma effusion of the yellowstone hotspot subsequent northward displacement of the carmacks group is attributed to coupling with the kula plate correlation of the carmacks group and the yellowstone hotspot fixes the paleolatitude and the paleolongitude of the terranes of the northern intermontane belt at 70 ma

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

surface movement in an earthflow complex raukumara peninsula new zealand abstract the surface movement of an unstable earthflow complex was studied over a 10 year period using a network of pegs inserted to a depth of 1 m the mean and maximum surface movement velocities in the transport zones of the two study earthflows ranged from 0 2 0 4 m and 1 7 2 8 m month respectively maximum velocities for individual pegs ranged up to 3 m month the movement data indicated that the earthflows were approximately in a steady state for the 10 year duration of the study application of iverson s theory for the kinematics of unsteady non uniform landslide movement indicated that the earthflows had pe values in the range of 0 1 to 2 0 pe is the dimensionless parameter known as the landslide peclet number these values indicated that the earthflows showeda blend of plastic and viscous behaviour and that diffusion might be more significant than kinematic wave propagation in transmitting disturbances

morphometric controls and geomorphic responses on fans in the southern alps new zealand morphometric variables associated with 41 debris ow and 18 uvial fans and their basins in the southern alps of new zealand are examined the results show statistically signi cant differences in the area maximum elevation relief and ruggedness melton s r of the basin and the area gradient and apex and toe elevations of the fan between debris ow and uvial sites concavity of the fan longitudinal pro le also differs between the two fan types although this could not be tested statistically most of these morphometric differences re ect differences in processes and environmental controls on them discriminant analysis indicates that basin area and fan gradient best differentiate the two fan types by process moderately strong correlations exist on both debris ow and uvial fans between basin area or melton s r and fan area correlations between basin area or melton s r and fan gradient are generally weaker the results of this study also indicate that on debris ow prone fans the fan gradient and basin melton s r have lower thresholds which overlap little with upper thresholds associated with basins where only stream ow reaches the fan these thresholds may therefore have value in preliminary morphometric assessments of debris ow hazard on fans in the southern alps copyright 2004 john wiley sons ltd

uplift faulting seismicity thermal spring and possible incipient volcanic activity in the lesotho natal region se africa the quathlamba hotspot hypothesis various features of the lesotho natal region of south eastern africa namely its anomalously high topographic elevation the occurrence of numerous thermal springs a few enigmatic co2 gas exhalation sites and a significant level of current seismicity in certain zones suggest that there is some neotectonic activity here in 1983 there were also media reports of a small volcanic eruption in lesotho it has been suggested that a process of continental margin parallel warping was in operation during the plio pleistocene period to produce the apparent uplift and seaward tilting of older geomorphological land surfaces but the fundamental geophysical cause of this process remained unclear this cymatogeny or anorogenic plateau uplift has recently been related to absolute motion of the african continent over the former position of an oceanic spreading ridge but the hotspot reference frame was not used in the absolute motion modelling as an alternative hypothesis for the lesotho natal phenomena the existence of a mantle hotspot near 30 s 29 e is invoked its cenozoic track is modelled and the ages of a chain of volcanic seamounts in the mozambique basin are predicted the results appear to confirm the self consistency of the hotspot frame as a preferred reference system for lithospheric absolute motion

global eocene tectonic unrest possible causes and effects around the north american plate abstract many of our planet s crises were the result of sudden changes in plate tectonic configuration or catastrophic outbursts of volcanism caused by mantle plume impingement at the base of the lithosphere at the paleocene eocene boundary and in the early eocene several mantle plumes continental collision and mid ocean ridge subduction triggered a series of changes in seafloor spreading dynamics we have constructed a detailed global model of oceanic lithosphere age and spreading rates for the 60 to 35 ma interval we revise evidence for changes in seafloor spreading direction in the north atlantic arctic and ne pacific oceans at least two periods of spreading rate highs which are separated by sharp value decrease occurred along the entire eastern north american plate boundary from c25 to c18 time c 57 to 40 ma the collision and incipient subduction of the early eocene siletzia oceanic lip may have caused the sharp decrease in spreading rate at c23 time in the labrador sea and north of charlie gibbs fracture zone the post c23 rapid farallon slab break off and subsequent upper mantle flow upwelling may have led to further variations in north atlantic spreading rates at c22 21 time eastward pacific subduction may have resumed at c 43 ma as indicated by a steady ne pacific seafloor spreading regime which resumed at or shortly after c21 the north atlantic realm shows a delayed response to tectonic events west of north america with an increase in spreading rate south of charlie gibbs fracture zone from c20 to c18 time followed by a steady decrease until the oligocene north american late paleocene early eocene kimberlite magma that erupted more than 1000 km from its western plate boundary constitutes additional evidence that tectonic stresses due to changes in the mantle lithosphere interactions may have affected the entire plate and therefore also its eastern boundaries

mantle plume influence on the neogene uplift and extension of the u s western cordillera espite its highly extended and thinned crust much of the western cordillera in the united states is elevated more than 1 km above sea level therefore this region cannot be thought of as thick crust floating isostatically in a uniform mantle rather the lithospheric mantle and or the upper asthenosphere must vary in thickness or density across the region utilizing crustal thickness and density constraints we modeled the residual mass deficit that must occur in the mantle lithosphere and asthenosphere beneath the western cordillera a major hot spot broke out during a complex series of cenozoic tectonic events that included lithospheric thickening backarc extension and transition from a subduction to a transform plate boundary we suggest that many of the characteristics that make the western cordillera unique among extensional provinces can be ttributed to the mantle plume that created the yellowstone hot spot

sedimentary response to mantle plumes implications from paleocene onshore successions west and east greenland the uplift history of the upper cretaceous paleocene sedimentary successions underneath the extensive tertiary flood basalts of west and east greenland supports recently described models for the generation of flood basalt provinces in response to rising hot mantle plumes however the sedimentary development indicates that the period of plume related uplift prior to eruption of volcanic rocks was very short 5 m y substantial regional uplift and faulting took place in west and east greenland in the early paleocene to earliest late paleocene resulting in a basinwide unconformity in west greenland the uplift was associated with fluvial peneplanation valley incision and catastrophic deposition in east greenland it was associated with fluvial peneplanation the cumulative uplift in west greenland is probably on the order of several hundred meters whereas in east greenland the observed uplift cannot be quantified in both west and east greenland this phase was shortly followed by rapid major subsidence associated with extensive volcanism it is suggested that this sequence of events reflects the arrival of the north atlantic mantle plume or plumes

cordilleran slab windows the geometry and geologic implications of subducted spreading ridges are topics that have bedeviled earth scientists ever since the recognition of plate tectonics as a consequence of subduction of the kula farallon and east pacific rises slab windows formed and migrated beneath the north american cordillera the probable shape and extent of these windows which represent the asthenosphere filled gaps between two separating subducting oceanic plates are depicted from the late cretaceous to the present possible effects of the existence and migration of slab windows on the cordillera at various times include cessation of arc volcanism and replacement by rift or plate edge volcanism lithospheric uplift attenuation and extension and increased intensity of compressional tectonism eocene extensional tectonism and alkaline magmatism in southern british columbia and the northwestern united states were facilitated by slab window development

magnetism and magnetic mineralogy of ash flow tuffs from yucca mountain nevada the magnetic susceptibility and remanent magnetization of an ash flow sheet are profoundly influenced by cooling history after emplacement spatial variations in these properties therefore provide a potentially useful tool for geological studies maxima and minima in measured along profiles at yucca mountain nevada identify persistent magnetic marker horizons within vitric portions of the tiva canyon and underlying topopah spring members of the paintbrush tuff the correlatable variations of with vertical position in these units exist over the 8 km of strike examined the observed stratigraphic changes in magnetic properties reflect variations in amounts and mineralogy of fe ti oxide phenocrysts and the presence shape size and mineralogy of magnetic fe oxide microcrystals that precipitated at high temperature after emplacement of each sheet vitrophyre near the top of the topopah spring member has a distinctive maximum in due to titanomagnetite phenocrysts susceptibility in the lower portion of the overlying tiva canyon member reaches maximum values of about 1 3 10 2 si near the base of the member beneath the columnarly jointed vitrophyre due to the presence of abundant superparamagnetic cubic fe oxide these elongate microcrystals are several tens of nm long and are typically deformed and tapered up section in the tiva canyon member the susceptibility decreases going to a minimum within the columnar vitrophyre at this stratigraphic level the precipitated fe oxides are larger and carry intense nrm of up to 30 a m is only 3 10 3 the whisker like microcrystals of fe oxide which typically nucleated on what appears to be chain silicate grew as needles up to 25 m in length the size variations of the precipitated fe oxides which were established using transmission electron microscopy tem and petrographic observation are consistent both with variations in magnetic susceptibility measured at the outcrop and with variations in the intensity of remanent magnetization several interpretations of the shape anisotropy of the precipitated feoxide are possible including growth by a dislocation mechanism additionally the observed elongation of precipitated microcrystals is consistent with theoretical predictions for growth in a uniaxial stress field susceptibility variations as established at the outcrop as well as in the borehole offer a potentially useful tool for stratigraphic correlation of ash flow sheets

the human impact in geomorphology 50 years of change abstract concern with the human impact in geomorphology has a long history what is new is that since 1969 a number of developments have taken place that have led to an increasing realisation of its importance these developments are in four main areas i intellectual and policy related ii technological developments that alter geomorphological processes iii demographic trends and iv the proliferation of techniques for the study of landform and process change there has been a realisation of the role of humans in landscape transformation in ancient times the human impact has developed through time but particularly notable are the potential early effects of fire extinctions and deforestation on geomorphological processes the spread of european agriculture particularly in the nineteenth century transformed erosion and sedimentation rates in many parts of the world notwithstanding the importance of some of these changes in prehistoric and historic times recent researches have demonstrated that humans have become an increasingly important agent of geomorphological change during the period of the great acceleration of the past five or six decades the interest in global warming that has developed since the early 1980s has created considerable interest in its consequences for a range of geomorphological phenomena it is also becoming apparent that anthropogenic geomorphological change is having an impact on the earth system as a whole finally geomorphologists have taken an increasing interest in how they can make an impact in the field of landscape conservation

post last glacial maximum fluvial incision and sediment generation in the unglaciated waipaoa catchment north island new zealand abstract small river systems contribute a significant component of sediment delivered to oceans but the temporal evolution of fluvially eroded landscapes is needed a sequence of postglacial terraces in the unglaciated waipaoa river catchment provides the opportunity to document fluvial incision and sediment flux on an 2000 year timescale since the last glacial maximum lgm which has previously only been undertaken for the entire post lgm period this study also calculates sediment mass where previously sediment volume was calculated using a 15 m dem field mapping and surveying and tephrochronology we calculate rates of fluvial incision and sediment volumes excavated during successive age constrained postglacial incision events and correlate these with a framework of inferred climatic events established for new zealand we identify seven periods of terrace formation each succeeded by a period of fluvial incision six in total although the magnitude of the response during each incision event and thus the sediment volumes generated varied through time and across subcatchments draining two contrasting lithological terrains we conclude that incision events were essentially synchronous at least within the timeframe constrained by the ca 2000 year interval between successive eruptive airfall events slope relaxation processes were simultaneous with incision thereby indicating that both processes were likely climate driven we identify a period of accelerated fluvial incision 7 mm y 1 commencing before ca 14 0 cal ka bp during the early postglacial period and ceasing ca 7 9 cal ka bp toward the end of the early holocene warming period the magnitude of this incision response was significantly higher in subcatchments draining highly erodible lithologies in the higher uplifting parts of the catchment when river bedload was at over capacity in contrast within the remainder of subcatchments draining the more resistant lithologies and in areas of lower uplift and in parts subsiding incision and sediment generation was moderated by the presence of knickpoints overall since abandonment of the lgm to present day fluvial incision in the waipaoa and the adjacent waimata catchments generated 16 7 km3 of sediment of which 10 km3 90 of the estimated 35 mt of glacial postglacial slope and shelf sediment mass was potentially available for transport offshore of this 14 08 km3 7 4 km3 derived from upper and 6 7 km3 from remainder of subcatchments was excavated from waipaoa catchment at an average of 0 6 km3 ka 1 of which 80 was generated by ca 7 9 cal ka bp this potentially validates previous accounts of high rates of offshore sediment flux before 8000 14c ybp ca 8877 cal ybp thereafter for the period mid holocene cooling and variability mhcv ca 6 5 cal ka bp until the present day the rate of incision across all subcatchments slowed to 2 mm y 1 and generated just 20 of the total sediment volume in part this reflected a depletion of available sediment as rivers in the upper subcatchments returned to a steady state and coincidental with an increase in accommodation space in the rapidly growing coastal floodplain sediment flux to the marine depocentres was thereby limited

reconstructing the ancestral yellowstone plume from accreted seamounts and its relationship to flat slab subduction recent geodynamic analyses have emphasized the relationship between modern flat slab subduction zones and the overriding of buoyant oceanic crust although most models for the evolution of the late mesozoic cenozoic laramide orogeny in the southwestern united states involve flat slab subduction the mechanisms proposed are controversial an examination of the geological evolution of the 60 50 ma crescent terrane of the coast ranges indicates that it was formed in a shallowing upward loihi type oceanic setting culminating in the eruption of subaerial lavas plate reconstructions indicate that the crescent terrane was emplaced into ca 20 ma crust and the presence of subaerial lavas implies an uplift due to the plume of ca 4 2 km which we use to calculate a minimum buoyancy flux of 1 1 mg s 1 similar to that of the modern yellowstone plume published paleomagnetic data indicate that the crescent terrane was formed at a paleolatitude similar to that of the yellowstone plume the crescent seamount was accreted within 5 my of the cessation of plume magmatism plate reconstructions indicate that it would have originated about 750 km to the west of the north american plate margin if it developed above a fixed yellowstone plume and are therefore consistent with the recorded very short interval between its formation and tectonic emplacement we interpret the crescent terrane as due to the ancestral yellowstone plume such a plume would have generated an elongate swell and related plateau that would have been overridden by the north american margin taken together the relationship between flat slab and overriding of oceanic plateau in laramide times would have been analogous to the relationship between modern andean flat slab subduction zones and the juan fernandez and nazca oceanic plateaus d 2003 elsevier science b v all rights reserved

the erosional and uplift history of ne atlantic passive margins constraints on a passing plume new apatite fission track analyses from nw britain indicate that a maximum of 2 5 km of erosion has occurred there during the cenozoic similar to values for se greenland and the east greenland coast north of scoresby sund the erosion may have been facilitated by magmatic underplating during break up however at kangerdlugssuaq east greenland 4 6 km of erosion is measured since 45 ma lower mid eocene marine sedimentary rocks overlying the lavas on the blosseville coast indicate that magmatic underplating on the central greenland coast substantially post dated flood volcanism and break up behaviour not predicted by simple plume rift models subsidence reconstructions of the hebrides shelf and the east and west greenland coasts show that rapid dynamic uplift was effectively synchronous at 63 ma and preceded volcanism by c 400 m is compatible with a mantle temperature anomaly of c 100 c these data suggest very rapid lateral flow of the impacting iceland plume head the predicted crossing of the plume by the east greenland coast in the mid late eocene would account for post rift magmatic underplating and dynamic support on the greenland but not the european side of the north atlantic basin

internal deformation of a fast moving earthflow raukumara peninsula new zealand abstract sub surface deformation of a fast moving earthflow was studied in the east coast region of the north island new zealand for a period of 2 years tiltmeter profiles indicated that earthflow materials were subjected to a variety of movement mechanisms including internal deformation by gravity shearing flow extension flow compression flow rotation over curved slpes rotation of material beneath the earthflor and sliding overall internal deformation accounted for less than 25 of the total surface movement the remaining 75 being the result of sliding movement along the basal shear plane gravity shearing flow occurs along the basal shear plane which is thought not to be more than a few centimetres thick micro topography features on a scale of 1 10 m largely affected tilting behaviour internal deformation of fastmoving earthflows in the longitudinal direction tiltmeter profiles on curved slopes were monoclinal and rotation was the principal mechanism causing tilt on concave slopes the tiltmeter profile had a forward downslope convex shape with compression being the principal deformation mechanism on even planar slopes extension flow creep predominated with the profile showing little evidence of rotation however minimal deformation tilting was likely to be caused by a combination of either sub earthflow rotation extension flow or compression flow in the lateral direction topographic influences produced considerable deformation particularly on concave slopes as a result of compression flow there was little or no lateral deformation on even slopes

syngenetic magnetic anomaly sources three examples aeromagnetic anomalies encountered in three areas two in the western united states and one in central america are shown to arise from magnetic sedimentary formations these examples are selected from a larger number of similar areas surveyed by applied geophysics inc in various places in the u s midcontinent and rocky mountain regions the first area discussed is the northwest corner of nebraska where the miocene arikaree formation comprised of magnetic airfall and windblown tuffs causes anomalies in areas of incised topography the second area is located in south central utah where the upper cretaceous kaiparowits sandstones contain detrital magnetite that causes large anomalies in tilted structures and over incised topography the third area treated covers over half of southern belize in central america including much of the offshore portion here the toledo formation of paleocene eocene age contains a thick section of clastic detritus rich in lithic grains of volcanic rocks that produce magne

last glacial aggradation and postglacial sediment production from the non glacial waipaoa and waimata catchments hikurangi margin north island new zealand abstract the sediment flux generated by postglacial channel incision has been calculated for the 2150 km 2 non glacial waipaoa catchment located on the tectonically active hikurangi margin eastern north island new zealand sediment production both at a sub catchment scale and for the waipaoa catchment as a whole was calculated by first using the tensioned spline method within arc map to create an approximation of the aggradational waipaoa 1 surface contemporaneous with the last glacial maximum and second using grid calculator functions in the gis to subtract the modern day surface from the waipaoa 1 surface the waipaoa 1 surface was mapped using stereo aerial photography and global positioning technology fixed the position of individual terrace remnants in the landscape the recent discovery of kawakawa tephra within waipaoa 1 aggradation gravels in this catchment demonstrates that aggradation was coincidental with or began before the deposition of this 22 600 14 c year old tephra and using the stratigraphic relationship of rerewhakaaitu tephra the end of aggradation is dated at ca 15 000 14 c years ca 18 000 cal years bp the construction of the waipaoa 1 terrace is considered to be synchronous and broadly correlated with aggradation elsewhere in the north island and northern south island indicating that aggradation ended at the same time over a wide area subsequent downcutting a manifestation of base level lowering following a switch to postglacial incision at the end of glacial age aggradation points to a significant southern hemisphere climatic warming occurring soon after ca 15 000 14 c years ca 18 000 cal years bp during the older dryas interval elevation differences between the waipaoa 1 c 15 ka terrace and the level of maximum channel incision i e before aggradation since the turn of the 20th century suggest about 50 of the topographic relief within headwater reaches of the waipaoa catchment has been formed in postglacial times the postglacial sediment flux generated by channel incision from waipaoa catchment is of the order of 9 5 km 3 of which 6 6 km 3 is stored within the confines of the poverty bay floodplain thus although the postglacial period represented a time of high terrigenous sediment generation and delivery only 30 of the sediment generated by channel incision from waipaoa catchment probably reached the marine shelf and slope of the hikurangi margin during this time the smaller adjacent waimata catchment probably contributed an additional 2 6 km 3 to the same depocentre to give a total postglacial sediment contribution to the shelf and beyond of 5 5 km 3 sediment generated by postglacial channel incision represents only 25 of the total sediment yield from this landscape with 75 of the estimated volume of the postglacial storage offshore probably derived from hillslope erosion processes following base level fall at times when sediment yield from these catchments exceeded storage

geomorphology and forest management in new zealand s erodible steeplands an overview abstract in this paper we outline how geomorphological understanding has underpinned forest management in new zealand s erodible steeplands where it contributes to current forest management and suggest where it will be of value in the future we focus on the highly erodible soft rock hill country of the east coast region of north island but cover other parts of new zealand where appropriate we conclude that forestry will continue to make a significant contribution to new zealand s economy but several issues need to be addressed the most pressing concerns are the incidence of post harvest storm initiated landslides and debris flows arising from steepland forests following timber harvesting there are three areas where geomorphological information and understanding are required to support the forest industry development of an improved national erosion susceptibility classification to support a new national standard for plantation forestry terrain analysis to support improved hazard and risk assessment at detailed operational scales and understanding of post harvest shallow landslide debris flows including their prediction and management

large wood lw 3d accumulation mapping and assessment using structure from motion photogrammetry in the laboratory abstract a structure from motion sfm photogrammetry based methodology for precise mapping of large wood lw accumulations in fluvial systems is presented the technique may be useful for routine inventory and rapid volume estimation of complex lw structures that tend to divert or obstruct flow in rivers our methodology is validated by means of laboratory experiments ranging from elementary to complex arrangements of lw components and organic fine material ofm seven experimental setups were used as the basis for i manual approximations of 2 5d and 3d geometric reference volumes ii 2 5d volume models based on mesh geometry iii a closed watertight 3d mesh from an unorganized point cloud and iv estimates of porosity a commercially available sfm photogrammetry software package pix4dmapper was used for point cloud and simplified mesh generation in order to obtain more precise volumes 3d surface models are required accordingly we generated 3d watertight mesh models of the unorganized point cloud using the screened poisson surface reconstruction psr technique the pix4d volume tool 2 5d resulted in an overestimation 2 9 to 52 7 of the geometric volume 3d due to the convex hull approximation of the geometry normal to the surface plane psr 3d resulted in more precise volumes showing deviations from the geometric volume 3d in a range of 15 9 to 10 6 as the algorithm could capture concavities and involuted surfaces on the accumulation assuming that the difference between 3d and 2 5d volume models represents many of the voids visible within or on the surface of the deposit this volume can be used as an estimate of porosity our assessment suggests that image based sfm methodology is well suited for further investigations in lw research due to its time and cost efficiency in comparison with other conventional surveying techniques the methodology can be used to generate high quality point cloud and mesh models of log jam formations these may be used by river managers and researchers to quantify accumulation volume and thus gain a better understanding of lw composition and the influence of wood geometry on hydraulic flow conditions

the bear river dykes 1265 1269 ma westward continuation of the mackenzie dyke swarm into yukon canada abstract the 1 27 ga mackenzie dyke swarm the largest on earth radiates from a point in the western canadian arctic and extends across much of the canadian shield possible western extensions of the swarm are largely obscured by younger sedimentary cover paleoproterozoic inliers in northern yukon host the bear river dykes brd herein dated by u pb baddeleyite and zircon methods at 1268 5 1 5 ma and 1264 6 1 2 ma the brd share similar geochemical and nd isotopic characteristics with the mackenzie dykes and the coeval coppermine river basalts and are regarded as products of the same plume hydrothermal activity at 1270 ma in breccia of the nor mineral occurrence northwest of the brd was probably generated by brd at depth the brd generally strike northwest approximately 90 to the orientation predicted by the radiating dyke model this difference may be explained by an anomalous local stress field at the time of brd emplacement or reorientation of brd during subsequent events of cordilleran deformation using the nor mineral occurrence as the westernmost locale of mackenzie dyking and assuming a model of uniform dyke radiation the arc of the mackenzie swarm is at least 50 greater than previously recognized bringing the total arc of dyke radiation to 150

constraints on the evolution of the east greenland margin evidence from detrital apatite in offshore sediments we test a new approach to understanding the tectonic evolution of passive margins by using fission track analysis on detrital apatites from sediments deposited offshore east greenland these apatites have not undergone postdepositional track annealing and therefore reflect provenance the apatites preserve a component of the source rocks thermal history that otherwise may not be retainedwithinthepresent dayoutcrop fission track deriveddenudational histories from samples at ocean drilling program drill sites offshore east greenland at lat 63 n are compared with data fromtheonshoresingertatcomplex previousapatitefission track studies and geomorphic mapping of the east greenland coast have shown that locally up to 6 km of denudation may have occurred implying significant tectonic or magmatic activity starting as much as30m y afterbreakupat56ma incontrast apatitefission track datapresentedhererecord 2kmofcenozoicdenudationinsoutheast greenland probably driven by magmatic underplating at the time of breakup large magnitude postrift denudation of east greenland is restricted to the area around kangerdlugssuaq 68 n thetiming 40 50ma andmagnitudeareinaccordwith revised plume track models suggesting that the iceland plume crossed the margin here during the late eocene

the eocene southern vancouver island orocline a response to seamount accretion and the cause of fold and thrust belt and extensional basin formation abstract a deflection of the fault controlled southwestern coastline of vancouver island suggests the presence of a minor orocline with a southern crustal block south of barkley sound alberni inlet rotated 20 counterclockwise relative to a northern fixed crustal block about a pole of rotation located northeast of port alberni in this paper two models of orocline development one of pure block rotation and one of pure bending are proposed the predictions of these models are tested against available geological maps structural orientation data identified regions of extension and contraction and paleomagnetic data structural orientation and paleomagnetic data are consistent with 18 of post late cretaceous counter clockwise rotation of the southern crustal block relative to the northern fixed crustal block a southward increase in the magnitude of rotation evident in the structural orientation data argues for a model of bending both bending and block rotation models predict the development of a zone of contraction along the northeast margin of the southern crustal block coincident with the location of the eocene cowichan fold and thrust belt that diminishes northward toward the pole of rotation as predicted the fold and thrust belt is characterized by a northerly decrease in the amount of shortening from 30 at the south end of the thrust belt to 0 shortening north of port alberni the northerly decrease in shortening is complemented by a north to south change in structural style from cylindrical to conical folds and finally to planar undeformed strata the model of block rotation predicts the presence of a zone of extension extending southwest from the zone of rotation coincident with the location of eocene extensional structures within barkley sound and with horst and graben structures in the offshore eocene to miocene tofino basin extension is less than predicted by a model of pure block rotation and suggests that much of the oroclinal rotation was accommodated by bending timing constraints indicate that orocline development was coeval with and resulted from the eocene accretion of seamounts of the crescent terrane these findings demonstrate that oroclinal orogeny the buckling of a linear crustal beam about vertical axes of rotation can significantly impact the geometry structure and character of an orogenic belt even where the buckles are minor

porosity and volume assessments of large wood lw accumulations abstract the formation of large wood lw accumulations during floods represents a major hazard for constricted river cross sections e g bridges and weirs as it affects flow hydraulics and sediment transport to better assess lw accumulations reliable strategies and techniques are required there are currently practical limits on monitoring accumulation configurations both laser scans and photogrammetric techniques can be used to scan the outer contours of lw accumulations but cannot practically assess the wood content and porosity details of the outer deposit are captured in high resolution but the core of the deposit remains occluded and estimation is necessary this becomes more challenging for deposits of increasing size relative to wood elements to develop a more efficient workflow for lw accumulation assessment in the field we performed a laboratory study to develop a relationship between the envelope volume of water worked lw jams during a single flood hydrograph and the volume of woody elements within explicitly accounting for porosity we used photogrammetric techniques now in common use for reconnaissance surveys of debris accumulations on wood accumulations scaled for the laboratory the study s aim is to develop a semi automated assessment method enabling efficient image acquisition processing and computation of lw accumulation volume using a multi camera array above the laboratory channel and applying structure from motion photogrammetry we developed 3d models for 16 experimental flow formed wood accumulations each with 50 individual wooden dowels no correlations were found between porosity and flow magnitude porosity was found to be similar for most deposits 66 as a result of this accumulation structure the envelope volume used in 3d and 2 5d photogrammetric methods tended to overestimate wood content by 3 and 2 6 respectively the results obtained here will contribute to a more reliable volumetric assessment for inventories of wood mass in river systems

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

microlites and nanolites in rhyolitic glass microstructural and chemical characterization we used transmission electron microscopy tem and scanning electron microscopy sem to study magmatic crystals in the ben lomond rhyolite lava dome taupo volcanic center new zealand using tem and sem to investigate the size distributions of these crystals we identified three size populations microphenocrysts 1 2 m wide microlites 0 6 m wide and smaller crystals 0 6 m wide which we term nanolites the predominant mineral phases of the microlites and nanolites are augites pigeonites and hypersthenes the compositions and microstructures within these pyroxenes indicate disequilibrium crystallization at approximately 850 900 c and undercoolings as high as 300 c from equilibrium crystallization temperatures complex microstructures resulting from subsolidus reactions in augite and pigeonite are consistent with moderate cooling rates within the upper obsidian layer of the ben lomond rhyolite dome this study demonstrates the existence of sub micron magmatic crystals in a rhyolite and illustrates the potential of tem to provide unique information about the crystallization and cooling histories of glassy volcanic rocks

provenance of fluvial terrace sediments within the waipaoa sedimentary system and their importance to new zealand source to sink studies late pleistocene fluvial terrace deposits within the waipaoa river system of north island new zealand provide some insight into the fluvial history of the region that can be potentially translated to the marine sedimentary record pebble counts and sand detrital modes from terrace remnants suggest significant compositional differences between these terraces and the modern stream deposits the terrace deposits are enriched in sandstone lithics sand and gravel as well as monomineralic quartz and feldspar sand in contrast the modern waipaoa river is dominated by mudstone fragments mainly products of gullying in the waipaoa river headwaters region both the terrace and modern river sand show a compositional dependency on grain size with increasing lithic components in the coarse sand fractions carbonate lithic content and proportions of lithic types in the modern river and terrace sediments can be related to the distribution of calcareous geological units across the region for example the calcareous lithics sand and gravel in the mangatu river a major tributary of the waipaoa are derived from deep water facies allochthon that dominate the catchment these carbonate facies are petrographically distinct from the marl calcareous mudstone that dominates elsewhere in the waipaoa river system such as the pliocene units in the waimata river catchment the combined petrologic data sets from the modern rivers and terraces in the waipaoa river system provide a model to interpret the provenance of sandy deposits in the offshore marine realm

forest roads and geomorphic process interactions cascade range oregon a major flood in february 1996 triggered more than 100 geomorphic features affecting forest roads in a 181 km 2 study area in the western cascade range oregon eight types of features including mass movements and fluvial features were mapped measured and analysed using geographic information systems and sediment budgets for the road network although roads functioned as both production and depositional sites for mass movements and fluvial processes the net effect of roads was an increase in basin wide sediment production debris slides from mobilized road fills were the dominant process of sediment production from roads road related sedimentation features were concentrated in a portion of the study area that experienced a rain on snow event during the storm and was characterized by the oldest roads and steep slopes underlain by unstable highly weathered bedrock the downslope increase in frequency of features and volumes of sediment produced combined with the downslope increase in relative frequency of fluvial over mass wasting processes suggests that during an extreme storm event a road network may have major impacts on stream channels far removed from initiation sites overall this study indicated that the nature of geomorphic processes influenced by roads is strongly conditioned by road location and construction practices basin geology and storm characteristics published in 2001 by john wiley sons ltd

middle to late paleozoic acadian orogeny in the northern appalachians a laramide style plume modified orogeny the laramide orogeny of the western united states is proposed as a modern analogue for the silurian devonian acadian orogeny and subsequent diachronous voluminous short lived magmatism and basin formation in the northern appalachians shallowing of the benioff zone accounts for several enigmatic features associated with plate convergence in the northern appalachians including 1 wenlockian ludlovian termination of arc related magmatism in the avalon terrane followed by a period of relative magmatic quiescence from 395 to 380 ma and 2 diachronous migration of the acadian deformation front from ca 415 ma in the southeast to ca 370 ma in the northwest extending more than 600 km into the continental interior the flattening of the subduction zone is attributed to overriding of a plume by the convergent margin which may explain 1 the abrupt termination of magmatic quiescence by 380 370 ma and voluminous felsic magmatism and production of plume related lamprophyres in the southeast meguma terrane as the plume thermally eroded the oceanic lithosphere causing melting of the lower crust 2 late devonian regional high temperature low pressure metamorphism in the meguma terrane related to the thermal anomalies above a plume 3 synchronous devonian emplacement of meguma gold deposits and associated siderophile elements possibly derived from fluid circulation above an ascending plume 4 rapid late devonian uplift and erosion of as much as 10 km due to dynamic uplift over a plume 5 migration of magmatism to the north avalon terrane cobequid highlands so that plume related carboniferous magmatism occurred in and around the carboniferous permian maritimes basin 6 the high density lens at the base of the crust beneath the maritimes basin the product of plume derived underplated mafic rocks and 7 a subsidence mechanism for formation of the maritimes basin by cooling of a decapitated plume head

using structure from motion photogrammetry to assess large wood lw accumulations in the field abstract river systems in forested catchments are strongly influenced by wood and sediment loading from both natural e g mass wasting and anthropogenic forestry sources in order to effectively manage impacts on property infrastructure and the broader ecosystem as well as to better assess the interactions between large wood lw channel morphology and flow hydraulics more efficient and accurate surveying techniques are required we present an evaluation of structure from motion sfm photogrammetry and point cloud based techniques for capturing the geometry and volume of lw in the field wood accumulations can be notoriously complex 3d objects with multi scalar features and thus difficult to quantify with photogrammetric methods we introduce a novel workflow to generate volumetric information of organic material accumulations using sfm and a suite of meshing algorithms the volumes of two accumulations are assessed individually using several meshing techniques and are compared with more conventional volume estimates results show volumetric variations of

erosion process contribution to sediment yield before and after the establishment of exotic forest waipaoa catchment new zealand abstract the east coast region of the north island new zealand is well known for its severe erosion high sediment yields flooding and sedimentation following extensive deforestation of its indigenous forest during the late 19th and early 20th centuries for six decades thereafter extensive grazing cattle and sheep left a legacy of highly degraded hill country much of which has since been retired and planted in exotic forest primarily to control erosion previous studies have documented the extent of gully erosion calculated erosion rates and sediment delivery from gullies to the channel load within the study basin but this has not been quantified for the more extensive mass movement processes including slump earthflow and shallow landslides additionally the magnitude of the effect of reforestation on sediment load at subcatchment level and ultimately on sediment yield at catchment scale for this combination of erosion processes and over the time frame of a rotation of exotic forest 28 years is unknown for a 140 km 2 study basin located in the headwaters of the 2150 km 2 waipaoa river catchment we establish the contribution to basin sediment load by each of these erosion processes spanning a 50 year period that includes a 28 year reforestation effort we quantified the effectiveness of exotic reforestation as an erosion control strategy by using the mapped extent of each of the erosion processes before planting i e 1939 59 as the benchmark against which any subsequent change in eroded area km 2 was measured based on this process based erosion load was calculated for the pre planting period 1939 59 for the period 10 years after planting commenced 1960 69 and again for the period 1970 88 which marked the completion of planting within the study basin the study basin sediment load is then expressed as a proportion percentage of the measured sediment yield mt y 1 of the wider waipaoa river catchment the net area affected by erosion and erosion rates within the study basin peaked at 10 all processes combined and 28000 4000 t km 2 y 1 respectively during the early planting period 45 of study basin planted at this time gullies contributed 59 of the total sediment load at a rate of 2 3 0 3 mt y 1 slumps 34 1 3 0 2 mt y 1 shallow riparian landslides 6 0 2 0 03 mt y 1 and earthflows 1 0 05 0 08 mt y 1 although reforestation proved effective in stabilising shallow landslides and earthflows the resultant reduction in their contribution to basin sediment load and to overall catchment yield was minimal the greatest reduction in sediment load occurred during the latter part of the reforestation period 1970 88 as the numerous small to medium sized gullies stabilised coincident with canopy closure 8 10 years after planting however the larger gully mass movement complexes failed to stabilise in response to reforestation and they remained the dominant source of sediment contributing an order of magnitude more than slumps and two orders of magnitude more than shallow landslides and earthflows basin scale erosion and denudation rates all processes combined but dominated by gullies for the pre reforestation period averaged 22 000 3000 t km 2 y 1 11 mm y 1 peaked during the early reforestation period at 28 000 4000 t km 2 y 1 14 mm y 1 then decreased to 13 500 2000 t km 2 y 1 7 mm y 1 in response to reforestation and averaged 20 000 3000 t km 2 y 1 10 mm y 1 for the duration of the study period significantly the anthropogenic influence following european settlement of the study basin produced degradation rates an order of magnitude greater than the 1 mm y 1 estimated for the 17 6 cal ka bp post last glacial maximum period retirement of the most severely eroding hill country and subsequent establishment of an exotic forest covering 6 of the waipaoa catchment area effected an overall 62 reduction in the erosion affected area and a 51 reduction in the denudation and erosion rates potentially equivalent to an estimated 12 reduction in sediment yield of the waipaoa river we conclude that a greater or similar level of success could be achieved within three decades of forest establishment elsewhere in the east coast region by specifically targeting gully mass movement complexes particularly in high sediment yielding river systems such as the waiapu catchment

gully erosion and sediment production te weraroa stream new zealand conversion to pasture early in the twentieth century was ameliorated by reforestation that commenced in 1962 estimates of sediment production were made using the change in gully area observed in sequential aerial photographs channel storage was assessed from stream cross section surveys at its peak gully erosion affected 6 of the total catchment area the amount of sediment contributed from gullies declined by 62 as the forest became established but of the 28 7 mt of sediment generated by gully erosion between 1950 and 1988 48 was stored in the channel along the lower 8 km of te weraroa stream even if the amount of sediment generated by gully erosion continues to decline it likely will be many decades before the gravel is released from storage index terms 1815 hydrology erosion and sedimentation 1824 hydrology geomorphology 1625 1878 hydrology water energy interactions keywords channel storage gully erosion sediment production citation gomez b k banbury m marden n a trustrum d h peacock and p j hoskin gully erosion and sediment production te weraroa stream new zealand water resour res 39 7 1187 doi 10 1029 2002wr001342 2003

metchosin igneous complex southern vancouver island ophiolite stratigraphy developed in an emergent island setting the metchosin igneous complex of southern vancouver island has three components gabbro stocks formerly sooke gabbro a newly recognized sheeted dike complex and a basaltic volcanic sequence formerly the metchosin volcanics the sheeted dikes occupy a position transitional between the gabbro stocks and submarine volcanics which they tie together in an ophiolitic pseudostratigraphy the submarine volcanics shoal upward and pass into subaerial sheet flows the complex formed in an area of regional extension as an emergent island