biogeomorphic relationships between slope processes and globular grimmia mosses in haleakala s crater maui hawai i abstract globular mosses were found in haleakala s crater maui at five locations between 2175 and 2725 m the highest altitude site with abundant epilithic mosses growing on alkali olivine basalt outcrops and a large mossball population was studied mossballs form when moss cushions are dislodged from rocks but continue growing unattached to substrate detachment agents include rainsplash desiccation wind frost and disturbance by birds dark rumped petrels that burrow nests under outcrops or by goats when loosened moss polsters are transported down steep 26 34 slopes by different geomorphic processes including frost mainly needle ice activity runoff and wind mossballs contained two species grimmia trichophylla grev and grimmia torquata drumm growing separately or commingled weight size and various shape indices were determined for 260 specimens shape and size were correlated larger mosses become less spheroidal because heavier specimens are less disturbed by needle ice remaining immobile for increasingly longer time periods thus becoming flattened distance of downslope transport from source rockwalls was measured for 330 specimens 83 shifted 100 cm but only 5 had moved 200 839 cm heavier mossballs moved short distances thus 88 of all biomass remained within 200 cm from outcrops substrate soils were compared with those within globoids surface site soils were much coarser than mossball grains twelve substrate samples had on average 21 3 gravel 2 mm 6 1 fines 0 063 mm and 2 1 organic matter in contrast 12 mossballs contained this area is frequently subjected to freezing temperatures while fog interception from incoming tradewinds contributes significant moisture amounts to precipitation ground disturbance by frost activity seemed significant needle ice grows frequently on this slope as evidenced by widespread presence of miniature sorted stripes striated soils fine earth flags below stones gaps around stones and fine soil raised patches observed during multiple visits biogeomorphic interactions between mossballs and substrate at haleakala are briefly discussed from the perspective of self organized criticality and interpreted to represent a self replicating moss dispersal system dependent on slope geomorphic processes

the relationship between riverine lithium isotope composition and silicate weathering rates in iceland abstract this study presents lithium isotope and elemental data for the dissolved phase and suspended and bedload sediments of the major icelandic rivers for the dissolved phase 7li values range between 10 1 and 23 8 while river sediments display lower and much more homogeneous values 7li 3 1 4 8 close to the composition of unweathered mid ocean ridge basalt morb high 7li values are associated with high k li na li and mg li ratios in waters draining mainly old and weathered basalt catchments whereas low 7li rivers are located in younger parts of the island simple mixing between precipitation li rich hydrothermal springs and basalt weathering is unable to explain the entire range of 7li values instead a simple model of li uptake by secondary minerals associated with clay water li isotope fractionation 7li ranging from 1 to 7 5 can explain both water and sediment 7li values a negative correlation is observed between basalt chemical erosion rates and 7li measured in icelandic rivers and an empirical law is inferred comparison with literature data suggests that this relationship may be applicable at a more global scale and if confirmed could be of particular use for estimating the evolution of continental weathering preserved in marine sedimentary records however more data are now needed for rivers draining silicates typical of the continental crust in order to refine large scale modelling

chemical weathering of basalts southwest iceland effect of rock crystallinity and secondary minerals on chemical fluxes to the ocean river ground and peat water from a basaltic catchment area laxa in kjos southwest iceland were sampled and analyzed for major element concentrations to define the effect of glassy versus crystalline basalt the formation of secondary minerals and runoff on fluxes of dissolved elements to the ocean the proportions of the dissolved solids in the water samples derived from precipitation air and rock weathering were estimated the amounts of na mg ca k and s originating from precipitation were calculated from the respective solute cl marine ratios and the estimated aqueous cl originated from precipitation which was calculated using measured b content of the waters and b cl molal marine and rock ratios the rock contribution from weathering ranged from 22 to 46 percent of the total dissolved solids of the waters iron and al showed low mobility compared to na this was primarily due to consumption of these elements by ferrihydroxides allophane imogolite and clay minerals also si and to a lesser degree ca show apparent slightly lower mobility than na these results are in good agreement with these phases being dominant in the soils of the study area wada and others 1992 and the main secondary minerals of basaltic glass in iceland crovisier and others 1992 reaction progress calculations support these findings according to a model interaction of basaltic glass and meteoric water al fe and si are consumed by amorphous fe and al hydroxides and imogolite and allophane at low reaction progress with increasing reaction progress ca fe mg smectite became the primary secondary minerals limiting the mobility of ca fe mg si and al these findings suggest that the weathering in the laxa in the kjos catchment area has evolved into the beginning of the smectite weathering stage and that it is dominated by a relatively low reaction progress and a high water to rock ratio in the present study the effect of runoff and rock crystallinity was quantified for dissolved elemental fluxes temperature lithology other than rock crystallinity and rock age were similar in all of the catchment areas in this study silica ca f s al k mg and b had a very similar dependence on runoff on the other hand na fluxes were found to be less dependent on runoff and fe fluxes were found to be independent of runoff basaltic glass dissolves faster than fully crystallized basaltic rocks gislason and eugster 1987a therefore increased glass content of the primary rocks is thought to increase the leaching and elemental fluxes at constant runoff however because some of the solutes particularly al and fe were highly influenced or even controlled by the formation of secondary minerals this increasing dissolution with increasing glass content was hidden on the other hand basaltic glass was observed to enhance the fluxes of more mobile elements like na si ca f and s by a factor of 2 to 5 at a constant runoff of 200 cm yr constant vegetative cover and 0 to 100 percent glass content of the rocks the k and mg fluxes were found to be independent of rock crystallinity however runoff alone cannot explain the fluxes of these elements and it seems that vegetative cover and seasonal variations in biomass activities influence the k and mg fluxes

suspended sediment and total dissolved solid yield patterns at the headwaters of urumqi river northwestern china a comparison between glacial and non glacial catchments in order to understand the differences in the suspended sediment and total dissolved solid tds yield patterns between the glacial and non glacial catchments at the headwaters of urumqi river northwestern china water samples were collected from a glacier catchment and an empty cirque catchment within the region during three melting seasons from 2006 to 2008 these samples were analyzed to estimate suspended sediment and tds concentrations fluxes and erosion rates in the two adjoining catchments there were remarked differences in suspended sediment and tds yield patterns between the two catchments suspended sediment concentrations were controlled mainly by the sediment source whereas tds concentrations were primarily related to the hydrologic interaction with soil minerals generally the glacial catchment had much higher suspended sediment and tds yields together with higher denudation rates than the non glacial catchment overall glacial catchment was mainly dominated by physical denudation process whereas the non glacial catchment was jointly influenced by physical and chemical denudation processes the observed differences in material delivery patterns were mainly controlled by the runoff source and the glacial processes the melting periods of glacier and snow were typically the most important time for the suspended sediment and tds yields meanwhile episodic precipitation events could generate disproportionately large yields subglacial hydrology dynamics glaciers pluck and grind processes could affect erodibility and the large quantities of dust stored on the glacier surface provided additional sources for suspended sediment transport in the glacial catchment these mechanisms imply that in response to climate change the catchment behaviour will be modified significantly in this region in terms of material flux copyright c 2013 john wiley sons ltd

assessing the role of climate on uranium and lithium isotope behaviour in rivers draining a basaltic terrain this study presents uranium u and lithium li isotope and major and trace element data for the dissolved load suspended particles and bedload from rivers draining dominantly basaltic catchments on the island of sao miguel in the azores archipelago uranium activity ratios are at secular equilibrium in the bedload but are higher for suspended material suggesting sorption of uranium from the solution onto particle surfaces the 234u 238u of the riverine dissolved phase varies between 1 02 and 1 86 and lies on a mixing trend between the values expected from chemical weathering of basalt high u 234u 238u at secular equilibrium and an endmember with low u and high 234u 238u which probably reflects recoil effects associated with physical weathering and or soil formation lithium isotope ratios are consistently lighter in suspended material than the corresponding bedload suggesting preferential retention of 6li in the suspended load in turn the 7li of the dissolved load is always isotopically heavier ranging from 5 9 to 36 2 although the lightest values are affected by hydrothermal input the lithium isotopic composition of the dissolved load reflects the balance of primary mineral dissolution to secondary mineral formation comparison of the behaviour of u and li isotopes between sao miguel iceland and other basaltic terrains suggests that whilst u isotopes are dominated by weathering regimes dependent on factors such as weathering rates temperature runoff and climate neither weathering intensity nor climate exerts a direct influence on li isotope behaviour rather the formation of secondary minerals which is indirectly controlled by climate weathering primary mineralogy and biology appears to play the dominant role

the continental si cycle and its impact on the ocean si isotope budget abstract the silicon isotope composition of biogenic silica 30sibsi in the ocean is a function of the 30si of the available dissolved si dsi h2sio4 the degree of utilisation of the available dsi and for some organisms the concentration of dsi this makes 30sibsi in sediment archives a promising proxy for past dsi concentrations and utilisation at steady state mean 30sibsi must equal a weighted average of the inputs the majority of which are of continental origin variation in the functioning of the continental si cycle on timescales similar to the residence time of dsi in the ocean 10 ka may therefore contribute to downcore variability in 30sibsi on millennial or longer timescales the direction and magnitude of change in published 30sibsi records over the last few glacial cycles is consistent among ocean basins and between groups of silicifiers they document glacial values that are typically 0 5 to 1 0 lower than interglacial values and together hint at coherent and predictable glacial interglacial variability in whole ocean 30si driven by a change in mean 30si of the inputs in this contribution we review the modern inputs of dsi to the ocean and the controls on their isotopic composition and assess the evidence for their variability on millennial plus timescales today 9 55 1012 mol yr 1 dsi enters the ocean of which roughly 64 and 25 are direct riverine inputs of dsi and dsi from dissolution of aeolian and riverborne sediment respectively the remainder derives from alteration or weathering of the ocean crust each input has a characteristic 30si with our current best estimate for a weighted mean being 0 74 although much work remains to be done to characterise the individual fluxes many aspects of the continental si cycle may have differed during glacial periods that together can cumulatively substantially lower the mean 30si of dsi entering the ocean these changes relate to i a cooler drier glacial climate ii lowered sea level and the exposure of continental shelves iii the presence of large continental ice sheets and iv altered vegetation zonation using a simple box model with a monte carlo approach to parameterisation we find that a transition from a hypothesised glacial continental si cycle to the modern si cycle can drive an increase in whole ocean 30si of comparable rate and magnitude to that recorded in 30sibsi this implies that we may need to revisit our understanding of aspects of the si cycle in the glacial ocean although we focus on the transition from the last glacial our synthesis suggests that the continental si cycle should be seen as a potential contributory factor to any variability observed in ocean 30sibsi on millennial or longer timescales

molybdenum isotope behaviour accompanying weathering and riverine transport in a basaltic terrain the application of the molybdenum mo isotope system as a proxy for determining changes in the redox state of the oceans is predicated on the assumption that the composition of continental input can be characterised from crustal rock types and remains constant however it has recently been shown that the 98 95mo composition of global rivers varies between 0 15 and 2 4 and is therefore systematically heavier than the average composition of the continental crust 0 in order to understand the processes that control mo isotope fractionation during weathering this study presents 98 95mo and mo abundance data for rivers and estuarine samples from iceland that drain predominantly basaltic terrains resolvable differences are observed in the isotopic composition of the riverine mo sources ice 98 95moice 1 8 basaltic bedrock 98 95mobedrock 0 0 and hydrothermal waters 98 95mohydrothermal 3 4 systematic changes in the dissolved mo isotope composition are also observed within river catchments with 98 95mo values increasing from 0 in glacial rivers close to the source to 1 downstream consistent with mo isotopes being fractionated during weathering analysis of other riverine phases bedload colloids and iron precipitates demonstrates that these phases preferentially incorporate light mo isotopes and remain coupled to the dissolved load during riverine transportation a 98 95mo profile through the borgarfjor eth ur estuary exhibits a predominantly conservative mixing behaviour but suggests that the release of isotopically light mo from the particulate and or colloidal phases may occur in the low salinity part of the estuarine mixing zone 2010 elsevier b v

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

the erosion and suspended matter seawater interaction during and after the 1996 outburst flood from the vatnajokull glacier iceland abstract the gjalp subglacial eruption 1996 within the vatnajokull glacier iceland triggered a catastrophic outburst flood bringing at least 180 million tonnes of suspended solids to the sea in only 42 h this amounts to 1 of the total annual global river suspended flux to the oceans the specific bet surface area of the suspended solids was measured to be 11 8 18 9 m2 g translating to the average total bet surface area of 2 8 10 9 km2 providing enormous potential for adsorption desorption and precipitation dissolution fluxes at the suspended solids ocean water interface altered basalt glass was the major constituent of the suspended matter 80 secondary minerals such as zeolites and calcite amounted to 11 but only 5 was fresh volcanic glass the suspended grains were generally rounded the glass carried by the flood is different in chemical composition from the glass produced by the gjalp eruption the gjalp material has higher feototal tio2 and tio2 p2o5 ratios than the suspended glass in the flood waters the majority of the flood samples match the composition of the volcanic system down stream from the eruption site the large amount of altered material in the flood and its chemical composition suggests erosion conforming to a 2 m deep 1000 m wide and 50 000 m long channel in less than 42 h the behaviour of 28 elements on the surface of the suspended solids exposed to seawater was quantified by experiments in the laboratory the altered basaltic glass dissolved in seawater as recorded by the si release from the glass the dissolved concentrations of na ca si ba cd co cu hg mn ni and total dissolved inorganic n increased considerably when the suspended solids come into contact with the seawater but the concentrations of mg k s sr fe pb and zn decreased the experimental seawater solutions were supersaturated with respect to calcite mg montmorillonite and amorphous iron hydroxide the rate of release mol m2 s of si mn ba co ni and cd decreased continuously during the one week exposure to sweater after one week the logarithm of the dissolution rate of the altered basaltic glass was 11 9 to 11 6 si mole m2 sec significantly lower than the steady state rates for fresh basaltic glass at similar conditions calculated one day desorbed dissolution suspended material fluxes are greater than the integrated dissolved flood fluxes for mn ba ni co and cd but the si dissolved food flux was greater than the one day desorbed dissolved suspended material flux

the effect of the 2002 glacial flood on dissolved and suspended chemical fluxes in the skafta river iceland abstract this study describes the chemical composition of dissolved degased and suspended fluxes of the 2002 skafta glacial flood which emerged from one of the skafta subglacial lake due to geothermal activity beneath the icelandic vatnajokull glacier the dissolved and suspended fluxes during the flood are compared with those normally observed in the skafta river to determine the effect of such floods on the annual fluxes of material delivered to the coastal waters concentrations of most dissolved elements during the flood were significantly higher than those normally observed in the skafta river in addition dissolved concentrations of nutrients such as sio 2 fe and v increased more than an order of magnitude during the flood these will affect biological processes on a local scale the 34 s composition in the flood water suggests that the dissolved so 4 was derived from the oxidation of h 2 s and the geothermal fluid the total suspended particulate load measured in the skafta river during the 8 day 2002 flood was approximately half of the non flood total annual skafta suspended load as particles carry the bulk of limiting nutrients to the oceans this demonstrates the importance of glacial floods for primary production of coastal waters the composition of the flood water and the skafta subglacial lake together with reaction path modelling suggest that substantial degasing of co 2 and h 2 s occurred at the glacial outlet during the flood this degasing may have released as much as 262 000 and 7 980 tonnes of co 2 and h 2 s respectively to the atmosphere having a considerable impact on the local carbon and sulphur cycles during the flood event

early diagenetic remineralization of sedimentary organic c in the gulf of papua deltaic complex papua new guinea net loss of terrestrial c and diagenetic fractionation of c isotopes oceania supplies 40 of the global riverine flux of organic carbon approximately half of which is injected onto broad continental shelves and processed in shallow deltaic systems the gulf of papua on the south coast of the large island of new guinea is one such deltaic clinoform complex it receives 4 mt yr 1 particulate terrestrial organic carbon with initial particle corg loading 0 7 mg m 2 corg loading is reduced to 0 3 mg m 2 in the topset upper foreset zones of the delta despite additional inputs of mangrove and planktonic detritus and high net sediment accumulation rates of 1 4 cm yr 1 carbon isotopic analyses 13c 14c of co2 and corg demonstrate rapid 100 yr remineralization of both terrestrial 13c 28 6 and marine corg 13c 20 5 ranging in average age from modern bomb 14c 60 to 1000 yr 14c 140 efficient and rapid remineralization in the topset upper foreset zone is promoted by frequent physical reworking bioturbation exposure and reoxidation of deposits the seafloor in these regions particularly 20 m apparently functions as a periodically mixed suboxic batch reactor dominated by microbial biomass although terrestrial sources can be the primary metabolic substrates at inshore sites relatively young marine corg often preferentially dominates pore water co2 relative to bulk corg in the upper foreset thus a small quantity of young rapidly recycled marine organic material is often superimposed on a generally older less reactive terrestrial background whereas the pore water co2 reflects both rapidly cycled marine and terrestrial sources terrestrial material dominates the slower overall net loss of corg from particles in the topset upper foreset zone i e recycled marine corg leaves little residue preferential utilization of corg subpools and diagenetic fractionation of c isotopes supports the reactive continuum model as a conceptual basis for net decomposition kinetics early diagenetic fractionation of c isotopes relative to the bulk sedimentary corg composition can produce changes in 14c activity independent of radioactive decay in the gulf of papua topset upper foreset 14c of pore water co2 averaged 300 greater than corg sediment between 1 3 m depth in deposits diagenetic fractionation and decomposition aging of sedimentary corg compromises simple application of 14c for determination of sediment accumulation rates in diagenetically reactive deposits

monitoring of jokulhlaups and element fluxes in proglacial icelandic rivers using osmotic samplers the quantification of volatile emissions from volcanoes is an integral part of understanding magmatic systems with the exsolution and extent of volcanic degassing having a large impact on the nature of an eruption measurements of volatiles have traditionally focused on gas emissions into the atmosphere but volatiles can also become dissolved in proximal water bodies en route to the surface thus the monitoring of rivers draining active volcanic areas can provide insights to identifying changes in activity this process is particularly important for sub glacial volcanoes in iceland where much of the volatile release is transported within glacial outbreak floods termed jokulhlaups monitoring and characterising these phenomena is hampered by the dependence on spot sampling of stochastic events under challenging field conditions which often leads to bias in the collected data a recent technological advance is the osmotic sampler an electricity free pump that continuously collects water that can subsequently be divided into time averaged samples this technique allows for continued and unsupervised deployment of a sampler for weeks to months representing a cost efficient form of chemical monitoring in this study we deployed osmotic samplers in two rivers in southern iceland skalm is a proglacial river from m rdalsjokull glacier and katla volcano while skafta is a larger drainage system from the western part of vatnajokull glacier both rivers are prone to jokulhlaups from geothermal and volcanic sources and a small jokulhlaup of geothermal origin occurred during the second deployment in skafta in january 2014 the two deployments show that osmotic samplers are capable of delivering accurate chemical data in turbulent conditions for several key elements total dissolved fluxes for the deployment at skafta are calculated to be na 9 9 tonnes day mg 10 5 t d si 34 7 t d cl 11 0 t d ca 31 6 t d dic 50 8 t d and so4 28 3 t d with significant elevations of element concentrations during the jokulhlaup dissolved fluxes vary considerably on temporal scales from days to seasons so that spot sampling may miss pulses in concentrations this is particularly important for elements such as mn the continuous geochemical records from the osmotic samplers make it possible to identify pulses of fluxes attributed to sea spray groundwater and subglacial sources the samplers can also be combined with existing methods of river monitoring such as conductivity and discharge to accurately assess changes to fluvial chemistry due to volcanic inputs moreover there is the potential to deploy osmotic samplers in a range of other affected water bodies e g wells springs lakes to gain further insights into volcanic processes

role of river suspended material in the global carbon cycle comment and reply reply the main point made by schwartzman in his comment is that because the interaction of suspended basalt material and seawater in deltas leads to the consumption of mg concurrent with the release of ca the overall effect of suspended material transport from the continents and volcanic islands to the

future trends in paleoseismology integrated study of the seismic landscape as a vital tool in seismic hazard analyses this paper forms the introduction to this special issue of tectonophysics devoted to selected scientific research presented during events sponsored by the inqua subcommission on paleoseismicity in the past few years in this note we summarize the contents of the contributed papers and use the issues they raise to review the state of the art in paleoseismology from a quaternary geology perspective in our opinion the evolution of paleoseismological studies in the past decade clearly demonstrates that in order to properly understand the seismic potential of a region and to assess the associated hazards broad based multidisciplinary studies are necessary to take full advantage from the geological evidence of past earthquakes a major challenge in future paleoseismic research is to build detailed empirical relations between various categories of coseismic effects in the natural environment and earthquake magnitude intensity these relations should be compiled in a way that is fully representative of the wide variety of natural environments on earth in terms of climatic settings quaternary tectonic evolution rheological parameters of the seismogenic crust and stress environment for instance available data indicate that between earthquake magnitude and surface faulting parameters different scaling laws exist and they are a function of the local geodynamic setting including style of faulting typical focal depths heat flow in this regard we discuss in some detail the concept of seismic landscape which provides the necessary background for developing paleoseismological research strategies the large amount of paleoseismological data collected in recent years shows that each earthquake source creates a signature on the geology and the geomorphology of an area that is unequivocally related with the order of magnitude of its earthquake potential this signature is defined as the seismic landscape of the area e g serva l vittori e ferreli l michetti a m 1997 geology and seismic hazard in grellet b mohammadioun b hays w eds proceedings of the second france united states workshop on earthquake hazard assessment in intraplate regions central and eastern united states and western europe october 16 1995 nice france 20 24 ouest editions nantes france michetti a m hancock p l 1997 paleoseismology understanding past earthquakes using quaternary geology

biogeomorphic influence of soil depth to bedrock volcanic ash soils and surface tephra on silversword distribution haleakalā crater maui hawai i abstract this research examines the spatial distribution of haleakal silverswords argyroxiphium sandwicense dc subsp macrocephalum over basaltic a lava flows at silversword loop haleakal crater maui hawai i the overall study goal is to situate an extensive field data set within an historical geomorphic framework to propose a conceptual biogeomorphic model of landscape development at silversword loop landscape features were investigated along two belt transects 111 120 m long crossing lava flow deposits at 2175 m the lava flows 4 5 km long originated 2700 ybp at pu u o m ui a large cinder cone transects consist of contiguous 3 3 m 9 m2 quadrats plot data include topographic profiles soil depth to bedrock size of surface tephra determined by photosieving and plant density 23 soil samples were analyzed within 10 profiles weathered lava outcrops tephra blocks 10 cm and cobbles 5 10 cm cover lava flow ridges the gently sloping flanks of lava flow deposits merge into intervenient concave troughs filled with volcanic ash and small tephra soils along ridges are thin 17 cm whereas profiles on troughs are deeper 110 cm soils are sandy volcanic inceptisols lithic typic and aridic lithic haplustepts averaging 21 6 gravel 96 8 sand and 3 2 fines silt clay mean organic matter is just 0 92 these soils provide low water retention 23 2 at field capacity and rapid infiltration deeper trough soils are largely devoid of plants in contrast silverswords are virtually restricted to shallow soils on lava flow crests where they densely cluster about outcrops and blocks 90 of plants grow on soils 40 cm deep and 71 3 occupy plots with 40 ash cover 84 4 of rosettes are rooted on outcrops or near stones only 4 4 grow on soil and 11 2 germinated on plant litter patterns of lava flow weathering and soil depth to bedrock control silversword distribution at silversword loop shallow basalt bedrock and outcrops restrict soil drainage providing a perched water table that silversword roots can exploit surface blocks also provide safe stable microhabitats thus rosettes grow preferentially near stones geomorphological pedological and ecological data are integrated into a biogeomorphic sequence of soil development and landscape evolution at silversword loop for the past three millennia first through the eruptions and ash deposits of pu u o m ui followed 970 940 bp by pyroclastic activity in hal li i and ka lu u o ka o o cinder cones

quantifying the impact of riverine particulate dissolution in seawater on ocean chemistry the quantification of the sources and sinks of elements to the oceans forms the basis of our understanding of global geochemical cycles and the chemical evolution of the earth s surface there is however a large imbalance in the current best estimates of the global fluxes to the oceans for many elements in the case of strontium sr balancing the input from rivers would require a much greater mantle derived component than is possible from hydrothermal water flux estimates at mid ocean ridges current estimates of riverine fluxes are based entirely on measurements of dissolved metal concentrations and neglect the impact of riverine particulate dissolution in seawater here we present 87sr 86sr isotope data from an icelandic estuary which demonstrate rapid sr release from the riverine particulates we calculate that this sr release is 1 1 7 5 times greater than the corresponding dissolved riverine flux if such behaviour is typical of volcanic particulates worldwide this release could account for 6 45 of the perceived marine sr budget imbalance with continued element release over longer timescales further reducing the deficit similar release from particulate material will greatly affect the marine budgets of many other elements changing our understanding of coastal productivity and anthropogenic effects such as soil erosion and the damming of rivers

the repeat time of the 1811 and 1812 new madrid earthquakes a geological perspective abstract the great new madrid earthquakes of 1811 and 1812 were accompanied by extensive liquefaction within the meizoseismal zone we examined tens of kilometers of freshly excavated ditch banks within the southern limb of the new madrid seismic zone for evidence of prehistoric liquefaction events radiocarbon dates indicate that the exposures studied provide a record of the last 5000 to 10 000 years analyses of the statistics of historical seismicity imply a relatively short 550 to 1100 yr repeat time for 1811 to 1812 type earthquakes in contrast our search did not reveal definitive evidence of widespread paleoliquefaction events and hence provides no independent support for the relatively short 550 to 1100 yr return time implied by statistics of historical seismicity

contemporary suspended sediment dynamics within two partly glacierized mountain drainage basins in western norway erdalen and bodalen inner nordfjord abstract this paper focuses on environmental controls spatiotemporal variability and rates of contemporary fluvial suspended sediment transport in the neighboring partly glacierized and steep erdalen 79 5 km 2 and bodalen 60 1 km 2 drainage basins in the fjord landscape of the inner nordfjord in western norway field work including extended samplings and measurements was conducted since 2004 in erdalen and since 2008 in bodalen the distinct intra and inter annual temporal variability of suspended sediment transport found is mostly controlled by meteorological events with most suspended sediment transport occurring during pluvial events in autumn september november followed by mostly thermally determined glacier melt in summer july august and by mostly thermally determined snowmelt in spring april june extreme rainfall events 70 mm d 1 in autumn can trigger significant debris flow activity that can cause significant transfers of suspended sediments from ice free surface areas with sedimentary covers into main stream channels and is particularly important for fluvial suspended sediment transport in years with occurring relevant debris flow activity the total annual drainage basin wide suspended sediment yields are strongly determined by these single extreme events the proportion of glacier coverage followed by steepness of slopes and degree of vegetation cover in ice free surface areas with sedimentary covers are the main controls for the detected spatial variability of suspended sediment yields the contemporary sediment supply from glacierized surface areas and the jostedalsbreen ice cap through different defined outlet glaciers shows a high spatial variability the fact that the mean annual suspended sediment yield of bodalen is with 31 3 t km 2 yr 1 almost twice as high as the mean annual suspended sediment yield of erdalen 16 4 t km 2 yr 1 is to a large extent explained by the higher proportion of glacier coverage in bodalen 38 of the drainage basin surface area as compared to erdalen 18 of the drainage basin surface area and by a significantly higher sediment yield from the glacierized area of the bodalen drainage basin compared to the glacierized surface area in erdalen when looking at the total annual mass of suspended sediments being fluvially exported from both entire drainage basin systems the total amount of suspended sediments coming from the ice free drainage basin surface areas altogether dominates over the total amount of suspended sediments coming from the glacierized surface area of both drainage basins drainage basin wide annual suspended sediment yields are rather low when compared with yields of other partly glacierized drainage basin systems in norway and in other cold climate environments worldwide which is mainly due to the high resistance of the predominant gneisses towards glacial erosion and weathering the altogether only small amounts of sediments being available within the entire drainage basin systems the stable and nearly closed vegetation cover in the ice free surface areas with sedimentary covers and the efficiency of proglacial lakes in trapping sediments supplied by defined outlet glaciers both contemporary and long term suspended sediment yields are altogether supply limited contemporary suspended sediment transport accounts for nearly two thirds of the total fluvial transport and accordingly plays an important role within the sedimentary budgets of the entire erdalen and bodalen drainage basins

evidence for episodic sand blow activity during the 1811 1812 new madrid missouri earthquake series four major earthquakes of the 1811 1812 new madrid series caused widespread ground disturbance mostly in the form of sand blows in the alluvial valley of the mississippi river although a recurrence interval of 600 700 yr has been estimated for major shocks recent excavations at an archeological site in northeastern arkansas revealed no evidence of ground disturbance for at least 1 3 ka prior to 1811 sand blows attributed to the new madrid series show that such features can have multiple episodes of sand extrusion through a single dike and vent

hot soils and cooler stones geoecological influence of volcanic tephra and boulders on soil temperature and significance for plant distribution in haleakalā crater maui hawai i abstract this project i investigates the geoecological influence of boulders and their dimensions thickness length on maximum daily soil temperatures beneath them at two sites 2175 and 2685 m in haleakal crater maui ii contrasts temperatures in bare volcanic ash soils with adjacent substrates covered by reddish tephra at 7 study sites 2170 2735 m these encompass most of the altitudinal range of k paoa and silversword two common plants in this mountain area and iii analyzes effects of tephra depth on soil maxima midday soil temperatures were measured with thermocouple thermometers 5 cm recording thermographs also monitored temperatures continuously in various contrasting substrates for 8 day periods both boulders and tephra substantially decreased soil maxima bare soil highs n 100 reached 47 6 c mean 37 2 4 4 c maxima below boulders n 40 4 109 cm thick 6 265 cm long peaked at 20 5 c mean 16 0 2 54 c whereas 80 readings under tephra 9 95 mm depth reached 32 0 c mean 25 2 5 2 c larger boulders were most effective in lowering temperatures spearman and kendall correlation tests indicate block thickness was slightly more important p p p values caused greater albedo higher tephra reflectivity helped reduce absorption of solar radiation and consequently soils remained cooler below stones such temperature reduction is ecologically significant for plant survival on stone covered areas as soil maxima 35 c may be deleterious to seed and or seedling survival

how important is it to integrate riverine suspended sediment chemical composition with depth clues from amazon river depth profiles abstract the vertical variability in mineralogical chemical and isotopic compositions observed in large river suspended sediments calls for a depth integration of this variability to accurately determine riverine geochemical fluxes in this paper we present a method to determine depth integrated chemical particulate fluxes of large rivers based on river sampling along depth profiles and applied to the amazon basin lowland tributaries the suspended particulate matter spm concentration data from depth profiles is modeled for a number of individual grain size fractions using the rouse model which allows to predict the grain size distribution of suspended sediment throughout the whole river cross section then using 1 the relationship between grain size distribution and the al si ratio 2 relationships between the al si ratio and the chemical concentrations the chemical composition of river sediment is predicted throughout the river cross section and integrated to yield the depth integrated chemical particulate flux for a number of chemical elements e g si al fe na rees for elements such as al fe rees th the depth integrated flux is around twice as high as the one calculated from river surface sample characteristics for na and si the depth integrated flux is three times higher than the surface estimate due to the enrichment of albite and quartz at the bottom of the river depth integrated 87sr 86sr composition of suspended sediment also predictable using this method differs by more than 10 3 from the surface sample composition finally potential implications of depth integrated estimates of amazon sediment chemistry are explored depth integration of particulate 87sr 86sr isotopic ratios is necessary for a reliable use of sr isotopes as a provenance tracer the concept of steady state weathering of a large river basin is revisited using depth integrated sediment composition this analysis shows that in the amazon basin river the previously observed discrepancy between 1 weathering intensities of channel surface sediment and 2 silicate derived dissolved fluxes is only slightly accounted for by the vertical variability of suspended sediment weathering intensities this observation confirms that most large rivers basins are not eroding at steady state

lithium isotope behaviour during weathering in the ganges alluvial plain the ganges river system is responsible for the transportation of a large flux of dissolved materials derived from himalayan weathering to the oceans silicate weathering driven cooling resulting from uplift of the himalayas has been proposed to be a key player in cenozoic climate variation this study has analysed li isotope 7li ratios from over 50 ganges river waters and sediments in order to trace silicate weathering processes sediments have 7li of 0 identical to bulk continental crust however suspended sediment depth profiles do not display variations associated with grain size that have been observed in other large river systems dissolved 7li are low 11 in the ganges headwaters but reach a constant value of 21 1 6 within a relatively short distance downstream which is then maintained for almost 2000 km to the ganges mouth given that li isotopes are controlled by the ratio of primary mineral dissolution to secondary mineral formation this suggests that the ganges floodplain is at steady state in terms of these processes for most of its length low 7li in the mountainous regions suggest silicate weathering is therefore at its most congruent where uplift and fresh silicate exposure rates are high however there is no correlation between 7li and the silicate weathering rate in these rivers suggesting that li isotopes cannot be used as a weathering rate tracer although they do inform on weathering congruency and intensity the close to constant 7li values for the final 2000 km of ganges flow also suggest that once the size of the alluvial plain reached more than 500 km the flow distance after which riverine 7li stops varying the ganges exerted little influence on the changing cenozoic seawater 7li because riverine 7li attained a near steady state composition

recognizing and dating prehistoric liquefaction features lessons learned in the new madrid seismic zone central united states the new madrid seismic zone nmsz which experienced severe liquefaction during the great new madrid missouri earthquakes of 1811 and 1812 as well as during several prehistoric earthquakes is a superb laboratory for the study of world class earthquake induced liquefaction features and their use in paleoseismology in seismically active regions like the nmsz frequent large earthquakes can produce a complex record of liquefaction events that is difficult to interpret lessons learned studying liquefaction features in the nmsz may help to unravel the paleoseismic record in other seismically active regions soil characteristics of liquefaction features as well as their structural and stratigraphic relations to native american occupation horizons and other cultural features can help to distinguish prehistoric liquefaction features from historic features in addition analyses of artifact assemblages and botanical content of cultural horizons can help to narrow the age ranges of liquefaction features future research should focus on methods for defining source areas and estimating magnitudes of prehistoric earthquakes from liquefaction features also new methods for dating liquefaction features are needed

the influence of surface volcaniclastic layers from haleakala maui hawaii on soil water conservation this study focuses on the soils and surficial volcaniclastic layers of haleakala s crater maui hawaii the main objective is to assess the effects of covers with fragments of various sizes ash cinder lapilli on soil water conservation soil and gravel samples were collected in haleakala national park from a site at 2505 m where the hawaiian silversword a giant rosette plant grows densely on pyroclastic materials an evaporation experiment lasting 22 days showed a gradual drop in seven pairs of soil samples initially at field capacity one set of samples was left bare the other was covered by gravel mulches gm these resulted in lengthening of t100 total desiccation time by a factor of 2 3 5 2 bare soils dried after 70 140 h but drying time under gravel was 246 509 h mean grain size mz and sorting had the greatest influence on evaporation rates coarse lapilli mz 13 8 mm were less effective than fine ash mz 2 9 3 8 mm in preventing water losses while medium grained cinder mz 4 5 2 mm produced the greatest water savings lapilli mean 0 48 and ash 0 6 were moderately to well sorted cinders with a broader grain size range 1 13 were poorly sorted this allowed infilling of large interstices between coarse fragments by smaller grains effectively reducing pore size and therefore evaporation rates a second experiment determined water storage and rates of water loss by mulches wetting occurred swiftly within 3 4 min all gravel types were dry within 26 h this drying process is important for water conservation as it effectively prevents further water loss from the mulch surface larger fragments stored less water this is related to their surface area weight ratio which increases for smaller particles thus fine ash or cinder grains with a high total area intercept more water than larger lapilli a 5 cm thick layer of ash intercepted an average of 6 8 mm of rain slightly more than the same depth of cinder 6 3 mm but lapilli retained only 4 7 mm therefore light rainfall events are more likely to contribute water to soil under lapilli than below finer pyroclastic material volcaniclastic covers serve an important ecological role in haleakala by prolonging periods of water availability to plants thus allowing hawaiian silverswords to grow for longer time spans

the role of supergene sulphuric acid during weathering in small river catchments in low mountain ranges of central europe implications for calculating the atmospheric co2 budget abstract the geochemistry of dissolved and suspended loads in river catchments of two low mountain ranges in central europe allows comparison of pertinent chemical weathering rates distinct differences in lithology i e granites prevailing in the black forest compared to palaeozoic sediments in the rhenish massif provide the possibility to examine the influence of lithology on weathering here we determine the origin of river water using the stable isotope ratio 18oh2o and we quantify the geogenic proportions of sulphate from stable isotope ratios 34sso4 and 18oso4 particularly in catchments with abundant pyrite determination of the geogenic amount of sulphate is important since oxidation of pyrite leads to acidity which increases weathering our results show that spatially averaged silicate weathering rates are higher for the river catchments acher and gutach in the black forest 10 12 t km2 yr compared to the river catchments of the mohne dam and the aabach dam in the rhenish massif 2 6 t km2 yr correspondingly the co2 consumption by silicate weathering in the black forest 334 395 103 mol km2 yr is more than twice as high as in the rhenish massif 28 151 103 mol km2 yr these higher rates for watersheds of the black forest are likely due to steeper slopes leading to higher mechanical erosion with respective higher amounts of fresh unweathered rock particulates and due to the fact that the sediments in the rhenish massif have already passed through at least one erosion cycle carbonate weathering rates vary between 12 and 38 t km2 yr in the catchments of the rhenish massif the contribution of sulphuric acid to the silicate weathering is higher in the catchments of the rhenish massif 9 16 than in the catchments of the black forest 5 7 due to abundant pyrite in the sediments of the rhenish massif three times higher long term erosion rates derived from cosmogenic nuclides compared to short term erosion rates derived from river loads in central europe point to three times higher co2 consumption during the past 103 to 104 years

sinking mafic body in a reactivated lower crust a mechanism for stress concentration at the new madrid seismic zone we propose a geodynamic model for stress concentration in the new madrid seismic zone nmsz the model postulates that a high density mafic body situated in the deep crust directly beneath the most seismically active part of the nmsz began sinking several thousands of years ago when the lower crust was suddenly weakened based on the fact that deformation rates in the nmsz have accelerated over the past 9 k y we envision the source of this perturbation to be related to the last north american deglaciation excess mass of the mafic body exerts a downward pull on the elastic upper crust leading to a cycle of primary thrust faulting with secondary strike slip faulting after which continued sinking of the mafic body reloads the upper crust and renews the process this model is consistent with the youth of activity the generation of a sequence of earthquakes and the velocity evolution during interseismic periods which depend upon the density contrast of the mafic body with respect to the surrounding crust its volume and the viscosity of the lower crust

biogeochemistry of glacial landscape systems abstractglaciers affect biogeochemistry of landscapes through their sediments glacial erosion rates are high and the sediments produced are distinctively fine grained hence glaciers can be thought of as producers of mineral surface area although this mineral surface area is highly reactive temperature limits chemical weathering fluxes from glaciers and their surroundings more significant effects may be associated with silt deposited in loess and on continental margins thick deposits in both settings contribute to carbon cycling through both silicate weathering and organic carbon burial the impact of glaciers on biogeochemical cycles will be long lasting as the legacy of glacial erosion processes continues as long as sediment yields are elevated

characteristics of atmospheric dust deposition in snow on the glaciers of the eastern tien shan china wind blown mineral aerosol dust derived from the crustal surface is an important atmospheric component affecting the earth s radiation budget deposition of water insoluble dust was determined in snow deposited on urumqi glacier no 1 haxilegen glacier no 51 and miaoergou glacier eastern tien shan china analysis of the horizontal distribution of snow depth and concentration and flux of dust particles in the snow cover suggests that dust deposition differs on each of these glaciers as the atmospheric environment changes from west to east mean mass concentrations of micro particles in the size range 0 57 26 mm diameter at the three locations are respectively 969 1442 and 3690 m gk g 1 with an increasing trend from west to east dust layers in the snow cover contain na and ca rich materials typically found in central asian dust particles volume size distributions of dust particles in the snow showed single modal structures having volume median diameters of 3 22 mm dust profiles in the snow cover over the past 4 years reveal frequent sporadic high dust concentrations with a large year to year variability implying that dust deposition in the eastern tien shan is very sensitive to atmospheric environment change

using mg isotope ratios to trace cenozoic weathering changes a case study from the chinese loess plateau abstract the magnesium isotope system is a useful tracer of weathering processes due to its sensitivity to secondary mineral formation we present elemental and isotopic data in bulk loess and paleosol sediments from the luochuan profile in the chinese loess plateau clp due to a relatively constant pre weathering mineralogy changes in the sediment chemistry with depth can be interpreted to reflect changes in weathering processes that are ultimately controlled by climate we find that the luochuan sediments are all enriched in light mg relative to the upper continental crust ucc 0 22 the isotopically light signature is a result of three way mixing between mg sourced from silicate calcite and dolomite changes in 26 mg between loess and paleosol reflect the higher weathering intensities during pedogenesis and corresponding loss of easily leachable calcite enriched in light mg isotopes from the loess layers this is confirmed by the results of a simple leaching procedure in which the leachate phase contains high ca concentrations and isotopically light 26 mg values of up to 2 any isotopic fractionation of mg imparted by isotopically heavy clay mineral formation appears to be insignificant and is obscured by the presence of detrital dolomite that is resistant to acid leaching and is isotopically light the isotopic composition of mg at luochuan broadly follows the magnetic susceptibility record in that loess layers are relatively isotopically light and have lower magnetic susceptibilities than their adjacent paleosol as such the changes in 26 mg values with depth do correspond to changes in chemical weathering however the driving factor behind these changing 26 mg values is carbonate preservation which in itself is not a highly sensitive paleoclimate proxy from a global perspective the 26 mg value of luochuan loess is similar to other loess sediments which are often isotopically light relative to the ucc we have recalculated the average 26 mg value of global loess sediments to be 0 58 1 18 this reflects the fact that 26 mg values in loess are highly heterogeneous and are generally enriched in 24 mg compared to typical ucc rocks due to preservation of high amounts of isotopically light carbonate minerals for this reason loess sediments cannot be used to approximate the isotopic composition of mg in the earth s crust

archeological and pedological evidence for large prehistoric earthquakes in the new madrid seismic zone central united states prehistoric liquefaction features have been identified by careful observation of their structural and stratigraphic relations to native american occupation horizons and their subtle soil characteristics the ages of these liquefaction features have been estimated from radiocarbon dating of wood associated with the features and native american artifacts found within bounding occupation horizons at three sites near blytheville arkansas in the central part of the new madrid seismic zone one sand blow crater formed between a d 800 and 1400 two sand blow deposits formed between a d 800 and 1670 and three possibly four sand dikes formed since 4035 b c where not found in association with native american occupation horizons and artifacts prehistoric liquefaction features can be difficult to distinguish from features that formed during the great new madrid earthquakes of a d 1811 and 1812 this raises the possibility that prehistoric liquefaction features may have been misinterpreted during previous studies in the area nevertheless a paleoearthquake chronology is beginning to emerge for the new madrid seismic zone our findings are consistent with paleoseismological studies in the northern part of the seismic zone and suggest a recurrence interval of hundreds of years for earthquakes large enough to induce liquefaction in this region m 6 4 by mapping the age distribution of liquefaction features a more accurate assessment of the long term earthquake potential of the region will be possible

the record of seismically induced liquefaction on late quaternary terraces in northwestern tennessee between december 1811 and february 1812 the four largest historical earthquakes mb 7 0 in eastern north america occurred in the new madrid missouri seismic zone nmsz although this area has been the focus of considerable seismological and geological research estimates of the repeat time of large magnitude seismic events remain poorly constrained the available estimates are based primarily on earthquake frequency statistics and limited paleoseismology studies johnston and nava 1985 analyzed about 180 yr of historical seismicity data and 10 yr of instrumental data and concluded that the repeat time for largemagnitude events m b 7 0 is between 550 and 1100 yr this estimate assumes that the data set is representative of the seismicity in the nmsz and that the slope of the line relating earthquake frequency to magnitude b value is constant from smallto large magnitude earthquakes johnston and nava 1985 however pacheco et al 1992 reported that b values may not be constant in earthquake frequency magnitude distributions and thus the estimated recurrence interval of johnston and nava 1985 must be considered tentative two geological studies suggest that the recurrence interval of large magnitude earthquakes in the nmsz is on the order of 450 to 600 yr two exploratory trenches across the reelfoot scarp in northwestern tennessee fig 1 revealed the only unequivocal example of holocene surface faulting in the upper mississippi embayment russ et al 1978 russ 1979 kelson et al 1993 stratigraphic relations across the northern part of the scarp indicate at least two episodes of faulting had occurred after about 2250 yr b p and before the 1811 to 1812 seismic events russ 1979 based on these two prehistoric earthquakes the dating error limits and the 1811 to 1812 events russ 1979 estimated an average recurrence interval of 600 yr or less for large magnitude earthquakes in the nmsz this estimated average recurrence interval is corroborated by a radiocarbon age estimate of a d 1310 to 1540 for fault scarp colluvium along the central reelfoot scarp kelson et al 1993 however inasmuch as russ 1979 found no evidence that offset occurred on the reelfoot scarp during the 1811 to 1812 earthquakes the relation between surface ruptures on the reelfoot scarp and large paleo earthquakes in the nmsz is not clear the widespread development of liquefaction features during the 1811 to 1812 earthquake series obermeier 1989 obermeier et al 1990 and the probable development of similar features during previous large magnitude seismic events m b 6 2 nuttli 1982 has been the basis for several efforts to identify paleoliquefaction features saucier 1991 estimated an average recurrence

glaciers show direct linkage between erosion rate and chemical weathering fluxes field studies suggest a linkage between high physical erosion rates and rates of chemical denudation mechanical erosion by temperate glaciers is commonly an order of magnitude higher than in mountainous fluvial catchments leading to an expectation that chemical weathering fluxes should also be high from glacierized basins yet solute fluxes from glaciers are not found to be higher than non glacierized catchments application of a model of silicate weathering from glaciers based on mineral surface area production and mineralogy shows that solute fluxes are consistent with the low temperatures dilute water chemistry and high mineral surface area production in these environments low temperatures reduce silicate weathering rates this effect explains the difference between silica fluxes from glaciers and from non glacierized basins as in laboratory flow through reactors glacial solute flux should depend on surface area production and mineral weathering rate constants the surface area production is significant a typical glacial erosion rate and grain size distribution produces on the order of 104 km2 of mineral surface area per square kilometer per year this new surface area is highly reactive because mineral weathering rates decline with surface age application of the reactor model yields results largely consistent with measured solute fluxes for the example of bench glacier alaska the model underpredicts potassium fluxes probably due to accelerated initial dissolution of biotite strained by abrasion the success of the model in predicting other silicate weathering fluxes reflects the far from equilibrium conditions in glacial runoff such that mineral weathering rate constants are not limited by saturation state in a small data set from glacial catchments both annual silica fluxes and mean concentrations increase with water discharge this suggests that mineral surface area increases with water discharge from glaciers an effect plausibly linked to erosion rates those glaciers for which both erosion rate and silica flux data are available support the idea that production of new reactive mineral surface area by glacial erosion drives silicate weathering fluxes

direct evidence of the feedback between climate and nutrient major and trace element transport to the oceans abstract climate changes affect weathering denudation and riverine runoff and therefore elemental fluxes to the ocean this study presents the climate effect on annual fluxes of 28 dissolved elements and organic and inorganic particulate fluxes determined over 26 42 year period in three glacial and three non glacial river catchments located in eastern iceland annual riverine fluxes were determined by generating robust correlations between dissolved element concentrations measured from 1998 to 2003 and suspended inorganic matter concentrations measured from 1962 to 2002 with instantaneous discharge measured at the time of sampling in each of these rivers these correlations were used together with measured average daily discharge to compute daily elemental fluxes integration of these daily fluxes yielded the corresponding annual fluxes as the topography and lithology of the studied glacial and non glacial river catchments are similar we used the records of average annual temperature and annual runoff to examine how these parameters and glacier melting influenced individual element fluxes to the oceans significant variations were found between the individual elements the dissolved fluxes of the more soluble elements such as mo sr and na are less affected by increasing temperature and runoff than the insoluble nutrients and trace elements including fe p and al this variation between the elements tends to be more pronounced for the glacial compared to the non glacial rivers these observations are interpreted to stem from the stronger solubility control on the concentrations of the insoluble elements such that they are less affected by dilution the dilution of the soluble elements by increasing discharge in the glacial rivers is enhanced by a relatively low amount of water rock interaction increased runoff due to glacial melting tend to be collected rapidly into river channels limiting water rock interaction it was found that the climate effect on particle transport from the glacial rivers is far higher than all other measured fluxes this observation together with the finding that the flux to the oceans of biolimiting elements such as p and fe is dominated by particulates suggests that particulate transport by melting glaciers have a relatively strong effect on the feedback between continental weathering atmospheric chemistry and climate regulation over geologic time

role of river suspended material in the global carbon cycle the reaction of ca derived from silicate weathering with co2 in the world s oceans to form carbonate minerals is a critical step in long term climate moderation ca is delivered to the oceans primarily via rivers where it is transported either as dissolved species or within suspended material the relative importance for climate moderation of riverine dissolved ca vs suspended ca transport stems from the total ca flux and its climate dependence data in the literature suggest that within uncertainty global riverine dissolved ca flux is equal to suspended material ca flux to determine how these fluxes depend on temperature and rainfall a 40 yr field study was performed on 4 catchments

mechanisms for chemostatic behavior in catchments implications for co2 consumption by mineral weathering a r t i c l e i n f o article history concentrations of weathering products in streams often show relatively little variation compared to changes in discharge both at event and annual scales in this study several hypothesized mechanisms for this chemostatic behavior were evaluated and the potential for those mechanisms to in uence relations between climate weathering uxes and co2 consumption via mineral weathering was assessed data from loch vale an alpine catchment in the colorado rocky mountains indicates that cation exchange and seasonal precipitation and dissolution of amorphous or poorly crystalline aluminosilicates are important processes that help regulate solute concentrations in the stream however those processes have no direct effect on co2 consumption in catchments hydrograph separation analyses indicate that old water stored in the subsurface over the winter accounts for about one quarter of annual stream ow and almost one half of annual uxes of na and sio2 in the stream thus ushing of old water by new water snowmelt is an important component of chemostatic behavior hydrologic ushing of subsurface materials further induces chemostatic behavior by reducing mineral saturation indices and increasing reactive mineral surface area which stimulate mineral weathering rates co2 consumption by carbonic acid mediated mineral weathering was quanti ed using mass balance calculations results indicated that silicate mineral weathering was responsible for approximately two thirds of annual co2 consumption and carbonate weathering was responsible for the remaining one third co2 consumption was strongly dependent on annual precipitation and temperature these relations were captured in a simple statistical model that accounted for 71 of the annual variation in co2 consumption via mineral weathering in loch vale published by elsevier b v

an optical age chronology of late pleistocene fluvial deposits in the northern lower mississippi valley the lower mississippi valley lmv contains many large braided channel belts that are preserved west of the holocene floodplain previous efforts to establish geochronologic control on channel belt construction have been hindered by the lack of organic material for radiocarbon dating luminescence techniques provide a burial date for the sediment itself and may prove useful in this context samples from three channel belts in the northern lmv were analyzed using the single aliquot regenerative technique on 90 125mm quartz optical ages 19 7 17 8 16 1 15 0 and 12 5 12 1 ka are consistent with geomorphic relationships and indicate that channel belts were formed in the late pleistocene under glacial conditions these optical ages provide the first detailed chronology of lmv channel belt formation and are the first step towards developing a chronology for the entire lmv r 2003 elsevier science ltd all rights reserved

multiple late holocene earthquakes along the reelfoot fault central new madrid seismic zone the reelfoot fault is an east vergent reverse fault underlying the lake county uplift a low amplitude late holocene anticline bordered on the east by the 32 km long reelfoot scarp fluvial deposits across the scarp define an 8 m high east facing monocline most near surface deformation along the scarp is accommodated via folding rather than faulting we interpret the scarp as a fault propagation fold developed over a wcst dipping reverse fault interpreted from shallow seismic reflection data trench exposurcs provide evidence for three episodes of deformation along the reelfoot fault within thc past approximately 2400 years between a d 780 and 1000 between a d 1260 and 1650 and during a d 1812 our best estimate of the average recurrence interval for deformation along the scarp is 400 500 years each episode of deformation had a slightly different style the third most recent event produced a small graben a few tens of centimeters deep in the hanging wall of the reverse fault the second most recent earthquake produced about 1 3 m of throw in the graben as well as folding along the updip projection of the reverse fault and development of the scarp thesc relations suggest that graben development increased through time concomitant with growth of the monocline or that the events are of different magnitude the 1811 1812 episode of deformation produced abundant liquefaction prominent folding of fluvial strata along the scarp and minor faulting in the graben

tracking the weathering of basalts on mars using lithium isotope fractionation models lithium li the lightest of the alkali elements has geochemical properties that include high aqueous solubility li is the most fluid mobile element and high relative abundance in basalt forming minerals values ranking between 0 2 and 12 ppm li isotopes are particularly subject to fractionation because the two stable isotopes of lithium 7li and 6li have a large relative mass difference 15 that results in significant fractionation between water and solid phases the extent of li isotope fractionation during aqueous alteration of basalt depends on the dissolution rate of primary minerals the source of li and on the precipitation kinetics leading to formation of secondary phases consequently a detailed analysis of li isotopic ratios in both solution and secondary mineral lattices could provide clues about past martian weathering conditions including weathering extent temperature ph supersaturation and evaporation rate of the initial solutions in contact with basalt rocks in this paper we discuss ways in which martian aqueous processes could have lead to li isotope fractionation we show that li isotopic data obtained by future exploration of mars could be relevant to highlighting different processes of li isotopic fractionation in the past and therefore to understanding basalt weathering and environmental conditions early in the planet s history

direct evidence of the feedback between climate and weathering long term climate moderation is commonly attributed to chemical weathering the higher the temperature and precipitation the faster the weathering rate weathering releases divalent cations to the

reconciling short recurrence intervals with minor deformation in the new madrid seismic zone at least three great earthquakes occurred in the new madrid seismic zone in 1811 and 1812 estimates of present day strain rates suggest that such events may have a repeat time of 1000 years or less paleoseismological data also indicate that earthquakes large enough to cause soil liquefaction have occurred several times in the past 5000 years however pervasive crustal deformation expected from such a high frequency of large earthquakes is not observed this suggests that the seismic zone is a young feature possibly as young as several tens of thousands of years old and no more than a few million years old

erosional and climatic effects on long term chemical weathering rates in granitic landscapes spanning diverse climate regimes abstract we used cosmogenic nuclide and geochemical mass balance methods to measure long term rates of chemical weathering and total denudation in granitic landscapes in diverse climatic regimes our 42 study sites encompass widely varying climatic and erosional regimes with mean annual temperatures ranging from 2 to 25 c average precipitation ranging from 22 to 420 cm year 1 and denudation rates ranging from 23 to 755 t km 2 year 1 long term chemical weathering rates range from 0 to 173 t km 2 year 1 in several cases exceeding the highest granitic weathering rates on record from previous work chemical weathering rates are highest at the sites with rapid denudation rates consistent with strong coupling between rates of chemical weathering and mineral supply from breakdown of rock a simple empirical relationship based on temperature precipitation and long term denudation rates explains 89 95 of the variation in long term weathering rates across our network of sites our analysis shows that for a given precipitation and temperature chemical weathering rates increase proportionally with fresh material supply rates we refer to this as supply limited weathering in which fresh material is chemically depleted to roughly the same degree regardless of its rate of supply from breakdown of rock the temperature sensitivity of chemical weathering rates is two to four times smaller than what one would expect from laboratory measurements of activation energies for feldspar weathering and previous inter comparisons of catchment mass balance data from the field our results suggest that climate change feedbacks between temperature and silicate weathering rates may be weaker than previously thought at least in actively eroding unglaciated terrain similar to our study sites to the extent that chemical weathering rates are supply limited in mountainous landscapes factors that regulate rates of mineral supply from erosion such as tectonic uplift may lead to significant fluctuations in global climate over the long term

earthquake size as a function of fault slip rate abstract estimates of the potential size of earthquakes on mapped active faults are generally based on regressions of earthquake magnitude m w versus length l of fault rupture for historical earthqukes the fault slip rate s has been ignored in formal prediction equations but more accurate predictions of future earthquake magnitudes on mapped faults may be obtained when it is included a least squares regression for a data set of 43 earthquakes occurring on faults for which slip rates are reported shows m w 5 12 1 16 log l 0 20 log s where l is in units of km and s is in units of mm yr the result indicates that the largest earthquakes will occur on the slowest slipping faults if the rupture length is held constant

steady as a rock biogeomorphic influence of nurse rocks and slope processes on kūpaoa dubautia menziesii shrubs in haleakalā crater maui hawai i abstract this study examines biogeomorphic interactions between nurse rocks slope processes and 300 k paoa dubautia menziesii shrubs in haleakal crater maui hawai i research objectives were to assess the association of k paoa with substrates upslope and downslope of plants and proximity to the closest rock uphill contrast shrub substrate relationships with site frequency of sediment types measure surface soil shear strength and compressibility on 50 paired locations near boulders and investigate the aggregation characteristics and spatial patterns of k paoa in relation to rock and substrate variation data analyzed came from three 100 plant surveys at 3 sites a plant census at 2720 2975 m altitude and wandering quarter transects wqts across two areas 2610 2710 m ground sediment cover was estimated along four phototransects on these sites data for the three 100 plant surveys included substrate type outcrops blocks cobbles pebbles exposed soil organic litter upslope from each plant and distance to the largest rock upslope the two surveys examined along wqts included substrate type found downslope from k paoa plant height plant diameters across and along the slope and distance between successively censused plants most plants grew downslope of nurse rocks 74 were adjacent to blocks or outcrops and 17 near cobbles plants showed avoidance for finer substrates only 5 3 and 2 7 grew on near bare soils and pebbles respectively about 92 of k paoa were 10 cm downslope of rocks 89 grew 2 cm away and 83 in direct contact with a rock some seedlings also grew on pukiawe leptecophylla tameiameiae nurse plants several stable rock microsites protected plants from disturbance by slope processes causing debris shift site sediments were significantly finer than substrates near plants shrubs grew preferentially adjacent to boulders 20 cm wide which were more common near plants than across sites soils downslope of 50 boulders mean 41 3 cm showed higher shear strength and compressibility than soils along rock sides these boulder dams stop descending debris steadily deflecting them toward rock sides whereas protected soils downslope of blocks are infrequently disturbed and develop into downslope elongated clast free fine earth flags k paoa were uniformly dispersed across slopes showing a single phase mosaic arrangement without apparent aggregation slopes where k paoa grows had a relatively uniform distribution of surface sediments observed k paoa patterns may have resulted from the array of microsites generated by surface rocks and sediments as shrubs simply responded to such spatial structure

chemical weathering of silicate rocks in karelia region and kola peninsula nw russia assessing the effect of rock composition wetlands and vegetation this study is aimed at assessing the effect of factors including lithology forest peatland coverage dissolved organic carbon and vegetation on chemical fluxes and concentrations of major elements in rivers the mean annual element concentrations and dissolved fluxes of acid and basic rock dominated watersheds of the karelia region and kola peninsula nw russia have been estimated from the chemical composition of river water samples collected in the summers of 1996 2000 and from annual discharge and chemical composition data of 16 watersheds collected from 1961 to 1975 the mean annual flux corrected for atmospheric input varies from 0 5 to 5 6 t km2 y and is dominated by alkali metals for the kola alkaline rocks and by calcium for the karelian granito gneisses the pure granitic and pure basaltic river chemical denudation rates in the baltic shield are 0 33 and 2 3 t km2 y respectively the cationic and silica fluxes of both granitic and basaltic watersheds are comparable with those of other boreal regions having similar runoff compositions and climate the cationic flux of the rivers is positively correlated with the basic rock fraction of the watershed whereas the dissolved organic carbon flux increases with the increasing peatland fraction the chemical composition of the river water is controlled by bedrock dissolution during dry periods and by plant litter degradation and washout of organic debris from the topsoil horizon during wet periods taking account the chemical composition of the plant litter and the biological turnover intensity it was estimated that the plant litter degradation in kola and karelia regions provides 10 40 of total annual dissolved riverine element flux

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

late pleistocene evolution of the lower mississippi river valley southern missouri to arkansas the mississippi river served as the principal conduit for meltwaters discharging from the southern margins of north american ice sheets the northern half of the mississippi river alluvial valley in missouri and arkansas can be subdivided into two distinct channel courses the western and eastern lowlands which are separated by crowleys ridge the eastern lowlands contain two entry points the bell city oran and thebes gaps the latter is a narrow bedrock gorge that contains the modern river this paper summarizes a model for evolution of channel courses in the western and eastern lowlands during the illinoian and wisconsin glacial stages for the western lowlands stratigraphic relations between loess units and subjacent fluvial deposits show that major continuous terrace surfaces or valley trains are illinoian or late wisconsin in age investigations of tributary valley fills further show the western lowlands were deeply incised during the early to middle wisconsin stage then aggraded during the late wisconsin stage to such an extent that tributary valleys were backfilled with slackwater deposits moreover analysis of loess thinning and fining trends shows that early to middle wisconsin roxana silt and the late wisconsin peoria loess covers on western lowlands valley trains were derived from deflation of valley trains in the eastern lowlands we conclude that the western lowlands were the primary mississippi river course during illinoian deglaciation but were abandoned shortly thereafter then episodically reoccupied during the late wisconsin stage for the eastern lowlands course valley trains of early to middle wisconsin age are not preserved with the exception of a small remnant where the mississippi river broke through a gap in the southern margins of crowleys ridge and reentered the western lowlands all valley trains in the eastern lowlands are late wisconsin age a series of discontinuous terrace surfaces in the bell city oran gap represent dissected remnants of the primary late wisconsin full glacial and early late glacial course of the mississippi river or combined mississippi and ohio rivers whereas younger continuous braided stream surfaces in the bell city oran and thebes gap courses represent valley trains of latest wisconsin and earliest holocene age hence the bell city oran gap was the primary course during the entire wisconsin stage and the thebes gap was permanently occupied in earliest holocene time as much as 5 m difference in elevation between successive late wisconsin terrace surfaces of the eastern lowlands indicates that valley trains were rapidly constructed incised and abandoned in response to fluctuations in the delivery of meltwater and outwash from the former ice margin moreover a variety of data indicates that deglacial meltwater floods were commonly of sufficient magnitude to overflow from the primary course in the bell city oran gap throughout the late wisconsin substage floodwaters overflowed into the western lowlands constructed a series of secondary valley trains and filled tributary valleys with slackwater deposits during the latest wisconsin stage perhaps in association with the drainage of glacial lake agassiz floodwaters overflowed into the western lowlands and broke through the thebes gap the charleston fan represents the initial deposits of the thebes gap course following deposition of a large crevasse splay at the western lowlands entrance that course was no longer active but flow was routed through the thebes gap during periods of high magnitude flooding until the bell city oran gap was abandoned and the thebes gap course was permanently occupied during earliest holocene time

weathering and the global carbon cycle geomorphological perspectives abstract the links between the weathering of silicate minerals the global carbon cycle and climate change are complex and involve a whole range of often inter related tectonic climatic geomorphological and biological factors silicate weathering rates are known to have varied through geological time and increasingly sophisticated models now link such variation to the long term carbon cycle and climate change in order to improve the modelling further one key research need is for more and better datasets on weathering and the factors that control it as a contribution to this we review the nature of the weathering carbon cycle system the sources of evidence used to understand it and the challenges that remain in quantifying the feedbacks between weathering and the global carbon cycle we propose that increased understanding of geomorphological diversity of landscapes and processes and especially the dynamic relationships between weathering and erosion will aid clearer portrayal of the links between weathering and the long term carbon cycle

preliminary studies on the geochemistry of the mahanadi river basin india water and suspended and bed sediments were collected during 1986 1987 for the two seasons and analysed to study the geochemistry of the mahanadi river basin which is one of the eight major drainage systems in india the water chemistry reflects the control exercised on weathering by the most abundant lithology namely the carbonates in the basin water composition is in equilibrium with dolomite kaolinite and chlorite xrd studies in suspended and bed sediments show the presence of dolomite kaolinite chlorite and minor quantities of montmorillonite the mahanadi annually delivers 15 74 106t of sediments to the bay of bengal which is high compared to its basin size the dissolved load dominates over physical load by a factor of 4 with 95 of the transport taking place in the monsoon season the basin is characterised by an erosion rate of 138 24 t km 2 yr 1 with a lowering rate of 0 31 mm yr 1 textural studies indicate that the bed sediments are relatively coarser grained than the suspended sediments due to reworking the sediments are finer downstream fe mn cu zn and pb concentrations in the sediments are higher compared to the other peninsular indian rivers eventhough mahanadi transports annually to the bay of bengal 10 of the total load by other indian rivers and its weathering in a complex geological terrain with rich mineral deposits controls to a larger extent the chemistry of the sediments in the bay of bengal

enhancement of cyanobacterial growth by riverine particulate material abstract particulate material plays a major role in the transport of sparingly soluble nutrients such as p and fe in natural surface waters microbes might gain access to these nutrients either indirectly through particulate dissolution or directly through microbial attack as such it seems reasonable to expect a link between the particulate material concentration and bacterial growth in natural surface waters to explore this link a series of microcosm growth experiments were performed in the presence of a typical freshwater cyanobacteria synechococcus sp grown in dilute bg 11 culture media in the presence and absence of basaltic and continental riverine particulate material results demonstrate that riverine particulates can increase bacterial biomass by 1 triggering bacterial growth in otherwise unfavourable conditions 2 increasing total maximum biomass concentration and 3 inducing bacteria growth during the post exponential phase these effects are found to be enhanced by increasing particulate concentration results also indicate a positive feedback between the nutrient release from the particulates and growing bacteria where dissolving particulates enhance bacterial growth which further promotes particulate dissolution by altering fluid ph microscopic analysis showed direct physical contact between particulates and cyanobacteria suggesting that bacteria attach directly on mineral surfaces to gain required nutrients furthermore frequent bacteria clusters were observed associated with particulates indicating an increasing aggregation of bacteria in the presence of particulate material which may facilitate a higher burial efficiency of organic carbon

elemental geochemistry of river sediments from the deccan traps india implications to sources of elements and their mobility during basalt water interaction abstract the abundances of several major na ca mg k al ti fe and minor elements sr ba mn p v cr ni cu and zn have been measured in twenty eight sediment samples from seventeen rivers belonging to the krishna headwaters and west flowing western ghat rivers all of which drain the deccan trap basalts these results particularly those of na ca mg and sr coupled with those reported for these elements in the dissolved phase of the same rivers provide an assessment of their relative mobility and insight into the nature of chemical weathering of deccan basalts the sediments are heavily depleted in na ca mg and sr relative to parent basalts by 60 the abundance ratios of these elements in sediments are roughly the same as those in basalts and in dissolved phases of these rivers das a krishnaswami s sarin m m pande k 2005a chemical weathering in the krishna basin and the western ghats of the deccan traps rates of basalt weathering and their controls geochim cosmochim acta 69 2067 2084 suggesting their near congruent release from basalts to water during chemical weathering both at present and over the residence time of particles in the basin k and ba show limited mobility relative to the above four elements the abundances of k and ba are strongly correlated most likely due to their association in rock forming minerals al fe and ti are generally enriched in the sediments resulting from the loss of more mobile elements from basalts and their association with secondary minerals formed during weathering the data also provide evidence for the fractionation of fe and al during chemical weathering and erosion fe and ti exhibit significant correlation attributable either to their co occurrence in weathering resistant minerals and or due to scavenging of ti by fe oxy hydroxides formed during weathering of basalts the abundance of minor elements mn p v cr ni cu and zn and their ratios with al show significant scatter by and large bracketing the range reported for deccan basalts the wide and overlapping ranges in the concentration of these elements and their ratios relative to al between sediments and basalts place severe constraints in assessing their mobility during weathering and erosion and in judging the role of anthropogenic sources in contributing to their abundances among the minor elements there is a hint that zn concentration may have been influenced by anthropogenic inputs mn v and ni analogous to ti show significant correlation with fe either due to their association with fe ti minerals or their sequestration by fe oxy hydroxides the mobility of elements during weathering and erosion of deccan basalts follows the trend na ca mg sr k ba al fe ti there is considerable spatial variability in the intensity of chemical weathering of deccan basalts the cia chemical index of alteration values for the sediment range between 42 and 92 compared to 37 for the deccan basalts the lower cia values are in sediments richer in caco 3 this may be a result of semi arid climate of the region which facilitate caco 3 precipitation and restrict chemical weathering erosion higher cia values are generally associated with sediments from basins with higher runoff modeling the major element composition of sediment and water yields estimates of particulate abundances in water these estimates agree with the measured values within a factor of 2 for some of the rivers whereas in some others they differ by more than a factor of 3 4 the use of sediment composition instead of that of the suspended matter spatial and temporal variations in sediment flux and non steady state erosion all can contribute to this discrepancy these factors also seem to be contributing to difference in co 2 consumption estimated from sediment composition and that reported based on dissolved phase data

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

sediment geochemistry and mineralogy from a glacial terrain river system in southwest iceland abstract the weathering of basalt has implications for the global carbon cycle on earth as well as for understanding sedimentary processes on other terrestrial bodies dominated by a basaltic crust e g mars but yet studies in mafic terrains are limited in comparison to their felsic counterpart our work details the compositional transformations resulting from the sedimentation process of first cycle sediments generated in a basalt dominated watershed of southwest iceland by sampling multiple sites along the hvita s river transport pathway and analyzing the sedimentology geochemistry and mineralogy this work provides a geologically integrated approach to understanding a fluvial source to sink system in mafic terrains environmental conditions such as climate hydrology and transport distance all influence the overall sediment composition and in response chemical weathering physical abrasion sorting transport and mixing are all sedimentary processes unraveled in the geochemical and mineralogical relationships of individual grain size bins chemical weathering initiates in the upper reaches of the watershed with the alteration of primary mafic phases to form secondary weathering products as sediment continues to move downstream the entire sediment suite becomes more altered and the extent of chemical weathering is intensified as evidenced by a higher abundance of clay minerals and glassy material fluvial sorting separates detritus by particle size and differentiates them by compositional gradients in geochemistry and mineralogy as grain size decreases mafic minerals become less abundant and the finer grain sizes are preferentially enriched in immature weathering minerals and mineraloids e g smectite clays and x ray amorphous phases this grain size trend is also correlated with elemental fractionation illustrated most notably by the clay size fraction

bootheel lineament a possible coseismic fault of the great new madrid earthquakes a remote sensing examination of the new madrid seismic zone has revealed a feature the bootheel lineament that may be the surface expression of one of the coseismic faults of the great new madrid earthquakes of 1811 and 1812 the lineament extends about 135 km in a north northeast direction through northeastern arkansas and southeastern missouri the morphology and pattern of the lineament suggest that it reflects a fault with strike slip displacement field data indicate that liquefied sand was injected along the lineament probably in 1811 and 1812 the bootheel lineament does not coincide with any of the major arms of new madrid seismicity possibly indicating that the current seismicity does not precisely reflect the faults that ruptured in 1811 and 1812

lithium magnesium and uranium isotope behaviour in the estuarine environment of basaltic islands this study presents major and trace elements and uranium u lithium li and magnesium mg isotope data for dissolved and suspended particulate material from estuaries draining dominantly basaltic terrains in iceland borgarfjor ur and sao miguel povoacao in the azores archipelago the concentrations of dissolved sodium na calcium ca potassium k sulphate so4 mg and li and 7li 6li and 26mg 24mg isotope ratios vary directly as a function of the dissolved chloride concentration cl indicating that these species are non reactive in these estuaries however u appears to be affected either by colloid flocculation or the formation of fe oxyhydroxides in borgarfjor ur the major element composition of suspended particulate material in the estuary at borgarfjor ur shows that the detrital silicates delivered to the estuarine mixing zone are relatively unweathered accordingly the 26mg isotope composition of the suspended material is indistinguishable from that of the parent basalts however the 234u 238u activity ratios of the suspended material are significantly different from the parent basalt indicating rapid equilibration of the u isotopes between particles and seawater the li concentration and 7li isotope composition of the suspended load are also observed to increase with increasing cl consistent with ongoing weathering of detrital material and the formation of secondary minerals in seawater depending on the particle residence time in the estuary this process could remove as much as 15 25 of the global riverine input of li to the ocean

rock fragments in top soils significance and processes this introductory paper reviews various aspects of rock fragments in top soils such information is required for various reasons and in particular for predicting the impact of climatic or landuse changes on the response of these soils particular attention is paid to the definition and measurement of rock fragment content in top soils the density of soils containing rock fragments the spatial distribution and movement of rock fragments in top soils the effects of rock fragments on some key hydrological processes thermal properties of top soils physical soil degradation soil erosion and soil productivity

influence of substrate on the distribution of the hawaiian silversword argyroxiphium sandwicense dc in haleakala maui hi the spatial patterns of the hawaiian silversword argyroxiphium sandwicense dc were studied in haleakala maui hi the silversword is a giant rosette plant nearly brought to extinction by human impact and goat browsing during the 1920s but stern protection has resulted in the resurgence of plant populations silversword regeneration is occurring vigorously in soils with surficial layers of volcaniclastic fragments ten sites with sizable silversword populations and the associated substrates were examined in haleakala s crater between 2175 and 2755 m at each site the population structure of 100 plants was determined along wandering quarter transects which limit sampling bias substrates where rosettes were rooted and the size of the biggest stone fragments upslope and downslope from the plant s base were determined volcaniclastic substrates were examined with photographs along 12 m long transverse transects fine debris samples gravel and pebbles were analyzed by mechanical sifting of surficial fragments gathered from 15 15 cm miniplots volcaniclastic fragments in silversword areas have different sources i most were ejected during eruptions yielding pyroclastic materials ash to blocks that built cinder cones on haleakala s crater ii on steep slopes weathering of olivine alkali basalt outcrops and subsequent mass wasting of rock fragments contributed a mantle of clasts to slopes below iii on some cinder cones welded spatter was produced during late eruptive stages this coalesced into ruff like agglutinate layers around crater rims called pohaku o hanalei wreath of stones agglutinate deposits weather gradually supplying clasts that roll downhill and accumulate on cone flanks iv on weathered aa lava flows stone fragments and rocky crags abound along eroding lava flow ridges associated with vegetation but the intervening troughs covered with fine ash and cinder remain bare silversword population structures indicate healthy regeneration all populations display a typical pattern of decreasing silversword numbers with increasing size age nearly 65 of the rosettes are rooted near cobbles 5 10 cm long or pebbles 2 5 5 cm and 23 grow at the base of blocks 10 cm or outcrops 9 of the plants are on gravel 2 5 cm but only 1 have germinated on sandy soil without granules or stones 2 of the silverswords grow on organic litter of dead rosettes plants on six sites showed noticeable differences in clast size between their upslope and downslope sides particles are significantly larger upslope from rosettes this suggests that successful seedlings germinate below clasts which deflect finer downslope moving sediment thus protecting young plants from burial by descending debris statistical tests indicate a few blocks above plants may have been stopped by adult rosettes such a relationship underscores the dynamic nature of steep cinder and rubble talus slopes regularly affected by dry debris slides frost creep and other mass wasting processes slope instability is also evinced by i common bending and deformation of silversword roots particularly in seedlings which trail upslope ii pronounced downhill tilting and asymmetry of tall rosettes on steep gradients iii presence of accumulated fine debris steps 9 9 13 8 cm thick upslope from plants and blocks iv ubiquitous fine earth flags exposed below embedded blocks which intercept descending debris and deflect it laterally v widespread miniature sorted stripes

interdecadal patterns of total sediment yield from a montane catchment southern coast mountains british columbia canada article i nfo we reconstruct sediment yield for a mountain watershed of western canada since the mid twentieth century from studies of annually laminated lake sediments delta progradation and solute transfer total yield averaged 320 40 mg km 2 a 1 and comprised 35 suspended load 50 bedload and 15 dissolved load ratios between the individual yield components varied approximately threefold at interannual timescales because of significant variability in the suspended and bedload fractions asynchronous flux in suspended and bedload fractions through time arise from differences in sediment availability and transitory sediment storage in the channel periods of elevated yield coincide with rapid glacier recession an extreme rainstorm and a landslide our results indicate that in montane environments extrapolation from even decade long monitoring programs may lead to biased projections of long term yield and delivery mode proportions if variations in sediment supply and catchment response to hydroclimatic and geomorphic controls are not considered

implications of fault slip rates and earthquake recurrence models to probabilistic seismic hazard estimates abstract increasingly fault slip rates are being used to constrain earthquake recurrence relationships for site specific probabilistic seismic hazard ground motion assessments this paper shows the sensitivity of seismic hazard assessments to variations in recurrence models and parameters that incorporate fault slip rates two models are considered to describe the partitioning of the slip rate or seismic moment rate into various magnitude earthquakes an exponential magnitude distribution and a characteristic earthquake distribution assuming an exponential distribution the activity rate n m 0 is constrained by the upper bound magnitude m u the b value for the region and the fault slip rate s for a given s variations in m u and b value have significant effects on recurrence and computed hazard depending on whether the assumption is made that the seismicity rate is constant or the moment rate is constant there is increasing evidence that the characteristic earthquake model is more appropriate for individual faults than the exponential magnitude distribution based on seismicity data from areas having repeated large earthquakes a generalized recurrence density function is developed and the resulting recurrence relationship requires only m u b value and s a comparison of the recurrence relationships from this model with the historical seismicity and paleoseismicity data on the wasatch and san andreas faults shows a good match the computed hazard based on the characteristic earthquake model differs from that obtained for the exponential model as a function of the fault to site distance and the acceleration level one check on the recurrence models using slip rate is to compare over large regions activity rates based on seismicity data and slip rate data such a comparison in the western transverse ranges shows a reasonable match for both the exponential and characteristic earthquake models in the moderate to large magnitude range

enhanced dissolution of basaltic glass in brackish waters impact on biogeochemical cycles in order to better constrain the geochemical budget of si in the ocean and potentially other elements released by the dissolution of silicates the alteration of riverine particulate material in estuaries and seawater needs to be estimated for this a series of alteration experiments of basaltic glass were performed at various degrees of salinity from 0 to 3 5 g l 1 in far from equilibrium conditions the solution used is a filtered natural seawater standard from the atlantic ocean the forward dissolution rates increase from 2 1 10 7 molsim 2s 1 s 0 gl 1 to 7 7 10 7 molsim 2s 1 s 3 5 gl 1 at 90 c and were extrapolated at 16 c from 2 9 10 10 molsim 2s 1 at s 0 gl 1 to 1 1 10 9 molsim 2s 1 at s 3 5 gl 1 this positive relationship between glass dissolution rate and salinity degree is consistent with published investigations concerning the role of specific cations and ligands present in seawater which can promote dissolution at the glass surface these results illustrate the potential of river basaltic glass particles to dissolve quickly in the water column after entering into the brackish waters of estuaries and before sinking on continental margins based on these dissolution rates and on assumptions on the particulate solid flux of fresh basaltic glass exported by rivers towards the ocean the corresponding flux of dissolved si is estimated to range between 2 and 8 1012 molsiyr 1 this is of the same order of magnitude as the estimated river dissolved si flux which represents therefore a significant input of si into the ocean additionally if the glass dissolution process remains congruent during the residence time of suspended particles into the water column the k flux to the ocean could also be significantly affected

chemical weathering and associated co2 consumption in six major river basins south korea abstract we report the chemical strontium sr and sulfur s isotopic compositions of water samples collected from six major south korean rivers to investigate seasonal and spatial variations in water chemistry and to estimate the chemical weathering rates and associated co 2 consumption overall the chemical compositions of river water exhibited significant temporal and spatial variations the magnitude of which varied depending on river size and geology the 87 sr 86 sr ratios and 34 s values of the rivers varied only spatially in close relation to basin lithology a mass balance calculation indicated that the dissolved loads of the six rivers were controlled by atmospheric 4 3 18 4 anthropogenic 6 0 27 2 and chemical weathering inputs 66 1 83 3 the average rates of carbonate weathering by sulfuric scw and carbonic acids ccw and silicate weathering by sulfuric ssw and carbonic acids csw were 4 50 and 11 0 t km 2 yr and 5 77 and 10 8 t km 2 yr respectively the associated mean co 2 consumption rates by ccw and csw were 312 10 3 and 471 10 3 mol km 2 yr respectively the calculated chemical weathering rates were closely related to runoff and the associated co 2 consumption rates tended to be higher in summer than in winter this study highlights the role of sulfuric acid in chemical weathering suggesting that it should be carefully considered in studies of co 2 consumption rate

biogeomorphological influence of slope processes and sedimentology on vascular talus vegetation in the southern cascades california abstract the vascular vegetation of alpine talus slopes between 2035 and 3095 m altitude was studied at lassen volcanic national park california in the cascade range taluses show a diverse flora with 79 plant species growth forms include coniferous trees shrubs suffrutices herbs graminoids and ferns spatial patterns of plant distribution were studied along 40 point intercept transects plant cover was low 0 32 7 on all slopes spatially variable and showed no consistent trends sedimentological characteristics were determined by photosieving next to 1500 plants this census indicated preferential plant growth on blocks and cobbles with 43 2 and 23 3 of the plants growing on these stones respectively fewer specimens were rooted on pebbles 13 or on stone free gravel areas 20 5 growth forms displayed different substrate preferences 92 5 of the shrubs and 83 of the suffrutices colonized blocks or cobbles but only 57 2 of the herbs and 59 8 of the graminoids grew on large stones plants are associated with large clasts because 1 coarse talus is more stable than fine sediment areas which are more frequently disturbed by various geomorphic processes and 2 large stones help conserve substrate water beneath them while moisture quickly evaporates from fine debris root patterns were studied for 30 plant species 10 specimens for each species were excavated and inspected and several root growth ratios calculated all species exhibited pronounced root asymmetry as roots for most plants grew upslope from their shoot base for 23 species all specimens had 100 of their roots growing upslope for the other 7 species 92 2 99 3 of below ground biomass extended uphill this uneven root distribution is ascribed to continual substrate instability and resulting talus shift as cascading debris progressively buries roots and stems plants are gradually pushed and or stretched downhill various disturbance events affect root development slope erosion following rubble removal often exposes plant roots debris deposition can completely bury plants some may survive sedimentation producing new shoots that grow through accumulated debris shrubs may propagate by layering as adventitious roots develop along buried stems or produce new clones along their roots slope processes may damage and transport plant pieces downhill some species can sprout from severed displaced root or stem fragments vegetation interacts with several geomorphic processes including debris flows grain flows rockfall snow avalanches frost creep and runoff larger plants may alter local patterns of debris movement and deposition damming cascading debris on their upslope side and deflecting sediments laterally to plant margins where they form narrow elongated stone stripes

natural controls of fluvial denudation rates in major world drainage basins we present a new compilation of estimates of modern rates of mechanical and chemical denudation for externally drained basins exceeding 5 105 km2 in area these estimates are based on sediment and solute load data selected in order to represent natural rates as far as possible chemical denudation rates have been calculated by deducting the nondenudational component of solute load mechanical denudation rates range from 1 mm kyr 1 for the st lawrence and dnepr basins to 670 mm kyr 1 for the brahmaputra basin chemical denudation rates vary from 1 mm kyr 1 kolyma niger nile and rio grande basins to 27 mm kyr 1 chiang jiang basin the kolyma basin has the lowest 4 mm kyr 1 and the brahmaputra basin the highest overall rate of denudation 688 mm kyr 1 relationships between denudation rates and a range of morphometric hydrologic and climatic variables are investigated through correlation and regression analysis morphometric variables such as mean local relief are accurately calculated for large basins for the first time by using the national geophysical data center 10 minute topographic database variables expressing basin relief characteristics and runoff are found to be most strongly associated with both mechanical and chemical denudation rates with more than 60 of the variance in total denudation being accounted for by basin relief ratio and runoff basin area runoff variability and mean temperature however are only weakly associated with rates of denudation although direct comparisons cannot be made it appears that rates of basin denudation derived from present day mass flux estimates are not overall significantly different from estimates of long term rates based on sediment volume and thermochronologic data it therefore appears that the key factors identified as controlling denudation rates here are also applicable to the geological time spans relevant to the interaction between tectonic and denudational processes

role of river suspended material in the global carbon cycle comment and reply comment gislason et al 2006 1 make a claim that would significantly change our understanding of the long term carbon cycle they argue that reaction of basalt glass in seawater especially in what they call the fluidized bed reactors in the delta environment constitutes a significant

use of liquefaction induced features for paleoseismic analysis an overview of how seismic liquefaction features can be distinguished from other features and how their regional distribution and properties of source sediment can be used to infer the location and strength of holocene paleo earthquakes abstract liquefaction features can be used in many field settings to estimate the recurrence interval and magnitude of strong earthquakes through much of the holocene these features include dikes craters vented sand sills and laterally spreading landslides the relatively high seismic shaking level required for their formation makes them particularly valuable as records of strong paleo earthquakes this state of the art summary for using liquefaction induced features for paleoseismic interpretation and analysis takes into account both geological and geotechnical engineering perspectives the driving mechanism for formation of the features is primarily the increased pore water pressure associated with liquefaction of sand rich sediment the role of this mechanism is often supplemented greatly by the direct action of seismic shaking at the ground surface which strains and breaks the clay rich cap that lies immediately above the sediment that liquefied discussed in the text are the processes involved in formation of the features as well as their morphology and characteristics in field settings whether liquefaction occurs is controlled mainly by sediment grain size sediment packing depth to the water table and strength and duration of seismic shaking formation of recognizable features in the field generally requires a low permeability cap above the sediment that liquefied field manifestations are controlled largely by the severity of liquefaction and the thickness and properties of the low permeability cap criteria are presented for determining whether observed sediment deformation in the field originated by seismically induced liquefaction these criteria have been developed mainly by observing historic effects of liquefaction in varied field settings the most important criterion is that a seismic liquefaction origin requires widespread regional development of features around a core area where the effects are most severe in addition the features must have a morphology that is consistent with a very sudden application of a large hydraulic force this article discusses case studies in widely separated and different geological settings coastal south carolina the new madrid seismic zone the wabash valley seismic zone and coastal washington state these studies encompass most of the range of settings and the types of liquefaction induced features likely to be encountered anywhere the case studies describe the observed features and the logic for assigning a seismic liquefaction origin to them also discussed are some types of sediment deformations that can be misinterpreted as having a seismic origin two independent methods for estimating prehistoric magnitude are discussed briefly one method is based on determination of the maximum distance from the epicenter over which liquefaction induced effects have formed the other method is based on use of geotechnical engineering techniques at sites of marginal liquefaction in order to bracket the peak accelerations as a function of epicentral distance these accelerations can then be compared with predictions from seismological models

temperature dependence of silicate weathering in nature how strong a negative feedback on long term accumulation of atmospheric co2 and global greenhouse warming estimation of the temperature dependence of natural feldspar weathering in two catchments at different elevations yields an apparent arrhenius activation energy of 18 4 kcal mol 77 0 kj mol much higher than most laboratory values this finding supports recent suggestions that hydrolytic weathering of silicate minerals may consume carbonic acid and thereby remove atmospheric carbon dioxide more rapidly with increasing temperature than previously thought this result provides a stronger negative feedback on long term greenhouse warming than has been assumed in most models of global carbon cycling the present estimate was determined from the ratio of feldspar weathering rates determined by geochemical mass balance in the southern blue ridge mountains of north carolina united states temperature a function of elevation is the only factor that differs between the two catchments parent rock type aspect hillslope hydrology and vegetation type and successional stage are the same in both

development of an osl chronology for late pleistocene channel belts in the lower mississippi valley usa abstract the broad alluvial valley of the lower mississippi river contains large channel belts for which age control has been limited by the lack of organic material for radiocarbon dating and deposit ages greater than the limit of radiocarbon in order to produce a detailed chronology of fluvial evolution samples for optical dating were collected from late pleistocene channel belt deposits quartz sand was analyzed using the coarse grained single aliquot regenerative dose sar technique samples showed little evidence of partial bleaching and optical ages are for the most part consistent with the available radiocarbon and relative age constraints optical ages range from 85 to 11 ka and along with geomorphic and stratigraphic relationships indicate that the mississippi river was meandering during the end of the last interglacial 85 83 ka and switched to a braided regime by 64 50 ka during initial marine oxygen isotope stage ois 4 3 glaciation of the upper mississippi drainage basin the mississippi river switched back to a meandering regime after formation of the youngest braid belt at 11 ka the 69 optical ages presented here provide the first detailed chronology of lower mississippi valley braid belt and pleistocene meander belt formation and provide an example of the utility of optical dating in fluvial settings where material for radiocarbon dating is scarce

geoarchaeological evidence of strong prehistoric earthquakes in the new madrid missouri seismic zone sand blows and fissures that cover 10 500 km sup 2 in northeastern arkansas and southeastern missouri attest to the severity of the 1811 1812 earthquake series in the new madrid seismic zone however except for one occurence near new madrid missouri the region has been devoid of any evidence of other major shocks for at least 1 3 ka prior to 1811 and possibly for 9 ka stratigraphic relations and radiocarbon dating at a recently excavated archaeological site near east prairie missouri have revealed liquifaction phenomena attributable to a shock dated to within about 100 yr prior to a d 539 and a probable second one dated between about a d 539 and 991

seasonal and annual variations of surface water chemistry solute fluxes and chemical denudation in a steep and glacier fed mountain catchment in western norway erdalen nordfjord abstract conducted during an investigation period of six full years 2004 2010 this study focuses on inter and intra annual temporal variations of surface water chemistry solute fluxes solute yields and chemical denudation in a steep cold climate and glacier fed drainage basin system in the fjord landscape of western norway the selected erdalen drainage basin 79 5 km2 is considered a typical valley system of the nordfjord region in western norway and is connected to the jostedalsbreen ice cap through two outlet glaciers the mean annual chemical denudation rate in erdalen is 6631 kg km 2 yr 1 which is of a similar range of magnitude for annual chemical denudation rates as a number of other cold regions catchments worldwide inter and intra annual temporal variations of surface water chemistry solute gross concentrations solute gross yields and chemical denudation rates are clearly determined by the combined effects of inter and intra annual temporal variations of precipitation solar radiation and air temperature intra annual temporal variations of surface water total dissolved solids tds values reflect the dilution of base flow from the drainage basin by i thermally controlled snowmelt in spring april june ii thermally determined glacier melt in summer july august and iii more frequent and more intense rainfall events in autumn september november the highest monthly solute gross yields over the year comprising 43 of the total annual solute gross yield are recorded in the spring period three month period from april to june which is due to high runoff during spring snowmelt and comparably higher tds values than during major glacier melt in summer july august in autumn september november comparably high amounts of ion poor rainwater in combination with a fast surface drainage saturation overland flow of a significant share of rainwater during heavy rainfall events and lower air temperatures as well as lower solar radiation inputs lead to comparably lower tds values in surface water than are found in spring

modelling seismites with a digital shaking table abstract soft sediment deformation structures induced by seismically triggered liquefaction and or fluidization seismites have been reproduced with a digital shaking table we have used natural sediments with variable granulometric ranges clay silt and sand and an earthquake simulator that is able to reproduce real tridimensional seismograms acceleration and pore pressure recording allowed us to follow liquefaction and or fluidization processes in unconsolidated sediments during earthquakes different types of seismites were produced by variations in the tested sedimentary column

the surface area and reactivity of granitic soils i dissolution rates of primary minerals as a function of depth and age deduced from field observations surface area normalised dissolution rates of the primary minerals in two distinct granitic soils located in 1 the dartmoor national park england and 2 glen dye scotland were determined as a function of depth each soil was sampled to a depth of 1 m the maximum soil ages based on 14c analysis of the humin fraction of the soil are 15 600 and 4400 years for the dartmoor and glen dye soil profiles respectively the measured bet surface areas of the soil minerals are close to 5 m2 g in the b and c horizons but decrease to less than 1 m2 g close to the surface retrieved geometric surface area normalised mineral dissolution rates are most rapid at the surface and at the bedrock soil interface this behaviour is interpreted to stem from a combination of the approach to equilibrium of the soil waters with depth and more rapid dissolution rates of fresh versus weathered surfaces at the soil surface the relative mineral dissolution rate order is found to be quartz feldspar mica with quartz geometric surface area dissolution rates as fast as 2 6 to 4 1 10 13 mol m2 s as observed in a number of past studies field based rates obtained in this study are significantly slower than corresponding rates obtained from laboratory studies suggesting that these latter rates may not accurately describe the reactivity of primary minerals in soils

slow deformation and lower seismic hazard at the new madrid seismic zone global positioning system gps measurements across the new madrid seismic zone nmsz in the central united states show little if any motion these data are consistent with platewide continuous gps data away from the nmsz which show no motion within uncertainties both these data and the frequency magnitude relation for seismicity imply that had the largest shocks in the series of earthquakes that occurred in 1811 and 1812 been magnitude 8 their recurrence interval should well exceed 2500 years longer than has been assumed alternatively the largest 1811 and 1812 earthquakes and those in the paleoseismic record may have been much smaller than typically assumed hence the hazard posed by great earthquakes in the nmsz appears to be overestimated

variations in suspended and dissolved matter fluxes from glacial and non glacial catchments during a melt season at urumqi river eastern tianshan central asia abstract the effects of climatic conditions on the delivery patterns of suspended solid and dissolved matter are evaluated by examining their correlation with air temperature precipitation and runoff from glacial and non glacial catchments at the headwaters of urumqi river in eastern tianshan central asia the results show that the physical and chemical weathering fluxes 168 and 23 t km 2 yr 1 respectively associated with the glacial catchment are higher than those of the non glacial catchment 34 and 12 t km 2 yr 1 respectively significant linear correlations are found between river fluxes and air temperature in both catchments for each degree of temperature increase the runoff physical weathering flux and chemical weathering flux from the glacial catchment increase by 12 16 and 5 respectively on the other hand in the non glacial catchment these values are 9 13 and 15 respectively if the temperature is below 4 c the variations in runoff physical and chemical weathering fluxes are irregular when the temperature exceeds 4 c such a pattern for the non glacial catchment during the melt season may be due to the influence of multiple water sources in contrast the relation to precipitation is relatively weak in both catchments furthermore although the glacial catchment has a higher increasing rate of physical weathering flux in response to temperature increase than the non glacial catchment this is not the case for the chemical weathering flux suggesting that glaciers play an important role in the effect of air temperature change on physical weathering flux

controls on the major ion chemistry of the urumqi river tian shan people s republic of china abstract water and snow samples were collected in may of 1990 and 1992 in headwater basins and along a longitudinal transect of the urumqi river located in northwestern china surface waters were dominated by ca2 and hco3 at all sites maximum measured so42 concentrations in surface waters were 550 egl 1 and were balanced by ca2 and hco3 ph was slightly alkaline at all locations several independent analyses each concluded that the solute composition of surface waters was dominated by dissolution of rocks with rapid weathering kinetics such as calcite and dolomite preliminary analysis of stable sulfur ratios in headwater basins shows 34s values of 6 8 for snow and 3 3 for surface waters changes in the 34s value of surface waters with increasing basin area were variable suggesting changes in the stable sulfur ratios of source materials the large amounts of hco3 and base cations at all sites indicates that the urumqi river is not sensitive to acidification from atmospheric deposition

estimation of intraplate strain accumulation in the new madrid seismic zone from repeat gps surveys the new madrid seismic zone nmsz a region within the eastern portion of the north american plate where great earthquakes occurred in 1811 1812 provides a type example of large earthquakes within a relatively stable continental interior assessing the scale and causes of deformation in such regions as well estimation of the recurrence interval for the large earthquakes within them has long been recognized as an important but challenging issue for which the advent of space based geodesy provides an important new tool here we report initial results from two global positioning system gps surveys of a geodetic network spanning the new madrid seismic zone because the expected strain signal is small the data were analyzed in three different ways first site velocities were estimated and analyzed for spatial gradients parallel and perpendicular to the trend of the major strike slip faults inferred from seismicity this analysis suggests but does not require a few millimeters per year of right lateral shear across the southern portion of the seismic zone consistent with the earthquake focal mechanisms second we divided the network into near field subnetworks and found possibly significant shear associated with approximately e w shortening within the southern nmsz and possible n s shortening across the left step connecting the presumed strike slip faults third we compared the strain observed along individual baselines to that predicted from the results of earlier near field surveys which combined gps and triangulation data in the southern part of the seismic zone we found general agreement with the earlier study although our data suggest lower strain rates hence after only 2 years of measurements the gps data suggest but do not yet require detectable strain accumulation however given that great earthquakes occur in the area and that our results are reasonably consistent with the results of other geodetic studies using different data and with earthquake mechanisms it seems likely that we are seeing strain accumulation in the southern nmsz a simple interpretation of the data as showing about 3 to 5 mm yr 1 of right lateral fault parallel motion implies a 1000 to 3300 year recurrence for great earthquakes with 5 to 10 m slip assuming all the accumulating strain is released seismically this recurrence interval may be an underestimate if the observed strains are largely postseismic effects of the 1811 1812 earthquakes a possibility suggested by the observation that plate wide data show less motion across the nmsz future surveys should resolve this issue as the longer measurement spans yield more precise velocity estimates

the role of tephra covers on soil moisture conservation at haleakala s crater maui hawai i abstract the influence of tephra covers on soil water was studied in haleakala maui hawai i during two summers eight sites with tephra layers and silverswords argyroxiphium sandwicense dc were sampled at 2415 2755 m at each site eight paired sample sets were obtained in bare soils and under adjacent tephra at three depths tephra were sharply separated from underlying soils and showed prominent vertical stratification tephra clast size distribution was assessed by photosieving and on interstitial gravel samples stones included 45 6 cobbles 29 4 pebbles and 25 blocks moisture content increased with depth in both positions but soils below tephra had more water at all depths than exposed areas surface soils beneath tephra contained 83 more water than bare ground soils at 5 10 cm had 106 greater moisture under rocks but only 70 at 10 15 cm differences between plots were statistically significant p all soils were coarse with 20 gravel and 94 sand most fine material 0 063 mm was silt as clay content was negligible organic matter percentage was low 1 65 bulk density and porosity were associated with moisture variation both in tephra insulated and bare soils 80 of field moisture was statistically p

the fluvial geochemistry and denudation rate of the guayana shield in venezuela colombia and brazil abstract the guayana shield is composed of early to mid precambrian igneous and metamorphic basement rocks with a quartzitic platform cover the complete absence of limestones and evaporites allows a clear chemical expression in the stream data of the primary weathering of the basement in a humid tropical environment total erosion rates are extremely slow 10 m m y with equal contributions from the dissolved and suspended loads however the former is largely silica with ratios of si to total cation equivalents si tz ranging to in excess of three weathering is complete to kaolinite and gibbsite i e the environment is one of active laterisation with a penetration rate of the weathering front into the fresh substrate about twice the denudation rate in basins of relatively homogeneous lithology rb sr isochrons constructed from the river data agree with the whole rock ages from the drainages thus all the common refractory rb containing minerals k feldspar mica are completely dissolved the thick lateritic regolith that is accumulating as a result of this intense weathering is a common relict feature on other southern hemisphere shields in the absence of active tectonics or greatly accelerated mechanical erosion the weathering rates of these basement rocks must be quite insensitive to environmental change

paleoliquefaction evidence and periodicity of large prehistoric earthquakes in shillong plateau india abstract the tectonic setting and the occurrence of the great assam earthquake m 8 7 of 1897 in the shillong plateau succeeded by three great earthquakes 1905 1934 and 1950 in the adjoining himalayan frontal arc indicates the vulnerability of the shillong plateau to large earthquakes the lack of seismicity records of the region earlier than 100 years and data on the recurrence of damaging earthquakes led us to investigate the paleoseismicity of the shillong plateau our paleoseismic investigations in the meizoseismal area of the 1897 earthquake revealed well preserved liquefaction and deformed syndepositional features at 10 selected sites in the alluvial deposits along two north flowing tributaries of the brahmaputra river these features are 14c dated using associated organic samples as the liquefaction of sediments was an important feature of the 1897 earthquake we identified this seismic event and other large major prehistoric earthquakes through paleoliquefaction and other coseismic structural deformation at the investigated sites in addition to the 1897 event we provide geological evidence for at least three large seismic events two of them occurred during 1450 1650 and 700 1050 ad the third predates 600 ad the analysis of the 14c data suggests a return period of about 400 600 yr for the large earthquakes in the shillong plateau this finding is the first of its kind from the himalaya and adjoining region

predominant floodplain over mountain weathering of himalayan sediments ganga basin we present an extensive river sediment dataset covering the ganga basin from the himalayan front downstream to the ganga mainstream in bangladesh these sediments were mainly collected over several monsoon seasons and include depth profiles of suspended particles in the river water column mineral sorting is the first order control on the chemical composition of river sediments taking into account this variability we show that sediments become significantly depleted in mobile elements during their transit through the floodplain by comparing sediments sampled at the himalayan front with sediments from the ganga mainstream in bangladesh it is possible to budget weathering in the floodplain assuming a steady state weathering regime in the floodplain the weathering of himalayan sediments in the gangetic floodplain releases ca 189 92 10 9 and 69 22 10 9 mol yr of carbonate bound ca and mg to the dissolved load respectively silicate weathering releases 53 18 10 9 and 42 13 10 9 mol yr of na and k while the release of silicate mg and ca is substantially lower between ca 0 and 20 10 9 mol yr additionally we show that sediment hydration h2o is a sensitive tracer of silicate weathering that can be used in continental detrital environments such as the ganga basin both h2o content and the d h isotopic composition of sediments increases during floodplain transfer in response to mineral hydrolysis and neoformations associated to weathering reactions by comparing the chemical composition of river sediments across the floodplain with the composition of the eroded himalayan source rocks we suggest that the floodplain is the dominant location of silicate weathering for na k and h2o overall this work emphasizes the role of the gangetic floodplain in weathering himalayan sediments it also demonstrates how detrital sediments can be used as weathering tracers if mineralogical and chemical sorting effects are properly taken into account 2012 elsevier ltd all rights reserved

the chemical composition of rivers and snow affected by the 2014 2015 barðarbunga eruption iceland abstract the 2014 15 bar arbunga volcanic eruption was the largest in iceland for more than 200 years this eruption released into the atmosphere on average 60 000 tonnes day of so2 30 000 tonnes day of co2 and 500 tonnes day of hcl affecting the chemical composition of rain snow and surface water the interaction of these volcanic gases with natural waters decreases fluid ph and accelerates rock dissolution this leads to the enhanced release of elements including toxic metals such as aluminium to these waters river monitoring including spot and continuous osmotic sampling shows that although the water conductivity was relatively stable during the volcanic unrest the dissolution of volcanic gases increased the so4 f and cl concentrations of local surface waters by up to two orders of magnitude decreasing the carbon alkalinity in addition the concentration of sio2 ca mg na and trace metals rose considerably due to the water molten lava and hot solid lava interaction the presence of pristine lava and acidic gases increased the average chemical denudation rate calculated based on na flux within jokulsa a fjollum catchment by a factor of two compared to the background flux melted snow samples collected at the eruption site were characterised by a strong dependence of the ph on so4 f and cl and metal concentrations indicating that volcanic gases and aerosols acidified the snow protons balanced about half of the negatively charged anions the rest was balanced by water soluble salts and aerosols containing a variety of metals including al fe na ca and mg the concentrations of f al fe mn cd cu and pb in the snowmelt water surpassed drinking and surface water standards snowmelt river water mixing calculations indicate that low alkalinity surface waters such as numerous salmon rivers in east iceland will be more affected by polluted snowmelt waters than high alkalinity spring and glacier fed rivers