distributions and air sea fluxes of carbon dioxide in the western arctic ocean abstract the uptake of carbon dioxide co2 by the arctic ocean is most likely increasing because of the rapid sea ice retreat that lifted the barriers preventing gas exchange and light penetration for biological growth measurements of atmospheric and surface sea water partial pressure of co2 pco2 were conducted during the chinese national arctic research expedition chinare cruises from july to september in 2003 and 2008 the latitudinal distribution of pco2 along the 169 w transect showed a below atmopsheric pco2 level in most of the western arctic ocean with distinct regional differences from bering strait northward to the central acrctic ocean the average air sea co2 fluxes on the shelf and slope of the chukchi sea were 17 0 and 8 1 mmol m 2 d 1 respectively in the ice free zone the partially ice covered zone and the heavily ice covered zone of the canada basin the fluxes were 4 2 8 6 2 5 mmol m 2 d 1 respectively these rates are lower than other recent estimates our new results not only confirmed previous observations that most areas of the western arctic ocean were a co2 sink in general but they also revealed that the previously unsampled central basins were a moderate co2 sink analysis of controlling factors in different areas shows that pco2 in bering strait was influenced not only by the bering inflow waters but also by the high biological production however pco2 fluctuated sharply because of strong water mixing both laterally and vertically in the marginal ice zone chukchi sea pco2 was controlled by ice melt and biological production both of which would decrease pco2 onshore of the ice edge in the nearly ice free southern canada basin pco2 increasd latitudinally as a result of atmospheric co2 uptake due to intensive gas exchange increased temperature and decresed biological co2 uptake due to limited nutrient supply finally pco2 was moderately lower than the atmospheric value and was relatively stable under the ice sheet of the central arctic ocean in very high latitudes thus it appears that the arctic ocean has a strong potential capacity of absorbing atmospheric co2 in the future

rapid erosion of a small southern california beach fill abstract a winter storm eroded a small 160 000 m3 beach fill at torrey pines state beach in southern california the fill constructed in april 2001 was a 600 m long flat topped berm extending from a highway revetment seaward about 80 m terminating in a 2 m tall near vertical scarp the size distributions of the preexisting and fill beach sand were similar median 0 2 mm a total of 56 cross shore transects were surveyed between the revetment and 8 m water depth biweekly along 2 7 km of the beach centered on the fill area during summer and fall the incident significant wave heights measured 1 km offshore of the fill usually were below 1 m the scarp was not overtopped and the fill did not change greatly the beach face alongshore of the fill accreted consistent with the usual seasonal cycle in southern california during a storm 3 m significant wave height in late november erosion began when wave uprushes overtopped the scarp and reached the relatively flat elevated fill where the overwash flowed alongshore to initially small depressions that channeled the flow seawards the offshore flow rapidly deepened and widened the channels which maintained steep vertical faces and eroded by slumping thirty hours after the storm began the shoreward end of the eroded channels had retreated to the highway revetment leaving uneroded sand peninsulas protruding seawards 50 m from the revetment and elevated 1 75 m above the surrounding beach erosion of the beach adjacent to the fill was much less variable alongshore than within the fill region during the next few days the peninsulas eroded almost completely

quantitative analysis of insar digital elevation models for identification of areas with different tectonic activities in southern italy this work presents the results of a quantitative analysis of an interferometric sar insar digital elevation model dem obtained by the shuttle radar topography mission srtm the analysis aims to identify additional parameters to recognize areas in southern italy with different tectonic activities and behaviours the axial zone of the campania lucania apennine and the sila massif in calabria italy characterized by quite different evolutionary histories have been chosen as test areas sufficiently wide to validate observations on a sub regional scale at least geomorphological information on the shape of palaeosurfaces has been used to estimate uplift and or erosion amounts and rates palaeosurfaces are identified on the dem as regions with an altitude higher than 1000 m a s l and sub planar land surfaces dipping less than 6 information about the shape of palaeosurfaces during the first stage of uplift and before the tectonic induced block fragmentation has been extracted a fragmentation index has been computed for these erosional surfaces the first stage of this landscape evolution has been studied in terms of the geometric characteristics of fragmented blocks the last erosional stage has been recognized in terms of both geometric characteristics and fragmentation index of the sub horizontal land surfaces altitude and age of the palaeosurfaces referred to ancient base levels of the erosion have been used to estimate the erosional rate copyright 2008 john wiley and sons ltd

abnormal monsoon years and their control on erosion and sediment flux in the high arid northwest himalaya abstract the interplay between topography and indian summer monsoon circulation profoundly controls precipitation distribution sediment transport and river discharge along the southern himalayan mountain front shf the higher himalayas form a major orographic barrier that separates humid sectors to the south and arid regions to the north during the indian summer monsoon vortices transport moisture from the bay of bengal swirl along the shf to the northwest and cause heavy rainfall when colliding with the mountain front in the eastern and central parts of the himalaya precipitation measurements derived from passive microwave analysis ssm i show a strong gradient with high values at medium elevations and extensive penetration of moisture along major river valleys into the orogen the end of the monsoonal conveyer belt is near the sutlej valley in the nw himalaya where precipitation is lower and rainfall maxima move to lower elevations this region thus comprises a climatic transition zone that is very sensitive to changes in indian summer monsoon strength to constrain magnitude temporal and spatial distribution of precipitation we analyzed high resolution passive microwave data from the last decade and identified an abnormal monsoon year amy in 2002 during the 2002 amy violent rainstorms conquered orographic barriers and penetrated far into otherwise arid regions in the northwest himalaya at elevations in excess of 3 km asl while precipitation in these regions was significantly increased and triggered extensive erosional processes i e debris flows on sparsely vegetated steep hillslopes mean rainfall along the low to medium elevations was not significantly greater in magnitude this shift may thus play an important role in the overall sediment flux toward the himalayan foreland using extended precipitation and sediment flux records for the last century we show that these events have a decadal recurrence interval during the present day monsoon circulation hence episodically occurring amys control geomorphic processes primarily in the high elevation arid sectors of the orogen while annual recurring monsoonal rainfall distribution dominates erosion in the low to medium elevation parts along the shf

wavelet based regularization of the extracted topographic index from high resolution topography for hydro geomorphic applications high resolution topography e g 1 m digital elevation model dem from light detection and ranging lidar offers opportunity for accurate identification of topographic features of relevance for hydrologic and geomorphologic modelling yet the computation of some derived topographic properties such as the topographic index ti is characterized by daunting challenges that hamper the full exploration of topography based models particular problems for example arise when a distributed or semi distributed rainfall runoff model is applied to high resolution dems indeed the characteristic dependency between landscape resolution and the computed ti distribution results in the formation of un physical unconnected saturated zones which in turn cause unrealistic representations of rainfall runoff dynamics in this study we present a methodology based on a multi resolution wavelet transformation that by means of a soft thresholding scheme on the wavelet coefficients filters the noise of high resolution topography to construct regularized sets of locally smoother topography on which the ti is computed while the methodology needs a somewhat arbitrary definition of the wavelet coefficients threshold our study shows that when the information content entropy of the ti distribution is used as a filtering efficiency metric a critical threshold automatically emerges in the landscape reconstruction the methodology is demonstrated using 1 m lidar data for the elder creek river basin in california while the proposed case study uses a topmodel approach the methodology can be extended to different topography based models and is not limited to hydrological applications copyright 2012 john wiley sons ltd

biogenic sulfur emissions from the subantarctic and antarctic oceans measurements of the atmospheric distributions of dimethylsulfide dms sulfur dioxide so2 methanesulfonate msa non seasalt sulfate nss so42 and methylmercaptan mesh were made over the drake passage and the coastal and inshore waters west of the antarctic peninsula during the 1986 austral fall season dms concentrations were also measured in the surface ocean and vertical profiles were obtained at several locations in the inshore water areas surface seawater concentrations of dms were on the order of 2 nmol l 1 similar to values observed in temperate latitudes the vertical profiles showed maximum values at depths between 5 40 m dms concentrations in the atmosphere were near 4 nmol m 3 96 parts per trillion by volume pptv close to the global average for remote oceanic regions the sea to air flux of dms ranged between 1 5 mol m 2 d 1 with the highest values found in the open ocean areas the total sea to air flux of dms from the southern ocean is estimated to be 0 2 tmol yr 1 mesh was detected occasionally at concentrations up to 0 15 nmol m 3 3 6 pptv the average aerosol msa concentration 0 27 nmol m 3 was surprisingly high relative to the level of nss so42 0 31 nmol m 3 both compounds were found predominantly in fine particles the nss so42 values were extremely low comparable to winter values reported for the south pole so2 concentrations were also very low 0 45 nmol m 3 11 pptv consistent with the low levels of nss so42 the residence time of dms in the antarctic marine atmosphere is estimated to be about 2 3 days during clear weather and about 6 7 days during overcast conditions photooxidation of dms in the southern ocean atmosphere may lead to a higher yield of msa and a lower yield of so2 compared to other world ocean areas

influence of the drainage network identification method on geomorphological properties and hydrological response the influence of the method of identification of the drainage network on its geomorphological characteristics and on its hydrological response is analysed blue lines photo interpreted networks and networks generated from digital elevation models dems by an automatic algorithm are compared with field observations for two small alpine catchments the comparisons are carried out in quantitative terms by using several geomorphological indices and functions and by calculating the hydrological response of the networks as represented by their geomorphologic instantaneous unit hydrograph giuh the results show that the effect of the identification method on the geomorphological indices and on the hydrological response is significant and that the threshold area for channel initiation is not constant moreover the available data show a poor correlation between local slope and threshold area finally the influence of the threshold area on the shape of the giuh is larger when the residence time on the hillslopes is of the same order as the residence time in the network in the opposite case the variability of the flow velocity along the network seems to play an important role 1997 john wiley sons ltd

hazard assessment of rainfall induced landsliding in mexico abstract rainfall induced landsliding represents a major hazard in mexico about 200 municipalities in the states of puebla veracruz and hidalgo were affected by flooding and mass movement processes that resulted from a tropical depression from the atlantic ocean in october 1999 hundreds of slope failures were triggered by intense precipitation which in some localities reached 420 mm during a 24 h period according to official information 263 people died and 1 475 654 inhabitants were affected by flooding and landsliding rainfall event and cycle coefficient defined and the ratios between event and antecedent rainfalls respectively and the mean annual rainfall are summed to give a total coefficient for landslide triggering rainfalls in the sierra norte values for the total coefficient of 0 8 and 0 4 for beginning and end of the wet season respectively appear to be important in addition a hazard assessment was carried out through the development of a landslide susceptibility indicator this was elaborated by using aerial photographs integrating field observations and the coupling of slope instability analysis within a digital elevation model framework field validation indicated that this approach provides a good representation of shallow translational failures 81 of the observed landslides were satisfactorily predicted as potential unstable zones results suggested that this type of dem based hazard assessment can be extremely valuable not only after but also before any landslide related event so that disaster preparedness and planning could be adequately structured

beach nourishment effects on sand porosity variability abstract a standard assumption in coastal engineering is that the porosity of natural beach sand non cohesive is 40 however is this assumption correct for all beach sand this paper proposes an accurate and simplified method to assess changes in sand porosity after beach nourishment by means of in situ density surveys through a nuclear densimeter this novel application has been applied to different beaches in the southwest of spain according to the tidal range grain size and beach morphology in several terms general results show that sand porosities range from 25 6 to 43 4 after beach nourishment works this research can be considered a support tool in coastal engineering to find shifting sand volumes as a result of sand porosity variability after beach nourishment and later marine influence

spatial structures of stream and hillslope drainage networks following gully erosion after wildfire the drainage networks of catchment areas burned by wildfire were analysed at several scales the smallest scale 1 1000 m2 representative of hillslopes and the small scale 1000 m2 to 1 km2 representative of small catchments were characterized by the analysis of field measurements the large scale 1 1000 km2 representative of perennial stream networks was derived from a 30 m digital elevation model and analysed by computer analysis scaling laws used to describe large scale drainage networks could be extrapolated to the small scale but could not describe the smallest scale of drainage structures observed in the hillslope region the hillslope drainage network appears to have a second order effect that reduces the number of order 1 and order 2 streams predicted by the large scale channel structure this network comprises two spatial patterns of rills with width to depth ratios typically less than 10 one pattern is parallel rills draining nearly planar hillslope surfaces and the other pattern is three to six converging rills draining the critical source area uphill from an order 1 channel head the magnitude of this critical area depends on infiltration hillslope roughness and critical shear stress for erosion of sediment all of which can be substantially altered by wildfire order 1 and 2 streams were found to constitute the interface region which is altered by a disturbance like wildfire from subtle unchannelized drainages in unburned catchments to incised drainages these drainages are characterized by gullies also with width to depth ratios typically less than 10 in burned catchments the regions hillslope interface and channel had different drainage network structures to collect and transfer water and sediment copyright 2005 john wiley sons ltd

long term marine bedload segregation and sandy versus gravelly holocene shorelines in the eastern english channel abstract retreating cliffs comprising fringing gravel or sandy beaches line much of the english and french coasts in the eastern english channel locally gravel has formed significant barrier accumulations overlying thick finer grained deposits although sandy deposits are abundant on the bed of the eastern channel significant aeolian dunes are restricted to embayments on the west facing french coast between the somme estuary and cape gris nez these embayments show holocene continuity of deposition of relatively homogenous sand with the dunes overlying beach washover and estuarine sediments it is argued that the occurrence of gravelly shorelines or of sandy shorelines exhibiting significant aeolian dunes largely reflects a combination of three factors 1 the inherited coastal lithology and morphology characterised by soft rock cliffs with or without embayments that were potential holocene sediment sinks 2 coastal orientation relative to large scale tide and wind driven marine bedload segregation processes that operated during the holocene and have led to preferential sand concentrations in the eastern corner of the channel and possibly concomitant relative enrichment in nearshore gravel elsewhere 3 coastal orientation relative to the synoptic westerly wind field responsible for significant aeolian dune building where such sand concentrations occurred the only coast where these three conditions were met favourably for significant aeolian dune building is the west facing french coast north of the somme estuary which benefitted during the holocene from large scale eastward advection of sand from the bed of the channel this sand was concentrated along a well defined coast parallel transport pathway driven by tidal currents enhanced by coriolis forcing and especially by the coast orthogonal synoptic westerly winds as sea level rise slowed or stabilised following the middle holocene the sand was piled onshore in embayments to form aeolian dunes by these coast orthogonal winds leaving no scope for the formation of gravel shorelines this coastal sand transport pathway is still operational elsewhere the inherited coastal morphology and orientation in terms of both the coriolis effect and westerly wind forcing have not favoured similar large scale sand trapping in coastal sinks as a result the shorelines are characterised by retreating cliffs and fringing beaches with a few major gravel barriers formed in local downdrift sinks and comprising clasts reworked by storms from offshore gravel deposits on the bed of the channel and from cliff retreat the sharp change in facies from fine grained sediments to overlying gravel within these barriers may have been enhanced by sand depletion caused by the large scale holocene bedload segregation processes that operated in the eastern channel it is suggested that if the permanence of the present day 3 d morphology of the eastern english channel and the same hydrodynamic forcing notably the same wind field as during the holocene are accepted then the suggested model of coastal sedimentation involving preferential large scale drift of channel bed sand towards the north south oriented french coast north of the somme estuary would also predict permanent dominantly gravelly high sea level beach sedimentation on the opposite english coast

mapping of risk and susceptibility of shallow landslide in the city of sao paulo brazil abstract in the city of sao paulo where about 11 million people live landslides and flooding occur frequently especially during the summer these landslides cause the destruction of houses and urban equipment economic damage and the loss of lives the number of areas threatened by landslides has been increasing each year the objective of this article is to analyze the probability of risk and susceptibility to shallow landslides in the limoeiro river basin which is located at the head of the aricanduva river basin one of the main hydrographic basins in the city of sao paulo to map areas of risk we created a cadastral survey form to evaluate landslide risk in the field risk was categorized into four levels based on natural and anthropogenic factors r1 low risk r2 average risk r3 high risk and r4 very high risk to analyze susceptibility to shallow landslides we used the shalstab shallow landsliding stability mathematical model and calculated the distribution frequency df of the susceptibility classes for the entire basin finally we performed a joint analysis of the average risk concentration rc and risk potential rp we mapped 14 risk sectors containing approximately 685 at risk homes more than half of which presented a high r3 or very high r4 probability of risk to the population in the susceptibility map 41 of the area was classified as stable and 20 as unconditionally unstable although the latter category accounted a smaller proportion of the total area it contained a concentration rc of 41 of the mapped risk areas with a risk potential rp of 12 we found that the locations of areas predicted to be unstable by the model coincided with the risk areas mapped in the field this combination of methods can be applied to evaluate the risk of shallow landslides in densely populated areas and can assist public managers in defining areas that are unstable and inappropriate for occupation

morphometric indices as indicators of tectonic fluvial and karst processes in calcareous drainage basins south menorca island spain this study proposes using morphometric indices to discriminate the processes that shape calcareous drainage basins to illustrate this a dem of the southern part of menorca island migjorn was created and basin slope drainage density hypsometric curve and integral and the area occupied by open and closed dolines were extracted from it these indices show an important dependence on tectonics which govern the morphology of these drainage basins and encourage the predominance of karst and or fluvial processes in the different sectors the morphometric indices are clearly influenced by the geological migjorn structure a carbonate upper miocene reef platform gently folded as an asymmetrical anticline the hypsometric integral and curve discriminate the influence of tectonics and structure whilst the drainage density and the proportion of open dolines are associated with basins with more pronounced fluvial processes a cluster analysis based on these indices discriminated three sectors where different forms and processes are found in the western and eastern sectors rounded basins without major fractures predominate the basins slope at less than 5 and karst processes outweigh fluvial processes the central sector however has steeper slopes a clearly defined drainage system and a predominance of fluvial over karst processes greater uplift in this sector has facilitated the formation of elongated basins that follow the main fracture lines copyright 2007 john wiley sons ltd

susceptibility assessment of shallow landslides on oahu hawaii under extreme rainfall events abstract the deterministic stability index mapping sinmap model which integrates a mechanistic infinite slope stability model and a hydrological model was applied to assess susceptibility of slopes in 32 shallow landslide prone watersheds of the eastern to southern areas of oahu hawaii usa input to the model includes a 10 m digital elevation model dem an inventory of storm induced landslides that occurred from 1949 to 2006 and listings of soil strength and hydrological parameters including transmissivity and steady state recharge the study area of ca 384 km2 was divided into four calibration regions with different geotechnical and hydrological characteristics all parameter values were separately calibrated using observed landslides as references the study used a quasi dynamic scenario of soil wetness resulting from extreme daily rainfall events with a return period of 50 years the return period was based on almost 90 year long 1919 2007 daily rainfall records from 26 raingauge stations in the study area output of the sinmap model includes slope stability index distribution maps slope versus specific catchment area charts and statistical summaries for each region the sinmap model assessed susceptibility at the locations of all 226 observed shallow landslides and classified these susceptible areas as unstable about 55 of the study area was predicted as highly unstable highlighting a critical island problem the sinmap predictions were compared to an existing debris flow hazard map areas classified as unstable in the current study were classified as low to moderate and moderate to high debris flow hazard risks by the prior mapping the slope stability maps provided by this study will aid in explaining the causes of known landslides making emergency decisions and ultimately mitigating future landslide risks the maps may be further improved by incorporating heterogeneous and anisotropic soil properties and spatial and temporal variation of rainfalls as well as by improving the accuracy of the dem and the locations of shallow landslide initiation

field experiments of beach scarp erosion during oblique wave stormy conditions normandy france abstract a field based experimental study of beach scarp morphodynamic evolution was conducted on the shoreface of a macrotidal sandy beach subject to storms combined with spring tide events luc sur mer france both video and in situ measurements on an artificial berm are used to understand beach scarp evolution over one tide during stormy conditions image time stacks are used to analyze the swash action on the beach scarp and topographical data of the scarp are recorded with a terrestrial scanner laser to quantify the morphodynamic response of the beach scarp to wave action this work provides a new and unique dataset about beach scarp changes and berm morphology in particular under rising tide and oblique wind wave conditions during one stormy event the berm was completely destroyed however contrasting alongshore changes were measured during the erosive phase with different crest and foot scarp retreats and eroded volumes between the west and the east side of the berm the beach in front of the scarp also shows a contrasting residual evolution indicating an evident longshore sediment transport on the study area as a consequence of incident oblique wave conditions a strong connection between beach evolution and beach scarp changes is clearly identified the scarp erosion increases on the west side of the berm when the beach level is lowered and reduces when the beach surface rises on the east side the beach slope and foreshore elevation as a result of a longshore sediment transport between east and west profiles influence swash activity overall water depth and swash activity became progressively different along the scarp during the experiment swash measurements indicate that the presence of the beach scarp strongly influences the swash motion at high tide the reflection of the uprush on the scarp front induces a collision between the reflected backwash and the following uprush dynamic these collisions reduce and sometimes stop the motion of the following uprush reducing the incoming swash excursion consequently the scarp presence modifies the swash interaction that normally appears on a planar beach surface with a beach scarp the swash energy level is substantially attenuated and its spectrum is characterized by a large band the number of uprush impacts on the scarp front calculated from video images reaches about 25 per 5 min in spite of the swash energy attenuation due to swash swash interactions these impacts provoke the berm destruction in about two hours however the onshore migration of the swash zone induced by the rising tide appears to be important to explain scarp destruction compensating the attenuated swash activity due to backwash uprush interactions

channel initiation and the problem of landscape scale since the 1940s it has been proposed that landscape dissection into distinct valleys is limited by a threshold of channelization that sets a finite scale to the landscape this threshold is equal to the hillslope length that is just shorter than that necessary to support a channel head a field study supports this hypothesis by showing that an empirically defined topographic threshold associated with channel head locations also defines the border between essentially smooth undissected hillslopes and the valley bottoms to which they drain this finding contradicts assertions that landscapes are scale independent and suggests that landscape response to changes in climate or land use depends on the corresponding changes in the threshold of channelization

fractal scaling and power law landslide distribution in a micromodel of geomorphological evolution recent analyses of geographical data have shown that mountains can be well described in terms of fractals which raises the fundamental question about the mechanisms producing fractal surfaces in geomorphological evolution because the formation of mountain ranges takes place over an extremely long period of time direct observations of erosion mechanisms are hardly feasible therefore we expect that model experiments on the erosion of mountain ridges taking place on a limited time scale should contribute significantly to our understanding of the emergence of fractal structures in geomorphological phenomena during the watering of an initially smooth ridge made of a mixture of silica sand and earthy soil the surface evolves into a shape analogous to actual mountain profiles with self affine geometry for the exponents describing respectively the spatial and the temporal scaling of the surface width 0 78 0 05 and 0 8 0 06 have been obtained the former value is in a very good agreement with 0 8 0 1 calculated for genuine transect profiles the processes in our micromodel can be well described in terms of self organized criticality the system evolves into a critical state where surface roughening takes place due to power law distributed landslides

drainage basin responses to climate change recent investigations have shown that the extent of the channel network in some drainage basins is controlled by a threshold for overland flow erosion the sensitivity of such basins to climate change is analyzed using a physically based model of drainage basin evolution the golem model simulates basin evolution under the action of weathering processes hillslope transport and fluvial bedrock erosion and sediment transport results from perturbation analyses reveal that the nature and timescale of basin response depends on the direction of change an increase in runoff intensity or a decrease in vegetation cover will lead to a rapid expansion of the channel network with the resulting increase in sediment supply initially generating aggradation along the main network followed by downcutting as the sediment supply tapers off by contrast a decrease in runoff intensity or an increase in the erosion threshold will lead to a retraction of the active channel network and a much more gradual geomorphic response cyclic changes in runoff intensity are shown to produce aggradational degradational cycles that resemble those observed in the field cyclic variations in runoff also lead to highly punctuated denudation rates with denudation concentrated during periods of increasing runoff intensity and or decreasing vegetation cover the sediment yield from threshold dominated basins may therefore exhibit significant variability in response to relatively subtle environmental changes a finding which underscores the need for caution in interpreting modern sediment yield data

spatial distribution of pco2 δo2 ar and dimethylsulfide dms in polynya waters and the sea ice zone of the amundsen sea antarctica we report the first simultaneous measurements of surface water pco2 biological oxygen saturation o2 ar and dimethylsulfide dms concentrations in polynya waters and the sea ice zone of the amundsen sea antarctica across our survey region we observed large spatial variability in surface water gas concentrations tied to strong gradients in hydrography and phytoplankton biomass variability in sea surface temperature and salinity was attributed to the interacting effects of surface ocean circulation and heat fluxes sea ice melt and the upwelling of relatively warm saline and nutrient rich modified circumpolar deep water phytoplankton biomass ranged from 1 g l 1 to 40 g l 1 chlorophyll a chl a with the highest values observed in regions of shallow mixed layer depths phytoplankton assemblages were dominated by the colonial haptophyte phaeocystis antarctica at most sampling stations with lesser abundances of diatoms found throughout the polynya and sea ice zone cryptophytes were abundant at a few stations along the continental shelf break across the open polynya waters and sea ice zone o2 ar ranged from 40 to 40 mean 8 6 pco2 ranged from 80 to 530 atm mean 250 atm and dms concentrations varied from 1 nm to 350 nm strong gradients in gas concentrations were observed over short i e 10 km spatial scales the distribution of pco2 and o2 ar across our survey transects reflected the balance between deep water entrainment and net community production with a significant imprint of air sea exchange chl a concentrations were significantly correlated to both pco2 and o2 ar and the slope of the o2 ar vs pco2 relationship was consistent with photosynthetic stoichiometry 1 25 mol o2 evolved per mol dic removed dms and chl a concentrations were also correlated in surface waters but the spatial distribution of dms was often uncoupled from pco2 and o2 ar likely due to complex microbial cycling processes sea surface temperature and salinity were related to surface gas concentrations through their effects on mixed layer depth and as tracers of upwelling during the time of our cruise the amundsen sea acted as an overall net sink for co2 mean sea air flux 15 9 mmol m 2 d 1 and a dms source mean sea air flux 23 1 mol m 2 d 1 sea air co2 and dms fluxes were more than 2 fold higher in open polynya waters relative to the overall cruise means simple calculations suggest that the amundsen sea contributes 5 of total southern ocean co2 fluxes and 1 of dms fluxes

beachrock occurrence characteristics formation mechanisms and impacts beachrocks are hard coastal sedimentary formations consisting of various beach sediments lithified through the precipitation of carbonate cements the objectives of this contribution are to a collate and review information on the reported occurrences characteristics and formation mechanisms of beachrocks and b consider their impacts on the coastal zone the analysis of the available information has shown that a beachrock formation is a global and diachronic phenomenon and b the great majority of beachrocks are found in tropical subtropical and low temperate latitude microtidal coasts the cementing agents of beachrocks are composed predominantly of the metastable carbonate phases high magnesian calcite hmc and aragonite ar appearing in a diverse crystalline morphology it has been suggested that cement precipitation in the coastal environment is controlled by i the physicochemical conditions ii the presence of organic compounds and microbes iii the magnitude and distribution of the wave energy along the coast and iv the textural characteristics of the constituent sediments various theories have been proposed to explain beachrock formation itself linking the phenomenon to either physicochemical or biological processes these theories however do not seem to be of universal validity and acceptance as each is able to explain only some of the reported occurrences the presence of beachrocks appears to affect beach morphodynamics by i locking the beach profile ii modifying the nearshore hydrodynamics iii changing the porous character of the beach and thus its response to wave forcing and iv differential bed erosion at the margins of the beachrock outcrops that can alter significantly the long and particularly the cross shore sediment transport therefore although relict submerged beachrock outcrops may provide some coastal protection by reducing the wave energy impinging onto the coastline modern beachrocks may promote offshore loss of unconsolidated beach sediments and buried beachrock outcropping finally the presence of beachrocks may have also significant ecological impacts as the indigenous mobile substrate fauna and flora of the beach is replaced by hard substrate benthic assemblages which are commonly arranged in hydrodynamically controlled zones

under what conditions do parallel river networks occur abstract geologists have long recognized that channel networks can deviate from a typical dendritic form when they develop under certain geologic or topographic constraints one such deviation is the parallel form which is thought to occur when networks develop on sloping surfaces the objectives of this research are to determine the specific conditions under which parallel networks occur and the nature of the transition between dendritic and parallel networks natural and simulated channel networks are considered in this study the natural networks were obtained from the digital elevation models of basins that include remnants of the preexisting topographic surface these remnants were identified as locations with small drainage areas and topographic curvatures that are close to zero for each basin the average slope of the preexisting surface was calculated and the channel network was classified using an existing method that can distinguish five network types including dendritic and parallel based on measures that are derived from scaling invariance the natural networks become consistently parallel when the average slope of the preexisting surface exceeds about 3 simulated channel networks were also generated using a detachment limited model for fluvial erosion the parameters of the model were determined to imitate the natural basins and the average slopes of the observed preexisting surfaces were used for the slopes of the initial surfaces in the simulations the model can also produce a transition between dendritic and parallel networks for an initial slope around 3 but this transition depends on the roughness of the initial surface and the boundary conditions

scaling regimes of local slope versus contributing area in digital elevation models four scaling regimes are observed in digital elevation models dems when the average local slope is calculated for pixels grouped according to the values of the contributing area threshold criteria proposed by various researchers to identify the extent of the channel network are examined relative to the slope area scaling diagram the scaling response observed in dems is reproduced with a landscape evolution and channel network growth model originally developed by willgoose et al 1989 the threshold criterion proposed in this model is a useful tool to separate two different slope area scaling regimes observed in dem data

the landscape evolution observatory a large scale controllable infrastructure to study coupled earth surface processes abstract zero order drainage basins and their constituent hillslopes are the fundamental geomorphic unit comprising much of earth s uplands the convergent topography of these landscapes generates spatially variable substrate and moisture content facilitating biological diversity and influencing how the landscape filters precipitation and sequesters atmospheric carbon dioxide in light of these significant ecosystem services refining our understanding of how these functions are affected by landscape evolution weather variability and long term climate change is imperative in this paper we introduce the landscape evolution observatory leo a large scale controllable infrastructure consisting of three replicated artificial landscapes each 330 m 2 surface area within the climate controlled biosphere 2 facility in arizona usa at leo experimental manipulation of rainfall air temperature relative humidity and wind speed are possible at unprecedented scale the landscape evolution observatory was designed as a community resource to advance understanding of how topography physical and chemical properties of soil and biological communities coevolve and how this coevolution affects water carbon and energy cycles at multiple spatial scales with well defined boundary conditions and an extensive network of sensors and samplers leo enables an iterative scientific approach that includes numerical model development and virtual experimentation physical experimentation data analysis and model refinement we plan to engage the broader scientific community through public dissemination of data from leo collaborative experimental design and community based model development

the cow as a geomorphic agent a critical review cows are important agents of geomorphological change on the uplands heavy grazing compacts the soil reduces infiltration increases runoff and increases erosion and sediment yield however light and moderate grazing have effects that are much less significant in riparian zones grazing decreases erosional resistance by reducing vegetation and exposing more vulnerable substrate trampling directly erodes banks thus increasing turbulence and consequent erosion future studies should be framed within the hydroclimatological edaphic and geomorphological dimensions of the areas being studied so that controlling variables may be more readily isolated we believe that both empirical studies and deterministic modeling can provide insights as to the effects of grazing on geomorphology

geomorphic and paleoclimatic implications of latest pleistocene radiocarbon dates from colluvium mantled hollows california radiocarbon analyses of charcoal from basal colluvium in 11 california hollows show a clustering of dates between 9000 and 15 000 b p an indication that changes in the storage and discharge of colluvium from hillslopes accompanied the pleistocene holocene transition hollows are sites of topographically induced convergence and deposition of colluvial debris and evacuation of this debris was apparently more thorough and possibly more frequent in the latest pleistocene perhaps due to a combination of changes in vegetation and rainfall characteristics one hypothesis is that greater storm intensities occurred in the latest pleistocene and induced a higher frequency of landslides in hollows and a regional extension of channel heads upslope relative to the holocene during the last pleistocene california hollows apparently contained smaller volumes of colluvium in storage the increased storage of debris during the holocene may have resulted in a diminished supply of sediment to stream channels

scarping of artificially nourished mixed sand and gravel beaches sedimentological characteristics of hayling island beach southern england abstract beach cliffing is a wide spread characteristic of artificially replenished beaches which has many undesirable engineering environmental and economic consequences a sedimentological study undertaken on the replenished mixed gravel and sand beach of hayling island southern england has shown that the persisting beach cliff consists typically of three distinct layers the textural geochemical and mineralogical analyses of the deposit showed that the development of the cliff and particularly the formation of the intermediate densely packed layer could be attributed to a series of processes firstly the techniques used to emplace the recharge material on the beach i e placement by heavy dumper trucks bulldozers result in a compaction and grain fracture of the recharge material and therefore a denser packing arrangement than that expected by its textural characteristics alone secondly percolating water transfers medium and fine grained material to deeper parts of the deposit resulting in the clogging of the interstices between the gravels and the formation of a densely packed poorly sorted layer the above processes promote the interactions between the clay minerals of the deposit with ca2 cations resulting in the formation of particular cementing materials such as calcium silicate hydrates csh

predicting the susceptibility to gully initiation in data poor regions permanent gullies are common features in many landscapes and quite often they represent the dominant soil erosion process once a gully has initiated field evidence shows that gully channel formation and headcut migration rapidly occur in order to prevent the undesired effects of gullying there is a need to predict the places where new gullies might initiate from detailed field measurements studies have demonstrated strong inverse relationships between slope gradient of the soil surface s and drainage area a at the point of channel initiation across catchments in different climatic and morphological environments such slope area thresholds s a can be used to predict locations in the landscape where gullies might initiate however acquiring s a requires detailed field investigations and accurate high resolution digital elevation data which are usually difficult to acquire to circumvent this issue we propose a two step method that uses published s a thresholds and a logistic regression analysis lr s a thresholds from the literature are used as proxies of field measurement the method is calibrated and validated on a watershed close to the town of algiers northern algeria where gully erosion affects most of the slopes the gullies extend up to several kilometres in length and cover 16 of the study area first we reconstruct the initiation areas of the existing gullies by applying s a thresholds for similar environments then using the initiation area map as the dependent variable with combinations of topographic and lithological predictor variables we calibrate several lr models it provides relevant results in terms of statistical reliability prediction performance and geomorphological significance this method using s a thresholds with data driven assessment methods like lr proves to be efficient when applied to common spatial data and establishes a methodology that will allow similar studies to be undertaken elsewhere

erosion thresholds and land surface morphology we propose a graphical technique to analyze the entirety of landforms in a catchment to define quantitatively the spatial variation in the dominance of different erosion processes high resolution digital elevation data of a 1 2 km2 hilly area where the channel network had been mapped in the field were used in the digital terrain model topog to test threshold theories for erosion the land surface was divided into 20 m2 elements whose shapes were then classified as convergent planar or divergent the entire landscape plotted on a graph of area per unit contour length against surface gradient shows each planform plotting as a separate field a simple steady state hydrologic model was used to predict zones of saturation and areas of high pore pressure to mimic the extreme hydrologic events responsible for erosive instability of the land surface the field observation that saturation overland flow is rare outside convergent zones provided a significant constraint on the hydrologic parameter in the model this model was used in threshold theories to predict areas of slope instability and areas subject to erosion by saturation overland flow both of which can contribute to channel initiation the proportion of convergent elements predicted to exceed the threshold varies greatly with relatively small changes in surface resistance demonstrating a high sensitivity to land use such as cattle grazing overall the landscape can be divided using erosion threshold lines into areas prone to channel instability due to runoff and stable areas where diffusive transport predominates

the superficial sediments of the english channel and its western approaches the english channel and its western approaches constitute a 700 km long epicontinental sea located in a temperate environment and in a tectonic setting where subsidence is minimal a sedimentological survey of this region reveals quite distinct provinces a central sector western channel where predominantly bioclastic sediments are widely represented bounded by two mainly terrigenous rich zones the outer terrace of the celtic sea and the eastern channel lateral sedimentary variations of decreasing grain size are interpreted in terms of current velocity patterns the various types of such sequences may relate to the degree of mixing of older lithoclastic sediments with the holocene bioclastic supply a scenario for the evolution of the recent sedimentation of this epicontinental sea is presented starting from a permanent marine zone at least since the wurm period that bounds the bay of biscay the holocene transgression progressed over the english channel in the western channel earlier terrigenous deposits were gradually overlapped by bioclastic sediments that originated on the pre mesozoic rocky substratum and which were particularly extensive off the armorican massif in the subsequently submerged eastern channel the pre holocene clastic source has undergone comparatively less modification and still crops out in most of the area with the opening of the straits of dover at about 9000 yr bp submersion was complete and new hydrodynamic conditions developed as the eustatic level stabilized the present sediment distribution is in harmony with the hydrodynamic setting except on the southern rise of the celtic sea where both morphology and sedimentary patterns still largely reflect pre holocene conditions resume la mer de la manche et ses approches occidentales constituent une plateforme epicontinentale qui s etend suivant un axe ne sw d environ 700 km depuis le pas de calais jusqu au rebord continental c est un milieu sedimentaire de climat tempere a subsidence negligeable et a faible taux de sedimentation la couverture de depots meubles est mince quelques metres en general sauf au niveau des bancs sableux et des paleovallees souvent comblees s alluvions anciennes la repartition des sediments superficiels est essentiellement controlee par les courants de maree particulierement forts le long des cotes armoricaines et en manche centrale en manche occidentale un important gradient de vitesses decroissantes se developpe du sud est au nord ouest les houles s exercent principalement sur la frange cotiere ou leur action devient dominante dans l ensemble les depbts fins sont rares et concentres dans les baies et les estuaires ou les suspensions se decantent par contre les sediments graveleux a caillouteux sont largement repartis une opposition nette se dessine entre une province orientale surtout terrigene et une province occidentale au materiel bioclastique abondant presentant un gradient de dispersion en direction du sud ouest ces caracteres morphologiques et sedimentaires du milieu sont fortement marques par son histoire quaternaire notamment par la derniere oscillation marine un schema de mise en place et d evolution du modele sedimentaire au cours du quatenaire recent est propose partant de la zone en permanence submergee durant le wurm la transgression holocene progressa sur la manche le pas de calais s ouvrit vers 9000 bp et peu a peu les conditions hydrodynamiques actuelles se mirent en place sous un climat devenu tempere progressivement les depots terrigenes anciens furent contamines par du materiel bioclastique holocene

spatial distributions of volatile sulfur compounds in surface seawater and overlying atmosphere in the northwestern pacific ocean eastern indian ocean and southern ocean 1 distributions of volatile sulfur compounds carbonyl sulfide cos carbon disulfide cs2 hydrogen sulfide h2s dimethyl sulfide dms in surface seawater and overlying atmosphere were measured in the northwestern pacific eastern indian and southern oceans 40 n 66 s 40 e 140 e in november december 1996 during the 38th japanese antarctic research expedition cruise seawater measurements revealed that dms was the dominant sulfur compound with concentrations of 0 5 15 8 nm high values were found in the southern ocean s marginal ice zone 84 e 63 e 59 s 63 s suggesting that the area during the bloom acts as an important source of atmospheric dms atmospheric concentrations were 456 471 pptv for ocs n d not detected level 13 pptv for cs2 n d 17 pptv for h2s and n d 755 pptv for dms concentrations of ocs were nearly constant concentrations of cs2 and h2s were high in terrigenic air masses and low in those of oceanic origin comparison of atmospheric dms data and a steady state box model using sea to air fluxes of dms and assumed oh radical concentrations revealed that atmospheric dms concentrations in the equatorial region and most of the southern ocean were balanced with local oceanic emission residues and photochemical oxidation simultaneous measurements in the atmosphere showed dms was the dominant sulfur gas that was oxidized rapidly to sulfate aerosols in the marine atmosphere

characteristics of the surface water dms and pco2 distributions and their relationships in the southern ocean southeast indian ocean and northwest pacific ocean oceanic dimethyl sulfide dms is of interest due to its critical influence on atmospheric sulfur compounds in the marine atmosphere and its hypothesized significant role in global climate high resolution shipboard underway measurements of surface seawater dms and the partial pressure of carbon dioxide pco2 were conducted in the atlantic ocean and indian ocean sectors of the southern ocean so the southeast indian ocean and the northwest pacific ocean from february april 2014 during the 30th chinese antarctic research expedition the so particularly in the region south of 58 s had the highest mean surface seawater dms concentration of 4 1 8 3 nm ranged from 0 1 to 73 2 nm and lowest mean seawater pco2 level of 337 50 atm ranged from 221 to 411 atm over the entire cruise significant variations of surface seawater dms and pco2 in the seasonal ice zone siz of so were observed which are mainly controlled by biological process and sea ice activity we found a significant negative relationship between dms and pco2 in the so siz using 0 1 degree resolution dms seawater 0 160 pco2 seawater 61 8 r2 0 594 n 924 p 0 001 we anticipate that the relationship may possibly be utilized to reconstruct the surface seawater dms climatology in the so siz further studies are necessary to improve the universality of this approach

experimental modelling of beachrock cementation under microbial influence a laboratory model has been developed which reproduces natural conditions of beachrock formation these conditions include the porosity of beach sand tidal movements alternation of phreatic and vadose conditions temperature evaporation illumination and water composition seawater with a control of the following parameters salinity ca mg co2 ph caco3 saturation the conditions of two beachrocks from the red sea egypt and shark bay australia have been simulated and the influence of the micro organism population undetermined sampled in these beachrocks was observed for 3 4 months in the experiments inoculated with micro organisms biomineralization produced characteristic crystals of various forms from 1 to 20 m in size the precipitates resemble the micritic cements of natural beachrocks on the contrary precipitation was much less developed in the control experiments under nearly sterile conditions these results confirm the importance of microbial activity during beachrock formation the first micritic cement which seems to control cementation and produce the initial consolidation is formed under a strong microbial influence in or near a biofilm covering the grain surface the presence of this micritic cement is necessary for the development of the subsequent prismatic cement which probably results from an abiotic precipitation during higher fluid circulation

modeling shallow landsliding susceptibility by incorporating heavy rainfall statistical properties abstract we present an index based shallow landsliding susceptibility model which allows explicit incorporation of local heavy rainfall statistical properties the model called quasi dynamic shallow landsliding model qd slam is developed upon a theory for coupled shallow subsurface flow and landsliding of the soil mantle the model uses a quasi dynamic wetness index to predict the spatial distribution of soil saturation in response to a rainfall of specified duration and can take into account the spatial variability of soil properties the rainfall predicted to cause instability in each topographic element is characterized by intensity and duration the incorporation of a scaling model for the rainfall frequency duration relationship provides a parsimonious and robust way to include heavy rainfall statistical properties into shallow landsliding modeling the model is used to determine the return period of the critical rainfall needed to cause instability for each topographic element the model is validated over six different study sites where detailed inventories of shallow landslides are available two study sites are located in the north of taiwan and four are located in the italian alps the sites are characterized by different climates and by different duration of the landslide triggering storms model results are evaluated against the surveyed landslides and compared to those obtained by using a steady state model resembling shalstab it is shown that qd slam improves significantly over the steady state approach in predicting existing landslides as represented in the considered landslide inventory moreover the improvement is higher for the cases where the landslide triggering storm duration is short with respect to the length of time required for every point on a catchment to reach subsurface drainage equilibrium the results of our work highlight the capability of the model to incorporate a robust description of the heavy rainfall properties in the analysis and mapping of shallow landsliding susceptibility by using an index style approach

seasonal accretion and erosion patterns of a microtidal sandy beach monthly elevation surveys of a 1 5 km stretch of coast at noordwijk the netherlands were made 1 to quantify seasonal variability in the cross shore position of high mean and low tide contours beach width and beach volume and 2 to examine the dependence of the variability on the offshore wave characteristics additionally daily cross shore positions of contours obtained from video images were used to examine daily beach response to wave characteristics between successive surveys the more intense and frequent storm events in winter than in summer resulted in a seasonal change from a wide beach with a small volume at the end of winter to a narrow large volume beach in summer the seasonal pattern in beach width resulted from the cross shore sediment exchange between the supratidal and lower intertidal part of the beach in contrast to the coupling between beach behaviour and wave characteristics on a seasonal scale beach variability between successive surveys was unrelated to day to week averages of the preceding offshore wave conditions partly due to the precise timing of a storm relative to the two survey moments moreover daily variability determined from the video images showed that differing antecedent morphology to storms and alongshore variations in beach morphology contributed to spatially and temporally variable beach response

experimental evidence for hillslope control of landscape scale landscape evolution theory suggests that climate sets the scale of landscape dissection by modulating the competition between diffusive processes that sculpt convex hillslopes and advective processes that carve concave valleys however the link between the relative dominance of hillslope and valley transport processes and landscape scale is difficult to demonstrate in natural landscapes due to the episodic nature of erosion here we report results from laboratory experiments combining diffusive and advective processes in an eroding landscape we demonstrate that rainsplash driven disturbances in our experiments are a robust proxy for hillslope transport such that increasing hillslope transport efficiency decreases drainage density our experimental results demonstrate how the coupling of climate driven hillslope and valley forming processes such as bioturbation and runoff dictates the scale of eroding landscapes

volatile production during contact metamorphism the role of organic matter in pelites elemental analyses of palaeozoic mudrocks from south cornwall indicate the presence of 0 04 0 74 wt carbon primarily in an elemental and or organic form in addition to 0 04 0 10 wt nitrogen as nh 4 in micas and in organic material both elements are depleted in samples from the lithologically homogeneous mylor slate formation next to the tregonning granite an offshoot of the cornubian batholith the depletions are due to an h 2 o co 2 n 2 ch 4 fluid formed during contact metamorphic devolatilization of the pelitic country rocks fluids of this type have been reported from a number of hercynian sn w provinces and may play an important role in mobilizing metals in pelitic rocks during granite related contact metamorphism and hence in the metallogenic evolution of such regions

initial spreading of a mega feeder nourishment observations of the sand engine pilot project sand nourishments are a widely applied technique to increase beach width for recreation or coastal safety as the size of these nourishments increases new questions arise on the adaptation of the coastal system after such large unnatural shapes have been implemented this paper presents the initial morphological evolution after implementation of a mega nourishment project at the dutch coast intended to feed the surrounding beaches in total 21 5 million m3 dredged material was used for two shoreface nourishments and a large sandy peninsula the sand engine peninsula a highly concentrated nourishment of 17 million m3 of sand in the shape of a sandy hook and protruding 1 km from shore was measured intensively on a monthly scale in the first 18 months after completion we examine the rapid bathymetric evolution with concurrent offshore wave forcing to investigate the feeding behaviour of the nourishment to the adjacent coast our observations show a large shoreline retreat of o 150 m along the outer perimeter of the peninsula with locally up to 300 m retreat the majority 72 of the volumetric losses in sediment on the peninsula 1 8 million m3 were compensated by accretion on adjacent coastal sections and dunes confirming the feeding property of the mega nourishment further analyses show that the morphological changes were most pronounced in the first 6 months while the planform curvature reduced and the surf zone slope flattened to pre nourishment values in the following 12 months the changes were more moderate overall the feeding property was strongly correlated to incident wave forcing such that months with high incoming waves resulted in more alongshore spreading months with small wave heights resulted in minimal change in sediment distribution alongshore and mostly cross shore movement of sediment

escarpment evolution on high elevation rifted margins insights derived from a surface processes model that combines diffusion advection and reaction experiments with a surface processes model of large scale 1 1000 km long term 1 100 m y erosional denudation are used to establish the controls on the evolution of a model escarpment that is related to the rifting of a continent the model describes changes in topographic form as a result of simultaneous short and long range mass transport representing hillslope diffusive processes and fluvial transport advection respectively fluvial entrainment is modeled as a first order kinetic reaction which reflects the credibility of the substrate and therefore the fluvial system is not necessarily carrying at capacity one dimensional and planform models demonstrate that the principal controls on the evolution of an initially steep model escarpment are 1 antecedent topography drainage 2 the timescale or equivalently a length scale in the fluvial entrainment reaction 3 the flexural response of the lithosphere to denudation and 4 the relative efficiencies of the short and long range transport processes when rainfall and substrate lithology are uniform a significant amount of discharge draining over the escarpment top causes it to degrade only when the top of the model escarpment coincides with a drainage divide can escarpment retreat occur for these conditions an additional requirement for retreat of a model escarpment without decline is a long reaction time scale for fluvial entrainment this corresponds to a substrate that is hard to detach by fluvial erosion and therefore to fluvial erosion that is not transport limited continuous backtilting of an escarpment due to flexural isostatic uplift in response to denudational unloading helps maintain the scarp top as a divide it is essential if the escarpment gradient is to be preserved during retreat in a uniform lithology low flexural rigidities promote steep and slowly retreating escarpments for given rainfall and substrate conditions the morphology of a retreating model escarpment is determined by the ratio of the short range diffusive and long range advective transport efficiencies a low ratio which is interpreted to correspond to a relatively arid climate and weathering limited conditions promotes steep sharp topped escarpments with straight main slopes and escarpment retreat occurs over a wide range of height scales a high ratio interpreted to correspond to a more humid temperate climate produces a convex upper slope and concave lower slope morphology and only major escarpments are predicted to preserve a high scarp gradient lithological contrasts in the model produce more complex morphologies and predict the formation of scarps crowned by an erosionally resistant caprock however resistant caprocks are not an essential requirement for model scarps to retreat we conclude that the inferred controls and model behavior are both consistent with the present day morphology of rifted continental margins and with modern conceptual models of landscape evolution

evaluation of digital channel network derivation methods in a glaciated subalpine catchment the digital elevation model dem has become an essential tool for an increasing array of mountain runoff analyses particularly the derivation and mapping of stream channel networks this study examines how well commonly applied dem based channel derivation methods at different spatial resolutions can represent the channel network for a glaciated rocky mountain headwater catchment the specific objectives are to 1 examine how differences in gridded dem resolution affect spatially distributed values of local slope specific contributing area and topographic wetness index derived from both eight and infinite directional flow algorithms 2 map the actual stream channel network to examine the influence of surface variables on channel initiation and 3 assess accuracy of dem derived networks compared with the field surveyed network results show that for the same contributing area threshold increasing grid cell size leads to increased channelization of modeled networks a plot of local slope versus contributing area reveals a negative relationship similar to that of prior studies in un glaciated areas but with breaks in slope at contributing areas that are too small to represent thresholds for channelization field survey results and evaluation of dem derived channel networks suggest that channel network formation is not clearly related to surface topographic variables at loch vale digitally derived channel networks do not accurately predict low order channel locations but approximations of the channel network with drainage density and headward extent of channelization similar to the observed network can be derived with both a 1 m and 10 m dem using a contributing area threshold of approximately 4x104 m2 copyright 2014 john wiley sons ltd

objective extraction of channel heads from high resolution topographic data fluvial landscapes are dissected by channels and at their upstream termini are channel heads accurate reconstruction of the fluvial domain is fundamental to understanding runoff generation storm hydrology sediment transport biogeochemical cycling and landscape evolution many methods have been proposed for predicting channel head locations using topographic data yet none have been tested against a robust field data set of mapped channel heads across multiple landscapes in this study four methods of channel head prediction were tested against field data from four sites with high resolution dems slope area scaling relationships two techniques based on landscape tangential curvature and a new method presented here which identifies the change from channel to hillslope topography along a profile using a transformed longitudinal coordinate system our method requires only two user defined parameters determined via independent statistical analysis slope area plots are traditionally used to identify the fluvial hillslope transition but we observe no clear relationship between this transition and field mapped channel heads of the four methods assessed one of the tangential curvature methods and our new method most accurately reproduce the measured channel heads in all four field sites feather river ca mid bailey run oh indian creek oh piedmont va with mean errors of 11 7 5 and 24 m and 34 3 12 and 58 m respectively negative values indicate channel heads located upslope of those mapped in the field importantly these two independent methods produce mutually consistent estimates providing two tests of channel head locations based on independent topographic signatures

vegetation precipitation controls on central andean topography climatic controls on fluvial landscapes are commonly characterized in terms of mean annual precipitation however physical erosion processes are driven by extreme events and are therefore more directly related to the intensity duration and frequency of individual rainfall events climate also influences erosional processes indirectly by controlling vegetation in this study we explore how interdependent climate and vegetation properties affect landscape morphology at the scale of the andean orogen the mean intensity duration and frequency of precipitation events are derived from the trmm 3b42v7 product relationships between mean hillslope gradients and precipitation event metrics mean annual precipitation vegetation and bedrock lithology in the central andes are examined by correlation analyses and multiple linear regression our results indicate that mean hillslope gradient correlates most strongly with percent vegetation cover r 0 56 where vegetation cover is less than 95 mean hillslope gradients increase with mean annual precipitation r 0 60 and vegetation cover r 0 69 where vegetation cover is dense 95 mean hillslope gradients increase with increasing elevation r 0 74 decreasing inter storm duration r 0 69 and decreasing precipitation intensity by 0 5 mm d 1 r 0 56 thus we conclude that at the orogen scale climate influences on topography are mediated by vegetation which itself is dependent on mean annual precipitation r 0 77 observations from the central andes are consistent with landscape evolution models in which hillslope gradients are a balance between rock uplift climatic erosional efficiency and erosional resistance of the landscape determined by bedrock lithology and vegetation

modelling the location of shallow landslides and their effects on landscape dynamics in large watersheds an application for northern new zealand in this study we propose a model to assess the location of shallow landslides and their impact on landscape development within a timeframe of years to decades processes that need to be incorporated in the model are reviewed then followed by the proposed modelling framework the capabilities of the model are explored through an application for a forested 17 km2 study catchment in northern new zealand for which digital elevation data are available with a grid resolution of 25 25 m the model predicts the spatial pattern of landslide susceptibility within the simulated catchment and subsequently applies a spatial algorithm for the redistribution of failed material by effectively changing the corresponding digital elevation data after each timestep on the basis of a scenario of triggering rainfall events relative landslide hazard and trajectories with runout criteria for failed slope material the resulting model will form a landslide module within the dynamic landscape evolution model lapsus the model forms a spatially explicit method to address the effects of shallow landslide erosion and sedimentation because digital elevation data are adapted between timesteps and on and off site effects over the years can be simulated in this way by visualization of the modelling results in a gis environment the shifting pattern of upslope and downslope in stability triggering of new landslides and the resulting slope retreat by soil material redistribution due to former mass movements can be simulated and assessed

analysis of topographic and climatic control on rainfall triggered shallow landsliding using a quasi dynamic wetness index abstract a model for the prediction of both topographic and climatic control on shallow landslide initiation processes in hilly mountainous terrain is proposed the model develops upon a theory for coupled shallow subsurface flow and landsliding of the soil mantle previously proposed by montgomery and dietrich water resour res 30 1994 1153 the model uses a quasi dynamic wetness index to predict the spatial distribution of soil saturation in response to a rainfall of specified duration the rainfall predicted to cause instability in each topographic element is characterised by duration and frequency of occurrence the incorporation of a rainfall frequency duration relationship into assessment of landslide hazard provides a practical way to include climate information into estimation of the relative potential for shallow landsliding the model is applied to a mountain experimental basin where high resolution digital elevation data are available the cordon catchment 5 km2 in north eastern italy an inventory of landslide scars is used to document sites of instability and to provide a test of model performance by comparing observed landslide locations with model predictions the model reasonably reproduces the observed distribution of landslides although spatial variability of soil properties and hydrologic complexities not accounted for by the model complicate prediction of where landslides occur within areas of similar topographic climatic control model predictions from the quasi dynamic model are compared with those provided by the steady state model water resour res 30 1994 1153 these results suggest that the quasi dynamic model offers significant improvement over the steady state model in predicting existing landslides as represented in the considered landslide inventory

characterizing the primary material sources and dominant erosional processes for post fire debris flow initiation in a headwater basin using multi temporal terrestrial laser scanning data abstract wildfire dramatically alters the hydrologic response of a watershed such that even modest rainstorms can produce hazardous debris flows relative to shallow landslides the primary sources of material and dominant erosional processes that contribute to post fire debris flow initiation are poorly constrained improving our understanding of how and where material is eroded from a watershed during a post fire debris flow requires 1 precise measurements of topographic change to calculate volumetric measurements of erosion and deposition and 2 the identification of relevant morphometrically defined process domains to spatially constrain these measurements of erosion and deposition in this study we combine the morphometric analysis of a steep small 0 01 km 2 headwater drainage basin with measurements of topographic change using high resolution 2 5 cm multi temporal terrestrial laser scanning data made before and after a post fire debris flow the results of the morphometric analysis are used to define four process domains hillslope divergent hillslope convergent transitional and channelized incision we determine that hillslope divergent and hillslope convergent process domains represent the primary sources of material over the period of analysis in the study basin from these results we conclude that raindrop impact induced erosion ravel surface wash and rilling are the primary erosional processes contributing to post fire debris flow initiation in the small steep headwater basin further work is needed to determine 1 how these results vary with increasing drainage basin size 2 how these data might scale upward for use with coarser resolution measurements of topography and 3 how these results change with evolving sediment supply conditions and vegetation recovery