early diagenesis in deep sea turbidites the imprint of paleo oxidation zones sediment cores up to 35 m long have been recovered from turbidite sequences in the madiera abyssal plain and the southern nares abyssal plain detailed geochemical analyses of these sediments si al fe mn ca organic and inorganic carbon and associate pore waters nitrate ammonia silicate fe2 mn2 and alkalinity provide representative profiles of both steady state and nonsteady state diagenetic reactions initiated by oxidation and reduction processes models demonstrate that chemical transport in the pore water system is diffusion dominated over periods of a few thousands of years to several hundreds of thousands of years mn and fe mobilized in the subsurface mildly reducing sediments are precipitated as easily reducible oxyhydroxides in the near surface oxidized sediments nonsteady state profiles show the influence of episodic and rapid turbidite deposition and the imprint of oxidation zones that developed as the result of oxygen diffusion into the upper portions of turbidites during intervals of slow pelagic deposition the time required for development of oxidation zones between turbidites ranges from 2 0 to 15 ka in the madeira abyssal plain and from 0 2 to 2 4 ka in the southern nares abyssal plain paleo oxidation zones can be recognized in old turbidites by distinct changes in color between lower and upper portions of the deposit in the basal unoxidized portion of the turbidite the sediments are characteristically dark green gray or brown in the paleo oxidized zone the sediments are pale green blue or yellowish brown these zones in both the madeira and southern nares abyssal plains contain distinctly less organic c and carbonate in the paleo oxidized zone as compared with the unoxidized sediments depletion of carbonate content in the oxidized zones in the southern nares abyssal plain is particularly significant in that as much as 80 of the initial carbonates have been lost also the relative amounts of weak acid soluble fe and mn are generally less in the paleo oxidized zones due to the initial oxidation of metal carbonate and metal hydroxide forms to easily reducible oxide forms which are then subsequently solubilized under the mildly reducing conditions at depth in the sediment column

the spatial distribution and source of arsenic copper tin and zinc within the surface sediments of the fal estuary cornwall uk abstract estuarine sediments commonly form major sinks for contaminants released during industrial activity many industrial processes lead to the release of metals initially in solution which can then be adsorbed on to for example fe hydroxides or clay minerals however in the mining industry there are two major contaminant waste streams 1 metals discharged in solution via mine drainage and 2 particulate grains of the ore forming or related minerals released after ore processing the release of particulate waste can have a major long term impact on environmental geochemistry in this study we have mapped the distribution of arsenic copper tin and zinc within the surficial sediments of the fal estuary cornwall uk an area that drains a historically important polymetallic mining district there are clear spatial variations in the contaminants with the highest levels 2800 p p m as 5000 p p m cu 3000 p p m sn and 6000 p p m zn within restronguet creek on the western side of the estuary mineralogical studies show that small 20 m grains of detrital arsenopyrite chalcopyrite cassiterite and sphalerite are very abundant within the surface sediments most of the sulphide grains are fractured but mineralogically unaltered although some grains show alteration rims caused by oxidation of the sulphides the geochemistry and mineralogy are indicative of sediment supply from the discharge of particulate waste into the estuary during historical mining activity subsequently this particulate waste has been largely physically and biologically reworked within the surface sediments although considerable effort has been made to minimize contaminants released via mine drainage into the estuary the potential flux of contaminants present within the intertidal and subtidal sediments has not been addressed benthic invertebrates living within the area have adapted to be metal tolerant and it is likely that the dominant source of bioavailable metals is a result of alteration of the particulate mine waste present within the intertidal and subtidal sediments

impact of landslides on soil characteristics implications for estimating their age the slopes of mount elgon a complex volcano at the border between uganda and kenya are frequently affected by landslides with disastrous effects on the livelihood of its population since local people greatly depend on the land for crop production this paper examines if and how fast physico chemical characteristics in landslide scars recover a chronosequence of 18 landslides covering a period of 103 years was sampled in order to explore differences between topsoil inside and outside landslide scars for each landslide two topsoil samples were taken within the landslide and two in nearby undisturbed soils to compare their physico chemical characteristics samples inside the landslides were located at the transition zone between the depletion and accumulation zone which is situated at the contact line between the plan concave and plan convex section of the landslide no differences were found for available phosphorus ca2 mg2 content or for the fine earth texture recent landslides had however lower content of soil organic carbon oc and k and higher content of rock fragments and na than the adjacent soils soil oc content increased significantly with age and reached levels of the corresponding undisturbed soils after ca 60 years older landslides had even higher oc contents than soils adjacent to the landslide hence landslide scars act as local carbon sink we suggest that the occurrence of rock fragments in the topsoil is a useful indicator for mapping past landslides moreover the difference in soil oc content between landslide scars and adjacent soil could be used for estimating the age of landslides in data poor regions

incised channels and gully erosion in northern iberian peninsula controls and geomorphic setting abstract gully erosion has scarcely been reported in the cantabrian cordillera northern iberian peninsula even though this phenomenon is relatively frequent in this mountain range a total of 133 permanent channels with evidences of gully erosion have been mapped in a 71 8 km2 study area on the northern slope of this mountain range the underlying ordovician unit comprises quartzite sandstone and slate which are partially mantled by different surficial deposits the relief is fairly steep with average slopes of 27 and hillsides with level drops of the order of 700 m and generally vegetated by atlantic heaths a result of the degradation suffered by the natural vegetation following forest fires the mapped channels present different morphological features shallow and deep channels some of them with associated ravines and are usually related to headcut in first and second order pre existing channels although some of them are located on unchanneled hillsides with no evidence of pre existing channels moreover lower reaches of first and second order channels are often incised into bedrock a field description and morphometric study has been carried out on channels affected by gully erosion based on their cartography digital terrain models and several layers of thematic mapping this study describes some of the relations between relief factors the type of substratum and the development of gully erosion i there are robust correlations between morphometry relief and erosion intensity and ii gullying is strongly influenced by the presence of a deep regolith the erosion forms observed and the described relations suggest that gully development is associated to landsliding processes which are ultimately controlled by ground water movement through a porous regolith regional uplift and deforestation are argued to be the most likely causes of channel incision and gullying

lidar supported prediction of slope failures using an integrated ensemble weights of evidence and analytical hierarchy process the present study investigates a potential application of different resolution topographic data obtained from airborne lidar and an integrated ensemble weight of evidence and analytic hierarchy process woe ahp model to spatially predict slope failures previously failed slopes of the pellizzano italy were remotely mapped and divided into two subsets for training and testing purposes 1 2 5 10 15 and 20 m topographic data were processed to extract nine terrain attributes identified as conditioning factors for landslides slope degree aspect altitude plan curvature profile curvature stream power index topographic wetness index sediment transport index and topographic roughness index landslide slope failure susceptibility maps were produced using a single woe model 1 an ensemble woe ahp model that used all conditioning factors model 2 and an ensemble woe ahp model that only used highly nominated conditioning factors model 3 the validation results proved the efficiency of high resolution 5 m topographic data and the ensemble model particularly when all factors were used in the modeling process model 2 the average success rates and prediction rates for model 2 that used 5 m resolution datasets were 84 26 and 82 78 respectively the finding presented in this paper can aid in planning more efficient lidar surveys and the handling of large datasets and in gaining a better understanding of the nature of the predictive models

geochemical characteristics of contaminated surficial sediments in halifax harbour impact of waste discharge analyses of 274 surface sediment samples collected from halifax inlet between 1986 and 1990 permit assessment of the chemical environmental quality of this major east coast canadian harbour contamination of the marine sediments is due to discharge of untreated sewage and industrial waste directly into the harbour and leaching of solid waste deposits on land concentrations of total cu pb zn hg and cd in the uppermost 2 cm of sediments on the sea floor ranks halifax harbour among the most contaminated marine areas in the industrialized world statistical factor analysis has been used to identify five types of sediments based on sedimentological and geochemical characteristics the dominant factor type accounts for 41 of the chemical variance and represents sediments that are highly contaminated with metals and organics derived from sewage effluents and waste deposits more than 50 of the total cu zn and pb in the sediments is potentially reactive as reducible or oxidizable metal a simple two laye

the influence of dissolved fesi3o3 oh 08 on chemical equilibria in pore waters from deep sea sediments abstract pore water extracted from unconsolidated fine grained sediments from the southern sohm abyssal plain contain dissolved iron at concentrations greater than 100 m in glacial age sediments deeper than 2 0 m below the sea floor slightly reducing conditions pe and elevated dissolved sio 2 concentrations 300 m coincide with dissolved iron concentrations which are 2 to 4 orders of magnitude greater than would be predicted by conventional phase equilibria it is proposed that this fe exists in a fesi 3 o 3 oh 8 aq form and when its solubility is exceeded fe oh 3 or fesio 3 can be precipitated

the environmental significance of the remobilisation of ancient mass movements in the atbara tekeze headwaters northern ethiopia abstract old landslides are prominent features in the landscape around hagere selam tigray highlands ethiopia the available evidence suggests their late pleistocene to middle holocene age and conditions of soil humidity the affected geological layers often silicified lacustrine deposits prone to sliding rest upon or above the water holding amba aradam sandstone aquifer three examples of present day remobilisation of old mass movements are illustrated and discussed the aims of the study were to unravel the environmental conditions of the present day remobilisation of ancient flows as well as those of first time landslides the first two mass movements discussed are slumps located in areas with vigorous regeneration of grassy vegetation their activation is thought to be the consequence of an increase in infiltration capacity of the soils under regenerating vegetation one of these slumps had a horizontal movement of the order of 10 20 m in 1 day the other case is the remobilisation of the may ntebteb debris flow below the amba aradam sandstone cliff the debris flow presently creeps downslope at a rate of 3 6 cm year 1 palynological evidence from tufa shows that the reactivation of the flow started 70 years ago shear resistance measurements indicate the danger for continuous or prefailure creep from the soil mechanics point of view the reactivation of the debris flow is due to the combination of two factors 1 the reduction of flow confining pressures as a result of gully incision over the last hundred years and 2 the increase of seepage pressure as a consequence of the cumulative effect of this incision and the increase in infiltration rates on the lobe since grazing and woodcutting have been prohibited 8 years ago the role of such exclosures as possible landslide triggers is discussed from the geomorphological point of view the ancient movements and their present day reactivation cannot be compared the ancient movements led to the development of debris flows whereas the reactivations relate to the dissection of these mass movement deposits

mass movement mapping for geomorphological understanding and sustainable development tigray ethiopia abstract mass movement topography characterises the escarpments and piedmont zones of the tabular ridges in the western part of the mekelle outlier tigray ethiopia several types of mass movements can be distinguished the first type is rockfall produced by 357 km rocky escarpments and cliffs during the rainy season in the study area every current kilometer of amba aradam sandstone cliff annually produces 3 7 m3 of rock fragments however this is an under estimation of the actual cliff and escarpment evolution which is also characterised by debris slides and small rock slides in the debris flow class three dormant flow types are recognised the first type comprises preferential or undifferentiated mobilisations of the so called plateau layers the whitish sandy clayey lacustrine deposits and the lower and upper basalts and more especially the swelling clays derived from the basalts these debris flows start on the nearly horizontal amba aradam sandstone tabular extensions jump over cliff recessions or even spurs and go very far into the valley in some instances parts of amba aradam sandstone and antalo limestone cliffs are transported secondly some debris flows take their origin in the antalo limestone supersequence it concerns deeply weathered layers resting upon aquicludes aquitards finally gigantic debris flows and rock slides occur around dolerite dyke ridges about 20 of the total surface of the study area is occupied by landslide topography most of the landslides affect the steep edges of the table mountains or the dykes sills mapping and listing of active and dormant mass movements increases knowledge in three domains which are crucial for sustainable development of the study area the first one is geomorphological risk assessment the distribution map of active rockfall and dormant landslides shows the areas where potential risks are located land use changes which improve the water infiltration capacity of dormant landslides should be followed up secondly the impact of global climate change on these risk areas can be assessed the second domain is the water sector which needs attention in the study area and in many parts of africa landslides mobilised by hydrostatic pressures are related to the occurrence of aquicludes and aquifers in the study area landslide mapping led to the location of three aquitards not described before the third domain is the pedological mapping in the study area soil distribution is very well explained by the morphology and extension of dormant landslides finally mapping of dormant landslides stimulates the academic debate on the geomorphological significance of mass movements in hillslope retreat in tropical areas

modelling landslide hazard soil redistribution and sediment yield of landslides on the ugandan footslopes of mount elgon in this study the lapsus ls landslide model together with a digital terrain analysis of topographic attributes is used as a spatially explicit tool to simulate recent shallow landslides in manjiya county on the ugandan slopes of mount elgon manjiya county is a densely populated mountainous area where landslides have been reported since the beginning of the twentieth century to better understand the causal factors of landsliding 81 recent landslides have been mapped and investigated through statistical analysis it was shown that steep concave slopes high rainfall soil properties and layering as well as human interference were the main factors responsible for landslides in the study area lapsus ls is used to construct a landslide hazard map and to confirm or reject the main factors for landsliding in the area the model is specifically designed for the analysis of shallow landslide hazard by combining a steady state hydrologic model with a deterministic infinite slope stability model in addition soil redistribution algorithms can be applied whereby erosion and sedimentation by landsliding can be visualized and quantified by applying a threshold critical rainfall scenario the model is tested in the manjiya study area for its ability to delineate zones that are prone to shallow landsliding in general and to group the recent landslides into a specific landslide hazard category the digital terrain analysis confirms most of the causal topographic factors for shallow landsliding in the study area in general shallow landslides occur at a relatively large distance from the water divide on the transition between steep concave and more gentle convex slope positions which points to concentration of sub surface flow as the main hydrological triggering mechanism in addition lapsus ls is capable to group the recent shallow landslides in a specific landslide hazard class critical rainfall values of 0 03 0 05 m day 1 by constructing a landslide hazard map and simulating future landslide scenarios with the model slopes in manjiya county can be identified as inherently unstable and volumes of soil redistribution can yield four times higher than currently observed more than half of this quantity can end up in the stream network possibly damming rivers and causing major damage to infrastructure or siltation and pollution of streams the combination of a high population density land shortage and a high vulnerability to landslides will likely continue to create a major sustainability problem 2007 elsevier b v all rights reserved

geomorphic threshold conditions for ephemeral gully incision abstract ephemeral gully erosion in cultivated land is an important source of sediment that is frequently being overlooked and not accounted for in soil erosion studies furthermore little is known about the factors controlling ephemeral gully erosion in this paper the available information on the initiation and location of ephemeral gullies is summarised focusing on the relationship between the upslope drainage area a and the critical slope gradient s cr for ephemeral gully initiation by plotting the non linear relationship between critical slope gradient measured immediately upstream of the incision head and drainage area at the incision head for gullied sites it was possible to draw a straight line on log log paper through the lower most points for each of the available datasets representing a critical slope area relationship for incision consequently below this line no incision occurs this line or critical relation can also be written as a power function between critical slope and area although many factors vary between the different datasets the exponent of the drainage area relationship 0 4 showed very little variation the observed critical slope area relationship can be related to a simple model of channel initiation by overland flow furthermore this relationship can be used to identify potentially unstable sites where control measures should be undertaken

the topographic thresholds of hillslope incisions in southwestern rwanda abstract this article presents new quantitative evidence that land use in rwanda contributes to the development of hillslope incisions two types of hillslope incisions can be distinguished in southern rwanda incisions of the first type drain an area depending on the form and extension on the natural topography and geology the runyinya gully 25 and the rugabano soil slippage 39 are two examples on a logarithmic plot of critical slope inclination at the incision head versus drainage area towards the incision head both incisions lay sensibly to the right of the montgomery dietrich m d envelope the latter gives the range of these topographical thresholds for gully and mass wasting incision in parts of north america the runyinya and rugabano cases obey the linear equation s cr 0 6 a 0 6 where scr critical slope gradient tangent of slope in at the gully head or the scar and a the area ha drained towards the incision head hillslope incisions of the second group rely on a run on area larger than normal because they are localised at the outlet of artificially runoff collecting systems like roads soil conservational contour trenches tracks and other linear landscape elements such systems often drain a surface much larger in extension than the natural run on area to the outlet these hillslope incisions taking into account their artificially big drainage area concentrate more or less along the line s cr 0 3 a 0 6 this line is about in the center of the montgomery dietrich envelope if however only the natural drainage area of these outlet incisions is taken into account all points fall close to the left border or even to the left of the montgomery dietrich envelope this indicates a much higher probability for incision in those localities receiving supplementary runoff or interflow from outside the natural drainage area in the case of a soil slippage at rwaza hill detailed stability calculations show that the slope failure should be due to excessive water infiltration into the bottom of a trench the digging of the trench provoked an increase in the area drained to the slippage head by a factor of 6 the phenomenon of forward erosion is compatible with the existence of threshold combinations of slope and drained area for slopes steeper than 7 8 the phase of regressive erosion does often follow the forward incision event with a delay of several years or more finally the scanty data set now available for rwanda suggests that the drainage area critical to hillslope incision on the red brown ferrallitic soils in rwanda might be nearly twice as big as those in north america

slope area thresholds of road induced gully erosion and consequent hillslope channel interactions pikes peak highway is a partially paved road between cascade colorado and the summit of pikes peak significant gully erosion is occurring on the hillslopes due to the concentration of surface runoff the rearrangement of drainage pathways along the road surface and adjacent drainage ditches and the high erodibility of weathered pikes peak granite that underlies the area as a result large quantities of sediment are transported to surrounding valley networks causing significant damage to water quality and aquatic wetland and riparian ecosystems this study establishes the slope drainage area threshold for gullying along pikes peak highway and a cesium 137 based sediment budget highlighting rates of gully erosion and subsequent valley deposition for a small headwater basin

a 20th century record of climatologically modulated sediment accumulation rates in a canadian fjord abstract the geochronology of a gravity core collected from an anoxic high sedimentation rate 2 5 cm yr setting near the head of the saguenay fjord in quebec has been established for the period 1900 1979 to a resolution of better than 1 yr using a constant flux 21 pb model interannual variations of the sedimentation rate of between 28 and 50 are caused by rapid inputs of coarse silt and fine sand during spring freshet events a significant correlation between sand percentage and sediment accumulation rate reflects the increase in stream competence during the spring freshet the sand percentage parameter can be used in conjunction with sediment size parameters to estimate temporal variations in river discharge intensity between 1914 and 1979 sediment accumulation rates were about 60 higher during the spring and summer compared to fall and winter seasons both the magnitude of the saguenay river spring discharge and the quantity of precipitation stored as snow decrease through the 20th century suggesting that the freshet intensity was governed largely by natural rather than anthropogenic e g dam construction factors a direct correlation between sand flux peak river discharge and a snow storage parameter provides a link between sediment texture and climate detailed analyses of the grain size distributions for dated core intervals offer a method for the reconstruction of a proxy record of paleodischarge for the saguenay river spring freshets

evaluation of trace element concentration acid leachable in sediments from river panuco and its adjacent lagoon areas ne mexico a set of forty one surface sediment samples were collected in river panuco and its adjoining lagoon areas in ne mexico to identify the enrichment pattern of trace elements the samples were analyzed for sediment texture carbonates organic carbon and acid leachable trace elements altes using autoclave method fe mn cr cu ni co pb zn cd v be ba sr as geochemical results of fe cr ni co v and sr in zone 1 indicate that erosion in the upland region sierra madre oriental mountains is very high the above feature is supported by the supremacy of finer sediments 82 12 carbonates 44 67 and organic carbon 10 74 which are brought down from the drainage basin the overall average concentration of altes mn 607 g g 1 cu 28 29 g g 1 ni 16 56 g g 1 pb 46 11 g g 1 cd 1 81 g g 1 and zn 92 18 g g 1 indicates higher values than the lowest effect level lel and effects range low erl of environmental indicators the results suggest that they are due to the increase in oil refineries metal based industries shipping activities and the effluent input which could enter the biological cycle and might create human health problems

landslide susceptibility assessment in limbe sw cameroon a field calibrated seed cell and information value method the dissected volcanic terrains around limbe sw cameroon are frequently affected by small scale but destructive landslides in this study a raster based data driven method involving seed cells is used to build a landslide susceptibility model for the limbe area factors considered to be potential controls of slope failure within this area include slope gradient rock type distance from roads slope orientation mean annual precipitation soil type land cover type stream density and distance from stream 63 small to very small translational and rotational landslide scars were identified through extensive field work landslide data is randomly divided into a training 75 and validation set 25 and seed cells are generated by creating 25 m buffer zones around the head scarp of each scar the quantitative relationship between landslide seed cells and the above mentioned factors is established by a data driven approach to obtain weighted factor classes summing weighted factor layers a continuous scale of susceptibility indices is obtained and reclassified into 5 susceptibility classes seed cells obtained from the validation data set were used to evaluate the quality of several models involving different controlling factors our preferred model combines the weight of 6 factors i e slope gradient land cover mean annual precipitation stream density proximity to roads and slope orientation 78 of the validation seed cells are located within the high to very high susceptibility class which occupy 16 9 of the study area the obtained susceptibility map is combined with the outline of urban areas and key infrastructures to evaluate zones that are vulnerable to the impact of future slope failures such an approach will assist civil protection and urban planning efforts in sw cameroon language en

why is there an early spring cooling shift downstream of the tibetan plateau abstract the temperature shift over the eastern flank of the tibetan plateau is examined using the last 50 yr of chinese surface station observations it was found that a strong cooling shift occurs in early spring march and april and late summer july august and september in contrast to the warming shift in other seasons the cause of the march april ma cooling is investigated in this study the ma cooling shift on the lee side of the tibetan plateau is found to be not a local phenomenon but rather it is associated with an eastward extension of a cooling signal originating from north africa that is related to the north atlantic oscillation nao in the previous winter the midtropospheric westerlies over the north atlantic and north africa tend to intensify during positive nao phases the enhanced westerlies after passing over the tibetan plateau result in strengthened ascending motion against the lee side of the plateau which favors the formation of midlevel stratiform clouds the increased a

assessing the anthropocene with geochemical methods anthropogenic chemical contamination is one of the most evident signals of human influence on the environment the large amounts of industrially produced pollutants that have been introduced over decades into air soil and water have caused modifications to natural elemental cycling anthropogenic contamination usually leads to enrichment in many elements particularly in industrial areas thus certain elements and their isotopes can be used as geochemical tracers of anthropogenic impact some human induced changes in the environment may be regarded as a secondary effect of pollution such as acidification which causes increased geochemical mobility of several trace elements in surficial deposits methods used by geochemists to assess the scale of anthropogenic influence on the environment include calculations of anthropogenic influence on the environment via enrichment and contamination factors geoaccumulation index and pollution load index the use of geochemical background levels for delineating between natural and anthropogenic pollution is important a historical perspective of anthropogenic contamination allied with isotopic and geochemical signatures in dated sediment cores may be applied to help define the anthropocene human influence on the environment has been complex encompassing different environmental compartments air water soil and scales of changes local regional global the earth is a dynamic system and geochemical dynamics are best illustrated by consideration of element cycling although anthropogenic pollution sources have contributed to chemical changes in the atmosphere hydrosphere pedosphere and biosphere their impact on the total environment is best preserved in sediments which are often referred to as archives of contamination choi wania 2011 significant evidence of a distinctive anthropocene signal can be found in recent sedimentary deposits that have been impacted by anthropogenic activity and dated sediment cores can be used to reconstruct the chronology of contamination buckley et al 1995 in assessing the anthropocene it is important to quantify the human influence on the environment the results of this influence recorded in sediments can be evaluated using different approaches and criteria depending on the nature of the signal mechanical biological or chemical fig 1 zalasiewicz et al 2011a b price et al 2011 vane et al 2011 schrag 2012 geochemical methodology may help discriminate natural and anthropogenic sources of a given substance in the environment some of the methods and concepts e g anomaly background concentrations geochemical calculations and geochemical tracers traditionally used in geochemical exploration and further adapted to the needs of environmental geochemistry have found application in the study of anthropogenic contamination reimann de caritat 2005 reimann et al 2005 galuszka 2007 galuszka migaszewski 2011 these methods may be extended in assessment of the anthropocene anthropogenic anomalies and geochemical background concept geochemical anomalies can be defined as abnormal concentrations of elements in earth materials compared with background levels allaby allaby 1999 anomalous concentrations of elements are both of natural origin e g via oreforming processes weathering of ore bodies or mineralized rock formations sorption by mineral phases volcanic and hydrothermal activity and of anthropogenic origin mcqueen 2009 of the different types of geochemical anomalies fig 2 the positive anthropogenic anomalies of regional scale may provide a useful marker for the anthropocene selinus esbensen 1995 identification of geochemical anomalies requires knowledge of the normal or average distribution of elements in the environment which is usually referred to as a geochemical background lower and upper limits of the geochemical background from waters c n zalasiewicz j a williams m ellis m a snelling a m eds a stratigraphical basis for the anthropocene geological society london special publications 395 http dx doi org 10 1144 sp395 5 the geological society of london 2013 publishing disclaimer www geolsoc org uk pub ethics range are considered thresholds of negative depletion in an element and positive enrichment in an element anomalies fig 3 historically the search for positive anomalies has been essential to mineral exploration and in the 1960s geochemists established several methodologies for separating anomalies from the geochemical background hawkes webb 1962 miesch 1967 many fig 1 types of human induced changes their possible effects and sedimentary record fig 2 systematics of geochemical anomalies a ga uszka et al

a possible causal relationship between creep and sliding on rwaza hill southern rwanda stability calculations on a strongly creeping 28o slope on rwaza hill in southern rwanda reveal an apparent contradiction terracette formation within the kaolinitic soil mantle should only be possible during hydrological conditions of high phreatic surfaces for which the entire soil mantle should already have slid down in a translational sliding movement this apparent contradiction can only be explained if it is accepted that the soil shear resistance can fall temporarily below the residual soil shear strength a creep experiment confirms the theoretical possibility of this hypothesis furthermore the configuration of the sliding surfaces in the field consisting in fact of lenses of crumbled earth shows close affinities with the pattern of potential ruptures in a creeping soil as provided by rheological theory these data strongly suggest that on natural slopes creep should be the ultimate soil mechanical resason for sudden failures

tectonic control of complex slope failures in the ameka river valley lower gibe area central ethiopia implications for landslide formation abstract even though major faults represent important landslide controlling factors the role the tectonic setting in actively spreading rifts plays in the development of large complex landslides is seldom discussed the ameka complex landslide area is located on the eastern scarp of the gibe gorge approximately 45 km to the west of the main ethiopian rift and 175 km to the southwest of addis ababa investigation of the complex landslide failures required a combination of satellite and airborne data based geomorphology geological field survey complemented with structural analysis radiocarbon geochronology and vertical electric sounding the obtained observations confirmed the multiphase evolution of the landslide area we have documented that apart from climatic and lithological conditions the main triggering factor of the ameka complex landslide is the tectonic development of this area the e w extension along the nne ssw trending main ethiopian rift is associated with the formation of numerous parallel normal faults such as the gibe gorge fault and the almost perpendicular scissor faults the geometry of the slid blocks of coherent lithology have inherited the original tectonic framework which suggests the crucial role tectonics play in the fragmentation of the compact rock masses and the origin and development of the ameka complex landslide area similarly the main scarps were also parallel to the principal tectonic features the local tectonic framework is dominated by faults of the same orientation as the regional structures of the main ethiopian rift such parallel tectonic frameworks display clear links between the extension of the main ethiopian rift and the tectonic development of the landslide area the ameka complex landslide developed in several episodes over thousands of years according to the radiocarbon data the last of the larger displaced blocks representing only 2 of the total area most likely slid down in the seventh century ad the main scarps namely the high scarps in the western part are unstable over the long term and toppling and falling type slope movements can be expected here in the future

landslides in a densely populated county at the footslopes of mount elgon uganda characteristics and causal factors manjiya county on the ugandan slopes of mount elgon is a densely populated mountainous area where landslides have been reported since the beginning of the twentieth century the numerous fatalities and the damage done during the extreme rainfall events of 1997 to 1999 drew attention to this phenomenon in order to better understand the causal factors of these landslides 98 recent landslides in the study area mostly debris slumps were mapped and investigated together they displaced 11 millions m 3 of slope material statistical analysis shows that landslides dominate on steep concave slope segments that are oriented to the dominant rainfall direction northeast and at a relatively large distance from the water divide based on landslide occurrence and impact four different zones can be distinguished within the study area causal factors as well as landslide characteristics differ greatly between the four zones besides the fact that steep slopes high rainfall and typical soil properties and stratification turn manjiya into an inherently unstable area human interference cannot be neglected whereas deforestation has reduced the stability of the shallow soils on the eastern slopes of the study area the excavation of slopes mainly for house building is an important destabilizing factor for the western slopes the growing population density not only increases the risk on damage but hampers the search for solutions for the landslide problem as well d 2005 elsevier b v all rights reserved

inventory of landslides and susceptibility mapping in the dessie area northern ethiopia abstract a comprehensive study of landslide processes was carried out in the city of dessie and its environs in northern ethiopia the study area consists of a graben bounded by steep fault scarps and characterized by highly weathered tertiary basaltic rocks covered with quaternary deposits a method of landslide susceptibility mapping that adapts to the area of the hillside about 16 km2 is presented first a preliminary zoning was made by dividing the area into a discrete number of smaller units having similar susceptibility to sliding followed by semi quantitative field investigation of the geological geotechnical geomorphological hydrogeological and anthropogenic factors that contribute to the susceptibility of the units to landslide activity the final landslide susceptibility map was accomplished by using classical overlay procedures of established maps representing the different influencing factors the validity of the method was checked by means of a landslide hazard map that showed the actual distribution of landslide episodes that have occurred in the past finally four broad landslide susceptibility zones and 22 specific active landslide sites were identified the most important landslide types were complex earth and debris slides and flows in silty clay soils associated with alluvial and colluvial deposits overlying highly weathered basalts intact basaltic rocks experienced rock fall and toppling in steep slope areas large scale landslides have been initiated mostly by surface water and groundwater during the wet season

the complex nature of creep movements on steeply sloping ground in southern rwanda long term soil creep motion is often represented as a type of laminar flow with velocity vectors parallel to the slope and constant in time records on a hillslope in southern rwanda reveal that creep movements there compare more with turbulent flow characterized by a a1 humic horizon superlayer creeping over a subsoil affected by more irregular creep deformation

size distribution of loess slides in relation to local slope height within different slope morphologies abstract loess slides are widespread and dangerous gravity induced surface processes on the loess plateau of north central china the local slope height and slope morphology have been considered as important conditioning factors for landslide susceptibility mapping however the quantitative relationship between landslide size and local slope height within different slope morphologies is not very clear in this study an inventory of 155 loess slides was developed based on detailed field investigation and remote sensing image interpretation statistical analysis and gis were applied to find the quantitative relationships between the size of these loess slides and local slope height in different types of slope morphologies the analysis shows that the relationship between the loess slides volume and area exhibits a similar trend within different types of slope morphologies in addition the analysis demonstrated that loess slides are more frequent on local slope height from 40 to 100 m stepped slopes with higher pore water pressure are prone to sliding and approximate 34 19 of total loess slides occur in these stepped slopes moreover the analysis shows that the mean loess slide area and volume rapidly increase with increasing local slope height furthermore the result underlines the fact that both the local slope height and the slope morphology are two fundamental factors that control the occurrence as well as size distribution of loess slides the loess slide size remarkably increases with increasing local slope height within every type of slope morphologies these findings indicate that local slope height can limit the loess slide size and their spatial extent moreover we quantified the correlation between the loess slide size and local slope height using power law form and the scaling exponents of the correlations are different within different slope morphologies

characteristics of the size distribution of recent and historical landslides in a populated hilly region despitetheavailabilityofstudiesonthefrequencydensityoflandslideareasinmountainousregions frequency areadistributions of historical landslide inventories in populated hilly regions are absent this study revealed that the frequency area distribution derived from a detailed landslide inventory of the flemish ardennes belgium is significantly different from distributions usually obtainedinmountainousareaswherelandslidesaretriggeredbylarge scalenaturalcausalfactorssuchasrainfall earthquakesorrapid snowmelt instead the landslide inventory consists of the superposition of two populations i e i small b1 2 10 2 km 2 shallow complexearthslides that areat most30yrold and ii large n1 2 10 2 km 2 deep seatedlandslides that areolder than100yr both subpopulations are best represented by a negative power law relation with exponents of 0 58 and 2 31 respectively this study focused on the negative power law relation obtained for recent small landslides and contributes to the understanding of frequency distributions of landslide areas by presenting a conceptual model explaining this negative power law relation for small landslides in populatedhilly regions according to the model hilly regions canberelatively stable under the present dayenvironmental conditions andlandslidesaremainlytriggeredbyhumanactivitiesthathaveonlyalocalimpactonslopestability therefore landslidescausedby anthropogenic triggers are limited in size and the number of landslides decreases with landslide area the frequency density of landslide areas for old landslides is similar to those obtained for historical inventories compiled in mountainous areas as apart from the negative power law relation with exponent 2 31 for large landslides a positive power law relation followed by a rollover is observed for smaller landslides however when analysing the old landslides together with the more recent ones the present day higher temporal frequency of small landslides compared to large landslides obscures the positive power law relation and rollover 2007 elsevier b v all rights reserved

heavy metals content and distribution in the surface sediments of the guangzhou section of the pearl river southern china the long term industrialization and urbanization of guangzhou city may lead to heavy metal contamination of its aquatic sediment nevertheless only few studies have been published on the distribution and contamination assessment of heavy metals in this urban river sediment thus the major objective of this study was to quantitatively assess contamination of heavy metals and their chemical partitioning in the sediments of the guangzhou section of the pearl river gspr surface sediment samples were collected at 10 sites in the main river and 12 sites in the creeks of the gspr the total content of cd was determined by graphite furnace atomic adsorption spectrometry gf aas and content of cr cu pb and zn was determined by inductively coupled plasma atomic emission spectrometry icp aes the chemical partitioning of these heavy metals in the sediments of the main river was determined by the sequential selective extraction sse method results indicated that the average total concentrations of cd cr pb cu and zn in the sediments of the main river were 1 44 63 7 95 5 253 6 and 370 0 mg kg respectively whereas they were 2 10 125 5 110 1 433 7 and 401 9 mg kg in the sediments of the creeks the sediment at m4 and c9 sites was heavily contaminated with about 8 and 11 of toxic unit respectively cr cu pb and zn were mostly bound to organic matter and in the residual phase whereas cd was mostly associated with the soluble and exchangeable phase and the residual phase the mobility and bioavailability of cd zn and cr in the sediments of the main river were relatively higher than cu and pb due to higher levels in the soluble and exchangeable fraction and the carbonate fraction the potential acute toxicity in the sediments of the main river and creeks was mainly caused by cu contamination accounting for 21 7 37 1 and 16 9 46 3 of the total toxicity respectively followed by zn and pb adverse biological effects induced by heavy metals would be expected in the sediments of the gspr therefore the sediments of the gspr especially at m4 and c9 sites need to be remediated to maintain aquatic ecosystem health

topographic and road control of mega gullies in kinshasa dr congo abstract diachronic mapping 1957 1967 2007 and 2010 shows an exponentially growing mega gully network since roads were constructed through in the forests and plantations which occupied the sandy soils of the high town of kinshasa we found that the spatial occurrence of the mega gullies width 5 m in this newly urbanized environment is controlled by two factors first there is a topographic control given by the relation s 0 00008 a 1 459 with s being the slope gradient m m 1 of the soil surface at the gully head and a the drainage area ha above the head there is also a road control expressed by s 22 991 lc 1 999 with lc being the cumulated length of roads in the basin above the gully head the co existence of both controls reflects the fact that the local sands are highly permeable and hence roads are more important generators of continuous runoff the s a relation noted above should not be applied outside the town where the road network is less dense in contrast the s lc relation may be used in both the town and rural areas underlain by porous soils where roads are the only generators of continuous runoff we further conclude that the high town of kinshasa is one of the most vulnerable places for gullying and gullying can potentially transform the town into a badland artisanal gully treatment is more successful than generally believed and the s lc relation can be a tool for mega gully prevention

the extent and significance of mass movements in eastern africa case studies of some major landslides in uganda and kenya the east african region has experienced major landslides in recent years these landslides have caused many fatalities and injuries loss of many hectares of productive farmlands and destruction to infrastructure such as roads railways and bridges the warm and wet climate of the landslide prone regions causes rapid weathering and produces a regolith weaker than the underlying rock with an interface between the two layers this interface serves as the most common plane along which landslides are initiated once it becomes saturated landslides in the region are associated with steep topography human activities such as deforestation overgrazing and unplanned farming on steep slopes and are induced by earthquakes and high intensity of rainfall the landslide prone areas are agriculturally very productive and the inhabitants depend on agriculture for their livelihood the areas also contribute substantially to the national food reserve the landslides are therefore a burden to the economies of the individual farmers and national governments of the region

human impact on the environment in the ethiopian and eritrean highlands a state of the art abstract this review analyses the environmental evolution of the ethiopian highlands in the late quaternary the late pleistocene 20 000 12 000 14c years bp was cold and dry with 1 low lake levels in the rift valley 2 large debris fans on the flanks of lake abhe basin and 3 the blue nile transporting coarse bedload then a period with abundant and less seasonal rains existed between 11 500 and 4800 14c years bp as suggested by increased arboreal pollen high river and lake levels low river turbidities and soil formation around 5000 4800 14c years bp there was a shift to more arid conditions and more soil erosion many phenomena that were previously interpreted as climate driven might however well be of anthropic origin thick sediment deposits on pediments as well as an increase of secondary forest scrub and ruderal species in pollen diagrams are witnesses of this human impact one important aspect of the late quaternary palaeoenvironment is unclear changes in nile flow discharges and rift valley lake levels have been linked to changes in precipitation depth most authors do not take into account changes in land use in the highlands nor changes in the seasonality of rain both of which can lead to a change in runoff coefficients tufa and speleothem deposition around 14 000 years ago tend to indicate that at the end of the last glacial maximum lgm conditions might have been wetter than generally accepted the most important present day geomorphic processes are sheet and rill erosion throughout the country gullying in the highlands and wind erosion in the rift valley and the peripheral lowlands based on existing sediment yield data for catchments draining the central and northern ethiopian highlands an equation was developed allowing to assess area specific sediment yields sy 2595a 0 29 n 20 r 2 0 59 where sy area specific sediment yield t km 2 year 1 and a drainage area km2 with respect to recent environmental changes temporal rain patterns apart from the catastrophic impact of dry years on the degraded environment cannot explain the current desertification in the driest parts of the country and the accompanying land degradation elsewhere causes are changing land use and land cover which are expressions of human impact on the environment deforestation over the last 2000 3000 years was probably not a linear process in ethiopia studies on land use and land cover change show however a tendency over the last decades of increasing removal of remnant vegetation which is slowed down or reversed in northern ethiopia by a set aside policy ongoing land degradation requires urgent action at different levels of society soil and water conservation swc structures are now widely implemented local knowledge and farmer s initiatives are integrated with introduced swc techniques at various degrees impact assessments show clear benefits of the soil conservation measures in controlling runoff and soil erosion in high rain areas runoff management requires greater emphasis during the design of soil conservation structures in such areas investment in swc might not be profitable at farm level although benefits for society are positive this pleads in favour of public support the present land degradation in the ethiopian highlands has a particular origin which includes poverty and lack of agricultural intensification causes of these are to be found in the nature of past and present regional social relations as well as in international unequal development this review strengthens our belief that under improved socio economic conditions land husbandry can be made sustainable leading to a reversal of the present desertification and land degradation of the ethiopian highlands

quantitative analysis of land surface topography land surface topography significantly affects the processes of runoff and erosion a system which determines slope aspect and curvature in both the down slope and across slope directions is developed for an altitude matrix also the upslope drainage area and maximum drainage distance are determined for every point within the altitude matrix a fortran 66 program performs the analysis

enrichment and toxicity of trace metals in near shore bottom sediments of cuddalore se coast of india in order to identify contaminating trace metals and their sources studies on trace metals are often included in routine environmental monitoring programs twenty five near shore bottom sediment samples from the inner shelf region near cuddalore of the bay of bengal were analysed for sediment texture organic matter carbonate caco3 concentrations and total trace metal concentrations ttms fe mn cr cu ni co pb zn and cd in order to evaluate geochemical processes such as enrichment and their origin the presence of carbonates 2 5 5 8 indicates the dominance of calcareous shells in the region a relatively high percentage of organic matter 0 2 3 9 is attributed to the predominance of finer sediments entering through the minor rivers high concentrations of ttms in fine and organic rich sediments are influenced by municipal and industrial sources which contention is well supported by correlations of ttms concentrations with fe mn fractions geoaccumulation index igeo calculations indicate that cr cu ni pb and cd concentrations are above the values expected from their presence in the discharge of effluents from the industrial zones bordering the shoreline comparing the findings of the present study with those from different parts of the world cr cu ni pb appear to be enriched in the sediments of the region

revisiting nitic horizon properties of nitisols in sw ethiopia abstract nitisols are a soil group whose nature and genesis are relatively poorly documented in order to better understand the development of nitic horizons characterized by a blocky structure and shiny ped faces soil profiles in a major nitisol region in ethiopia were analysed using physico chemical mineralogical and micromorphological methods as well as mossbauer spectroscopy factors that are identified as contributing to nitisol development are i the presence of open 2 1 clays besides dominant kaolinite ii seasonal cycles of wetting and drying contributing to strong blocky soil structure development and iii exceptional fe oxide characteristics particularly extremely small particle size together with the presence of abundant clay coatings these fe oxide characteristics may explain the shiny aspect of ped faces that is characteristic of nitic horizons the profiles are affected by an admixture of surface derived volcanic ash components which might be common in nitisol regions and which puts into question the use of silt clay ratio as a requirement for this wrb reference soil group

does the topographic threshold concept explain the initiation points of sunken lanes in the european loess belt abstract sunken lanes or road gullies are a common geomorphic feature in the european loess belt these landforms are usually created by various processes over time water erosion mass movements and traffic they are important for ecology and biodiversity for recreation and transport as well as from a hydrological and geomorphological perspective e g by enhancing the runoff and sediment connectivity of the landscape nonetheless little is known about their origin and evolution the formation of sunken lanes is typically only understood in qualitative terms while no studies so far have provided a quantitative analysis of their initiation conditions to address this research gap and to improve our geomorphic understanding of this landform we investigated to what extent sunken lanes can be treated and described as a gully erosion process more specifically we explored to what extent their position in the landscape and their characteristics can be explained by the topographic slope area sa threshold that typically controls gully initiation s k a b with k and b empirical constants based on field surveys and lidar data analyses we determined the slope gradient of the soil surface s and contributing area a for 132 representative sunken lane heads in the belgian loess belt and collected data on several other characteristics position of initiation and sedimentation points width depth and length of each sunken lane our results show a very large scatter on the s and a values moreover the morphological characteristics of sunken lanes e g width and length showed no clear relation with these values however a very weak sa threshold relation with a low b exponent 0 016 and a low k coefficient 0 022 could be identified overall our results show that the formation of sunken lanes is not in line with the topographic threshold conditions that govern the initiation of gullies across different environments the low k coefficient and the lack of a strong correlation between initiation slope and contributing area point towards an overall higher susceptibility to the formation of sunken lanes than the formation of gullies this supports the conclusion that not only concentrated flow detachment and transport but especially human activities mainly traffic erosion play a major role in the initiation and development of sunken lanes

main types of soil mass failure and characteristics of their impact factors in the yuanmou valley china abstract gully erosion is a dominant process causing soil loss in the yuanmou valley of yunnan province china soil mass failure is a common process involved in gully development the development of the gully and the occurrence of mass failure are interdependent and mutually promotive but mass failure types have not been very well understood in this study we identify the main types of soil mass failure and the characteristics of their impact factors in the yuanmou valley a detailed field survey was conducted in may 2010 in a representative area of the studied region and selected soil parameters were measured in the field and laboratory results showed that there are four different soil mass failure types falling sliding exfoliating and toppling each having unique characteristics of geology topography soil and climate examination of these characteristics indicates that the occurrence of mass failure is controlled by four factors 1 the typical geological structure of the yuanmou group represented by alternating layers of sand and clay 2 the different terrain and landforms 3 the different gully development stages and 4 the particular soil properties under special weather conditions including a dry hot climate with distinct wet and dry seasons

accumulation of contaminant metals in marine sediments of halifax harbour nova scotia environmental factors and historical trends abstract sediments in halifax harbour have accumulated contaminant metals hg cu zn and pb as a result of discharge of untreated sewage and industrial waste leaching of land fill waste and surface drainage concentrations of contaminants in210pb dated sediment cores became significant about 1880 and rose rapidly after 1900 reaching maximum concentrations in the decades between 1950 and 1980 mean concentrations of hg increased from 0 2 g g 1 in pre 1890 sediments to 1 6 g g 1 in the 20th century similar enrichments for cu changed the concentration from 26 to 88 g g 1 for zn from 90 to 250 g g 1 and for pb the increase was from 12 to 206 g g 1 statistical factor analyses of geochemical data have been used to identify 1 primary contaminants directly associated with waste discharge these include total and organic bound forms of cu zn and pb 2 secondary contamination attributed to leaching and modification of primary contaminants include acid labile forms of zn ni and cu 3 diagenetic modification of buried sediments are identified by total and labile forms of mn 4 dispersion of contaminants from land surface drainage are characterized by fine grained aluminosilicates historical trends in the changing dominance of these environmental factors reflect changes in industrial activity urban growth and changes in the use of metals in paints domestic and industrial chemicals and in the combustion of fuels

relationship between middle stratiform clouds and large scale circulation over eastern china 1 eastern china is the globally unique land region with lots of middle stratiform clouds in cold seasons the distribution of this specific stratiform cloud is determined by three main factors viz relative humidity stable stratification and ascending motions the large relative humidity in cold seasons provides a basic moisture condition for clouds the ascending motions generated by the convergence in the low atmosphere and divergence in the middle troposphere provide a favorable dynamical condition for middle clouds and the midlatitude temperature inversion provides a favorable stable stratification for the stratiform clouds in addition the co effects of the divergence in the low and middle atmosphere dominate the middle stratiform cloud amount over eastern china

present environment of dam lake sambe southwestern japan a geochemical study of bottom sediments geochemical analyses of lakebed and core sediments from lake sambe on the outskirts of oda city in shimane prefecture in southwestern japan were carried out in order to assess the water quality and the concentration and distribution patterns of sixteen elements the lake water showed a stratified condition with respect to dissolved o2 and as fe and mn concentrations in the bottom layers which increased in the summer the chemical composition of the sediments as measured by x ray fluorescence included major and trace elements p ca sc ti v cr fe ni cu zn as sr zr pb and th and total sulfur ts elevated values of as zn v fe p and ts were present in several layers of the upper cores from 0 to 5 cm and other surface sediments increases in the abundances of these metals in lake sediments are probably related to the reducing condition of the sediments fine grained organic rich sediments and post depositional diagenetic remobilization moreover correlations between the concentrations of trace metals and iron in the sediments suggest their adsorption onto fe oxy hydroxides whereas correlations with sulfur indicate that they were precipitated as fe sulfides the average abundances of as pb zn and cu exceeded the lowest effect level and interim sediment quality guideline values that the new york state department of environmental conservation and the canadian council of ministers of the environment determined to have moderate impact on aquatic organisms in addition concentrations of as and zn exceeded the coastal ocean sediment database threshold value indicating potentially toxic levels therefore the presence of trace metals in the lake sediments may result in adverse effects on biota health

ravine formation on steep slopes forward versus regressive erosion some case studies from rwanda summary observations on steep slopes in rwanda reveal that human interventions on surficial drainage can introduce gullying on places where runoff normally leads to diffuse or ephemeral rill erosion in such cases an initial runoff incision or slide scar respectively due to an artificial concentration of runoff or underflow grows in downslope direction mainly by runoff incision this type of progressive or forward gully development contrasts with the more classical regressive development here only observed in places where the flow gradient is less than 7 8

regional mapping and characterisation of old landslides in hilly regions using lidar based imagery in southern flanders abstract analysis of lidar derived imagery led to the discovery of more than 330 pre holocene to recent landslides in southern flanders 4850 km 2 the morphology of three landslides including the 266 5 ha deep seated gravitational slope deformation in alden biesen was investigated in more detail the analysis of the morphological and topographical characteristics width length relation frequency area distribution and topographical threshold of the landslides revealed important differences compared to the characteristics reported in other landslide studies and helped understanding possible landslide triggering mechanisms especially the possibility of a seismic origin of the landslides was investigated finally a heuristic model for region wide landslide susceptibility mapping was successfully tested the susceptibility model and map allow prediction of future landslide locations and contribute to better understanding the role of individual causal factors on landslide location and spatial density the results suggest that landslides on low gradient soil mantled hills are a more important contributor to landscape evolution of hilly areas than was hitherto thought the morphology of all hilly regions of flanders is clearly marked by landslide processes and higher landslide densities often coincide with the presence of quaternary active faults this study further shows that high resolution topographical data such as lidar significantly contributes to a better detection of old previously unknown landslides

mechanism of reactivated badu landslide in the badu mountain area southwest china this paper presented the reactivated mechanism of badu landslide according to site investigations monitoring finite element and limit equilibrium analyses finite element analysis incorporating a stability analysis with the finite element stress based method revealed a large railway cut triggered a localized slide in the upper part of badu landslide rather than a global failure and piles in three rows were effective in stabilizing the reactivated zone monitoring results and the limit equilibrium analysis showed that the landslide underwent multi instabilities rather than a global failure due to a rise in groundwater table in rainy season the mechanism of reactivated badu landslide was finally proposed i e grading creeping sliding mechanism which helped designers to propose the most suitable mitigation measures to stabilize the landslide

land use changes on the slopes of mount elgon and the implications for the occurrence of landslides abstract a reconstruction of land use changes and the implications thereof for landslide occurrence on critical slopes of mount elgon in eastern uganda were undertaken aerial photographs taken in 1960 formed the benchmark for the analysis of respective land use changes between 1995 and 2006 using 30 m landsat tm and 20 m spot ms images landslide sites were mapped using a mobilemapper and terrain parameters were derived using a 15 m digital elevation model a supervised classification approach was employed to generate land cover maps from which the areas of three land cover classes agricultural fields woodlands and forests were calculated a post classification comparison change detection technique revealed different trends in land cover change between the periods 1960 1995 and 1995 2006 whereas there were minimal land use changes between 1960 and 1995 the period 1995 2006 marked a considerable loss of woodlands and forest cover particularly on steep concave slopes 36 58 of the national park the encroachment onto the critical slopes was noted to have induced a series of shallow and deep landslides in the area all the mapped landslides were noted to lie on steep concave slopes of a northerly orientation which had been opened up for cultivation deforestation and cultivation alter the soil hydrological conditions on steep concave slopes rendering them susceptible to saturation this may trigger debris flows during rainfall events there is a need to restore forest cover on the fragile steep slopes and restrain local communities from opening up new areas for cultivation on critical slopes particularly within the protected area

a data based landslide susceptibility map of africa abstract our understanding of the spatial patterns of landslides in africa is limited with available landslide studies typically focusing on only one or a few study areas moreover africa is clearly underrepresented in terms of available landslide inventories this study aims to produce a first continent wide landslide susceptibility map for africa calibrated with a well distributed landslide dataset we reviewed the literature on landslides in africa and compiled all available landslide inventories ca 10 800 landslides supplemented by additional landslide mapping using google earth imagery in underrepresented regions ca 7250 landslides this resulted in a dataset of approximately 18 050 landslides various environmental variables were investigated for their significance in explaining the observed spatial patterns of landslides to account for potential mapping biases in the dataset we used monte carlo simulations that selected different subsets of mapped landslides to test the significance of the considered environmental variables based on these analyses we constructed two landslide susceptibility maps for africa one for all landslide types and one excluding the known rockfalls in both maps topography is by far the most significant variable we evaluated the performance of the fitted multiple logistic regression models using independent subsets of landslides selected from the total dataset overall both maps perform very well in predicting intra continental patterns of landslides in africa and explain about 80 of the observed variance in landslide occurrence to further test the robustness and sensitivity to mapping biases we also modelled landslide susceptibility while excluding regions with arid climates as landslides in these environments are expected to be better preserved over time and therefore likely relatively overrepresented despite this potential bias the effect on the landslide susceptibility model is limited based on the constructed database and our analyses we further discuss potential research gaps for landslide prediction in africa and at continental scales for example analysis of the african countries mean landslide susceptibility shows a lack of landslide research in various countries prone to landsliding e g guinea gabon lesotho madagascar apart from the intrinsic value of this landslide susceptibility map as a natural hazard risk management tool the map and compiled database are highly promising for other applications for example we explored the potential significance of landslides as a geomorphic process by confronting our landslide susceptibility map with an available database of measured catchment sediment yield for 500 rivers in africa overall a significant positive but relatively weak relation between landslide susceptibility and sediment yield is observed

spatial patterns of old deep seated landslides a case study in the northern ethiopian highlands abstract during the last decade slope failures were reported in a 500 km2 study area in the geba werei catchment northern ethiopia a region where landslides were not considered an important hazard before field observations however revealed that many of the failures were actually reactivations of old deep seated landslides after land use changes therefore this study was conducted 1 to explore the importance of environmental factors controlling landslide occurrence and 2 to estimate future landslide susceptibility a landslide inventory map of the study area derived from aerial photograph interpretation and field checks shows the location of 57 landslides and six zones with multiple landslides mainly complex slides and debris flows in total 14 8 of the area is affected by an old landslide for the landslide susceptibility modelling weights of evidence wofe was applied and five different models were produced after comparison of the models and spatial validation using receiver operating characteristic curves and kappa values a model combining data on elevation hillslope gradient aspect geology and distance to faults was selected this model confirmed our hypothesis that deep seated landslides are located on hillslopes with a moderate slope gradient i e 5 13 the depletion areas are expected on and along the border of plateaus where weathered basalts rich in smectite clays are found and the landslide debris is expected to accumulate on the amba aradam sandstone and upper antalo limestone as future landslides are believed to occur on inherently unstable hillslopes similar to those where deep seated landslides occurred the classified landslide susceptibility map allows delineating zones where human interventions decreasing slope stability might cause slope failures the results obtained demonstrate that the applied methodology could be used in similar areas where information on the location of landslides is essential for present day hazard analysis

processes and rates of rock fragment displacement on cliffs and scree slopes in an amba landscape ethiopia abstract distinct rock fragment displacements occur on the ambas or structurally determined stepped mountains of the northern ethiopian highlands this paper describes the rock fragment detachment from cliffs by rockfall quantifies its annual rate and identifies factors controlling rock fragment movement on the scree slopes it further presents a conceptual model explaining rock fragment cover at the soil surface in these landscapes in the may zegzeg catchment dogu a tembien district tigray rockfall from cliffs and rock fragment movement on debris slopes by runoff and livestock trampling were monitored over a 4 year period 1998 2001 rockfall and rock fragment transport mainly induced by livestock trampling appear to be important geomorphic processes along a 1500 m long section of the amba aradam sandstone cliff at least 80 t of rocks are detached yearly and fall over a mean vertical distance of 24 m resulting in a mean annual cliff retreat rate of 0 37 mm y 1 yearly unit rock fragment transport rates on scree slopes ranged between 23 1 and 37 9 kg m 1 y 1 this process is virtually stopped when exclosures are established corresponding mean rock fragment transport coefficients k are 32 69 kg m 1 y 1 on rangeland but only 3 9 kg m 1 y 1 in densely vegetated exclosures a conceptual model indicates that besides rockfall from cliffs and argillipedoturbation all factors and processes of rock fragment redistribution in the study area are of anthropogenic origin

a comparison of statistical and deterministic methods for shallow landslide susceptibility zoning in clayey soils abstract shallow landslides are widespread in different geological contexts and generally occur as multiple events over large areas when these phenomena involve fine grained soils they may cause serious consequences in terms of environmental and property damages and thus their spatial forecasting becomes a relevant issue for land use planning and design purposes the existing literature provides several methods for landslide susceptibility assessment categorized in qualitative and quantitative methods when dealing with analyses at large scale 1 5000 quantitative methods are generally preferred in this paper landslide susceptibility maps are produced for a study area prone to shallow landsliding located in catanzaro southern italy to this aim two quantitative methods are implemented the statistical information value method and the deterministic trigrs model the two approaches are compared by means of two indicators of the grade of correctness of the landslide susceptibility maps the area under curve of the roc curve auc and the overestimation index oi the results of the analyses in terms of auc values demonstrate the effectiveness and consistency of both methods in performing the susceptibility mapping of the study area when the oi values are considered the results provided by the deterministic model are slightly better than the ones resulting from the statistical analysis this does not come as a surprise for the case study at hand and it can be ascribed to the availability within the study area of a reliable database of soil properties and an in depth knowledge of the behaviour of the considered landslides

evaluation of trace metal enrichments from the 26 december 2004 tsunami sediments along the southeast coast of india the tsunami sediments deposited after the december 2004 tsunami were sampled immediately in the coastal environment of tamil nadu state on the southeast coast of india fifty four sediment samples were collected and 14 representative samples were selected to identify the level of metal contamination in tsunami sediments the results indicate that the sediments are mainly of fine to medium grained sand and contain significantly high contents of dissolved salts in sediments na k ca 2 mg 2 cl in water soluble fraction due to seawater deposition and evaporation correlation of acid leachable trace metals cr cu ni co pb zn indicate that fe mn oxyhydroxides might play an important role in controlling their association between them enrichment of trace metals is observed in all the locations with reference to the background samples high values of trace metals in the southern part of the study area are due to the large scale industries along the coast and they are probably anthropogenic in nature and of marine origin which could cause serious environmental problems

spatial patterns causes and consequences of landslides in the gilgel gibe catchment sw ethiopia abstract the gilgel gibe catchment in sw ethiopia is one of the areas in east africa affected by landslides to better understand the patterns and the causal factors of these landslides all landslides in a small study area 14 km in the hilly parts of the gilgel gibe catchment were mapped and analyzed in total 60 landslides were mapped these landslides caused a displacement of 1 million m slope material which corresponds to a mean displaced volume of 50 ton ha 1 y 1 in the last 20 years moreover many landslides deliver directly sediment to the rivers and hence increase the sediment load in the rivers this soil loss to the rivers was estimated at 11 ton ha 1 y 1 during the same period high annual rainfall ca 2000 mm y 1 lithological and pedological properties and to a lesser extent steep 16 slopes turn the area into an inherent unstable situation and can be indicated as preconditions for the landslides in the study area distance to rivers is significantly the most important precondition as slopes near rivers are less stable than slopes further away from the rivers this is mainly caused by river incision and bank erosion which often occur in the area and which can be attributed to increased runoff due to deforestation over the past 20 years therefore recent deforestation caused more shallow landslides but also indirectly more deep seated landslides close to the rivers heavy rainfall is indicated as the main triggering factor for almost all landslides

a geomorphological assessment of landslide origin at bukavu democratic republic of the congo abstract bukavu on the south coast of lake kivu in the democratic republic of the congo suffers from slow but never ending landsliding this leads to the continuous degradation and destruction of houses buildings and of the roads waterworks and sewerage infrastructure in several districts of the town research of mass wasting processes is hampered by the limited geotechnical and hydrogeological information concerning the deeply weathered tertiary and quaternary lavas there is also a disagreement about the exact location of active faults believed to play a role in the mass wasting additionally there is little information about the exact location and the rate of soil movements and whether ground instability is caused by tectonics and seismics or by increase in hydrostatic pressure based on aerial photographic interpretation landslides cover more than 15 of the town of bukavu thirty one landslides occur outside the bukavu microrift and do not contact active faults rather they occur in actively incising river basins ostensibly caused by neotectonic activity four from the six landslides within the micrograben are bigger and wider than the others apparently governed by pre existing tectonically induced landforms they are adjacent to or crossed by active faults they also fall far below the envelope of topographic thresholds for landslides established for north america and verified in rwanda therefore this threshold a combination of slope at the head of the slide and surface drained to it seems a promising tool to discriminate hydrologically from tectonically seismically induced landslides recent soil movements in bukavu generally correspond to landslide distribution portrayed on the geomorphologic map most bukavu soil movements occur on previous slides therefore from an engineering geologic standpoint old landslides should be avoided or if economically feasible be mitigated

landslide erosion controlled by hillslope material landslide erosion is a primary control of landscape relief a wide ranging analysis of landslide geometry shows that soil based landslides are generally less voluminous than landslides that involve the failure of bedrock and provides refined metrics for estimating the volume of a landslide from the area of the failure

the environmental impact of landslides on the population living on the eastern footslopes of the aberdare ranges in kenya a case study of maringa village landslide landslides are a recognized but poorly studied phenomena in the eastern footslopes of the aberdare ranges in central kenya the aberdare ranges traverse the murang a kiambu nyeri and nyandarua districts of kenya where fatal landslides have occurred in the past a detailed study of a major landslide which occurred at maringa village in murang a district on 30 april 1997 has been undertaken the landslide buried three houses at the toe of a slope and killed all the 11 occupants in their sleep it is shown that the geology and climate of the study area contribute to the prevalence of landslides not only in murang a but in all the andosol covered areas throughout the eastern footslopes of aberdare ranges rapid weathering of pyroclastic rocks in a warm and wet climate create a regolith which is generally weaker than the underlying better cemented basalt and basaltic agglomerates the landsliding occurred when the weathered pyroclastic regolith become saturated after a heavy rainstorm on high mechanically unstable slope which slid over the more stable basalts over saturation of clay soils andosol which were also derived from weathering of pyroclastic rocks contributed to the slope failure the results of the study show that besides fatalities and injuries the landslide destroyed homes plantations and roads

tibetan plateau westerly forcing on the cloud amount over sichuan basin and the early asian summer monsoon 1 data show that a sizeable mechanical effect of the tibetan plateau tp on the westerly referred to as tp westerly forcing is related to a sizeable midlevel cloud amount over sichuan basin sb centered near 30 n and 105 e to the east of the tp an investigation of the interannual variability of clouds over sb demonstrated that the tp westerly forcing closely correlates to the early asian summer monsoon asm when the monsoon commences in mid may the east asian upper tropospheric jet stream moves northward with a southwest northeast tilt the tilt of the jet considerably influences the tp westerly forcing because of the stationary wave pattern superimposed on the westerly jet the early asm is substantially distinct by year in the years the midlevel cloud amount in sb is sizeable which corresponds to a strong tp westerly forcing the tilt of the upper level jet increases and the ascending southerly east of sb in 110 e 125 e strengthens the warming of the troposphere in 110 e 125 e centered near 35 n corresponds to the westerly and southerly changes farther downstream in the 125 e 140 e region the ascending southerly weakens correspondingly an anomalous anticyclonic circulation occurs between sb and japan leading to a westward extension of the north pacific high pressure in the lower troposphere and a reduction in precipitation of the early mei yu season coincidentally the midtropospheric monsoon trough south of the tp weakens implying a weak monsoon in both east asia and south asia furthermore the weak monsoon continues through the early summer

time dependent modeling of fallout radionuclide transport in a drainage basin significance of slow erosional and fast hydrological components abstract the sediment depth distributions of 238pu 239 240pu 241am and 137cs have been measured in a sediment core from the saguenay fjord quebec canada which has been dated to better than 1 yr resolution over the past 100 yr using 210pb the historical record of fallout radionuclide fluxes to the sediments has been estimated using a 210pb constant flux model and variations in the flux distributions have been directly related to changes in the atmospheric input function rates of radionuclide transport through the drainage basin have been predicted using a two component time dependent model composed of terrestrial soil and water phases the latter including catchment basins upstream of the fjord the residence times of 137cs and 239 240pu in the soil component are 1000 and 3000 yr respectively while both radionuclides have equivalent residence times of 1 yr in the water column component the atmospheric burn up of a nuclear powered snap 9a satellite in 1964 has resulted in a well defined 238 pu 239 240 pu horizon appearing in the sediments at the 1967 1968 level the magnitude and timing of the snap 9a derived 238pu distribution are in agreement with the drainage basin model predictions and confirm the absence of post depositional remobilization of pu in these anoxic sediment regimes theoretical estimates of the change in the 241 am 239 240 pu activity ratio in sediments deposited since the 1950 s determined using the drainage basin model are in agreement with the experimental results and indicate that the initial 241 pu 239 240 pu activity ratio for the 1950 s weapons tests was 15 or more while the later weapons tests were characterized by an activity ratio closer to 12

geomorphological evolution and present day processes in the dessie graben wollo ethiopia abstract this paper presents a detailed geomorphological overview of the landforms and processes characterizing the dessie basin a small graben located on the western afar margin ethiopia which is a physiographic province characterized by small closed basins and mountain ranges produced by regional extension large scale geomorphological survey and mapping of the basin allowed to point out the noteworthy morphodynamic role of the present day slope processes including numerous landslides of different typology and size these processes heavily interact with the built up area of dessie town one of the most important cities of ethiopia with ca 200 000 inhabitants which occupies a large part of the basin floor the potential incidence of landslides of different typology in the basin and their possible impact on the urban settlement are put in relation with the distribution of the different landform units which make up the basin surface

compositional analysis and phase relations of soil mass from the active landslides of babai river watershed siwalik zone of nepal abstract the present study focuses on the compositional analysis and phase relationship of soil mass and their role to trigger landslides in the babai river watershed siwalik zone of nepal a total of 76 landslides are selected for sampling and further analysis among 769 active landslides from the total study area for the classification of soil the unified soil classification system uscs is adopted by using both the sieve and hydrometer analysis the centered log ratio clr and mean component fraction of sand silt and clay are obtained from the compositional analysis by using r and codapac v 2 02 21 software correlation of phase relationships like moisture content unit weight specific gravity void ratio porosity and degree of saturation of each soil samples are obtained the results indicate that the degree of saturation is highly correlated with moisture content and void ratio but less correlated with the specific gravity and dry density furthermore the highly correlated variables are checked by multiple regression analysis and the best fitted regression equation was obtained from the phase relation the centered log ratio and mean log of silt clay fraction indicate that silt and clay constituents in the soil are responsible for the landslide initiation in the study area

a new approach to triggering mechanism of volcano landslides based on zeta potential and surface free energy balance abstract the layers of almagre iron rich deposits from tenerife island are the result of thermal metamorphism of soils in contact with lava flow 1073 1273 k these layers of small thickness relative to the basaltic wash are interesting for geotechnical study because the stability of the deposits is determined by the weakest element in this case almagre which acts as a sliding plane the flow of maritime air over the hillsides of the volcanic islands increases the content of cations in ashes deposits this modifies the superficial properties of material that composes the substratum this modification affects the retention of water and the cohesion of material making up the deposit the results show that the presence of sodium and magnesium increased the hydrophobicity of the material which had a weak water retention capacity and strong cohesion at basic ph when there is iron in solution repulsion between the particles is greater than one obtained with other studied electrolytes hence the deposit is less stable and almagre under saturated water conditions constitutes an ideal layer for landslides

channel network extent in the context of historical land use flow generation processes and landscape evolution in the north carolina piedmont intensive agricultural land use in the 18th to early 20th centuries on the southeastern piedmont resulted in substantial soil erosion and gully development today many historically farmed areas have been abandoned and afforested and such landscapes are an opportunity to study channel network recovery from disturbance by gullying channel initiation mapping watershed area slope relationships and field monitoring of flow generation processes are used to identify channel network extent and place it in hydrologic historical and landscape evolution context in six study areas in the north carolina piedmont 100 channel heads were mapped in fully forested watersheds revealing a channel initiation relationship of 380 as1 27 where a is contributing area m2 and s is local slope m m flow in these channels is generated by subsurface and overland flow the measured relative slope exponent is lower than expected based on literature values of 2 for forested watersheds with subsurface and overland flow suggesting that the channel network extent may reflect a former hydrological regime however geomorphic evidence of recovery in channel heads within fully forested watersheds is greater than those with present day pasture present day channel heads lie within hollows or downslope of unchanneled valleys which may be remnants of historical gullies and area slope relationships provide evidence of colluvial aggradation within the valleys channel network extent appears to be sensitive to land use change with recovery beginning within decades of afforestation channel initiation mapping and area slope relationships are shown to be useful tools for interpreting geomorphic effects of land use change copyright 2012 john wiley sons ltd