rotational bulge and one plume convection pattern influence on martian true polar wander abstract motion of the entire solid planet with respect to its spin axis have been proposed on mars this movement is known as true polar wander tpw according to the conservation of angular momentum with no external torque on geological time scales the axis of maximum inertia of a planet is aligned with the rotation axis then rearrangement of masses within the mantle disturbs the planet s inertia and induces tpw the convection pattern on mars is possibly controlled by a sequence of single plumes originating from the core mantle boundary using a homogeneous model of the martian mantle and modelling the plume as a sphere we calculate the inertial tensor perturbations caused by the plume mass anomaly we investigate the stabilizing influence of the remnant rotational bulge due to the lithosphere elasticity on these perturbations it appears that during early martian history the elastic lithosphere was thin enough to allow its fractures under the inertia perturbations induced by a hot plume consequently the lithosphere s behaviour became effectively viscoelastic and the plume could induce large tpw we conclude that one plume convection pattern should have greatly influenced the rotation pole behaviour during early mars history around 4 gyr ago mars already could have experienced two tpw events lasting possibly only a few million years each we then compare our scenario with others already published in the literature

regional test of a model for shallow landsliding landslides mapped in 14 watershed analyses in oregon and washington provide a regional test of a model for shallow landsliding a total of 3224 landslides were mapped in watersheds covering 2993 km2 and underlain by a variety of lithologies including tertiary sedimentary rocks of the coast ranges volcanic rocks of the cascade range and quaternary glacial sediments in the puget lowlands gis geographical information system techniques were used to register each mapped landslide to critical rainfall values predicted from a theoretical model for the topographic control on shallow landsliding using 30 m dems digital elevation models a single set of parameter values appropriate for simulating slide hazards after forest clearing was used for all watersheds to assess the regional influence of topographic controls on shallow landsliding model performance varied widely between watersheds with the best performance generally in steep watersheds underlain by shallow bedrock and the worst performance in generally low gradient watersheds underlain by thick glacial deposits landslide frequency slides km2 varied between physiographic provinces but yielded consistent patterns of higher slide frequency in areas with lower critical rainfall values simulations with variable effective cohesion predicted that high root strength effectively limits shallow landsliding to topographic hollows with deep soils and locations that experience excess pore pressures but that low root strength leads to higher probabilities of failure across a greater proportion of the landscape 1998 john wiley sons ltd language en

modelling the erosional susceptibility of landslide catchments in thick loess chinese variations on a theme by jan de ploey abstract in his 1990 paper catena 17 175 183 jan de ploey proposed a system whereby catchments are viewed as functional units in which geomorphic work results from the combined effects of water erosion and mass movements his measure of erosional susceptibility of catchments es introduced the gravitational potential in addition to the kinetic energy of the eroding agents this modelling of the erosional susceptibility of catchments in terms of energy was being used to explore time dependent variations of es when jan de ploey died also at this time he extended an invitation to the present authors to test and extend his model using our data base on the landslide dominated catchments in the thick loess country of north central china this paper presents a series of new equations expressing variations in es using a data base for over 200 landslides in the loess covered mountainous terrain relative relief up to 1500 m of the lanzhou region of eastern gansu province these equations express the loss of potential energy of the landslide mass in relation to the relative relief and the pressure energy input in the form of rainfall these indices of erosional susceptibility can be used to analyse the differences in response from one catchment to another and through time between the characteristics of vegetation cover including land use hydrology geomechanical behaviour and mechanisms of movement on slopes using certain assumptions on percentage area of catchments affected by mass movement and long term mean annual precipitation in the lanzhou region the es equation suggests an estimate for non clayey materials of about 10 4 m 2 s 2 which is a significantly higher susceptibility value than the mean worldwide value for non clayey materials obtained by de ploey

the use of landslide units in geomorphological mapping an example in the italian dolomites the mapping of processes and landforms found in a particular territory is usually achieved by means of methods and instruments which are universally accepted and adopted such as those of geomorphological mapping in some cases however these methods do not always give complete understanding of a landscape s evolution in particular this happens in environments with a large number of deposits resulting from gravitational processes this paper aims at illustrating an innovative method for mapping gravitational deposits by considering in particular their spatial and temporal relationships and by grouping them into homogeneous units called landslide units the use of these landslide units would facilitate landscape analysis and allow better understanding of areas which are rather complex from the geomorphological standpoint this type of approach is particularly important for application purposes and the dissemination of results on landslide research especially for non specialists within the framework of the teslec project funded by the european union this investigation method has been applied to the area of cortina d ampezzo italian dolomites where more than thirty landslides have been identified and grouped in 12 landslide units these landslide units also incorporate superficial deposits alluvial and lacustrine deposits scree slopes etc genetically linked to the main landslide phenomena each landslide unit includes lower ranked units which may be either landslide bodies or other deposits directly or indirectly related to them as an example the case of the cortina d ampezzo landslide unit is illustrated and discussed

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

the earth as a planet paradigms and paradoxes the independent growth of the various branches of the earth sciences in the past two decades has led to a divergence of geophysical geochemical geological and planetological models for the composition and evolution of a terrestrial planet evidence for differentiation and volcanism on small planets and a magma ocean on the moon contrasts with hypotheses for a mostly primitive still undifferentiated and homogeneous terrestrial mantle in comparison with the moon the earth has an extraordinarily thin crust the geoid which should reflect convection in the mantle is apparently unrelated to the current distribution of continents and oceanic ridges if the earth is deformable the whole mantle should wander relative to the axis of rotation but the implications of this are seldom discussed the proposal of a mantle rich in olivine violates expectations based on evidence from extraterrestrial sources these and other paradoxes force a reexamination of some long held assumptions

seismic performance of loess mudstone slope in tianshui centrifuge model tests and numerical analysis abstract dynamic behavior and failure mechanism of slope during earthquake are hot topics in geotechnical engineering community in tianshui area northwest of china the deformation features of loess mudstone slopes induced by earthquakes are still not well understood the current study aims to discuss the dynamic behavior of the slope under earthquake by performing a series of centrifuge shaking table tests and numerical simulations the results are processed for pga amplificatory effect study and to evaluate the earthquake induced deformation mechanism better agreement is obtained between the results of numerical simulations and centrifuge tests the results indicated that the acceleration response of the loess mudstone slope showed several amplifying characteristic the height effect lithologic effect and surface effect it also proves that the displacements in the loess layer are much larger than mudstone as the input amplitude increased the shear plastic zone developed along a further slide surface tension plastic zone mainly occurred at the crest roughly the regions of earthquake induced deformation state increased with the increase in amplitude of earthquake wave deformations occurred at the upper part of the slope tensile cracks evolved on the crest and the upper part of slope in loess layer moreover failures occurred at slope surface and only slight deformation at slope toe deformations with continuous shear cracks and slope surface upheavals developed at the middle part of slope

neogene clay and its relation to landslides in the southwestern loess plateau china loess occurs widely in northwestern china covering neogene clay and other sedimentary units that overlie the bedrock the neogene clays of the baoji region of shaanxi province north china including the eolian hipparion and paleo sanmen lake fluvial deposits are typical clays of the southern chinese loess plateau these clays are also sensitive key strata controlling the development of large scale landslides along the slope of the loess tableland surrounding the guanzhong basin to investigate the neogene clay types and landslides in the region soil samples were tested and the macro and micro structures of the clay strata were analyzed comprehensive analysis methods including the pipette method and fine x ray diffraction were applied to quantitatively analyze the sample composition and determine the clay mineral types the neogene clays are mainly composed of illite and montmorillonite mixed layer minerals on the williams discrimination diagram of swelling potential both types of clay are medium to strongly expansive soil two case studies illustrate that rainfall reduces the shear strength of the neogene clay and raises the groundwater level rainfall has gradually destroyed the structure of the neogene clay transforming it to sliding belt soil the sliding belt lies mainly within the neogene clay layers significantly affecting the occurrence and characteristics of landslides in baoji the rise in groundwater level and weakening of the shear strength of the neogene clay are important factors in the occurrence of landslides the long term strength is a key factor affecting the development of loess landslides along the loess tableland in baoji

gravity erosion on the steep loess slope behavior trigger and sensitivity abstract gravity erosion is a dominant geomorphic process on the widespread steep loess slopes yet it is not well understood due to the complexity of failure occurrence and behavior this study conducted a series of experiments in the laboratory to test the stability of different slope geometries and rainfalls and then performed a sensitivity analysis to quantitatively explore the triggering mechanisms of mass failure on the steep loess slope a topography meter designed by the authors was used to quantitatively measure the process of gravity erosion and the increase rate analysis method presented by the authors was also used to analyze the sensitivity of gravity erosion the following three types of gravity erosion were observed landslide avalanche and mudslide in an event of rainfall various types of gravity erosion might emerge in the same period and mass failures with the same mode and similar size often adjacently appeared sometimes a group of mass failures might happen on a large slowly slipping block then the increase rate analysis method was used to evaluate variations in the gravity erosion with respect to changes in other causal parameters of rainfall duration intensity and slope height gradient climate driven factors and topography triggers had prominent influences on gravity erosion whether for the total amount or the peak amount in an experiment the largest sensitivity parameter on both landslides and mudslides was that of rainfall duration in comparison topography was relatively less influential for the total amount in an experiment the sensitivity parameters of rainfall duration on the landslide and mudslide were 24 9 and 19 5 respectively while the sensitivity parameter of rainfall intensity on the avalanche was 2 2 for the peak amount in an experiment the sensitivity parameter of rainfall duration on the landslide and mudslide were 5 5 and 15 6 respectively meanwhile the sensitivity parameter of slope gradient on the avalanche was 4 6 the experimental results obtained here provide an insight into the pre failure mechanisms and processes of steep loess slopes

climate change loess and palaeosols proxy measures and resolution in north china the loess plateau of north china is a key region for the study of records of quaternary climatic change various techniques to abstract climatically sensitive data were first applied to the classic loess palaeosol site at luochuan and current views on climatic change in asia have been strongly moulded by results from this central part of the loess plateau data including the magnetic susceptibility granulometry mineralogy geochemistry micromorphology fossil content and inorganic and organic carbon content of asian loess palaeosol series have been used singly and in combination as surrogate measures of palaeoclimates to infer climatic changes with particular reference to changes in the asian monsoon some of this work is reviewed and the status of a number of parameters as climatic proxies is discussed some lithostratigraphic sequences from which proxy measures of climate have been derived are incomplete as shown by erosion surfaces water laminated zones and truncated palaeosol profiles while others provide records of relatively low resolution most descriptions of quaternary climatic changes based on studies of the loess emphasize alternations in the relative dominance of warm and moist v cool dry and dust laden monsoons some recent studies of the much higher resolution loess palaeosol successions on the western margins of the loess plateau have suggested that such changes may sometimes be out of phase with the inference that the current climate model is too simple means of testing this hypothesis are proposed

giant impact basins trace the ancient equator of mars 1 it is shown in this paper that five giant impact basins of mars argyre hellas isidis thaumasia and utopia are located on a single great circle this suggests that the projectiles orbital planes coincided with the equator of mars at the time of impact the projectiles were larger fragments of a heliocentric asteroid that broke apart as it entered the roche limit of mars the mass of the asteroid was at least 9 8 1020 kg 1 5 10 3 times the mass of mars

the source and transport of arsenic in a bedrock aquifer new hampshire usa the geographic distribution of elevated groundwater as concentrations in a fractured silicate bedrock aquifer in central new hampshire correlates with the presence of pegmatites which border late devonian granites and intrude metasedimentary rocks as concentrations in the pegmatites averaged 9 6 mg kg which is much higher than the associated granites 0 24 mg kg and metasedimentary rocks 0 8 mg kg as was concentrated in these pegmatites by partial melting of calcareous metapelites and subsequent recrystallization as granites with low as concentrations and pegmatites with high as concentrations arsenic behaves similarly to b which was also concentrated into these late stage fluids arsenopyrite feass with an oxidation reaction rim of scorodite feaso4 2h2o was observed in aquifer materials elevated as concentrations have been observed to occur in other new england locations in pelitic metasediments intruded by anatectic plutons it is proposed that pegmatite formation from partial melting of pelitic metasediments may be an important mechanism for concentrating as in crystalline aquifer materials which can then cause local as enrichment of groundwaters groundwater as concentrations ranged from 26 nmol l to 5300 nmol l with a median value 210 nmol l that is more than 30 times higher than the median for groundwaters from all of new hampshire 6 5 nmol l high chloride concentrations 1 mmol l resulting from road salt contamination of recharge waters suggest that groundwaters are most likely young 670 nmol l or 50 g l have very low fe concentrations 7 samples with low as 7 fe oxyhydroxides form rapidly and have a neutral or negative net surface charge that does not readily adsorb as at ph 7 fe oxyhydroxide formation is slow and depends on dissolved o2 availability however the resultant fe oxyhydroxides have a positive net surface charge and appear to adsorb as readily

continental lithospheric thickness and deglaciation induced true polar wander the secular drift of the earth s rotation pole which is evident in ils data is a memory of the planet of the last deglaciation event of the current ice age in order to fit the observed rate and direction of drift with an earth model whose viscosity profile is capable of reconciling the free air gravity and relative sea level data of postglacial rebound requires a lithospheric thickness which is substantially in excess of that which might be considered an appropriate average thickness for the entire planet this required thickness which is greater than 250 km is nevertheless in accord with independent estimates of the thickness of the continental lithosphere

the role of seismic triggering in a deep seated mudstone landslide china historical reconstruction and mechanism analysis abstract deep seated mudstone landslides are widely distributed in northwest china the zhengjiamo landslide occurred in 734 ce near taijing tianshui region it was triggered by the main shock of the historical ms 7 0734 ce earthquake the earthquake also induced a wide range of landslides in this area with hundreds of fatalities and many houses destroyed by landslide debris based on a detailed field survey borehole data and mapping a detailed geological reconstruction of the slope was achieved and the geo mechanical features of the claystone involved in the landslide were obtained using the particle flow code to simulate the mechanism of the zhengjiamo landslide the features of the landslide dynamics were obtained using a 5 stage model during the landslide process the slip mass at the front and upper edges exhibited higher mobility than at the rear and bottom edges furthermore the contact bond strength of the sliding body gradually weakened the model indicates that the particle bond strength has a larger influence on the maximum runout distance and landslide debris morphology than the type of weak intercalated layers the slip mass presented a rotational slide pattern and remained on the slip plane throughout the sliding process finally the earthquake uplifted the slope toe which prevented the slip mass from gliding the modelled scenario provided a reasonably good fit to the actual topography verifying the modelling results after the historical earthquake with the clay minerals swelling and shrinking under rainfall and efflorescence conditions the structure of the soft rock changed contributing to the weakening of the sliding rock mass the landslide gradually crept and evolved to its current topography

modelling the erosional susceptibility of catchments in terms of energy summary basically the paper proposes to consider catchments as functional units in which geomorphic work generally results from combined effects of erosion by water and by mass movements or from a combination of erosion by wind by runoff and by mass movements therefore a measure of the erosional susceptibility e s of catchments introduces the gravitational potential beside the kinetic energy of the eroding agents furthermore expressions of e s stress the impact of the spatial distribution of erosion as a much differentiating factor for future research it is recommended to look after timedependent variations of e s for representative drainage basins

influence of topography and volume on mobility of loess slides within different slip surfaces mobility of loess slides has been evaluated using an empirical approach based on a detailed field investigation and remote sensing image interpretation for all the loess slides the affected area increases with increasing loess slides volume from the statistical analysis it is seen that the travel distance has an increasing trend while the coefficient of friction has a decreasing trend with the increase in landslide volume landslide volume determine its travel distance and coefficient of friction that can be shown with a regression equation having simple power law form which indicates that the mobility of loess slides increases with increasing volumes by analogy the greater the energy of the sliding loess mass the stronger is the mobility of loess slide a plot of the travel distance of loess slide versus fall height shows a significant positive power law correlation indicating the increase in mobility of loess slide with fall height the negative power law correlation observed between the travel distance and slope inclination implies that the mobility decreases with the increase of slope inclination three datasets of loess slides characterized by different slip surfaces were distinguished the red clay contact landslides have the strong mobility than landslides in loess and bedrock contact

late quaternary landscape evolution in a small catchment on the chinese loess plateau abstract late quaternary landscape evolution was analysed with reference to a small 0 08 km 2 drainage basin system in southeastern gansu province southwestern chinese loess plateau in this region v shaped valleys with broad valley floors are prominent landscape features whose basic shape already existed prior to mis 2 during mis 2 the valley bottoms were infilled with fluvially reworked loess today forming accumulation terraces infrared optically stimulated luminescence irsl dating of these loess like deposits assigned them to the time span ranging from 22 5 to 17 7 ka bp during the late holocene valley fills were partly eroded and the receiving stream channel was deepened by at least 25 m close to the confluence of the study site s channels these alternating erosion and accumulation phases were triggered by climatic factors or human impact in the most recent past the high landscape sensitivity of the chinese loess plateau has led to increasing soil conservation measures that have effectively confined surface erosion however the lack of drainage on the artificial terraces induces piping processes

reorientation of planets with elastic lithospheres abstract the orientation of a planet is controlled by the positions of the principal axes of the inertia tensor relative to the planetary surface using the theory for the deflection of thin elastic shells the principal axes are computed after emplacement of an arbitrary axisymmetrical load the partial compensation of the load and the partial relaxation of rotational flattening are included in the computation it is found that the amount of reorientation is independent of lithosphere thickness the parameters controlling the amount of reorientation are the location of the load and the size of the load compared to the rotational flattening the results indicate that the tharsis rise has probably reoriented mars by only 3 to 9 and certainly less that 18 the position of the caloris basin on mercury indicates that if the surrounding lava sheet controls the planetary orientation then the lava sheet is probably less than 2000 m thick

time dependent rotational stability of dynamic planets with viscoelastic lithospheres we extend previous work to derive a non linear rotational stability theory governing true polar wander tpw of terrestrial planets with viscoelastic lithospheres we demonstrate analytically and using numerical examples that our expressions are consistent with previous results in the limiting cases of low and infinite i e purely elastic viscosity lithospheres to illustrate the stability theory we compute tpw on mars driven by a simple prescribed mass loading our calculations demonstrate that on short time scales relative to the relaxation time of the viscoelastic lithosphere the rotation axis follows a constrained path that reflects stabilization by remnant strength in the lithosphere but that on long times scales this stabilization disappears and the load ultimately reaches the equator earlier work based on the assumption of a permanent remnant bulge in the case of a purely elastic lithosphere has suggested that martian tpw would not persist for any significant time after a load is emplaced and thus an equilibrium stability theory is sufficient to model long term order 1 myr or longer polar motion of the planet our results suggest in contrast that tpw on mars can continue over time scales on the order of the relaxation time of the lithosphere after load emplacement for sufficiently high lithospheric viscosities this time scale may be comparable to the age of the planet

a sliding consolidation model for flow slides a model is proposed for the behaviour of flow slides in loose cohesionless materials in which the debris spreads out as a uniform sheet excess pore fluid pressures are assumed to be generated for example by undrained loading arising from the collapse of metastable structure in the source area of the flow slide under the influence of these the leading element of the debris moves downslope by basal sliding consolidating as it does so by single upward drainage as a result the pore pressure at the base of the element eventually decays to a value that brings the element to rest hence defining the run out of the flow slide the model is applicable in principle to subaqueous and subaerial flow slides and to pore fluids consisting of water gas or both of these the predictions of the model are tested against the observed behaviour and measured properties of the 1966 flow slide at aberfan south wales the results show that a sliding consolidation model provides a possible mechanism for that event