landslide driven erosion and slope channel coupling in steep forested terrain ruahine ranges new zealand 1946 2011 abstract landslides are an important means of conveying sediment from slopes to channels in steepland environments but landsliding is a discontinuous process this means that any single assessment in time of their contribution to the sediment cascade is of limited value to better understand landscape dynamics and the contribution of landslides to slope channel coupling over time this paper quantifies connectivity over a time span of 65 years in small steep headwater catchments in the southern ruahine range new zealand temporal variability in landsliding and slope channel coupling was assessed using six sets of aerial photography flown between 1946 and 2011 from which over 6900 landslides were mapped in arcgis of which up to 78 connected with the stream network estimates of the volume of material delivered by landslide erosion to headwater channels were based on ground survey measurements of selected landslide scars and suggest that between 1946 and 2011 over 5 million m 3 of sediment was delivered from slopes to channels in the 221 km 2 study area forest cover is not sufficient to prevent this erosion these catchment systems are particularly vulnerable to high magnitude storm events which significantly elevate landslide intensity and enhance sediment delivery as occurred in the mid 1970s the legacy of these events remains in these headwater channels with ongoing consequences for stream and hazard management in and adjacent to the ranges

locating and quantifying geological uncertainty in three dimensional models analysis of the gippsland basin southeastern australia abstract geological three dimensional 3d models are constructed to reliably represent a given geological target the reliability of a model is heavily dependent on the input data and is sensitive to uncertainty this study examines the uncertainty introduced by geological orientation data by producing a suite of implicit 3d models generated from orientation measurements subjected to uncertainty simulations the resulting uncertainty associated with different regions of the geological model can be located quantified and visualised providing a useful method to assess model reliability the method is tested on a natural geological setting in the gippsland basin southeastern australia where modelled geological surfaces are assessed for uncertainty the concept of stratigraphic variability is introduced and analysis of the input data is performed using two uncertainty visualisation methods uncertainty visualisation through stratigraphic variability is designed to convey the complex concept of 3d model uncertainty to the geoscientist in an effective manner uncertainty analysis determined that additional seismic information provides an effective means of constraining modelled geology and reducing uncertainty in regions proximal to the seismic sections improvements to the reliability of high uncertainty regions achieved using information gathered from uncertainty visualisations are quantified in a comparative case study uncertainty in specific model locations is identified and attributed to possible disagreements between seismic and isopach data further improvements to and additional sources of data for the model are proposed based on this information finally a method of introducing stratigraphic variability values as geological constraints for geophysical inversion is presented

geochronology geochemistry and tectonic evolution of the western and central cordilleras of colombia abstract autochthonous rocks of the pre cretaceous continental margin of nw south america the tahami terrane are juxtaposed against a series of para autochthonous rock units that assembled during the early cretaceous allochthonous oceanic crust of the caribbean large igneous province collided with and accreted onto the margin during the late cretaceous we present the first regional scale dataset of zircon u pb la icp ms ages for intrusive and metamorphic rocks of the autochthonous tahami terrane early cretaceous igneous para autochthonous rocks and accreted oceanic crust the u pb zircon data are complemented by multiphase 40ar 39ar crystallization and cooling ages the geochronological data are combined with whole rock major oxide trace element and ree data acquired from the same units to constrain the tectonic origin of the rock units and terranes exposed in the western cordillera cauca patia valley and the central cordillera of colombia the tahami terrane includes lower paleozoic orthogneisses 440 ma that may have erupted during the active margin stage of the rheic ocean basement gneisses were intruded by permian continental arc granites during the final assembly of pangea triassic sedimentary rocks were subsequently deposited in rift basins and partially melted during high t metamorphism associated with rifting of western pangea during 240 220 ma continental arc magmatism during 180 145 ma is preserved along the whole length of the central cordillera and was followed by an early cretaceous out board step of the arc axis and the inception of the quebradagrande arc that fringed the continental margin back stepping of the arc axis may have been caused by the collision of buoyant seamounts which were coeval with plateau rocks exposed in the nicoya peninsular of costa rica rapid westward drift of south america closed the quebradagrande basin in the late aptian and caused medium high p t metamorphic rocks of the arquia complex to exhume and obduct onto the continental margin subduction beneath hot spot derived rocks of the caribbean plateau 100 92 ma formed an intra oceanic arc 92 75 ma which collectively comprise the late cretaceous caribbean large igneous province the remnant ocean basin located between south america and the caribbean large igneous province was partly consumed via continental subduction forming the large antioquia batholith the caribbean large igneous province collided and accreted to south america during 75 70 ma along the cauca almaguer fault resulting in the cessation of both arcs and the paleocene onset of subduction beneath the accreted oceanic crust

chemical weathering in high sediment yielding watersheds new zealand 1 we have determined the chemical erosion yields for fifteen watersheds in new zealand ranging in size from 12 2 to 2928 km2 these rates coupled with previously measured physical erosion yields allow us to compare these two modes of landscape denudation the physical erosion yields are some of the highest measured in the world although in most instances the chemical erosion yields are only a small fraction of the total erosion yields the absolute values are very high our data strongly support the notion that chemical erosion rates are greatly influenced by the yield of physical erosion and that the rapid production of fresh surfaces as a result of high physical erosion rates and subsequent denudation is critical to the high chemical erosion yields observed

gis based landslide hazard predicting system and its real time test during a typhoon zhejiang province southeast china abstract yongjia county zhejiang province is located in southeast china statistics and previous reports have shown that 62 of study area has experienced various forms of slope instabilities including debris flows and landslides the geological buildup promotes the occurrence of landslides since most part of the area is covered by clayey sandstones volcanic tuffs and other types of pyroclastic rocks a gis based system is established to assess and visualize landslide hazards the information layers in the mapgis system are generated by using 11 397 regular grids with size of 5 mm 5 mm at first information matter element model is adopted to compile landslide susceptibility map by using input parameters such as lithology structural geology slope morphology and angle surface waters and human induced geomorphological changes rainfall data quantity of rainfall and rainfall intensity are obtained to calculate the effective rainfall model past landslide frequency with the combination of effective rainfall is used to determine rainfall threshold values and to generate a rainfall threshold map a warning map is compiled including five steps of warning levels by overlaying landslide hazard maps and rainfall threshold maps above the third level the population is noticed while at level five immediate evacuation takes place during yunna typhoon in august 2004 a real time warning was realized based on the landslide hazard susceptibility map and the real rainfall information the gis based system proved to be satisfactory in predicting areas of landslides marking nine critical localities during this catastrophic event

a 3d geological model for the ruiz tolima volcanic massif colombia assessment of geological uncertainty using a stochastic approach based on bezier curve design abstract the ruiz tolima volcanic massif rtvm is an active volcanic complex in the northern andes and understanding its geological structure is critical for hazard mitigation and guiding future geothermal exploration however the sparsity of data available to constrain the interpretation of this volcanic system hinders the application of standard 3d modelling techniques furthermore some features related to the volcanic system are not entirely understood such as the connectivity between the plutons present in its basement i e manizales stock el bosque batholith we have developed a methodology where two independent working hypotheses were formulated and modelled independently i e a case where both plutons constitute distinct bodies and an alternative case where they form one single batholith a monte carlo approach was used to characterise the geological uncertainty in each case bezier curve design was used to represent geological contacts on input cross sections systematic variations in the control points of these curves allows us to generate multiple realisations of geological interfaces resulting in stochastic models that were grouped into suites used to apply quantitative estimators of uncertainty this process results in a geological representation based on fuzzy logic and in maps of model uncertainty distribution the results are consistent with expected regions of high uncertainty near under constrained geological contacts while the non unique nature of the conceptual model indicates that the dominant source of uncertainty in the area is the nature of the batholith structure

exhaustion and steady state models for predicting landslide hazards in the canadian rocky mountains abstract the temporal distribution of landslides can be evaluated by steady state and exhaustion models the probability of landsliding remains constant through time in the steady state model but the probability decreases in the exhaustion model as more slopes fail rock sliding down bedding surfaces on overdip slopes exhausts hazardous sites to leave stable dipslope landforms in kananaskis country in the canadian rocky mountains the distribution of rock slides in this area can be better explained by the exhaustion model than by the steady state model

earthquake induced chains of geologic hazards patterns mechanisms and impacts large earthquakes initiate chains of surface processes that last much longer than the brief moments of strong shaking most moderate and large magnitude earthquakes trigger landslides ranging from small failures in the soil cover to massive devastating rock avalanches some landslides dam rivers and impound lakes which can collapse days to centuries later and flood mountain valleys for hundreds of kilometers downstream landslide deposits on slopes can remobilize during heavy rainfall and evolve into debris flows cracks and fractures can form and widen on mountain crests and flanks promoting increased frequency of landslides that lasts for decades more gradual impacts involve the flushing of excess debris downstream by rivers which can generate bank erosion and floodplain accretion as well as channel avulsions that affect flooding frequency settlements ecosystems and infrastructure ultimately earthquake sequences and their geomorphic consequences alter mountain landscapes over both human and geologic time scales two recent events have attracted intense research into earthquake induced landslides and their consequences the magnitude m 7 6 chi chi taiwan earthquake of 1999 and the m 7 9 wenchuan china earthquake of 2008 using data and insights from these and several other earthquakes we analyze how such events initiate processes that change mountain landscapes highlight research gaps and suggest pathways toward a more complete understanding of the seismic effects on the earth s surface

structural imprints at the front of the choco panama indenter field data from the north cauca valley basin central colombia abstract the northern andes are a complex area where tectonics is dominated by the interaction between three major plates and accessory blocks in particular the choco panama and northern andes blocks the studied cauca valley basin is located at the front of the choco panama indenter where the major romeral fault system active since the cretaceous changes its kinematics from right lateral in the south to left lateral in the north structural studies were performed at various scales dem observations in the central cordillera between 4 and 5 7 n aerial photograph analyses and field work in the folded oligo miocene rocks of the serrania de santa barbara and in the flat lying pleistocene quindio risaralda volcaniclastic sediments interfingering with the lacustrine to fluviatile sediments of the zarzal formation the data acquired allowed the detection of structures with a similar orientation at every scale and in all lithologies these families of structures are arranged similarly to riedel shears in a right lateral shear zone and are superimposed on the cretaceous romeral suture they appear in the central cordillera north of 4 5 n and define a broad zone where 060 oriented right lateral distributed shear strain affects the continental crust the romeral fault system stays active and strain partitioning occurs among both systems the southern limit of the distributed shear strain affecting the central cordillera corresponds to the e w trending garrapatas ibague shear zone constituted by several right stepping en echelon right lateral active faults and some lineaments north of this shear zone the romeral fault system strike changes from nne to n paleostress calculations gave a wnw ese trending maximum horizontal stress and 69 of compressive tensors the orientation of 1 is consistent with the orientation of the right lateral distributed shear strain and the compressive state characterizing the romeral fault system in the area it bisects the synthetic and antithetic riedels and is sub perpendicular to the active romeral fault system it is proposed that the continued movement of the choco panama indenter may be responsible for the 060 oriented right lateral distributed shear strain and may have closed the northern part of the cauca valley thereby forming the cauca valley basin conjugate extensional faults observed at surface in the flat lying sediments of the zarzal formation and quindio risaralda volcaniclastic fan are associatedwith soft sediment deformations these faults are attributed to lateral spreading of the superficial layers during earthquakes and testify to the continuous tectonic activity from pleistocene to present finally results presented here bring newinformation about the understanding of the seismic hazard in this area whereas the romeral fault systemwas so far thought to be themost likely source of earthquakes themore recent cross cutting fault systems described herein are another potential hazard to be considered

long term erosion and exhumation of the altiplano antioqueno northern andes colombia from apatite u th he thermochronology abstract the antioqueno plateau ap in the northern cordillera central colombia is the largest high elevation erosional surface in the northern andes apatite u th he thermochronometry ahe of samples collected from two elevation profiles spanning 2 km of exhumed crustal sections reveal the long term erosional exhumation of the ap sample profiles exhibit ahe ages that increase with elevation from ca 22 ma 760 m at the bottom of regional scarps to ca 49 ma 2350 m on top of the ap a marked inflection point in age versus elevation data at ca 25 ma defines the bottom of the exhumed post oligocene he partial retention zone he prz elevation invariant ages below ca 25 ma record the onset of rapid exhumation and surface uplift of the ap that led to river incision a subtle change in slope within the he prz ca 41 ma is interpreted as a less intense exhumation related cooling episode these two exhumation pulses coincide with the proto andina and pre andina orogenic phases previously proposed for the colombian andes and are synchronous with tectonically driven exhumation events reported for the peruvian bolivian and argentinean andes and for some orogenic systems in the caribbean the pulses are correlated with variations in the rates of convergence between nazca farallon and south america documented for the middle eocene and the late oligocene suggesting continental scale controls on uplift and denudation throughout the andean range ahe data provide an average erosion rate of 0 04 mm yr for the last 25 million years erosion rates during the exhumation pulses were in the order of 0 2 0 4 mm yr similarity between ahe profiles indicates the whole ap was uplifted and exhumed as a coherent structural block corroborating previous structural evidence for the rigidity and coherence of this crustal block in the northern andes our results are in agreement with tectonostratigraphic data in the magdalena and cauca basins and with proposed scenarios for paleogeographic evolution in the northern andes

characterization and comparison of landslide triggering in different tectonic and climatic settings 1 the spatial and temporal distributions of landslides in six catalogues are analyzed in order to better understand landslide triggering mechanisms the six landslide catalogs are new zealand yosemite california grenoble french alps val d arly french alps australia and wollongong new south wales australia landslides are clustered in time for all catalogs for new zealand yosemite australia and wollongong the frequency of landslides varies between 1 and 1000 events per day and is well fitted by a power law there is no characteristic scale for daily rates when the large rates of daily landslides are known to be rain or earthquake triggered our results suggest the same triggering may hold for the small daily rates earthquakes are found to trigger landslides for the new zealand yosemite and australia areas at distances as large as 20 times their fault lengths there is no evidence of landslides triggered by earthquakes for the three other catalogs small m 4 earthquakes have little influence on landslide triggering if any for all catalogs for new zealand yosemite val d arly australia and wollongong the number of landslides per month is significantly correlated with monthly rainfall a correlation with temperature is found only for grenoble and new zealand landslide triggering strong clustering in time and space is more important in new zealand than in grenoble probably because the forcing seismicity and climate is stronger in new zealand than in the french alps but possibly also because of a high sensitivity to landslides in new zealand we suggest that intensity of clustering in space and time can be used to assess the importance of landslide triggering and the processes responsible for triggering

plate motions in the north andean region repeated geodetic measurements with the global positioning system gps provide direct measurements of displacements due to plate motions and active crustal deformation in central america and northern south america an area of complex interaction of the nazca cocos caribbean and south american plates the displacement rates for the period 1988 1991 obtained from the results of the first three central and south america casa gps campaigns are in general agreement with the predictions of the nuvel 1 plate motion model but there are differences in detail between the observations and the model the nazca north andes convergence rate vector measured by gps is different from the nuvel 1 vector at 95 confidence the difference implies that the north andes are moving northward relative to south america the measured convergence between the caribbean plate and the north andes suggests that the southern margin of the caribbean plate is located in the south caribbean deformed belt the april 1991 costa rica earthquake and the cocos caribbean convergence rate determined by gps suggest the possibility of significant ongoing deformation between central america and the stable interior of the caribbean plate our gps results are consistent with deformation of the overriding plates at the convergent margins of central and south america and confirm that active convergence is occurring around much of the southern margin of the caribbean plate from colombia west to costa rica costa rica and panama are not part of the stable caribbean plate instead the south caribbean deformed belt and the north panama fold belt probably represent the southern margin of the caribbean plate

badass gullies fluvio mass movement gully complexes in new zealand s east coast region and potential for remediation abstract this paper reviews gully erosion in the east coast region of new zealand s north island and conceptualises fluvio mass movement gully complexes as badass gully systems tectonic setting and lithological control with steep slopes and a climate influenced by tropical cyclones predispose hill country in the east coast region to gully erosion the clearance of indigenous forest since the late 1800s has dramatically increased catchment erosion and paved the way for development of large scale fluvio mass movement gully complexes these features are a composite of fluvial and mass movement processes they are conceptualised as badass by not conforming to any existing gully model and by generating disproportionate results in east coast catchment sediment cascades their remediation is discussed but their nature means that prevention is better than a cure

thermochronology and tectonics of the central and western cordilleras of colombia early cretaceous tertiary evolution of the northern andes abstract new thermochronological data record a complex cooling history in the central and western cordilleras of colombia that is a function of early cretaceous to late miocene tectonic events alkali feldspar 40ar 39ar cooling ages of 138 130 ma immediately post date the cessation of jurassic arc magmatism and a major unconformity within the retro foreland region of the northern andes we interpret these ages as cooling driven by exhumation in response to either compression driven by subduction of a seamount or extension and oceanward migration of the slab during the earliest cretaceous giving rise to the lower cretaceous quebradagrande arc sequence biotite and alkali feldspar 40ar 39ar data from the palaeocontinental margin reveal the presence of a younger cooling event at 117 107 ma which was contemporaneous with hornblende 40ar 39ar cooling ages obtained from medium high p t metamorphic relicts of a late jurassic early cretaceous subduction channel this cooling event is attributed to exhumation driven by the collision and accretion of a fringing arc against the continental margin and obduction of the subduction channel onto the forearc inverse modelling of zircon and apatite fission track and u th he data from throughout the central and western cordilleras reveals three periods of rapid cooling since the late cretaceous the earliest phase is recorded by jurassic and cretaceous granitoids that cooled rapidly during 75 65 ma we attribute cooling to exhumation of the continental margin during 75 70 ma 1 6 km my which was forced by the collision and accretion of the caribbean large igneous province in the campanian the central cordillera exhumed at moderate rates of 0 3 km my during 45 30 ma which are also observed over widely dispersed regions along the andean chain and were probably caused by an increase in continent ocean plate convergence rates exhumation rates drastically increased in the middle late miocene with the greatest amount occurring in southern colombia as a consequence of the collision and subduction of the buoyant carnegie ridge at 15 ma

regolith stripping and the control of shallow translational hillslope failure application of a two dimensional coupled soil hydrology slope stability model hawke s bay new zealand rainfall triggered regolith landslides constitute a dominant erosional process in new zealand hill country conversion of forest to pasture about 150 years ago decreased the size of event required to trigger slope failure resulting in greater landslide activity recent research indicates that shallow landslides then cause progressive regolith stripping with redeposition at the slope base the exposed bedrock is less permeable than the pre existing regolith cover and the redeposited soil has a higher unit weight hence alterations in both hydrological and geotechnical conditions result changing the triggering thresholds for further failure in this paper three phases of regolith stripping are investigated using a process based model to define variations in both the triggering storms as well as the failure mechanisms under these altered hydrological and geotechnical conditions over time as the regolith is stripped progressively upslope the threshold for slope failure also changes such that the landscape becomes more stable however there is a varying sensitivity to storm type for each of the three phases which adds complexity to the relationship between regolith stripping and slope failure model results suggest different hydrological conditions for slope instability depending on the degree of stripping and redeposition adding further complexity future advances in process based modelling are required for detailed investigation of temporal changes in landscape susceptibility to slope failure and uncertainty in both model parameterisation as well as process representation should be emphasised when applying such models to the long term

explicit implicit integrated 3 d geological modelling approach a case study of the xianyan demolition volcano fujian china abstract explicit interactive modelling and implicit interpolation modelling are the two classic three dimensional 3 d modelling approaches for reconstructing 3 d geological structures from sparse data the limitations of using a single method appear when performing complex regional modelling containing various types of geological structures however due to the complication of spatial geometry computation the integration and coupling of explicit and implicit modelling approaches and modelling results remain difficult and unresolved in this paper we propose an explicit implicit integrated 3 d geological modelling approach for the geometric fusion of different types of complex geological structure models first suitable methods were chosen to model different types of structures for example a hermite radial basis function hrbf based implicit method was used to model general strata faults and folds from geological boundaries and attitudes in a regional geological map explicit approaches such as the skinning method and the free form surface were used to model local detailed structures such as quaternary deposits monoclinic strata and multi layer volcanic edifices from section constrained data finally the explicit models were resampled and converted to implicit models and were coupled with the implicit models leading to the integrated regional modelling of various types of geological structures the validity of the proposed method was tested using the geological map of the xianyan demolition volcano in fujian the results demonstrate that the proposed explicit implicit integrated 3 d geological modelling approach is efficient and effective and this approach provides a probable solution for coupling and integrating multiple modelling methods and geological models for an area containing complex geological structures the 3 d model established using this method can directly reflect the geomorphic features and volcanic passage facies of the xianyan demolition volcano moreover the simulation of radioactive fractures around the center of the volcano can also help to accurately determine the volcano type

remote sensing of hydrocarbon layers by seabed logging sbl results from a cruise offshore angola detecting and assessing hydrocarbon reservoirs without the need to drill test wells is of major importance to the petroleum industry seismic methods have traditionally been used in this context but the results can be ambiguous another approach is to use electromagnetic sounding methods that exploit the resistivity differences between a reservoir containing highly resistive hydrocarbons and one saturated with conductive saline fluids modeling presented by eidesmo et al 2002 demonstrates that by using seabed logging sbl a special application of frequency domain controlled source electromagnetic csem sounding the existence or otherwise of hydrocarbon bearing layers can be determined and their lateral extent and boundaries can be quantified such information provides valuable complementary constraints on reservoir geometry and characteristics obtained by seismic surveying

slope channel coupling in steepland terrain a field based conceptual model from the tarndale gully and fan waipaoa catchment new zealand abstract connectivity between an actively eroding gully complex and upper waipaoa catchment via a steep 1 km long alluvial fan is assessed using digital elevation models dems of the tarndale fan derived from 10 high resolution gps surveys between 2004 and 2008 repeat dem analysis provides a means of assessing transfer of sediment supplied from the tarndale gully through the fan to the te weraroa stream and thus inferring connectivity between these landscape components from which a conceptual coupling model is derived analysis indicates the operation of two critical junction switches at the i gully fan and ii fan stream nexus which contribute to considerable complexity in patterns of erosion and deposition on the fan as it responds to sediment supply or starvation from the tarndale gully and evacuation to the te weraroa stream described in fuller and marden 2010 the fan does not respond as a coherent unit each of six fan feeder tributaries behaves independently according to sediment supplied from six discrete source areas within the gully complex this reflects sediment production within specific activity zones of tarndale gully mass movements triggered by single rainstorm events and or wet periods contingent upon sediment availability and intrinsic slope mechanics frequently deliver sediment to the upper fan tributaries this enhanced gully fan coupling during storms or wetter periods promotes rapid fan aggradation with each feeder tributary responding to its discrete source zone infilling may propagate down fan in response to upper fan incision once the gully fan switch deactivates transferring sediment as far as the te weraroa stream coupling the fan with the stream system floods generated in the te weraroa stream may also activate the junction switch at the fan stream nexus by trimming the lower fan prompting up fan incision via head cutting in response to changed local base level slope channel coupling in this environment is a function of a range of slope and channel processes responding to discrete storms and intrinsic gully dynamics the high rates of geomorphic activity in this environment mean the tarndale system provides a natural laboratory in which to assess key slope channel coupling processes beyond the plot or discrete event scale

sediment budget to assess the geomorphic effect of a cyclonic storm new zealand abstract a short term sediment budget was constructed to assess the erosion response of a soft rock hill country watershed to an intense rainstorm event the watershed is located in a landslide prone area on the east coast of the north island new zealand during march 1988 753 mm of rain was recorded over a four day period with 320 mm and 329 mm on successive days known as cyclone bola this was the largest rainstorm event in the tutira watershed in the 93 year rainfall record the budget quantifies the total sediment generated during the storm the relative contribution of erosion processes involved the amount of sediment held in storage and the amount discharged into two lakes within the watershed a landform map of the watershed was constructed and the contribution of each landform type to the total budget was calculated a total of 1 35 0 13 million m3 of sediment was generated during the storm at an average of 420 m3 ha this is equivalent to a denudation value of 42 mm for the total watershed 3208 ha and 83 mm for the landforms severely affected by landsliding 1427 ha of the sediment generated 21 remained on hillslopes 22 was deposited on valley floors 51 was deposited on the lakebeds and the remaining 6 was discharged from the watershed via the lake outlet most of the sediment generated during the storm was from primary source areas on hill slopes with sediment in secondary storage providing only a small contribution landslide erosion was the main process accounting for 89 of the sediment generated channel tunnel gully and sheet erosion were only minor contributors to the budget six hillslope landforms which occupy only 44 of the watershed generated 90 of the sediment the results of this sediment budget when put in context with the storm magnitude frequency history being analysed from lake cores contribute to the identification of sustainable land use and management of soft rock hill country

landslide geomorphology an argument for recognition with examples from new zealand the role and significance that have been ascribed to landsliding within geomorphology were examined with respect to some of the influential historical concepts of landform evolution landsliding was almost completely ignored as a geomorphic process in the earliest models of landform evolution while there has been a growing acknowledgement of landsliding as a hillslope process capable of performing significant erosion and transportation it has received only sparse recognition as a formative process in its own right notable exceptions are the rarely referenced model of relief development of skempton a w 1953 soil mechanics in relation to geology proceedings of the yorkshire geological society 29 3 33 62 pt 1 and the reply of selby m j 1974 dominant geomorphic events in landform evolution bulletin international association of engineering geology 9 85 89 to the frequency magnitude findings of wolman m g miller j p 1960 magnitude and frequency of forces in geomorphic processes journal of geology 68 1 54 74 together these two contributions provide a sound basis of geomechanical theory and ample empirical evidence to indicate that landslides have the potential to control landform evolution it is proposed that landslide geomorphology systems exist within which landslides dominate form and process by governing the mechanisms rhythm and pace of geomorphic change in time and space a review of new zealand terrain suggests that these criteria are met in six distinctive landslide geomorphology systems each of these can be characterised not only by the landslide regime but also by the fundamental pre conditions of tectonic setting and geology it is argued that the existence of such systems and the complex interrelations involved require the recognition of a landslide geomorphology in its own right

landslide model performance in a high resolution small scale landscape the frequency and severity of shallow landslides in new zealand threatens life and property both on and off site the physically based shallow landslide model lapsus ls is tested for its performance in simulating shallow landslide locations induced by a high intensity rain event in a small scale landscape furthermore the effect of high resolution digital elevation models on the performance was tested the performance of the model was optimised by calibrating different parameter values a satisfactory result was achieved with a high resolution 1 m dem landslides however were generally predicted lower on the slope than mapped erosion scars this discrepancy could be due to i inaccuracies in the dem or in other model input data such as soil strength properties ii relevant processes for this environmental context that are not included in the model or iii the limited validity of the infinite length assumption in the infinite slope stability model embedded in the lapsus ls the trade off between a correct prediction of landslides versus stable cells becomes increasingly worse with coarser resolutions and model performance decreases mainly due to altering slope characteristics the optimal parameter combinations differ per resolution in this environmental context the 1 m resolution topography resembles actual topography most closely and landslide locations are better distinguished from stable areas than for coarser resolutions more gain in model performance could be achieved by adding landslide process complexities and parameter heterogeneity of the catchment

finding eruptive mechanisms through pyroclasts from the current eruption 1984 present at nevado del ruiz volcanic complex colombia abstract the dominant fragmentation mechanisms in the magma involved in a volcanic eruption can be understood from the compositional and textural analysis of the fragments emitted as pyroclasts individual pyroclasts can be juvenile accessory and accidental and detailed analyses of their relative proportions as well as the juvenile clast features can shed light into the fragmentation processes involved in the eruption despite the multiple hundreds eruptive pulses since the nevado del ruiz re activation in 1984 following a quiescence of nearly 100 years such analyses have not been carried out for the ash emissions preceding the recently emplaced plug here four deposits related to the recent emissions were analysed from their pyroclasts the samples correspond to eruptive pulses from the years 1985 1986 1988 and 2012 their characterisation allowed proposing differences between likely juvenile fragments i e representative of involved magma and accessory fragments i e pre existing co magmatic the results indicate that alteration can be used as a criterion to distinguish them although this could not account for syn eruptive hydrothermal alteration of juvenile glass or for the preservation of accessory glass emplaced in glacial conditions this criterion could serve as a foundation to direct fresh glass fragment analyses following this criterion the fresh glass fragments which are assumed to be juvenile fragments are highly vesicular they exhibit spongy and fibrous textures that are related to the predominant vesicle shape their predominance suggests a magmatic fragmentation mechanism while blocky shaped poorly vesicular cracked glass shards suggest a phreato magmatic origin specifically november of 1985 and january of 1986 glassy ashes are primarily highly vesicular suggesting magmatic explosive events by contrast samples from the march of 1988 and may of 2012 events are primarily characterised by low fresh glass content they also exhibit quenched surfaces indicating that the magma water interaction acted as an important factor for triggering the eruptive pulses real time componentry petrography and glass characterisation in fine ash could significantly complement traditional geophysical monitoring and importantly improve the hazard assessments on the civil aviation during the ongoing nevado del ruiz activity

enhanced subsurface response for marine csem surveying one of the main challenges of using marine controlled source electromagnetic csem sounding for hydrocarbon detection has been a relatively low resolution and restricted depth penetration in addition the use of csem in shallow waters has been perceived as particularly difficult a new robust method for enhancing marine csem subsurface response is particularly useful in shallow waters the method is designed to reduce acquisition imprints and attenuate the dominant primary airwave contribution synthetic examples show that it is possible to detect thin deeply buried 3d resistive bodies in a shallow water environment with a complex resistivity structure the results highlight the importance of a sufficient signal to noise ratio

geometrical control of subduction related magmatism the mesozoic and cenozoic plutonic history of western colombia radiometric age data from western colombia combined with geological evidence allow five main plutonic episodes ranging in age from triassic to tertiary to be recognized it is suggested that variation in the convergence angle of the oceanic plate relative to the continental edge was an important factor affecting the timing and spatial distribution of plutonic activity on a regional scale major breaks in activity are probably best attributed to either low angle parallel convergence or periods of accretion along the convergent margin

towards establishing climatic thresholds for slope instability use of a physically based combined soil hydrology slope stability model shallow landslides are often linked to high magnitude rainstorms research has attempted to establish threshold rainfall totals that trigger shallow landslides based mainly on field evidence complications arise because not all regolith has the same hydrological behaviour and research frequently fails to take this into account this paper uses a combination of field and modelling approaches to explore the triggering rainfall thresholds for shallow failures in deforested hill country of new zealand it emphasises the role of variations in regolith hydrology focussing on unsaturated and saturated zone responses by using a modelling approach detailed variations in pore pressure positive and negative responses are investigated developing ideas initially derived from field evidence this paper defines and develops earlier research that establishes values for maximum and minimum probability thresholds for shallow landslides and provides a more generalised model that can be applied more widely hydrological mechanisms for shallow landslides are investigated in greater detail than previously possible using a combined hydrology and stability model chasm

detection and imaging sensitivity of the marine csem method we have developed a formalism to systematically study the sensitivity of the marine controlled source electromagnetic method for hydrocarbon exploration taking into account measurement errors we utilize error propagation to estimate the data uncertainty and find that contributions that scale by the transmitter dipole moment give qualitatively different behavior than noise contributions that are independent of the dipole moment the uncertainty is used in quantitative criteria to determine if a hydrocarbon reservoir can be detected and whether it can be successfully imaged our formalism can be used to make detailed feasibility studies incorporating equipment accuracy limitations and to identify which experimental component that must be improved to ensure overall improvement in sensitivity the criteria can be applied to identify the limiting factors for detection and imaging of targets with increasing burial depth we have defined experimental accuracy conditions for next generation csem equipment to successfully image a large hydrocarbon reservoir at 5 km burial depth

paleostress evolution of the northern andes eastern cordillera of colombia implications on plate kinematics of the south caribbean region 1 new tectonic field data and paleostress determinations in the eastern cordillera of colombia enable us to identify stress regimes that prevailed in the northern andes since late cretaceous times until present day these regimes were characterized by an e w to wsw ene active contraction from late cretaceous to late paleocene this direction subsequently changed to nw se and finally became wnw ese during the andean tectonic phase the characteristics and relative chronology of these regimes were deduced from field structures and stratigraphic criteria using stress inversion of fault slip data sets to evaluate our model we used the rotation poles of the south america caribbean and nazca plates relative to north america and paleogeographic reconstructions of the caribbean region to derive a kinematic model of the northern andes assuming a general correspondence between the regional convergence directions and the regional compression we built a theoretical model of the regional stress regimes based on kinematics of the northwestern south america since late cretaceous times this model reveals a major variation at the end of the paleocene when relative divergence shifted to convergence between the americas this is in agreement with our tectonic model based on independent tectonic field data inversion in the eastern cordillera this regional kinematic and tectonic change which affected the caribbean at the end of the paleocene was responsible for and consistent with the major change in stress patterns and structural style in the eastern cordillera it is also coeval with the development of a major regional unconformity in colombia

towards an integrated inversion of geoscientific data what price of geology abstract the inversion of multiple geoscientific datasets to define structures in hard rock terrains has for the most part been limited to geophysical methods supported by rock property constraints in this paper we expand the range of constraints available to geological modellers by defining a series of misfit functions that are used to define the quality of a given geological model with respect to the available geological data these misfit functions encompass both spatial and temporal observations and include primary data such as the location of an outcrop or bore hole location of a given rock type the orientation of its different generations of foliations as well as secondary geologic observations such as age relationships when we combine geologic conditions with geophysical misfit functions which already exist for many geophysical measures we have the potential to better constrain two and 3d models of the earth as a first test a subset of these misfit functions are applied to a set of synthetic three dimensional volumetric models built with an implicit surface modelling scheme by perturbing the input structural data within a narrow range we can simulate a range of significantly different three dimensional models for which we can then apply both geological and geophysical misfit functions several joint geological geophysical inversion schemes may be developed based on this methodology with the ultimate goal being an inversion scheme that simultaneously minimizes both geological and geophysical misfit

current states of stress in the northern andes as indicated by focal mechanisms of earthquakes abstract systematic inversion of double couple focal mechanisms of shallow earthquakes in the northern andes reveals relatively homogeneous patterns of crustal stress in three main regions the first region presently under the influence of the caribbean plate includes the northern segment of the eastern cordillera of colombia and the western flank of the central cordillera north of 4 n it is characterized by wnw ese compression of dominantly reverse type that deflects to nw se in the merida andes of venezuela where it becomes mainly strike slip in type a major bend of the eastern thrust front of the eastern cordillera near its junction with the merida andes coincides with a local deflection of the stress regime sw ne compression suggesting local accommodation of the thrust belt to a rigid indenter in this area the second region includes the sw pacific coast of colombia and ecuador currently under the influence of the nazca plate in this area approximately e w compression is mainly reverse in type it deflects to wsw ene in the northern andes south of 4 n where it is accommodated by right lateral displacement of the romeral fault complex and the eastern front of the northern andes the third and most complex region is the area of the triple junction between the south american nazca and caribbean plates it reveals two major stress regimes both mainly strike slip in type the first regime involves sw ne compression related to the interaction between the nazca and caribbean plates and the panama micro plate typically accommodated in an e w left lateral shear zone the second regime involves nw se compression mainly related to the interaction between the caribbean plate and the north andes block which induces left lateral displacement on the uramita and romeral faults north of 4 n deep seismicity about 150 170 km concentrates in the bucaramanga nest and cauca valley areas the inversion reveals a rather homogeneous attitude of the minimum stress axis which dips towards the e this extension is consistent with the present plunge of the nazca and caribbean slabs suggesting that a broken slab may be torn under gravitational stresses in the bucaramanga nest this model is compatible with current blocking of the subduction in the western northern andes inhibiting the eastward displacement of slabs which are forced to break and sink in to the asthenosphere under their own weight

rapid channel response to variability in sediment supply cutting and filling of the tarndale fan waipaoa catchment new zealand abstract in the headwaters of the waipaoa catchment fluvio mass movement gully complexes are currently significant contributors of sediment delivery of which is buffered by fans which have developed in the small tributaries that lead from the gully complexes biannual channel cross section surveys made since 1983 show seasonal aggradation incision cycles channels generally incise in summer and infill during the winter months this seasonal pattern of cutting and filling is driven by variations in sediment supply from the gully complexes in this paper to better understand patterns and processes of sediment delivery at the top of the sediment cascade we examine cut and fill cycles on the 11 ha tarndale fan over a two and a half year period analysis of sequential dems compiled from survey data obtained between december 2004 and august 2007 indicates cutting and filling may involve up to 47 000 tonnes of sediment over as little as three months during discrete severe rainstorm and or wet weather periods mass movements in the gully complex are enhanced and contribute large quantities of sediment to the fan via debris flows and landslides which infill channels during drier periods mass movement activity is inhibited and runoff incises the feeder channels

towards incorporating uncertainty of structural data in 3d geological inversion abstract all geological models are subject to several kinds of uncertainty these can be classified into three different types data imprecision and quality inherent randomness and incomplete knowledge with our approach we address uncertainties introduced by input data quality in complex three dimensional 3d models of subsurface structures geological models as input data we consider parameters of geological structures i e formation and fault boundary points and orientation measurements our method consists of five steps construction of an initial geological model with an implicit potential field method assignment of probability distributions to data positions and orientation measurements simulation of several input data sets construction of several model realisations based on these simulated data sets and finally the visualisation and analysis of the uncertainties we test our approach in two generic models a simple graben setting and a complex dome structure the first model shows that our approach can evaluate uncertainties from different structures and their interaction furthermore it indicates that the final uncertainty of the model is not simply the sum of all input data uncertainties but complex interactions exist the second example demonstrates that our approach can handle full three dimensional settings with overturned surfaces results of the uncertainty simulation can be visualised and analysed in several ways ranging from borehole histograms to uncertainty maps for complex 3d visualisation and analysis we use indicator functions when we apply these we can treat the visualisation of uncertainties in complex settings in a self consistent manner with our simulation method it is possible to analyse and visualise the uncertainties directly introduced by imprecision in the input data our approach is intuitive and straight forward and suitable in both simple and complex geological settings it enables detailed insights into the model quality even for the non expert in cases where a geological model is the basis for geophysical simulation it opens up the way to geological data driven ensemble modelling and inversion

quaternary eruptive history of nevado del ruiz colombia abstract nevado del ruiz has a 1 8 m y long eruptive record that includes alternate construction and destruction of three edifices during three main eruptive periods termed ancestral ruiz older ruiz and ruiz nevado del ruiz is located on a complex intersection of four groups of faults the most significant being the n20 e palestina strike slip fault and the n50 w villamaria termales normal fault ancestral ruiz was a broad stratovolcano built by two eruptive stages of lava flows starting about 1 8 ma ago and ending 1 0 ma ago a partial collapse and formation of a caldera are thought to have occurred between 1 0 and 0 8 ma ago older ruiz was a stratovolcano constructed by lava flows in three stages starting about 0 8 ma ago and ending about 0 2 ma ago extensive and voluminous welded and nonwelded pyroclastic flow deposits that partly fill preexisting valleys record the formation of a young summit caldera between 0 2 and 0 15 ma ago present ruiz is formed by a cluster of composite lava domes that probably filled the summit caldera of older ruiz present ruiz eruptive activity is mostly explosive but also includes dome growth and parasitic dome activity of la olleta and alto la piramide twelve eruptive stages occurred during the last 11 000 years accompanied by rockslide debris avalanches pyroclastic flows or surges and their subsequent interactions with the ice cap as well as by glacial erosion and mass wasting diverse processes within these twelve stages have led to a partial destruction of the summit domes this long and complex pleistocene and holocene eruptive sequence helps to put the november 13 1985 eruption into a broader perspective

spatial and temporal patterns of off slope sediment delivery for small catchments subject to shallow landslides within the waipaoa catchment new zealand abstract the waipaoa catchment in new zealand has one of the highest measured specific suspended sediment yields measured in new zealand compared to basins of comparable size a significant source of this sediment is from shallow landslides which are often triggered on a regional scale during large magnitude storm events defined as 200 mm rainfall within 72 h the first step of this sediment cascade is removal of landslide material from the slope and into the fluvial system when the debris tail is in physical contact and hence considered connected the difference between the volume of sediment liberated in the event and the volume remaining on the slope immediately following the event is termed the off slope sediment delivery ratio this value ranged from 0 12 to 0 28 for small sub catchments within the waipaoa catchment depending on catchment morphology landslide and triggering event characteristics in the waipaoa catchment a decrease in the catchment sediment delivery ratio is observed as the sub catchment size increased a human induced process which may affect off slope sediment delivery is regolith exhaustion as scars move further upslope in response to removal of preferred weathered material during previous events on the lower sections of slope however it appears that temporal scar migration away from the channels is not prevalent therefore the hypothesis that hillslope relaxation since deforestation is prevalent in this setting is considered null rather the temporal pattern to sediment delivery ratios supports the context of evolving catchment in response to deforestation in the terrain event resistance model

vertical vertical controlled source electromagnetic instrumentation and acquisition abstract vertical vertical controlled source electromagnetic is an alternative to other techniques for providing three dimensional resistivity images of the subsurface it utilizes a large and powerful vertical dipole transmitter and arrays of e field receivers with vertical and horizontal dipole sensors the necessary instrumentation and acquisition procedures which differ strongly from other controlled source electromagnetic methods are described in the paper

quaternary eruptive history and hazard zone model at nevado del tolima and cerro machin volcanoes colombia the ice clad and fumarolic nevado del tourna volcano 4 39 n 75 20 w south of nevado del ruiz is offset toward the southeast from the axis of the volcanic ruiz tolima massif with respect to the major ne trending strike slip palestina fault it is composed of four units 1 a pre tolima plateau like basement of basaltic andesite lava flows of early quaternary age 2 a dissected ancestral tourna stratovolcano cut by a presumed collapse caldera of middle pleistocene age 3 an older tolima stratovolcano of late pleistocene age partly destroyed by a summit caldera and 4 composite domes of the cone shaped young and present tolima young tolima volcano is an andesitic and dacitic composite cone formed over the past 40 000 years within a 3 km wide caldera that opened around 0 14 ma deposits of welded and nonwelded pumice and scoria flows were emplaced toward the southeast rio combeima and northeast rio totare repeated growth of lava domes over the past 16 000 years is witnessed by thick block lava flows on the southern and eastern flanks and by block and ash or scoria rich pyroclastic flow deposits this activity occurred during at least six eruptives stages as follows el placer ca 16 200 14 000 yr b p romerales ca 13 000 12 300 yr b p canalones ca 11 500 9750 yr b p mesetas ca 7200 4600 yr b p encanto ca 3600 1700 yr b p and nieves historical interactions with the ice cap probably triggered debris flows that partly filled the combeima and totare valleys and formed the holocene terraces on the upper pleistocene volcaniclastic fans of ibagueand venadillo as much as 60 km from the source the latest major activity was a plinian eruption which deposited a pumice fall layer ca 3600 yr b p 0 5 km3 actual volume mainly toward the west and northwest minor tephra falls and debris flows occurred during the historical period before the reported 1918 and 1943 small phreatic events a general hazard zone map shows areas potentially affected by future eruptions both at nevado del tolima and at active cerro machin 12 km southward the extent of areas likely to be affected by tephra falls debris flows pyroclastic flows or surges debris avalanches and lava flows is shown subplinian and plinian eruptions of nevado del tolima were used to represent the moderate and large events to be expected 300 000 people live within a 35 km distance from those volcanoes which have exhibited a behaviour more explosive than nevado del ruiz despite the small sized ice cap debris flows are the most probable hazard for even a minor eruption because of the very steep slope gradient and because of probable interactions of hot eruptive products with ice and snow additionally scoria flows and debris avalanches can be directed toward the southeast and could be transformed into debris flows that would devastate the combeima valley and suburbs of ibaguecity where about 50 000 people live

signal detectability of marine electromagnetic methods in the exploration of resistive targets we compare selected marine electromagnetic methods for sensitivity to the presence of relatively thin resistive targets e g hydrocarbons gas hydrates fresh groundwater etc the study includes the conventional controlled source electromagnetic method the recently introduced transient electromagnetic prospecting with vertical electric lines method and the novel marine circular electric dipole method which is still in the stage of theoretical development the comparison is based on general physical considerations analytical mainly asymptotic analysis and rigorous one dimensional and multidimensional forward modelling it is shown that transient electromagnetic prospecting with vertical electric lines and marine circular electric dipole methods represent an alternative to the conventional controlled source electromagnetic method at shallow sea where the latter becomes less efficient due to the air wave phenomenon since both former methods are essentially short offset time domain techniques they exhibit a much better lateral resolution than the controlled source electromagnetic method in both shallow sea and deep sea the greatest shortcoming of the transient electromagnetic prospecting with vertical electric lines and marine circular electric dipole methods comes from the difficulties in accurately assembling the transmitter antenna within the marine environment this makes these methods significantly less practical than the controlled source electromagnetic method consequently the controlled source electromagnetic method remains the leading marine electromagnetic technique in the exploration of large resistive targets in deep sea however exploring laterally small targets in deep sea and both small and large targets in shallow sea might require the use of the less practical transient electromagnetic prospecting with vertical electric lines and or marine circular electric dipole method as a desirable alternative to the controlled source electromagnetic method

review paper instrumentation for marine magnetotelluric and controlled source electromagnetic sounding we review and describe the electromagnetic transmitters and receivers used to carry out magnetotelluric and controlled source soundings in the marine environment academic studies using marine electromagnetic methods started in the 1970s but during the last decade these methods have been used extensively by the offshore hydrocarbon exploration industry the principal sensors magnetometers and nonpolarizing electrodes are similar to those used on land but magnetotelluric field strengths are not only much smaller on the deep sea floor but also fall off more rapidly with increasing frequency as a result magnetotelluric signals approach the noise floor of electric field and induction coil sensors 0 1 nv m and 0 1 pt at around 1 hz in typical continental shelf environments fluxgate magnetometers have higher noise than induction coils at periods shorter than 500 s but can still be used to collect seafloor magnetotelluric data down to 40 100 s controlled source transmitters using electric dipoles can be towed continuously through the seawater or on the sea bed achieving output currents of 1000 a or more limited by the conductivity of seawater and the power that can be transmitted down the cables used to tow the devices behind a ship the maximum source receiver separation achieved in controlled source soundings depends on both the transmitter dipole moment and on the receiver noise floor and is typically around 10 km in continental shelf exploration environments the position of both receivers and transmitters needs to be navigated using either long baseline or short baseline acoustic ranging while sea floor receivers need additional measurements of orientations from compasses and tiltmeters all equipment has to be packaged to accommodate the high pressure up to 40 mpa and corrosive properties of seawater usually receiver instruments are self contained battery powered and have highly accurate clocks for timekeeping even when towed on the sea floor or in the water column behind a transmitter

a time space based approach for mapping rainfall induced shallow landslide hazard a rainfall induced shallow landslide is a major hazard in mountainous terrain but a time space based approach is still an unsettled issue for mapping rainfall induced shallow landslide hazards rain induces a rise of the groundwater level and an increase in pore water pressure that results in slope failures in this study an integrated infinite slope analysis model has been developed to evaluate the influence of infiltration on surficial stability of slopes by the limit equilibrium method based on this new integrated infinite slope analysis model a time space based approach has been implemented to map the distributed landslide hazard in a gis geographic information systems and to evaluate the shallow slope failure induced by a particular rainfall event that accounts for the rainfall intensity and duration the case study results in a comprehensive time space landslide hazard map that illustrates the change of the safety factor and the depth of the wetting front over time

a proposed cell model for multiple occurrence regional landslide events implications for landslide susceptibility mapping abstract multiple occurrence regional landslide events morles consist of hundreds to thousands of shallow landslides occurring more or less simultaneously within defined areas ranging from tens to thousands of square kilometres while morles can be triggered by rainstorms and earthquakes this paper is confined to those landslide events triggered by rainstorms globally morles occur in a range of geological settings in areas of moderate to steep slopes subject to intense rainstorms individual landslides in rainstorm triggered events are dominantly small shallow debris and earth flows and debris and earth slides involving regolith or weathered bedrock the model used to characterise these events assumes that energy distribution within the event area is represented on the land surface by a cell structure with maximum energy expenditure within an identifiable core and rapid dissipation concentrically away from the centre the version of the model presented here has been developed for rainfall triggered landslide events it proposes that rainfall intensity can be used to determine different critical landslide response zones within the cell referred to as core middle and periphery zones these zones are most readily distinguished by two conditions the proportion of the slope that fails and the particular type of the slope stability factor that assumes dominance in determining specific sites of landslide occurrence the latter condition means that the power of any slope stability factor to distinguish between stable and unstable sites varies throughout the affected area in accordance with the landslide response zones within the cell certain factors critical for determining the location of landslide sites in one part of the event area have little influence in other parts of the event area the implication is that landslide susceptibility maps and subsequently derived mitigation measures based on conventional slope stability factors may have only limited validity for many events the overall ability to predict the impact of these events and consequently the development of effective mitigation measures is limited by the ability to predict the travel path storm centre and intensity range within the cell structure of extreme weather systems

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

the convenient fiction of steady state soil thickness abstract steady state regolith or soil thickness ssst whereby surface removals are approximately balanced by production of new soil by bedrock weathering is a common assumption in most models of hillslope and landscape evolution ssst is also a fundamental assumption in the use of cosmogenic radionuclides crn to estimate erosion and weathering rates the steady state concept is based on feedbacks between soil thickness and weathering at the base of the regolith such that sometimes after an optimal or threshold thickness is achieved thicker soils lead to lower weathering rates and vice versa ssst is thus only applicable to soils formed chiefly from weathering of the underlying bedrock where sufficient time has elapsed for regolith accumulation and where effects of processes other than weathering and surface removals on thickness are negligible even within this domain the widespread occurrence of deep weathering profiles regolith stripping and inherited regolith features makes ssst problematic as a conceptual model for pedogenesis or weathering profile development the ratio of soil thickness to total weathering profile thickness is proposed as a simple index of steady state steady state profiles formed on weathered bedrock should exhibit ratios close to unity data from the cumberland plateau region of eastern kentucky show that soil weathering profile ratios in shallow 20 m and generally significantly greater than soil thicknesses in the region suggesting ratios convenient fiction facilitating the use of some models and tools the potential pitfalls arise from the possibility that the utility of ssst as a convenient fiction in some contexts may be mistaken for a realistic representation of the dynamics of pedogenesis and weathering profile evolution