objective landslide detection and surface morphology mapping using high resolution airborne laser altimetry a map of extant slope failures is the most basic element of any landslide assessment without an accurate inventory of slope instability it is not possible to analyze the controls on the spatial and temporal patterns of mass movement or the environmental human or geomorphic consequences of slides landslide inventory maps are tedious to compile difficult to make in vegetated terrain using conventional techniques and tend to be subjective in addition most landslide inventories simply outline landslide boundaries and do not offer information about landslide mechanics as manifested by internal deformation features in an alternative approach we constructed accurate high resolution dems from airborne laser altimetry lidar data to characterize a large landslide complex and surrounding terrain near christchurch new zealand one dimensional circular 2 d and spherical 3 d statistics are used to map the local topographic roughness in the dems over a spatial scale of 1 5 to 10 m the bedrock landslide is rougher than adjacent unfailed terrain and any of the statistics can be employed to automatically detect and map the overall slide complex furthermore statistics that include a measure of the local variability of aspect successfully delineate four kinematic units within the gently sloping lower half of the slide features with a minimum size of surface folds that have a wavelength of about 11 to 12 m and amplitude of about 1 m are readily mapped two adjacent earthflows within the landslide complex are distinguished by a contrast in median roughness and texture and continuity of roughness elements the less active of the earthflows has a surface morphology that presumably has been smoothed by surface processes the laplacian operator also accurately maps the kinematic units and the folds and longitudinal levees within and at the margins of the units finally two dimensional power spectra analyses are used to quantify how roughness varies with length scale these results indicate that no dominant length scale of roughness exists for smooth unfailed terrain in contrast zones with different styles of landslide deformation exhibit distinctive spectral peaks that correspond to the scale of deformation features such as the compression folds the topographic based analyses described here may be used to objectively delineate landslide features generate mechanical inferences about landslide behavior and evaluate relatively the recent activity of slides published by elsevier science b v

landslide movement in southwest colorado triggered by atmospheric tides the slumgullion landslide in the western united states has been moving almost continuously for over 100 years observations and numerical modelling show that air pressure changes from atmospheric tides trigger daily movement

investigation of the causes of the longitudinal variation of the electron density in the weddell sea anomaly this paper investigates and quantifies the causes of the weddell sea anomaly wsa a region near the tip of south america extending from approximately 30 to 120 w geographic longitude and 50 to 75 s geographic latitude at solar minimum between 2007 and 2010 this region is unusual because the midnight peak electron density exceeds the midday peak electron density in summer this study is far more quantitative than previous studies because unlike other models it assimilates selected data parameters to constrain a physical model in order to investigate other aspects of the data it is shown that the commonly accepted explanation that the wsa is related to the magnetic field declination and inclination effects on the neutral wind does not explain the longitudinal variation of the electron density rather longitudinal changes in the neutral winds and neutral densities are the most likely explanation for the wsa these longitudinal wind and density changes are attributed to the varying latitudinal distance from the auroral zone energy input no contributions from the plasmasphere or other sources are required furthermore it is shown that a widely used empirical thermosphere density model overestimates the longitudinal changes in the wsa region

permanent scatterers for landslide investigations outcomes from the esa slam project within the slam project service for landslide monitoring launched in 2003 by the european space agency esa the permanent scatterers ps technique a multi image interferometric approach coupled with the interpretation of aerial photos and optical satellite images was carried out for landslide investigations the ps analysis was applied at a regional scale as support for landslide inventory mapping and at local scale for the monitoring of single well known slope movements for the integration of the ps measurements within a landslide inventory the arno river basin italy was chosen as test site for the presence of a high number of mass movements to date about 300 areas at high landslide risk and more than 27 000 individual landslides mapped by the institutional authorities about 350 sar images have been interferometrically processed by means of the ps technique with the detection of about 600 000 ps the use of optical images contributed spatial meaning to the point wise information provided by the ps making it easier to identify terrain features related to slope instability and the landslide boundaries here we describe the employed methodology and its impact in the updating of a preexisting landslide inventory 6 8 of the total number of landslides were characterized by ground displacement measurements from the ps 6 1 of already mapped landslides and 0 8 of new unstable areas detected through the ps analysis moreover most of the ps are located in urban areas showing that the proposed methodology is suitable for landslide mapping in areas with a quite high density of urbanization but that over vegetated areas it still suffers from the limitations induced by the current space borne sar missions e g temporal de correlation on the other hand the use of insar for the monitoring of single slow landslides threatening built up areas has provided satisfactory results allowing the measurement of superficial deformations with high accuracy on the landslide sectors characterized by a good radar reflectivity and coherence

glacier surge dynamics of sortebrae east greenland from synthetic aperture radar feature tracking 1 we have measured the surface flow rate of the large east greenland glacier sortebrae through both the initiation and termination of a major surge using synthetic aperture radar sar feature tracking optimized to minimize error the sortebrae surge began between november and january 1992 1993 after at least 6 weeks of subfreezing temperatures over the whole glacier and propagated rapidly up glacier from a central nucleus sortebrae reached sustained fast flow rates of up to 24 m d 1 and the active phase lasted for 28 32 months before terminating in june 1995 termination was abrupt coinciding with the arrival of the spring thaw and the apparent release of a large volume of stored water from a single outlet at the front the surge mechanism is interpreted as a switch from channelized to distributed drainage which at present is best explained by kamb s linked cavity sliding model

a method for sub pixel scale feature tracking using radarsat images applied to the mertz glacier tongue east antarctica abstract tracking features between pairs of satellite synthetic aperture radar sar images using image cross correlation methods is a powerful tool for defining regions of image movement such as ice flow of antarctic glaciers unlike optical images processed sar images have various instrumental effects such as view angle distortions and lateral displacement errors caused by slant range mapping co registration issues are problematic and need to be addressed if there are few no suitable stationary tie points at or near sea level within the images methods are presented that use radarsat scansar images to reliably measure sub pixel displacements with errors of 0 25 pixels but this estimate is target dependent the techniques and issues are illustrated using examples from a long term study of the mertz glacier tongue in east antarctica for image pairs only a few days apart this extensive structure forms an excellent grid like test pattern which provides up to 5000 valid correlation matches images separated by 100 s of days can then be processed in the same way to reveal many subtle and some large changes over time the technique described is robust and may be widely applicable

probabilistic landslide susceptibility and factor effect analysis the susceptibility of landslides and the effect of landslide related factors at penang in malaysia using the geographic information system gis and remote sensing data have been evaluated landslide locations were identified in the study area from interpretation of aerial photographs and from field surveys topographical and geological data and satellite images were collected processed and constructed into a spatial database using gis and image processing the factors chosen that influence landslide occurrence were topographic slope topographic aspect topographic curvature and distance from drainage all from the topographic database lithology and distance from lineament taken from the geologic database land use from landsat thermatic mapper tm satellite images and the vegetation index value from spot hrv high resolution visible satellite images landslide hazardous areas were analyzed and mapped using the landslide occurrence factors employing the probability frequency ratio method using the all factors to assess the effect of these factors each factor was excluded from the analysis and its effect verified using the landslide location data as a result all factors had relatively positive effects except lithology on the landslide susceptibility maps in the study area

mineralogical interpretation of reflectance spectra of eros from near near infrared spectrometer low phase flyby high signal to noise near infrared spectrometer nis spectra acquired during the low phase flyby of the near earth asteroid rendezvous near mission to 433 eros are analyzed to determine mineral chemistry and proportions of mafic silicates across the asteroid s surface at 2 68 5 50 km spatial resolution spectral band parameters are derived and compared with those of laboratory samples of known mineral composition grain size distribution and terrestrial meteoritic and lunar pyroxene spectral properties the nis derived band parameters are consistent with ordinary chondrite meteorites we invoke the presence of a clinopyroxene component in the spectra which is consistent with ordinary chondrite mineralogy and or some degree of partial melting of ordinary chondritic material spectra measured across the surface of eros can reveal small but real spectral variations most relative spectra are uniform to within 1 2 some areas suggest compositional variations of a few percent spectral slope variations of a few percent are seen indicating a non uniform distribution of materials affecting the slope parameter but with no resolved absorption bands we find no correlation of slope with viewing geometry or compositional variation the band parameter values do not consistently indicate a specific ordinary chondrite class but eros is definitely undifferentiated with possible compositional variations of no more than 1 2

slope deformation prior to zhouqu china landslide from insar time series analysis abstract a major landslide in zhouqu china occurred on august 8 2010 and caused widespread damage and over 1700 casualties we study the deformation of the slopes over a time period of about three years prior to the landslide by an enhanced stamps sb technique with 16 ascending alos palsar images in particular the orbit error and stratified troposphere that were not well dealt with in the original stamps sb method have been satisfactorily corrected by a novel phase ramp correction method the deformation in four regions of the study area has been retrieved with a maximum of up to 70 mm yr in the luojiayu sanyanyu valley the slopes where the 2010 giant landslide occurred have been found to be quite unstable before the event deformation exceeding 30 mm yr has been detected in the suoertou slope which is a well known place for an ancient fault zone landslide fast movement larger than 40 mm yr is observed in the xieliupo slope which poses threats of landslide dam and dammed lake to the pai lung river together with another slope deformation detected in the opposite slope in the nanshanqiaotou slope the detected 30 mm yr deformation can be viewed as the prelude of the large landslide occurred in october 2010 more important it is found that the slope deformation time series has strong correlation with the precipitation in the area as well as with the devastating wenchuan earthquake that occurred in may 2008 whose epicenter is about 300 km away from zhouqu

landslide faults and tectonic faults analogs the slumgullion earthflow colorado recent geophysical observations of landslide movement support the hypothesis that processes involved in landslide faulting are analogous to those that operate in crustal scale faulting relative to crustal faulting studies quantitative seismic geodetic and creep measurements of landslide deformation may be made in a very short time with readily available instrumentation and at relatively minimal expense our results indicate that the displacement of landslide material occurs along discrete faults exhibiting a combination of brittle failure indicated by slide quakes and creep events and as stable sliding observed as steady state creep although slide quakes were observed a more steady state failure process of relieving accumulating strain is indicated

regional moisture balance control of landslide motion implications for landslide forecasting in a changing climate i correlated 12 years of annual movement of 18 points on a large continuously moving deep seated landslide with a regional moisture balance index moisture balance drought index mbdi i used mbdi values calculated from a combination of historical precipitation and air temperature data from a d 1895 to 2010 and downscaled climate projections using the intergovernmental panel on climate change a2 emissions scenario for 2011 2099 at the landslide temperature is projected to increase 0 5 c 10 yr between 2011 and 2099 while precipitation decreases at a rate of 2 mm 10 yr landslide movement correlated with the mbdi with integration periods of 12 and 48 months the correlation between movement and mbdi suggests that the mbdi functions as a proxy for groundwater pore pressures and landslide mobility i used the correlation to forecast decreasing landslide movement between 2011 and 2099 with the head of the landslide expected to stop moving in the mid 21 st century the mbdi or a similar moisture balance index that accounts for evapotranspiration has considerable potential as a tool for forecasting the magnitude of ongoing deep seated landslide movement and for assessing the onset or likelihood of regional deep seated landslide activity

mapping small elevation changes over large areas differential radar interferometry a technique that uses synthetic aperture radar sar images to measure very small 1 cm or less surface motions with good resolution 10 m over large swaths 50 km is presented along with experimental results the method could be used for accurate measurements of many geophysical phenomena including swelling and buckling in fault zones residual displacements from seismic events and prevolcanic swelling the method is based on sar interferometry where two images are made of a scene by simultaneously flying two physically separated antennas then the phases of corresponding pixels are differenced and altitude formation is deduced from some simple computation and image rectification it is also possible to use one antenna flown twice over the same scene then if the second flight exactly duplicates the track of the first an interesting possibility occurs there would be no phase changes between the images at all unless there was a physical change in the scene such as ground swelling that would alter the distance from some resolution element to the antenna since the phase changes all occur at the short carrier wavelength the basic limitation on sensitivity is only the phase noise in the system when the two imaging passes are made from flight tracks that are separated which is the case with the seasat images used here it is no longer possible to distinguish surface changes from the parallax caused by topography however with some additional computation a third image made at some other baseline may be used to remove the topography and leave only the surface changes this method was applied using seasat data to an imaging site in imperial valley california where motion effects were observed that were ascribed to the expansion of water absorbing clays phase change images of this area are shown along with associated ground truth about the presence of water problems with the technique are explored along with a discussion of future experimental possibilities on upcoming sar missions like earth observing system eos earth resources satellite ers 1 sir c and the venus imaging radar magellan

measuring near field coseismic displacements from sar images application to the landers earthquake we describe a procedure to compute sar interferograms based on the compensation of the images mis registrations due to the ground deformation and on a specific adaptive filtering to improve the snr in the measurement where displacement gradients are large applied to the landers earthquake case the registration reduces the phase noise by 20 rms near the fault and the interferogram reveals fringes that would not show out otherwise the interferogram is validated by comparison in the far field with a gps edm based model the inferred displacement field shows discontinuities that follow the fault within few hundred meters close to the fault the measured displacements differ significantly from that predicted by elastic modeling of the far field data interferometry and measurements derived from the images amplitude offsets appear to be complementary techniques providing original measurements that may help to reconcile seismological and geodetic models of coseismic deformation with measurements of fault slip at the surface

three dimensional surface deformation derived from airborne interferometric uavsar application to the slumgullion landslide author s delbridge bg burgmann r fielding e hensley s schulz wh abstract 2016 american geophysical union all rights reserved in order to provide surface geodetic measurements with landslide wide spatial coverage we develop and validate a method for the characterization of 3 d surface deformation using the unique capabilities of the uninhabited aerial vehicle synthetic aperture radar uavsar airborne repeat pass radar interferometry system we apply our method at the well studied slumgullion landslide which is 3 9 km long and moves persistently at rates up to 2 cm day a comparison with concurrent gps measurements validates this method and shows that it provides reliable and accurate 3 d surface deformation measurements the uavsar derived vector velocity field measurements accurately capture the sharp boundaries defining previously identified kinematic units and geomorphic domains within the landslide we acquired data across the landslide during spring and summer and identify that the landslide moves more slowly during summer except at its head presumably in response to spatiotemporal variations in snowmelt infiltration in order to constrain the mechanics controlling landslide motion from surface velocity measurements we present an inversion framework for the extraction of slide thickness and basal geometry from dense 3 d surface velocity fields we find that the average depth of the slumgullion landslide is 7 5 m several meters less than previous depth estimates we show that by considering a viscoplastic rheology we can derive tighter theoretical bounds on the rheological parameter relating mean horizontal flow rate to surface velocity using inclinometer data for slow moving clay rich landslides across the globe we find a consistent value for the rheological parameter of 0 85 0 08

glacier motion estimation using sar offset tracking procedures two image to image patch offset techniques for estimating feature motion between satellite synthetic aperture radar sar images are discussed intensity tracking based on patch intensity cross correlation optimization and coherence tracking based on patch coherence optimization are used to estimate the movement of glacier surfaces between two sar images in both slant range and azimuth direction the accuracy and application range of the two methods are examined in the case of the surge of monacobreen in northern svalbard between 1992 and 1996 offset tracking procedures of sar images are an alternative to differential sar interferometry for the estimation of glacier motion when differential sar interferometry is limited by loss of coherence i e in the case of rapid and incoherent flow and of large acquisition time intervals between the two sar images in addition an offset tracking procedure in the azimuth direction may be combined with differential sar interferometry in the slant range direction in order to retrieve a two dimensional displacement map when sar data of only one orbit configuration are available

deformation time series generation in areas characterized by large displacement dynamics the sar amplitude pixel offset sbas technique we exploit the amplitude information of a sequence of synthetic aperture radar sar images acquired at different times in order to generate displacement time series in areas characterized by large and or rapid deformation the size of which is on the order of the image s pixel dimensions we follow the same rationale of the small baseline subset sbas differential sar interferometry dinsar approach by coupling the available sar images into pairs characterized by a small separation between the acquisition orbits we exploit the amplitudes of the selected image pairs in order to calculate the relative across track range and along track azimuth pixel offsets po finally we apply the sbas inversion strategy to retrieve the range and azimuth displacement time series this approach referred to as pixel offset po sbas technique has been applied to a set of 25 envisat sar observations of the sierra negra caldera galapagos islands spanning the 2003 2007 time interval the retrieved deformation time series show the capability of the technique to detect and measure the large displacements affecting the inner part of the caldera that in correspondence to the october 2005 eruption reached several meters moreover by comparing the po sbas results to continuous gps measurements we estimate that the accuracy of the po sbas time series is on the order of 1 30th of a pixel for both range and azimuth directions

rainfall ground water flow and seasonal movement at minor creek landslide northwestern california physical interpretation of empirical relations simple ground water flow analyses can clarify complex empirical relations between rainfall and landslide motion here we present detailed data on rainfall ground water flow and repetitive seasonal motion that occurred from 1982 to 1985 at minor creek landslide in northwestern california and we interpret these data in the context of physically based theories we find that landslide motion is closely regulated by the direction and magnitude of near surface hydraulic gradients and by waves of pore pressure caused by intermittent rainfall diffusive propagation of pore pressure waves accompanies downward ground water flow along nearly vertical hydraulic gradients that exist in most of the landslide field data combined with a pore pressure diffusion analysis show that single rainstorms typically produce short period waves that attenuate before reaching the landslide base in contrast seasonal rainfall cycles produce long period waves that modify basal pore pressures but only after time lags that range from weeks to months such tune lags can depend on antecedent moisture storage and can explain variable delays between the onset of the wet season and seasonal landslide motion limit equilibrium analysis shows that when seasonal pressure waves reach the landslide base they establish a critical distribution of effective stress that delicately triggers landslide motion the critical effective stress balance is extremely sensitive to the direction and magnitude of hydraulic gradients although pervasively downward gradients instigate seasonal motion we infer from theory and limited data that ground water also may circulate locally in near surface cells the circulation can further reduce the landslide s frictional strength particularly in areas of nearly horizontal ground water flow that occur beneath steep faces of hummocks hummocky topography that results from slope instability may therefore cause ground water flow that perpetuates instability

investigating landslides with space borne synthetic aperture radar sar interferometry abstract this paper is addressed to readers without advanced knowledge of remote sensing it illustrates some current and potential uses of satellite synthetic aperture radar interferometry insar for landslide assessment data acquired by sar systems can provide 3d terrain models and be used to assist in regional scale investigations e g aimed at evaluation of susceptibility of slopes to failure under favourable environmental conditions the innovative permanent scatterers ps technique which overcomes several limitations of conventional sar differential interferometry dinsar applications in landslide studies is suitable for monitoring slope deformations with millimetric precision the ps technique combines the wide area coverage typical of satellite imagery with the capability of providing displacement data relative to individual image pixels with the currently available radar satellites however only very slow ground surface displacements can be reliably detected and measured the presented case study of a landslide from the liechtenstein alps indicates that the most attractive and reliable contribution provided by this remote sensing technique lies in the possibility of i wide area qualitative distinction between stable and unstable areas and ii qualitative relative hazard zonation of large slow landslides based on the identification of segments characterised by different movement rates since only the radar line of sight projection of the displacements can be detected a quantitative exploitation of the ps data is possible only where sufficient ground truth is available in site specific or single landslide investigations the ps data can represent a very useful complementary data source with respect to the information acquired through ground based observations and in situ surveying however the difficulties associated with the feasibility assessments of the applicability of sar data to local scale problems as well as with the interpretation of ps results require a close collaboration between landslide experts and specialists in advanced processing of radar satellite data the interpretation of the exact geotechnical significance of small radar sensed ground surface deformations is challenging especially where ground truth is lacking although any ground deformation is potentially of interest to an engineering geologist detection of movements in both vertical and horizontal directions is needed in the case of landslides to evaluate slope failure mechanisms with their high radar viewing angles however the current space borne systems can detect only a fraction of the horizontal component of movement it is expected that the upcoming sar dedicated missions with new sensors and different acquisition geometries combined with the rapid developments in the field of advanced radar data processing will allow a full 3d reconstruction of deformation data and help to further reduce the current limitations of the ps and similar dinsar approaches

basal topographic control of stationary ponds on a continuously moving landslide the slumgullion landslide in the san juan mountains of southwestern colorado has been moving for at least the last few hundred years and has multiple ponds on its surface we have studied eight ponds during 30 trips to the landslide between july 1998 and july 2007 during each trip we have made observations on the variability in pond locations and water levels taken ground based photographs to document pond water with respect to moving landslide material and vegetation conducted global positioning system surveys of the elevations of water levels and mapped pond sediments on the landslide surface additionally we have used stereo aerial photographs taken in october 1939 october 1940 and july 2000 to measure topographic profiles of the eight pond locations as well as a longitudinal profile along the approximate centerline of the landslide to examine topographic changes over a 60 to 61 year period of time results from field observations analyses of photographs mapping and measurements indicate that all pond locations have remained spatially stationary for 60 300 years while landslide material moves through these locations water levels during the observation period were sensitive to changes in the local spring fed stream network and to periodic filling of pond locations by sediment from floods hyperconcentrated flows mud flows and debris flows for pond locations to remain stationary the locations must mimic depressions along the basal surface of the landslide the existence of such depressions indicates that the topography of the basal landslide surface is irregular these results suggest that for translational landslides that have moved distances larger than the dimensions of the largest basal topographic irregularities about 200 m at slumgullion landslide surface morphology can be used as a guide to the morphology of the basal slip surface because basal slip surface morphology can affect landslide stability kinematic models and stability analyses of translational landslides should attempt to incorporate irregular basal surface topography additional implications for moving landslides where basal topography controls surface morphology include the following dateable sediments or organic material from basal layers of stationary ponds will yield ages that are younger than the date of landslide initiation and it is probable that other landslide surface features such as faults streams springs and sinks are also controlled by basal topography the longitudinal topographic profile indicated that the upper part of the slumgullion landslide was depleted at a mean vertical lowering rate of 5 6 cm yr between 1939 and 2000 while the toe advanced at an average rate of 1 5 m yr during the same period therefore during this 61 year period neither the depletion of material at the head of the landslide nor continued growth of the landslide toe has decreased the overall movement rate of the landslide continued depletion of the upper part of the landslide and growth of the toe should eventually result in stabilization of the landslide published in 2008 by john wiley sons ltd

global patterns of loss of life from landslides global loss of life from landslides is poorly quantifi ed a global data set of fatalities from nonseismically triggered landslides that resulted in loss of life between a d 2004 and 2010 permits for the fi rst time proper quantifi cation of impacts and spatial distributions in total 2620 fatal landslides were recorded worldwide during the 7 yr period of the study causing a total of 32 322 recorded fatalities these total numbers of landslides and victims are an order of magnitude greater than other data sets have indicated but analysis of the data suggests that it may still slightly underestimate the true human costs the majority of human losses occur in asia especially along the himalayan arc and in china this geographical concentration dominates the annual landslide cycle which peaks in the northern hemisphere summer months finally numbers of fatalities per event show a fat tailed power law distribution with the density of landslides being moderately correlated with the population density on a national basis

landslide monitoring by using ground based sar interferometry an example of application to the tessina landslide in italy abstract an innovative technique based on radar interferometry and implemented using ground based instrumentation has been applied for monitoring the tessina landslide italy belluno the technique has allowed us to derive multitemporal surface deformation maps of the entire depletion zone of the landslide with a high spatial resolution and accuracy the portable device used in this application is known as linear sar lisa and it is able to provide measurements at 17 ghz with a synthetic aperture of up to 2 8 m the results have been validated by comparing the recorded pixel displacements with independent measurements carried out by a motorized theodolite and electronic distance meter edm on two benchmarks

seasonal movement of the slumgullion landslide determined from global positioning system surveys and field instrumentation july 1998 march 2002 abstract measurements of landslide movement made by global positioning system surveys and extensometers over a 3 5 year period show that the slumgullion landslide in the san juan mountains of southwest colorado moved throughout the monitoring period but that daily velocities varied on a seasonal basis landslide velocities peaked in the early spring and summer in response to snowmelt and summer thunderstorms respectively velocities were slowest in mid winter when air and soil temperatures were coldest and precipitation was generally low and or in the form of snow with a low water content we hypothesize that the seasonal variability in velocities is due to ground water levels and corresponding pore pressures that decrease when surface water is unavailable or cannot infiltrate frozen landslide material and increase when surface water from melting snow or rainfall infiltrates unfrozen landslide material we also suggest that patches of bouldery debris and fractures created by continuous movement of the landslide are conduits through which surface water can infiltrate regardless of the frozen or unfrozen state of the landslide matrix material therefore the availability of surface water is more important than landslide temperature in controlling the rate of landslide movement this hypothesis is supported by field instrumentation data that show 1 landslide velocities coinciding with precipitation amounts regardless of the depth of freezing of landslide material 2 spring and annual landslide velocities that were greatest when the depth of freezing was also the greatest and 3 a rapid several weeks or less velocity and pore pressure response to rainfall the persistent but seasonally variable movement of the landslide fits the bathtub model for landslide movement described by baum and reid baum r l reid m e 2000 ground water isolation by low permeability clays in landslide shear zones in bromhead e n dixon n ibsen m l eds landslides in research theory and practice proc 8th int symp on landslides cardiff wales vol 1 139 144 in their model the landslide is isolated both mechanically and hydrologically from adjacent materials by low permeability clays these clays cause the landslide to retain water our data support this model by suggesting that pore pressures at the basal landslide surface are always adequate to maintain landslide movement and that any infiltration of water at the surface of the landslide is adequate to rapidly increase landslide velocity