satellite sar interferometry for the improved assessment of the state of activity of landslides a case study from the cordilleras of peru abstract in peru landslides have been causing damages and casualties annually due to the high mountain relief and distinct seasonal precipitation distribution satellite synthetic aperture radar sar interferometry represents one possibility for mapping surface deformation at fine spatial resolution over large areas in order to characterize aspects of terrain motion and potentially hazardous processes we present land surface motion maps derived from satellite sar interferometry insar for a part of the santa river basin between the cordilleras blanca and negra around the city of carhuaz in peru using both persistent scatterer interferometry psi and differential sar interferograms dinsar from alos 1 palsar 1 envisat asar alos 2 palsar 2 and sentinel 1 we mapped 42 landslides extending over 17 190 141 m2 within three classes of activity i e 0 2 cm a 2 10 cm a and 10 cm a a geomorphological inventory of landslides was prepared from optical satellite imagery and field experience and compared to the insar based slope instability inventory the two approaches provide slightly different information about landslide spatial and temporal activity patterns but altogether they can be combined for the assessment of the state of activity of landslides and possibly the development of hazard maps which are not systematically available in this region we conclude that alos palsar 1 and 2 and sentinel 1 data have a high potential to derive high quality surface deformation information of landslides in many mountainous regions worldwide due to their global and frequent acquisition strategies

representative rainfall thresholds for landslides in the nepal himalaya measuring some 2400 km in length the himalaya accommodate millions of people in northern india and pakistan nepal bhutan and parts of other asian nations every year especially during monsoon rains landslides and related natural events in these mountains cause tremendous damage to lives property infrastructure and environment in the context of the himalaya however the rainfall thresholds for landslide initiation are not well understood this paper describes regional aspects of rainfall thresholds for landslides in the himalaya some 677 landslides occurring from 1951 to 2006 were studied to analyze rainfall thresholds out of the 677 landslides however only 193 associated with rainfall data were analyzed to yield a threshold relationship between rainfall intensity rainfall duration and landslide initiation the threshold relationship fitted to the lower boundary of the field defined by landslide triggering rainfall events is i 73 90d 0 79 i rainfall intensity in mm h 1 and d duration in hours revealing that when the daily precipitation exceeds 144 mm the risk of landslides on himalayan mountain slopes is high normalized rainfall intensity duration relationships and landslide initiation thresholds were established from the data after normalizing rainfall intensity data with respect to mean annual precipitation map as an index in which ni 1 10d 0 59 ni normalized intensity in h 1 finally the role of antecedent rainfall in causing landslides was also investigated by considering daily rainfall during failure and the cumulative rainfall to discover at what point antecedent rainfall plays an important role in himalayan landslide processes rainfall thresholds presented in this paper are generalized so they can be used in landslide warning systems in the nepal himalaya 2008 elsevier b v all rights reserved

earthquake driven acceleration of slow moving landslides in the colca valley peru detected from pleiades images abstract major earthquakes in mountainous areas often trigger rapid landslides some observations also suggest that earthquakes can damage landslide prone areas or cause slow moving landslides to accelerate with a risk of evolution to rapid landslides in the following months after the earthquake here we use optical images from the pleiades satellites to detect slow moving landslides and quantify the effect of earthquakes on the landslide motion we process multi temporal pleiades images acquired in march april and july 2013 over an area of 210 km2 in the colca valley south peru to obtain two digital elevation models dem and three displacement fields of the area the processed dems have an uncertainty of 0 6 m 1 an order of magnitude better than two global and freely available dems gdem v2 and srtm whereas the displacement fields have an uncertainty of between 0 11 and 0 18 m 1 in both horizontal directions using these data we detect 9 slow moving landslides and compare their velocities during the march april and april july periods we find that landslide velocities are highest during the wet season which suggests a strong groundwater control and we also highlight a landslide acceleration caused by a regional mw 6 0 earthquake the major parameters controlling the acceleration of the slow moving landslides are the rock type and the distance to the source suggesting that friction at the basal interface in the weeks after the earthquake is dependent on the shaking intensity

monitoring landslides and tectonic motions with the permanent scatterers technique spaceborne differential synthetic aperture radar interferometry dinsar has already proven its potential for mapping ground deformation phenomena e g volcano dynamics however atmospheric disturbances as well as phase decorrelation have prevented hitherto this technique from achieving full operational capability these drawbacks are overcome by carrying out measurements on a subset of image pixels corresponding to pointwise stable reflectors permanent scatterers ps and exploiting long temporal series of interferometric data results obtained by processing 55 images acquired by the european space agency esa ers sar sensors over southern california show that the ps approach pushes measurement accuracy very close to its theoretical limit about 1 mm allowing the description of millimetric deformation phenomena occurring in a complex fault system a comparison with corresponding displacement time series relative to permanent gps stations of the southern california integrated gps network scign is carried out moreover the pixel by pixel character of the ps analysis allows the exploitation of individual phase stable radar targets in low coherence areas this makes spaceborne interferometric measurements possible in vegetated areas as long as a sufficient spatial density of individual isolated man made structures or exposed rocks is available the evolution of the ancona landslide central italy was analysed by processing 61 ers images acquired in the time span between june 1992 and december 2000 the results have been compared with deformation values detected during optical levelling campaigns ordered by the municipality of ancona the characteristics of ps gps and optical levelling surveying are to some extent complementary a synergistic use of the three techniques could strongly enhance quality and reliability of ground deformation monitoring d 2002 elsevier science b v all rights reserved

insar time series analysis of l band wide swath sar data acquired by alos 2 operating at l band 24 cm wavelength in wide swath modes is one of the characteristics of the new and next generation satellite synthetic aperture radar sar missions after 3 years of operation the japan aerospace exploration agency advanced land observing satellite 2 alos 2 satellite has acquired a wealth of l band wide swath sar data over many areas using its scansar mode we present interferometry sar insar time series analysis results from alos 2 scansar data we analyze the possible error sources in the insar and correct them if possible we present different time series analysis results including azimuth frequency modulation rate error line of sight los ionospheric phase azimuth shift caused by the ionosphere and los displacement processed using both full aperture and burst by burst workflows the final insar los displacement time series result reveals both large scale tectonic and small scale anthropogenic deformation components the results demonstrate the potential for measuring continental or even global scale tectonic deformation and illustrate the promise of upcoming l band wide swath sar missions such as the nasa isro sar mission

anthropogenic and geologic influences on subsidence in the vicinity of new orleans louisiana new measurements of ongoing subsidence of land proximal to the city of new orleans louisiana and including areas around the communities of norco and lutcher upriver along the mississippi are reported the rates of vertical motion are derived from interferometric synthetic aperture radar insar applied to uninhabited aerial vehicle synthetic aperture radar uavsar data acquired on 16 june 2009 and 2 july 2012 the subsidence trends are similar to those reported for 2002 2004 in parts of new orleans where observations overlap in particular in michoud the 9th ward and chalmette but are measured at much higher spatial resolution 6 m the spatial associations of cumulative surface movements suggest that the most likely drivers of subsidence are groundwater withdrawal and surficial drainage dewatering activities high subsidence rates are observed localized around some major industrial facilities and can affect nearby flood control infrastructure substantial subsidence is observed to occur rapidly from shallow compaction in highly localized areas which is why it could be missed in subsidence surveys relying on point measurements at limited locations

convergence rate across the nepal himalaya and interseismic coupling on the main himalayan thrust implications for seismic hazard we document geodetic strain across the nepal himalaya using gps times series from 30 stations in nepal and southern tibet in addition to previously published campaign gps points and leveling data and determine the pattern of interseismic coupling on the main himalayan thrust fault mht the noise on the daily gps positions is modeled as a combination of white and colored noise in order to infer secular velocities at the stations with consistent uncertainties we then locate the pole of rotation of the indian plate in the itrf 2005 reference frame at longitude 1 34 3 31 latitude 51 4 0 3 with an angular velocity of 0 5029 0 0072 myr the pattern of coupling on the mht is computed on a fault dipping 10 to the north and whose strike roughly follows the arcuate shape of the himalaya the model indicates that the mht is locked from the surface to a distance of approximately 100 km down dip corresponding to a depth of 15 to 20 km in map view the transition zone between the locked portion of the mht and the portion which is creeping at the long term slip rate seems to be at the most a few tens of kilometers wide and coincides with the belt of midcrustal microseismicity underneath the himalaya according to a previous study based on thermokinematic modeling of thermochronological and thermobarometric data this transition seems to happen in a zone where the temperature reaches 350 c the convergence between india and south tibet proceeds at a rate of 17 8 0 5 mm yr in central and eastern nepal and 20 5 1 mm yr in western nepal the moment deficit due to locking of the mht in the interseismic period accrues at a rate of 6 6 0 4 10 19 nm yr on the mht underneath nepal for comparison the moment released by the seismicity over the past 500 years including 14 m w 7 earthquakes with moment magnitudes up to 8 5 amounts to only 0 9 10 19 nm yr indicating a large deficit of seismic slip over that period or very infrequent large slow slip events no large slow slip event has been observed however over the 20 years covered by geodetic measurements in the nepal himalaya we discuss the magnitude and return period of m 8 earthquakes required to balance the long term slip budget on the mht

shear rate dependent strength control on the dynamics of rainfall triggered landslides tokushima prefecture japan a typhoon typhoon no 10 attacked shikoku island and the tyugoku area of japan in 2004 this typhoon produced a new daily precipitation record of 1317 mm on shikoku island and triggered hundreds of landslides in tokushima prefecture one catastrophic landslide was triggered in the shiraishi area of kisawa village and destroyed more than 10 houses while also leaving an unstable block high on the slope the unstable block kept moving after the event showing accelerating and decelerating movement during and after rainfall and reaching a displacement of several meters before countermeasures were put into place to examine the mechanism for this landsliding characteristic samples weathered serpentinite were taken from the field and their shear behaviours examined using ring shear tests the test results revealed that the residual shear strength of the samples is positively dependent on the shear rate which may provide an explanation for the continuous accelerating decelerating process of the landsliding the roughness of the shear surface and the microstructure of the shear zone were measured and observed by laser microscope and sem techniques in an attempt to clarify the mechanism of shear rate effect on the residual shear strength copyright 2010 john wiley sons ltd

interseismic strain accumulation across the central north anatolian fault from iteratively unwrapped insar measurements the north anatolian fault naf is a major tectonic feature in the middle east and is the most active fault in turkey the central portion of the naf is a region of global navigation satellite systems gnss scarcity previous studies of interseismic deformation have focused on the aseismic creep near the town of ismetpasa using radar data acquired in a single line of sight direction requiring several modeling assumptions we have measured interseismic deformation across the naf using both ascending and descending data from the envisat satellite mission acquired between 2003 and 2010 rather than rejecting incorrectly unwrapped areas in the interferograms we develop a new iterative unwrapping procedure for small baseline interferometric synthetic aperture radar insar processing that expands the spatial coverage our method corrects unwrapping errors iteratively and increases the robustness of the unwrapping procedure we remove long wavelength trends from the insar data using gnss observations and deconvolve the insar velocities into fault parallel motion profiles of fault parallel velocity reveal a systematic eastward decrease in fault slip rate from 30 mm yr 25 34 95 confidence interval ci to 21 mm yr 14 27 95 ci over a distance of 200 km direct offset measurements across the fault reveal fault creep along a 130 km section of the central naf with an average creep rate of 8 2 mm yr and a maximum creep rate of 14 2 mm yr located 30 km east of ismetpasa as fault creep is releasing only 30 40 of the long term strain in the shallow crust the fault is still capable of producing large damaging earthquakes in this region

recent advances in sar interferometry time series analysis for measuring crustal deformation abstract synthetic aperture radar sar interferometry is a technique that permits remote detection of deformation at the earth s surface and has been used extensively to measure displacements associated with earthquakes volcanic activity and many other crustal deformation phenomena analysis of a time series of sar images extends the area where interferometry can be successfully applied and also allows detection of smaller displacements through the reduction of error sources here we review recent advances in time series sar interferometry methods that further improve accuracy this is particularly important when constraining displacements due to processes with low strain rates such as interseismic deformation we include examples of improved algorithms applied to image deformation associated with the 2010 eruption of eyjafjallajokull volcano in iceland slow slip on the guerrero subduction zone in mexico and tectonic deformation in western anatolia turkey

rate weakening friction characterizes both slow sliding and catastrophic failure of landslides abstract catastrophic landslides cause billions of dollars in damages and claim thousands of lives annually whereas slow moving landslides with negligible inertia dominate sediment transport on many weathered hillslopes surprisingly both failure modes are displayed by nearby landslides and individual landslides in different years subjected to almost identical environmental conditions such observations have motivated the search for mechanisms that can cause slow moving landslides to transition via runaway acceleration to catastrophic failure a similarly diverse range of sliding behavior including earthquakes and slow slip events occurs along tectonic faults our understanding of these phenomena has benefitted from mechanical treatments that rely upon key ingredients that are notably absent from previous landslide descriptions here we describe landslide motion using a rate and state dependent frictional model that incorporates a nonlocal stress balance to account for the elastic response to gradients in slip our idealized one dimensional model reproduces both the displacement patterns observed in slow moving landslides and the acceleration toward failure exhibited by catastrophic events catastrophic failure occurs only when the slip surface is characterized by rate weakening friction and its lateral dimensions exceed a critical nucleation length h h that is shorter for higher effective stresses however landslides that are extensive enough to fall within this regime can nevertheless slide slowly for months or years before catastrophic failure our results suggest that the diversity of slip behavior observed during landslides can be described with a single model adapted from standard fault mechanics treatments

earthflow sediment production and holocene sediment record in a large apennine catchment abstract landscape evolution in active mountain chains can be dominated by gravitational slope movements this is observed in a large portion of the reno river catchment apennines italy where weak rocks such as clayshales are subject to earthflows that control hillslope morphology and supply sediments to the channel network in this paper we evaluate the sediment flux generated by earthflows and compare it with holocene averaged deposition rates to assess the contribution of mass movements to landscape evolution present day hillslope sediment flux is estimated by combining measured displacement rates 72 inclinometers and spatial attributes of earthflows and historical frequency of reactivations averaged sediment yield 1 6 x 10 3 t km 2 yr compares well with similar studies on earthflow dominated landscapes despite notable differences in methodology in the study area the connectivity between hillslopes and the stream network is well developed and no significant sediment sinks influence the sediment transport processes we document best estimates of regional sediment fluxes and related uncertainties based on available data coarse limestone fragments present in the clayshales are used as a natural sediment tracer to allow a comparison with sedimentation rates taking place at the mouth of the intramontane catchment here available borehole logs 14 c datings and stratigraphic correlations of the alluvial fan are used to obtain an estimate of the deposition that took place during holocene times taking also into account the role of solute transport sedimentation rates are compared to earthflow sediment production rates results show a good agreement and demonstrate that earthflows are the primary mass wasting process in these weak rock lithologies we document best estimates of regional sediment fluxes and related uncertainties present earthflow sediment production outpaces holocene averaged sedimentation rates by a factor of two the gap between sediment production and deposition can be partly justified by uncertainties associated with our estimates and by time scale differences with this respect the dynamic equilibrium between erosion and deposition is likely affected by intra holocene oscillations at a short time scale 10 to 1 ky attributable to climate variability terraced deposits documenting sedimentary episodes would also support such interpretation

forecasting giant catastrophic slope collapse lessons from vajont northern italy rapid giant landslides or sturzstroms are among the most powerful natural hazards on earth they have minimum volumes of similar to10 6 10 7 m 3 and normally preceded by prolonged intervals of accelerating creep are produced by catastrophic and deep seated slope collapse loads similar to1 10 mpa conventional analyses attribute rapid collapse to unusual mechanisms such as the vaporization of ground water during sliding here catastrophic collapse is related to self accelerating rock fracture common in crustal rocks at loads similar to1 10 mpa and readily catalysed by circulating fluids fracturing produces an abrupt drop in resisting stress measured stress drops in crustal rock account for minimum sturzstrom volumes and rapid collapse accelerations fracturing also provides a physical basis for quantitatively forecasting catastrophic slope failure c 2003 elsevier science b v all rights reserved

unsteady sediment discharge in earth flows a case study from the mount pizzuto earth flow southern italy abstract surface mapping gps surveys t lidar surveys boreholes seismic profiles and hvsr measurements were used to study the mechanisms of sediment transport along the mount pizzuto earth flow in southern italy the earth flow has several kinematic zones with transitional areas marked by changing structural styles from compressional structures thrusts upslope to extensional structures normal faults downslope we relate sediment discharge at these transitional zones to internal strain the results suggest that during surge events flow acceleration starts within the head and propagates downslope inducing a cascade effect between kinematic zones during surge events the average sediment discharge is nearly constant and a change from sliding to flowing allows propagation of movement towards the toe during slow movement kinematic zones are independent and sediment discharge varies along the flow in general the velocity profile and the structural style are controlled by the basal slip surface the implications are i sediment discharge is not constant but is a function of the earth flow activity ii during surge earth flow material behaves similar to an incompressible fluid and iii the distribution of surface structures can provide information about the geometry of the slip surface and the velocity profile additionally earth flows with a well defined neck seem to be more likely to surge with respect to those without

the size distribution and mobility of landslides caused by the 2015 mw7 8 gorkha earthquake nepal abstract coseismic landslides pose immediate and prolonged hazards to mountainous communities and provide a rare opportunity to study the effect of large earthquakes on erosion and sediment budgets by mapping landslides using high resolution satellite imagery we find that the 25 april 2015 m w 7 8 gorkha earthquake and aftershock sequence produced at least 25 000 landslides throughout the steep himalayan mountains in central nepal despite early reports claiming lower than expected landslide activity our results show that the total number area and volume of landslides associated with the gorkha event are consistent with expectations when compared to prior landslide triggering earthquakes around the world the extent of landsliding mimics the extent of fault rupture along the east west trace of the main himalayan thrust and increases eastward following the progression of rupture in this event maximum modeled peak ground acceleration pga and the steepest topographic slopes of the high himalaya are not spatially coincident so it is not surprising that landslide density correlates neither with pga nor steepest slopes on their own instead we find that the highest landslide density is located at the confluence of steep slopes high mean annual precipitation and proximity to the deepest part of the fault rupture from which 0 5 2 hz seismic energy originated we suggest that landslide density was determined by a combination of earthquake source characteristics slope distributions and the influence of precipitation on rock strength via weathering and changes in vegetation cover determining the relative contribution of each factor will require further modeling and better constrained seismic parameters both of which are likely to be developed in the coming few years as post event studies evolve landslide mobility in terms of the ratio of runout distance to fall height is comparable to small volume landslides in other settings and landslide volume runout scaling is consistent with compilations of data on larger slope failures in general the size ratios of landslide source area to full landslide area are smaller than global averages and hillslope length seems to largely control runout distance which we propose reflects a topographic control on landslide mobility in this setting we find that landslide size dictates runout distance and that more than half of the landslide debris was deposited in direct connection with stream channels connectivity which is defined as the spatial proximity of landslides to fluvial channels is greatest for larger landslides in the high relief part of the high himalaya although these failures are less abundant than those at lower elevations they may have a disproportionate impact on sediment dynamics and cascading hazards such as landslide reactivation by monsoon rainfall and landslide dams that lead to outburst floods the overall high fluvial connectivity of coseismic landsliding in the gorkha event suggests coupling between the earthquake cycle and sediment geochemical budgets of fluvial systems in the himalaya

insar based detection method for mapping and monitoring slow moving landslides in remote regions with steep and mountainous terrain an application to nepal abstract mapping and monitoring landslides in remote areas with steep and mountainous terrain is logistically challenging expensive and time consuming yet in order to mitigate hazards and prevent loss of life in these areas and to better understand landslide processes high resolution measurements of landslide activity are necessary satellite based synthetic aperture radar interferometry insar provides millimeter scale measurements of ground surface deformation that can be used to identify and monitor landslides in remote areas where ground based monitoring techniques are not feasible here we present a novel insar deformation detection approach which uses double difference time series with local and regional spatial filters and pixel clustering methods to identify and monitor slow moving landslides without making a priori assumptions of the location of landslides we apply our analysis to freely available copernicus sentinel 1 satellite data acquired between 2014 and 2017 centered on the trishuli river drainage basin in nepal we found a minimum of 6 slow moving landslides that all occur within the ranimatta lithologic formation phyllites metasandstones metabasics these landslides have areas ranging from 0 39 to 1 66 km2 and long term dry season displacement rates ranging from 2 1 to 8 8 cm yr due to periods of low coherence during the monsoon season june september each year and following the 25 april 2015 mw7 8 gorkha earthquake our time series analysis is limited to the 2014 2015 and 2016 2017 dry seasons september may we found that each of the landslides displayed slightly higher rates during the 2014 period likely as a result of higher cumulative rainfall that fell during the 2014 monsoon season although we do not have high quality insar data to show the landslide evolution directly following the gorkha earthquake the similar rates of movement before 2014 2015 and after 2016 2017 gorkha suggest the earthquake had negligible long term impact on these landslides our findings highlight the potential for region wide mapping of slow moving landslides using freely available remote sensing data in remote areas such as nepal and future work will benefit from expanding our methodology to other regions around the world

ionospheric correction of insar time series analysis of c band sentinel 1 tops data the copernicus sentinel 1a b satellites operating at c band in terrain observation by progressive scans tops mode bring unprecedented opportunities for measuring large scale tectonic motions using interferometric synthetic aperture radar insar although the ionospheric effects are only about one sixteenth of those at l band the measurement accuracy might still be degraded by long wavelength signals due to the ionosphere we implement the range split spectrum method for correcting ionospheric effects in insar with c band sentinel 1 tops data we perform insar time series analysis and evaluate these ionospheric effects using data acquired on both ascending dusk side of the sentinel 1 dawn dusk orbit and descending dawn side tracks over representative midlatitude and low latitude geomagnetic latitude areas we find that the ionospheric effects are very strong for data acquired at low latitudes on ascending tracks for other cases ionospheric effects are not strong or even negligible the application of the range split spectrum method despite some implementation challenges largely removes ionospheric effects and thus improves the insar time series analysis results

coseismic and postseismic motion of a landslide observations modeling and analogy with tectonic faults we document the first time series of a landslide reactivation by an earthquake using continuous gps measurements over the maca landslide peru our survey shows a coseismic response of the landslide of about 2 cm followed by a relaxation period of 5 weeks during which postseismic slip is 3 times greater than the coseismic displacement itself our results confirm the coseismic activation of landslides and provide the first observation of a postseismic displacement these observations are consistent with a mechanical model where slip on the landslide basal interface is governed by rate and state friction analogous to the mechanics of creeping tectonic faults opening new perspectives to study the mechanics of landslides and active faults

controls on valley width in mountainous landscapes the role of landsliding and implications for salmonid habitat a fundamental yet unresolved question in fluvial geomorphology is what controls the width of valleys in mountainous terrain establishing a predictive relation for valley floor width is critical for realizing links between aquatic ecology and geomorphology because the most productive riverine habitats often occur in low gradient streams with broad floodplains working in the oregon coast range western united states we used airborne lidar to explore controls on valley width and couple these findings with models of salmon habitat potential we defined how valley floor width varies with drainage area in a catchment that exhibits relatively uniform ridge and valley topography sculpted by shallow landslides and debris flows in drainage areas 0 1 km 2 valley width increases as a power law function of drainage area with an exponent of 0 6 consequently valley width increases more rapidly downstream than channel width exponent of 0 4 as derived by local hydraulic geometry we used this baseline valley width drainage area function to determine how ancient deep seated landslides in a nearby catchment influence valley width anomalously wide valleys tend to occur upstream of and adjacent to large landslides while downstream valley segments are narrower than predicted from our baseline relation according to coho salmon habitat potential models broad valley segments associated with deep seated landsliding resulted in a greater proportion of the channel network hosting productive habitat because large landslides in this area are structurally controlled our findings indicate a strong link between geologic properties and aquatic habitat

multi sensor advanced dinsar monitoring of very slow landslides the tena valley case study central spanish pyrenees abstract in this work it is demonstrated how the combination of multi sensor and multi temporal sar data improves the monitoring capacity of very slow landslides the study area is the upper tena valley central spanish pyrenees where mostly very slow earth flows have caused direct damage estimated at approximately 15 m in the last decade the advanced dinsar processing of ascending orbit alos palsar images 2006 2010 and descending orbit ers envisat 2001 2007 and terrasar x 2008 datasets has provided heterogeneous displacement velocity measurements the projection along the steepest slope of los displacements reduces the geometrical differences introduced by each satellite these results were compared and validated with available d gps measurements in a second step ps displacement data are combined with a landslide inventory increasing the number of monitored landslides with sufficient ps from 4 to 19 obtained from c and x band data to 38 of the total 294 finally the retrieved multi sensor landslides velocities are classified with respect to the magnitude of road damages that occurred in the 2008 2010 period at local scale the combination of multi sensor data was useful to differentiate different landslide displacement directions to measure different velocity patterns within the same moving mass and to distinguish the slower natural and faster human induced landslides the analysis of displacement time series permitted to evaluate the acceleration caused by a destabilising anthropogenic change and the correlation between displacement variability and seasonal precipitation and melting

spatial and temporal analysis of a global landslide catalog abstract landslide inventories are critical to support investigations of where and when landslides have happened and may occur in the future however there is surprisingly little information on the historical occurrence of landslides at the global scale this paper presents a new publicly available global landslide catalog glc which is based on media reports online databases and other sources this database is currently available at http ojo streamer herokuapp com the 5741 points in the glc provide a foundation for evaluating spatial and temporal trends in landslide activity from 2007 to 2013 globally landslides were reported most frequently from july to september most events occurred in asia north america and southeast asia in contrast fewer than 5 of the fatalities were reported in north america suggesting a significant amount of under reporting in other regions as well as potential discrepancies between developing and developed regions reported landslide events were also compared to satellite based precipitation estimates from the tropical rainfall measuring mission trmm to evaluate the co occurrence of extreme precipitation and landslide activity of the 3550 points considered in a subset of the glc approximately 60 of the reported landslides have daily precipitation exceeding the 95th percentile of precipitation calculated over a 14 year trmm record for the same location this study also investigated how the recurrence interval of extreme precipitation corresponded to some of the most catastrophic landslide events in spite of several reporting and cataloging biases spatial and temporal analysis of the glc suggests that it is a valuable database for characterizing global patterns of landslide occurrence and evaluating relationships with extreme precipitation at regional and global scales

coseismic deformation and triggered landslides of the 2016 mw 6 2 amatrice earthquake in italy the central apennines in italy have had multiple moderate size but damaging shallow earthquakes in this study we optimize the fault geometry and invert for fault slip based on coseismic gps and interferometric synthetic aperture radar insar for the 2016 mw 6 2 amatrice earthquake in italy our results show that nearly all the fault slip occurred between 3 and 6 km depth but extends 20 km along strike there was less than 4 cm static surface displacement at the town amatrice where the most devastating damage occurred landslides triggered by earthquake ground shaking are not uncommon but triggered landslides with submeter movement are challenging to be observed in the field we find evidence of coseismically triggered deep seated landslides northwest and northeast of the epicenter where coseismic peak ground acceleration was estimated 0 5 g by combining ascending and descending insar data we are able to estimate the landslide thickness as at least 100 and 80 m near monte vettore and west of castelluccio respectively the landslide near monte vettore terminates on the preexisting fault monte vettore fault mvef scarp our results imply that the long term fault slip rate of mvef estimated based on paleoseismic studies could potentially have errors due to triggered landslides from nearby earthquake events

exploiting uavsar for a comprehensive analysis of subsidence in the sacramento delta abstract the sacramento san joaquin delta like other heavily engineered deltas throughout the world has undergone substantial subsidence since the late 1800s when the natural estuary was leveed to form islands today islands within the delta have subsided to the point where most lie below mean sea level long term sustainability of the delta requires reversal of subsidence but spatially comprehensive maps of subsidence have not been available to inform and monitor remediation reported here is the first spatially dense map of recent subsidence rates across the delta based on synthetic aperture radar interferometry and constrained by gnss observations the analysis uses a temporally dense and spatially overlapping set of data acquired by the uninhabited aerial vehicle sar uavsar sensor in 2009 2015 on average the delta is subsiding by 9 2 4 4 mm yr with high variability even at the sub island scale including peak subsidence of 160 4 4 mm yr occurring just inland of the levee of the westernmost island and average subsidence of 11 mm yr along the planned path of water conveyance tunnels through the delta the results are compared to local sea level rise slr measured at a tidal gauge in san francisco bay to show that subsidence is currently the dominant contributor to local relative sea level rise rslr by nearly a factor of five based on recently measured and modeled acceleration of slr subsidence in the delta is likely to dominate rslr until the middle of the 21th century

systematic insar tropospheric phase delay corrections from global meteorological reanalysis data 1 despite remarkable successes achieved by differential insar estimations of low tectonic strain rates remain challenging in areas where deformation and topography are correlated mainly because of the topography related atmospheric phase screen aps in areas of high relief empirical removal of the stratified component of the aps may lead to biased estimations of tectonic deformation rates here we describe a method to correct interferograms from the effects of the spatial and temporal variations in tropospheric stratification by computing tropospheric delay maps coincident with sar acquisitions using the era interim global meteorological model the modeled phase delay is integrated along vertical profiles at the era i grid nodes and interpolated at the spatial sampling of the interferograms above the elevation of each image pixel this approach is validated on unwrapped interferograms we show that the removal of the atmospheric signal before phase unwrapping reduces the risk of unwrapping errors in areas of rough topography

a new method for measuring deformation on volcanoes and other natural terrains using insar persistent scatterers 1 we present here a new insar persistent scatterer ps method for analyzing episodic crustal deformation in non urban environments with application to volcanic settings our method for identifying ps pixels in a series of interferograms is based primarily on phase characteristics and finds low amplitude pixels with phase stability that are not identified by the existing amplitude based algorithm our method also uses the spatial correlation of the phases rather than a well defined phase history so that we can observe temporally variable processes e g volcanic deformation the algorithm involves removing the residual topographic component of flattened interferogram phase for each ps then unwrapping the ps phases both spatially and temporally our method finds scatterers with stable phase characteristics independent of amplitudes associated with man made objects and is applicable to areas where conventional insar fails due to complete decorrelation of the majority of scatterers yet a few stable scatterers are present

fifteen years of surface deformation in western taiwan insight from sar interferometry abstract geodetically measured surface displacements are produced by a combination of underlying deformation processes acting at different spatial and temporal scales a complete history of surface measurements in an area can help discriminate contributions from tectonic hydrologic and anthropogenic processes in this study we use synthetic aperture radar sar images of the active mountain front and adjacent coastal plain of southwestern taiwan to generate time series of surface deformation from 1995 to 2001 and from 2005 to 2008 based on the insar small baseline method the insar measurements agree well with los motions estimated from continuous gps measurements of 3d displacements between 2006 and 2008 a significant range increase in line of sight los is dominated by land subsidence in the coastal area of western and southwestern taiwan subsidence rates vary with annual periods and are highly correlated with seasonal precipitation which are likely associated with groundwater recharge and withdrawal the long term deformation is dominated by long term tectonic loading in sw taiwan during the interseismic period of the earthquake cycle including elastic strain along or continuous creep on the active faults our results show the ability of insar to reveal spatiotemporal crustal deformation in western taiwan with high spatial resolution and accuracy which is potentially important for evaluating seismic hazards

fault zone controls on the spatial distribution of slow moving landslides slow moving landslides earthflows can dominate hillslope sediment flux and landscape erosion in hilly terrain with mechanically weak fine grained rock controls on the occurrence of slow moving landslides are poorly constrained and need to be understood for landscape evolution models sediment budgets and infrastructure and hazards planning here we use airborne interferometric synthetic aperture radar insar and aerial photographs to document 150 previously unidentified active earthflows along the central creeping portion of the san andreas fault california the earthflows move seasonally in response to winter rainfall occur on hillslopes at 20 40 gradients less than typically associated with rapid catastrophic landslides and have similar morphological characteristics to earthflows in different climatic and tectonic settings although our data extend up to 10 km from the fault trace 75 of detected landslides occur within 2 km of the active fault topographic precipitation and rock type metrics alone are not enough to explain the observed spatial distribution of earthflows instead we hypothesize that earthflows cluster near the creeping san andreas fault because of a fault induced zone of reduced bulk rock strength that increases hillslope susceptibility to failure in addition similar lithology topography and climate exist north of the creeping section of the fault yet earthflows there are rare this may be due to large magnitude earthquakes episodically triggering coseismic rapid landslides which preferentially remove weak rock from the fault damage zone our analysis suggests that the necessary conditions for earthflow formation in central california include some combination of reduced rock strength fine grained sedimentary rock threshold precipitation and relief and possibly the absence of large magnitude earthquakes these conditions likely hold for earthflow development in other areas and our work suggests that local variations in rock strength and seismicity such as those associated with fault zones need to be taken into account in order to accurately predict earthflow occurrence

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

residual shear strength variability as a primary control on movement of landslides reactivated by earthquake induced ground motion implications for coastal oregon u s most large seismogenic landslides are reactivations of preexisting landslides with basal shear zones in the residual strength condition residual shear strength often varies during rapid displacement but the response of residual shear zones to seismic loading is largely unknown we used a ring shear apparatus to perform simulated seismic loading tests constant displacement rate tests and tests during which shear stress was gradually varied on specimens from two landslides to improve understanding of coseismic landslide reactivation and to identify shear strength models valid for slow gravitational failure through rapid coseismic failure the landslides we studied represent many along the oregon u s coast seismic loading tests resulted in 1 catastrophic failure involving unbounded displacement when stresses represented those for the existing landslides and 2 limited to unbounded displacement when stresses represented those for hypothetical dormant landslides suggesting that coseismic landslide reactivation may be significant during future great earthquakes occurring near the oregon coast constant displacement rate tests indicated that shear strength decreased exponentially during the first few decimeters of displacement but increased logarithmically with increasing displacement rate when sheared at 0 001 cm s 1 or greater dynamic shear resistance estimated from shear strength models correlated well with stresses observed during seismic loading tests indicating that displacement rate and amount primarily controlled failure characteristics we developed a stress based approach to estimate coseismic landslide displacement that utilizes the variable shear strength model the approach produced results that compared favorably to observations made during seismic loading tests indicating its utility for application to landslides

dynamics of slow moving landslides from permanent scatterer analysis high resolution interferometric synthetic aperture radar insar permanent scatterer data allow us to resolve the rates and variations in the rates of slow moving landslides satellite to ground distances range changes on landslides increase at rates of 5 to 7 millimeters per year indicating average downslope sliding velocities from 27 to 38 millimeters per year time series analysis shows that displacement occurs mainly during the high precipitation season during the 1997 1998 el nino event rates of range change increased to as much as 11 millimeters per year the observed nonlinear relationship of creep and precipitation rates suggests that increased pore fluid pressures within the shallow subsurface may initiate and accelerate these features changes in the slope of a hill resulting from increases in the pore pressure and lithostatic stress gradients may then lead to landslides

cenomanian turonian organic sedimentation in north west africa a comparison between the tarfaya morocco and senegal basins abstract the cenomanian turonian oceanic anoxic event was recognised in north western africa in various depositional settings from abyssal areas to continental shelves to derive information on environmental conditions in these different settings and define a depositional model a petrographical and geochemical study of the organic matter was performed on sediments from the tarfaya morocco and senegal basins the results obtained for these two locations were compared to those of previous studies namely from dsdp wells petrographic and geochemical data allow the differentiation of two main organofacies a shallow depositional facies continental shelf is characterised by low total organic carbon toc contents the second organofacies deposited in the deep marine environment slope and abyssal shows a high toc content 7 the predominance of fluorescing amorphous om combined with high hi values suggests good preservation conditions the s c ratio 0 36 and abundance of organic sulphur compounds support this interpretation and indicate a development of anoxic conditions to explain the organic contrast between both environments a depositional model has been developed which is based on limited water exchange between both depositional settings the main factor which has determined black shale sedimentation is the restricted water circulation related to the presence of isolated depositional environment during atlantic ocean opening compared to present upwelling zones the palaeoproductivity in the studied area was relatively moderate during cenomanian turonian and seems not to be the only determining factor of organic matter accumulation

improvement of seismic observation in the ocean by use of seafloor boreholes we developed a long term high quality seismic ocean floor borehole observatory system the neath seafloor equipment for recording earth9s internal deformation nereid four nereid borehole observatories were installed in the japan trench off sanriku area jt1 jt2 in the northwestern pacific basin wp2 and in the philippine sea wp1 the borehole sensors are cemented in the borehole to assure good coupling of sensors to the ground as well as to avoid effects of water flow around the sensors which may have been a problem in previous borehole installations the nereid seismic records from two of the observatories jt1 wp2 were free from long period noise due to turbulence in the seafloor boundary current or to water flowing around the sensor that is significant on the seafloor the infragravity wave noise clearly observed around 0 01 hz on the horizontal components was significantly higher in the jt1 seismometer in the sediment because of the low shear modulus of the sediment ocean waves of long wavelength cause the infragravity wave noise it is thus necessary to install seismometers in boreholes below the sediments to reduce the infragravity wave noise

widespread uplift and trapdoor faulting on galapagos volcanoes observed with radar interferometry volcanic uplift caused by the accumulation of magma in subsurface reservoirs is a common precursor to eruptions1 2 but for some volcanoes uplift of metres or more has not yet led to an eruption3 here we present displacement maps of volcanoes in the galapagos islands constructed using satellite radar interferometry that might help explain this dichotomy we show that all but one of the seven volcanoes on the islands of isabela and fernandina deformed during 1992 99 cerro azul and fernandina erupted4 5 6 during the observation period and show evidence of inflation co eruptive deflation and shallow dyke intrusion in contrast the largest volcano sierra negra has not erupted yet exhibits spatially and temporally variable deformation with a maximum uplift of 2 7 m between 1992 and 1999 which can be modelled by a shallow inflating sill inflation during 1997 98 however was accompanied by trapdoor faulting on a steeply dipping fracture system within the caldera repeated trapdoor faulting over geological time has formed an arcuate intra caldera ridge within sierra negra and may have acted to relax stresses above the magma chamber inhibiting summit eruptions similar processes may help explain large uplift unaccompanied by eruptive activity at other volcanoes

geomorphic and geologic controls of geohazards induced by nepal s 2015 gorkha earthquake the gorkha earthquake m 7 8 on 25 april 2015 and later aftershocks struck south asia killing 9 000 and damaging a large region supported by a large campaign of responsive satellite data acquisitions over the earthquake disaster zone our team undertook a satellite image survey of the earthquakes induced geohazards in nepal and china and an assessment of the geomorphic tectonic and lithologic controls on quake induced landslides timely analysis and communication aided response and recovery and informed decision makers we mapped 4 312 co seismic and post seismic landslides we also surveyed 491 glacier lakes for earthquake damage but found only 9 landslide impacted lakes and no visible satellite evidence of outbursts landslide densities correlate with slope peak ground acceleration surface downdrop and specific metamorphic lithologies and large plutonic intrusions

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

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

reassessing the 2006 guerrero slow slip event mexico implications for large earthquakes in the guerrero gap in guerrero mexico slow slip events have been observed in a seismic gap where no earthquakes have occurred since 1911 a rupture of the entire gap today could result in a mw 8 2 8 4 earthquake however it remains unclear how slow slip events change the stress field in the guerrero seismic region and what their implications are for devastating earthquakes most earlier studies have relied on a sparse network of global navigation satellite systems measurements here we show that interferometric synthetic aperture radar can be used to improve the spatial resolution we find that slip due to the 2006 slow slip event enters the seismogenic zone and the guerrero gap with 5 cm slip reaching depths as shallow as 12 km we show that slow slip is correlated with a highly coupled region and estimate that slow slip events have decreased the total accumulated moment since the end of the 2001 2002 slow slip event 4 7 years by 50 nevertheless even accounting for slow slip the moment deficit in the guerrero gap increases each year by mw 6 8 the guerrero gap therefore still has the potential for a large earthquake with a slip deficit equivalent to mw 8 15 accumulated over the last century correlation between the slow slip region and nonvolcanic tremor and between slow slip and an ultraslow velocity layer supports the hypothesis of a common source potentially related to high pore pressures

controls on the seasonal deformation of slow moving landslides article history precipitation drives seasonal velocity changes in slow moving landslides by increasing pore water pressure and reducing the effective normal stress along basal shear zones this pressure change is often modeled as a pore water pressure wave that diffuses through the landslide body such that the minimum time required for landslides to respond to rainfall should vary as the square of landslide depth which often approximates the saturated thickness and inversely with hydraulic diffusivity here we assess this model with new observations from the landslide prone eel river catchment northern california using satellite radar interferometry insar time series precipitation data and high resolution topographic data from airborne lidar we quantify the seasonal dynamics of 10 slow moving landslides which share the same lithologic tectonic and mediterranean climate conditions these slope failures have areas ranging from 0 16 to 3 1 km 2

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

the role of landslides in mountain range evolution abstract we review the role of landslides in current concepts of the topographic development of mountain ranges we find that many studies in this field address basin or orogen scale competition between rock uplift and fluvial bedrock erosion hillslopes in general and bedrock landslides in particular are often assumed to respond rapidly to incision and development of the fluvial drainage network this leads to a one sided view of the geomorphic coupling between hillslopes and rivers that emphasizes the fluvial control of hillslopes but ignores the alternative view that landslides can affect the fluvial network there is growing evidence that landslides are a dominant source of sediment in mountain belts and that they exert a direct geomorphic control on fluvial processes landslides can influence the river network in a variety of ways from determining basin area and drainage divide positions to setting streamwise variations in sediment load and calibre the geomorphic legacy of large landslides on hillslope and channel morphologies may persist for up to 104 yr adding considerable variability to fluvial erosion and sedimentation patterns over these timescales we identify a number of questions for future research and conclude that a better understanding and quantification of the geomorphic feedbacks between landslides and river channels builds an important link between short term 105 yr landscape evolution models

a network based enhanced spectral diversity approach for tops time series analysis for multitemporal analysis of synthetic aperture radar sar images acquired with a terrain observation by progressive scan tops mode all acquisitions from a given satellite track must be coregistered to a reference coordinate system with accuracies better than 0 001 of a pixel assuming full sar resolution in the azimuth direction such a high accuracy can be achieved through geometric coregistration using precise satellite orbits and a digital elevation model followed by a refinement step using a time series analysis of coregistration errors these errors represent the misregistration between all tops acquisitions relative to the reference coordinate system we develop a workflow to estimate the time series of azimuth misregistration using a network based enhanced spectral diversity nesd approach in order to reduce the impact of temporal decorrelation on coregistration example time series of misregistration inferred for five tracks of sentinel 1 tops acquisitions indicates a maximum relative azimuth misregistration of less than 0 01 of the full azimuth resolution between the tops acquisitions in the studied areas standard deviation of the estimated misregistration time series for different stacks varies from 1 1e 3 to 2e 3 of the azimuth resolution equivalent to 1 6 2 8 cm orbital uncertainty in the azimuth direction these values fall within the 1 sigma orbital uncertainty of the sentinel 1 orbits and imply that orbital uncertainty is most likely the main source of the constant azimuth misregistration between different tops acquisitions we propagate the uncertainty of individual misregistration estimated with esd to the misregistration time series estimated with nesd and investigate the different challenges for operationalizing nesd

ionospheric correction of insar data for accurate ice velocity measurement at polar regions abstract interferometric synthetic aperture radar insar has become an essential tool for measuring ice sheet velocity in the polar regions at low radar frequencies e g l band 1 2 ghz but also at higher frequency e g c band 5 6 ghz the ionosphere has been documented to be an important source of noise in these data in this paper we employ a split spectrum technique and investigate its performance for correcting ionospheric effects in insar based ice velocity measurements in greenland and antarctica three case studies using alos palsar data are used to assess the performance of the split spectrum technique for ionosphere correction over a range of environmental parameters we employ several approaches to evaluate the results including visual inspection profile analysis comparison of experimental and theoretic errors comparison with reference data from other sources generation of double difference interferograms and analysis of time series of multi temporal data our experiments show that ionospheric distortions are observed regularly and in our analyzed greenland dataset and antarctic dataset the ionospheric noise reaches 14 m yr and 10 m yr respectively which exceeds the signal associated with ice motion our analysis using several different approaches demonstrates that the split spectrum technique provides an effective correction the split spectrum technique is also found to be superior to currently used approaches such as baseline fitting and multi temporal averaging the noise level is reduced by a factor of 70 in greenland test areas and 90 in antarctic test areas

transient reactivation of a deep seated landslide by undrained loading captured with repeat airborne and terrestrial lidar landslides reactivate due to external environmental forcing or internal mass redistribution but the process is rarely documented quantitatively we capture the three dimensional 1 m resolution surface deformation field of a transiently reactivated landslide with image correlation of repeat airborne lidar undrained loading by two debris flows in the landslide s head rather than external forcing triggered reactivation after that loading the lower 2 km of the landslide advanced by up to 14 m in 2 years before completely stopping the displacement field over those 2 years implies that the slip surface gained 1 kpa of shear strength which was likely accomplished by a negative dilatancy pore pressure feedback as material deformed around basal roughness elements thus landslide motion can be decoupled from external environmental forcing in cases motivating the need to better understand internal perturbations to the stress field to predict hazards and sediment fluxes as landscapes evolve