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USGS2018

Factors controlling landslide frequency-area distributions

A power‐law relation for the frequency–area distribution (FAD) of medium and large landslides (e.g. tens to millions of square meters) has been observed by numerous authors. But the FAD of small landslides diverges from the power‐law distribution, with a rollover point below which frequencies decrease for smaller landslides. Some studies conclude that this divergence is an artifact of unmapped small landslides due to lack of spatial or temporal resolution; others posit that it is caused by the change in the underlying failure process. An explanation for this dilemma is essential both to evaluate the factors controlling FADs of landslides and power‐law scaling, which is a crucial factor regarding both landscape evolution and landslide hazard assessment. This study examines the FADs of 45 earthquake‐induced landslide inventories from around the world in the context of the proposed explanations. We show that each inventory probably involves some combination of the proposed explanations, though not all explanations contribute to each case. We propose an alternative explanation to understand the reason for the divergence from a power‐law. We suggest that the geometry of a landslide at the time of mapping reflects not just one single movement but many, including the propagation of numerous smaller landslides before and after the main failure. Because only the resulting combination of these landslides can be observed due to a lack of temporal resolution, many smaller landslides are not taken into account in the inventory. This reveals that the divergence from the power‐law is not necessarily attributed to the incompleteness of an inventory. This conceptual model will need to be validated by ongoing observation and analysis. Also, we show that because of the subjectivity of mapping procedures, the total number of landslides and total landslide areas in inventories differ significantly, and therefore the shapes of FADs also differ considerably.

Earth Surface Processes and Landforms↗

USGS2014

"Report a Landslide” A website to engage the public in identifying geologic hazards

Direct observation by people is the most practical way of identifying, locating, and describing most damaging landslides. In an effort to increase public awareness of landslide hazards and encourage public participation in collecting basic data about landslides, the USGS recently launched a website called “Report a landslide.” The website is modeled in part after the highly successful USGS website “Did you feel it?” which has been used for several years to gather data from the public about intensity of felt earthquakes. The new “Report a landslide” website encourages visitors to report where and when they observed a landslide and to classify the landslide by movement type. Interested users also can report information about damage and casualties, dimensions, and simple geological observations, and can submit photographs of the landslide. Once a user submits a report, the location of the reported landslide appears on a map, and the location is linked to a summary of submitted data. Photos are reviewed prior to posting on the event page. By adding existing USGS data from historical landslides and promoting the website in the wake of large, regional landslide events, we hope to generate widespread awareness and interest in the website. The “Report a landslide” site has great potential for eventually creating a nationwide source of basic landslide data.

Conference Paper↗

USGS2007

Plan curvature and landslide probability in regions dominated by earth flows and earth slides

Damaging landslides in the Appalachian Plateau and scattered regions within the Midcontinent of North America highlight the need for landslide-hazard mapping and a better understanding of the geomorphic development of landslide terrains. The Plateau and Midcontinent have the necessary ingredients for landslides including sufficient relief, steep slope gradients, Pennsylvanian and Permian cyclothems that weather into fine-grained soils containing considerable clay, and adequate precipitation. One commonly used parameter in landslide-hazard analysis that is in need of further investigation is plan curvature. Plan curvature is the curvature of the hillside in a horizontal plane or the curvature of the contours on a topographic map. Hillsides can be subdivided into regions of concave outward plan curvature called hollows, convex outward plan curvature called noses, and straight contours called planar regions. Statistical analysis of plan-curvature and landslide datasets indicate that hillsides with planar plan curvature have the highest probability for landslides in regions dominated by earth flows and earth slides in clayey soils (CH and CL). The probability of landslides decreases as the hillsides become more concave or convex. Hollows have a slightly higher probability for landslides than noses. In hollows landslide material converges into the narrow region at the base of the slope. The convergence combined with the cohesive nature of fine-grained soils creates a buttressing effect that slows soil movement and increases the stability of the hillside within the hollow. Statistical approaches that attempt to determine landslide hazard need to account for the complex relationship between plan curvature, type of landslide, and landslide susceptibility. ?? 2007 Elsevier B.V. All rights reserved.

Engineering Geology↗

USGS2015

Landslide mobility and hazards: implications of the 2014 Oso disaster

Landslides reflect landscape instability that evolves over meteorological and geological timescales, and they also pose threats to people, property, and the environment. The severity of these threats depends largely on landslide speed and travel distance, which are collectively described as landslide “mobility”. To investigate causes and effects of mobility, we focus on a disastrous landslide that occurred on 22 March 2014 near Oso, Washington, USA, following a long period of abnormally wet weather. The landslide's impacts were severe because its mobility exceeded that of prior historical landslides at the site, and also exceeded that of comparable landslides elsewhere. The &sim;8×10 6 m 3 landslide originated on a gently sloping (<20°) riverside bluff only 180 m high, yet it traveled across the entire &sim;1 km breadth of the adjacent floodplain and spread laterally a similar distance. Seismological evidence indicates that high-speed, flowing motion of the landslide began after about 50 s of preliminary slope movement, and observational evidence supports the hypothesis that the high mobility of the landslide resulted from liquefaction of water-saturated sediment at its base. Numerical simulation of the event using a newly developed model indicates that liquefaction and high mobility can be attributed to compression- and/or shear-induced sediment contraction that was strongly dependent on initial conditions. An alternative numerical simulation indicates that the landslide would have been far less mobile if its initial porosity and water content had been only slightly lower. Sensitive dependence of landslide mobility on initial conditions has broad implications for assessment of landslide hazards.

Washington↗

USGS2009

Assessment of tsunami hazard to the U.S. East Coast using relationships between submarine landslides and earthquakes

Submarine landslides along the continental slope of the U.S. Atlantic margin are potential sources for tsunamis along the U.S. East coast. The magnitude of potential tsunamis depends on the volume and location of the landslides, and tsunami frequency depends on their recurrence interval. However, the size and recurrence interval of submarine landslides along the U.S. Atlantic margin is poorly known. Well-studied landslide-generated tsunamis in other parts of the world have been shown to be associated with earthquakes. Because the size distribution and recurrence interval of earthquakes is generally better known than those for submarine landslides, we propose here to estimate the size and recurrence interval of submarine landslides from the size and recurrence interval of earthquakes in the near vicinity of the said landslides. To do so, we calculate maximum expected landslide size for a given earthquake magnitude, use recurrence interval of earthquakes to estimate recurrence interval of landslide, and assume a threshold landslide size that can generate a destructive tsunami. The maximum expected landslide size for a given earthquake magnitude is calculated in 3 ways: by slope stability analysis for catastrophic slope failure on the Atlantic continental margin, by using land-based compilation of maximum observed distance from earthquake to liquefaction, and by using land-based compilation of maximum observed area of earthquake-induced landslides. We find that the calculated distances and failure areas from the slope stability analysis is similar or slightly smaller than the maximum triggering distances and failure areas in subaerial observations. The results from all three methods compare well with the slope failure observations of the M w = 7.2, 1929 Grand Banks earthquake, the only historical tsunamigenic earthquake along the North American Atlantic margin. The results further suggest that a M w = 7.5 earthquake (the largest expected earthquake in the eastern U.S.) must be located offshore and within 100??km of the continental slope to induce a catastrophic slope failure. Thus, a repeat of the 1755 Cape Anne and 1881 Charleston earthquakes are not expected to cause landslides on the continental slope. The observed rate of seismicity offshore the U.S. Atlantic coast is very low with the exception of New England, where some microseismicity is observed. An extrapolation of annual strain rates from the Canadian Atlantic continental margin suggests that the New England margin may experience the equivalent of a magnitude 7 earthquake on average every 600-3000??yr. A minimum triggering earthquake magnitude of 5.5 is suggested for a sufficiently large submarine failure to generate a devastating tsunami and only if the epicenter is located within the continental slope.

Marine Geology↗

USGS2019

Widespread initiation, reactivation, and acceleration of landslides in the northern California Coast Ranges due to extreme rainfall

Episodically to continuously active slow-moving landslides are driven by precipitation. Climate change, which is altering both the frequency and magnitude of precipitation world21 wide, is therefore predicted to have a major impact on landslides. Here we examine the behavior of hundreds of slow-moving landslides in northern California in response to large changes in annual precipitation that occurred between 2016 and 2018. We quantify the landslide displacement using repeat-pass radar interferometry and pixel offset tracking techniques on a novel dataset from the airborne NASA/JPL Uninhabited Aerial Vehicle Synthetic Aperture Radar. We found that 312 landslides were moving due to extreme rainfall during 2017, compared to 119 during 2016, which was the final year of a historic multi-year drought. However, with a return to below average rainfall in 2018, only 146 landslides remained in motion. The increased number of landslides during 2017 was primarily accommodated by landslides that were smaller than the landslides that remained active between 2016 and 2018. Furthermore, by examining a subset of 51 landslides, we found that 49 had increased velocities during 2017 when compared to 2016. Our results show that slow-moving landslides are sensitive to large changes in annual precipitation, particularly the smaller and thinner landslides that likely experience larger basal pore water pressure changes. Based on climate model predictions for the next century in California, which include increases in annual precipitation and increases in the frequency of dry-to-wet extremes, we hypothesize that there will be an overall increase in landslide activity.

California↗

USGS2024

RegionGrow3D: A deterministic analysis for characterizing discrete three-dimensional landslide source areas on a regional scale

Regional-scale characterization of shallow landslide hazards is important for reducing their destructive impact on society. These hazards are commonly characterized by (a) their location and likelihood using susceptibility maps, (b) landslide size and frequency using geomorphic scaling laws, and (c) the magnitude of disturbance required to cause landslides using initiation thresholds. Typically, this is accomplished through the use of inventories documenting the locations and triggering conditions of previous landslides. In the absence of comprehensive landslide inventories, physics-based slope stability models can be used to estimate landslide initiation potential and provide plausible distributions of landslide characteristics for a range of environmental and forcing conditions. However, these models are sometimes limited in their ability to capture key mechanisms tied to discrete three-dimensional (3D) landslide mechanics while possessing the computational efficiency required for broad-scale application. In this study, the RegionGrow3D (RG3D) model is developed to broadly simulate the area, volume, and location of landslides on a regional scale (≥1,000 km 2 ) using 3D, limit-equilibrium (LE)-based slope stability modeling. Furthermore, RG3D is incorporated into a susceptibility framework that quantifies landsliding uncertainty using a distribution of soil shear strengths and their associated probabilities, back-calculated from inventoried landslides using 3D LE-based landslide forensics. This framework is used to evaluate the influence of uncertainty tied to shear strength, rainfall scenarios, and antecedent soil moisture on potential landsliding and rainfall thresholds over a large region of the Oregon Coast Range, USA.

Journal of Geophysical Research: Earth Surface↗

USGS2025

Dynamic feedbacks between river meandering and landsliding in northwestern Washington glacial terraces

Landsliding in river valleys poses unique risks for cascading hazards and can damage infrastructure and cause fatalities. In postglacial valleys, many landslides are posited to occur in relation to lateral river erosion, but the dynamics of fluvial-hillslope interactions are not well understood. Here, we investigate a section of the Nooksack River in western Washington State where the channel is flanked by landslide-prone glacial terraces similar to those that failed in the 2014 State Route 530 “Oso” landslide. We map 216 landslides through time across 17 aerial imagery data sets (1933–2022) and analyze them in relation to river meandering and curvature. We observe dynamic feedbacks between lateral river meandering and valley-adjacent landsliding. Terrace lateral retreat rates of up to 25 m/year owing to combined fluvial erosion and slope failure occur on pinned, outer meander bends immediately downstream from peaks in river curvature (>0.0075 1/m); these locations are predisposed to both shallow and deep-seated landslides. Deep-seated landslides extending 17%–32% of the active valley width into the floodplain can displace the river away from the floodplain margin and change the channel planform. River-displacing landslides relocate meanders up- or downstream, thereby conditioning the location of subsequent landslides. This conceptual model of coupled landslide-driven meander displacement and valley-adjacent landsliding is exemplified across western Washington river systems. The distance between up- and downstream valley-adjacent landsliding scales with valley width, meander wavelength, and terrace height. Our results can advance our understanding of the river-hillslope interface in landscape evolution and can be used to inform hazard management in river corridors.

Washington↗

USGS2011

Controls on large landslide distribution and implications for the geomorphic evolution of the southern interior Columbia River basin

Large landslides (>0.1 km 2 ) are important agents of geomorphic change. While most common in rugged mountain ranges, large landslides can also be widespread in relatively low-relief (several 100 m) terrain, where their distribution has been relatively little studied. A fuller understanding of the role of large landslides in landscape evolution requires addressing this gap, since the distribution of large landslides may affect broad regions through interactions with channel processes, and since the dominant controls on landslide distribution might be expected to vary with tectonic setting. We documented >400 landslides between 0.1 and ∼40 km 2 across ∼140,000 km 2 of eastern Oregon, in the semiarid, southern interior Columbia River basin. The mapped landslides cluster in a NW-SE–trending band that is 50–100 km wide. Landslides predominantly occur where even modest local relief (∼100 m) exists near key contacts between weak sedimentary or volcaniclastic rock and coherent cap rock. Fault density exerts no control on landslide distribution, while ∼10% of mapped landslides cluster within 3–10 km of mapped fold axes. Landslide occurrence is curtailed to the NE by thick packages of coherent basalt and to the SW by limited local relief. Our results suggest that future mass movements will localize in areas stratigraphically preconditioned for landsliding by a geologic history of fluviolacustrine and volcaniclastic sedimentation and episodic capping by coherent lava flows. In such areas, episodic landsliding may persist for hundreds of thousands of years or more, producing valley wall slopes of ∼7°–13° and impacting local channels with an evolving array of mass movement styles.

Idaho, Oregon, Washington↗

USGS2023

Evidence of Seattle Fault earthquakes from patterns of deep-seated landslides

Earthquake‐induced landslides can record information about the seismic shaking that generated them. In this study, we present new mapping, Light Detection and Ranging‐derived roughness dating, and analysis of over 1000 deep‐seated landslides from the Puget Lowlands of Washington, U.S.A., to probe the landscape for past Seattle fault earthquake information. With this new landslide inventory, we observe spatial and temporal evidence of landsliding related to the last major earthquake on the Seattle fault ∼1100 yr before present. We find spatial clusters of landslides that correlate with ground motions from recent 3D kinematic models of Seattle fault earthquakes. We also find temporal patterns in the landslide inventory that suggest earthquake‐driven increases in landsliding. We compare the spatial and temporal landslide data with scenario‐based ground motion models and find stronger evidence of the last major Seattle fault earthquake from this combined analysis than from spatial or temporal patterns alone. We also compare the landslide inventory with ground motions from different Seattle fault earthquake scenarios to determine the ground motion distributions that are most consistent with the landslide record. We find that earthquake scenarios that best match the clustering of ∼1100‐year‐old landslides produce the strongest shaking within a band that stretches from west to east across central Seattle as well as along the bluffs bordering the broader Puget Sound. Finally, we identify other landslide clusters (at 4.6–4.2 ka, 4.0–3.8 ka, 2.8–2.6 ka, and 2.2–2.0 ka) in the inventory which let us infer potential ground motions that may correspond to older Seattle fault earthquakes. Our method, which combines hindcasting of the surface response to the last major Seattle fault earthquake, using a roughness‐aged landslide inventory with forecasts of modeled ground shaking from 3D seismic scenarios, showcases a powerful new approach to gleaning paleoseismic information from landscapes.

Bulletin of the Seismological Society of America↗

USGS1987

Preliminary map showing landslides in Alabama

This map brings together data from all known reports on landslides in Alabama mentioned by Alger and Brabb (1985) and information provided by State and County Highway Departments in response to a questionnaire sent in 1981 by K. F. Rheams. Additional landslide data from the northern part of the state and from Jefferson County were added by Fred Taylor and E. E. Brabb from reports by Pomeroy (1982), Thomas (1979, 1982), and Szabo and others (1979). The locations of two landslides were provided by the U.S. Forest Service (written commun., 1982), and a few more additional landslide locations were noted by K. F. Rheams in 1981 and by E. E. Brabb in 1982. Locations of landslides from the various data sources were transferred to this map by measuring the distance from known landmarks. Substantial differences in scale, differential swelling and shrinking of paper source maps, and other technical problems in transferring the landslide data may have led to errors of as much as one mile in plotting the locations. The landslide locations, therefore, are located only approximately. Many more landslides exist in Alabama but have not yet been recognized or recorded in public documents. The absence of a landslide symbol on this map, therefore, does not indicate that an area is necessarily free of landslides. Conversely, the clustering of landslide symbols in an area should not be used to indicate that the area is unsafe, but rather that many landslides have been reported and that investigation of the problem by qualified geologists and engineers is prudent before development takes place. This map should be considered preliminary in the sense that a systematic evaluation of all areas in Alabama for landslides using standard photographic interpretation techniques has not yet been done. The user of this map is referred to Pomeroy and Thomas (1935) for a discussion of slope—stability problems in northern Alabama.

Alabama↗

USGS2002

Digital inventory of landslides and related deposits in Honduras triggered by Hurricane Mitch

Intense rainfall from Hurricane Mitch from October 27-31, 1998, exceeded 900 mm in places in Honduras and triggered in excess of 500,000 landslides throughout the country. Landslides damaged an estimated 70% of the road network in Honduras based on estimates by the U. S Army Corps of Engineers. Numbers of fatalities due to landslides are not accurately known due to the fact that numerous small villages throughout Honduras lost residents to landslides without an official count being recorded. A conservative estimate would place the number at near 1,000. Debris flows accounted for over 95% of the landslides and ranged in thickness from 1 to 15 m. Flow path lengths of these failures ranged from several meters to 7.5 km. The highest concentrations of debris flows occurred in the mountains near the town of Choluteca where over 900 mm of rain fell in three days. Although landslides other than debris flows were few, several deep-seated landslides in the city of Tegucigalpa severely impacted people and property. The 'El Berrinche' rotational slump/earth flow of approximately six million cubic meters volume destroyed the entire neighborhood of Colonia Soto near the center of the city. The landslide also dammed the Rio Choluteca and created a lagoon behind the landslide dam, which immediately posed a health problem for the city, because raw, untreated sewage was emptying into the Rio Choluteca. Several areas of highly concentrated landslides have been responsible for much of the flooding problem as well. Huge sediment influxes from landslide source areas near La Ceiba, La Libertad, Marale, and in several arms of El Cajon Reservoir have reduced stream capacities to practically nothing and have exacerbated flooding conditions in even the moderate rainfall seasons since Hurricane Mitch. The ongoing hazard to communities from landslides triggered during Hurricane Mitch are being analyzed using aerial photography taken by the U.S. Air Force and by supplemental photography taken by local contractors. Through the use of digital elevation models derived from 1:50,000-scale topographic maps and geologic maps, landslide susceptibility maps will be derived to aid land-use planning and relocation efforts.

Open-File Report↗

USGS2006

Estimating landslide losses - preliminary results of a seven-State pilot project

Introduction: In 2001, the U.S. Geological Survey Landslide Hazards Program provided funding for seven State geological surveys to report on the status of landslide investigation strategies in each of their States, and to suggest improved ways to approach the tracking of landslides, their effects, losses associated with the landslides, and hazard mitigation strategies. Each State was to provide a draft report suggesting innovative ways to track landslides, and to participate in subsequent workshops. A workshop was convened in June 2003 in Lincoln, Neb., to discuss the results and future strategies on how best to incorporate the seven pilot projects into one methodology that all of the 50 States could adopt. The seven individual reports produced by the State surveys are published here to put forth a forum for discussion of the varying methods of tracking landslides. The goal is to eventually adopt a single, universally applied methodology to track landslides that will provide a consistent framework for collecting data on landslide damage and economic impact. Participating States include: California (James Davis, Jack McMillan); Kentucky (Jim Cobb, John Kiefer, John Rockaway); Nebraska (Mark Kuzila, Duane Eversoll); Ohio (Thomas Berg, Jon Rockaway), Oregon (John Beaulieu, Yumei Wang, Renee Summers, Jon Hofmeister); Pennsylvania (Jay Parrish, Helen Delano); Utah (Richard Allis, Francis Ashland). The USGS personnel involved in the planning and meeting facilitation are Paula Gori, Peter Lyttle, and John Pallister. The general USGS strategy to address landslide loss reduction was developed with input from State geological surveys, the engineering-geology consulting community, and academic investigators. The strategy was reviewed by the National Research Council, 2004), is summarized in USGS Circular 1244 (Spiker and Gori, 2003) and is endorsed by the AASG. This pilot study, conducted by seven State geological surveys, examines the feasibility of collecting accurate and reliable information on economic losses associated with landslides. Each State survey examined the availability, distribution, and inherent uncertainties of economic loss data in their study areas. Their results provide the basis for identifying the most fruitful methods of collecting landslide loss data nationally, using methods that are consistent and provide common goals. These results can enhance and establish the future directions of scientific investigation priorities by convincingly documenting landslide risks and consequences that are universal throughout the 50 States. This report is organized as follows: A general summary of the pilot project history, goals, and preliminary conclusions from the Lincoln, Neb. workshop are presented first. Internet links are then provided for each State report, which appear on the internet in PDF format and which have been placed at the end of this open-file report. A reference section follows the reports, and, lastly, an Appendix of categories of landslide loss and sources of loss information is included for the reader's information. Please note: The Oregon Geological Survey has also submitted a preliminary report on indirect loss estimation methodology, which is also linked with the others. Each State report is unique and presented in the form in which it was submitted, having been independently peer reviewed by each respective State survey. As such, no universal 'style' or format has been adopted as there have been no decisions on which inventory methods will be recommended to the 50 states, as of this writing. The reports are presented here as information for decision makers, and for the record; although several reports provide recommendations on inventory methods that could be adopted nationwide, currently no decisions have been made on adopting a uniform methodology for the States.

Open-File Report↗

USGS2008

Landslides Mapped from LIDAR Imagery, Kitsap County, Washington

Landslides are a recurring problem on hillslopes throughout the Puget Lowland, Washington, but can be difficult to identify in the densely forested terrain. However, digital terrain models of the bare-earth surface derived from LIght Detection And Ranging (LIDAR) data express topographic details sufficiently well to identify landslides. Landslides and escarpments were mapped using LIDAR imagery and field checked (when permissible and accessible) throughout Kitsap County. We relied almost entirely on derivatives of LIDAR data for our mapping, including topographic-contour, slope, and hill-shaded relief maps. Each mapped landslide was assigned a level of 'high' or 'moderate' confidence based on the LIDAR characteristics and on field observations. A total of 231 landslides were identified representing 0.8 percent of the land area of Kitsap County. Shallow debris topples along the coastal bluffs and large (>10,000 m2) landslide complexes are the most common types of landslides. The smallest deposit mapped covers an area of 252 m2, while the largest covers 0.5 km2. Previous mapping efforts that relied solely on field and photogrammetric methods identified only 57 percent of the landslides mapped by LIDAR (61 percent high confidence and 39 percent moderate confidence), although nine landslides previously identified were not mapped during this study. The remaining 43 percent identified using LIDAR have 13 percent high confidence and 87 percent moderate confidence. Coastal areas are especially susceptible to landsliding; 67 percent of the landslide area that we mapped lies within 500 meters of the present coastline. The remaining 33 percent are located along drainages farther inland. The LIDAR data we used for mapping have some limitations including (1) rounding of the interface area between low slope surfaces and vertical faces (that is, along the edges of steep escarpments) which results in scarps being mapped too far headward (one or two meters), (2) incorrect laser-distance measurements resulting in inaccurate elevation values, (3) removal of valid ground elevations, (4) false ground roughness, and (5) faceted surface texture. Several of these limitations are introduced by algorithms in the processing software that are designed to remove non-ground elevations from LIDAR data. Despite these limitations, the algorithm-enhanced LIDAR imagery does effectively 'remove' vegetation that obscures many landslides, and is therefore a valuable tool for landslide inventories and investigations in heavily vegetated regions such as the Puget Lowland.

Open-File Report↗

USGS2015

Assessment of existing and potential landslide hazards resulting from the April 25, 2015 Gorkha, Nepal earthquake sequence

Introduction On April 25, 2015, a large ( M 7.8) earthquake shook much of central Nepal and was followed by a series of M >6 aftershocks, including a M 7.3 event on May 12, 2015. This earthquake and aftershocks, referred to as the “Gorkha earthquake sequence,” caused thousands of fatalities, damaged and destroyed entire villages, and displaced millions of residents. The earthquakes also triggered thousands of landslides in the exceedingly steep topography of Nepal; these landslides were responsible for hundreds of fatalities, and blocked vital roads and trails to affected villages (fig. 1). Landslides caused by the Gorkha earthquake sequence continue to pose both immediate and long-term hazards to villages and infrastructure within the affected region. Some landslides blocked rivers and thus created another potential concern for villages located downstream. With the support of the United States Agency for International Development (USAID), Office of Foreign Disaster Assistance (OFDA), and in collaboration with earthquake-hazard organizations from both the United States (for example, U.S. National Science Foundation Geoengineering Extreme Event Reconnaissance [GEER] Team) and Nepal (International Centre for Integrated Mountain Development [ICIMOD]), the U.S. Geological Survey (USGS) responded to this crisis by providing landslide-hazard expertise to Nepalese agencies and affected villages. In addition to collaborating with an international group of remote-sensing scientists to document the spatial distribution of landsliding in the first few weeks following the earthquake, the USGS conducted in-country landslide hazard assessments for 10 days beginning May 24, 2015. Much of the information obtained by the USGS during their time in Nepal was conveyed directly to affected villages and government agencies as opportunities arose. Upon return to the United States, data organization, interpretation, and synthesis began immediately to provide a rapid assessment of landslide hazards for use by Nepalese agencies during the 2015 summer monsoon (typically occurring from June through September). This report provides a detailed account of assessments performed in May and June 2015 and focuses on valley-blocking landslides because they have the potential to pose considerable hazard to many villages in Nepal. First, we provide a seismological background of Nepal and then detail the methods used for both external and in-country data collection and interpretation. Our results consist of an overview of landsliding extent, a characterization of all valley-blocking landslides identified during our work, and a description of video resources that provide high resolution coverage of approximately 1,000 kilometers (km) of river valleys and surrounding terrain affected by the Gorkha earthquake sequence. This is followed by a description of site-specific landslide-hazard assessments conducted while in Nepal and includes detailed descriptions of five noteworthy case studies. Finally, we assess the expectation for additional landslide hazards during the 2015 summer monsoon season.

Open-File Report↗

USGS1977

Large landslides, composed of megabreccia, interbedded in Miocene basin deposits, southeastern Arizona

The landslides in the Kearny and El Capitan Mountain quadrangles, Pinal and Gila Counties, Ariz., are tabular or lens like masses of megabreccia enclosed in Miocene basin deposits. The megabreccias within individual slide blocks are composed of pervasively brecciated Precambrian and younger formations that remain in normal stratigraphic sequence, indicating that each landslide moved as a fairly coherent mass. The megabreccias consist of fresh, mostly angular rock fragments in a comminuted matrix of the same composition as the fragments. The matrix ranges in amount from sparse to abundant. Where the matrix is sparse, the fragments fit tightly with little or no rotation. Locally fragments are rotated but not moved far; most units within a slide block are lithologically homogeneous. The Kearny landslides are conformably interbedded in steeply east-dipping playa and alluvial deposits. They form map units from a few tens of meters to nearly 4 km long and from less than 1 to 270 m wide. Narrow ridges expose sections through the landslides at about right angles to the direction of movement. The upper (proximal) ends have been eroded; the lower (distal) ends are buried. The El Capitan landslide dips very gently southward. Although partly dissected during erosion of the enclosing alluvial and lakebed deposits, its approximate original outline is still preserved. It forms a thin sheet, 5-15 m thick and at least 3.8 km long; the maximum outcrop width, near its distal end, is about 1.5 km. The Kearny landslides show little evidence of having exerted differential pressure on the underlying soft playa and alluvial deposits, and the contacts with the underlying sediments have little relief. The distal end of the El Capitan landslide, on the other hand, has considerable relief. As the landslide came to an abrupt stop, the end plowed into the underlying sediments, compressing them into fol9.s and forming sandstone dikes. The source of the El Capitan landslide is a well-defined amphitheater on the south side of El Capitan Mountain 1,500 to more than 3,000 m above and 1.5-3 km north of the proximal end of the landslide. The long distance traveled on a very gentle slope indicates that the El Capitan landslide had a very low coefficient of friction, similar to some modern and prehistoric avalanches. According to Shreve, they may have traveled on a thin lubricating layer of compressed air. The coefficient of friction of the Kearny landslides cannot be determined. However, the nonturbulent character of both the Kearny and El Capitan landslides indicates that they slid rather than flowed.

Professional Paper↗

USGS2008

Multiple Landslide-Hazard Scenarios Modeled for the Oakland-Berkeley Area, Northern California

With the exception of Los Angeles, perhaps no urban area in the United States is more at risk from landsliding, triggered by either precipitation or earthquake, than the San Francisco Bay region of northern California. By January each year, seasonal winter storms usually bring moisture levels of San Francisco Bay region hillsides to the point of saturation, after which additional heavy rainfall may induce landslides of various types and levels of severity. In addition, movement at any time along one of several active faults in the area may generate an earthquake large enough to trigger landslides. The danger to life and property rises each year as local populations continue to expand and more hillsides are graded for development of residential housing and its supporting infrastructure. The chapters in the text consist of: *Introduction by Russell W. Graymer *Chapter 1 Rainfall Thresholds for Landslide Activity, San Francisco Bay Region, Northern California by Raymond C. Wilson *Chapter 2 Susceptibility to Deep-Seated Landsliding Modeled for the Oakland-Berkeley Area, Northern California by Richard J. Pike and Steven Sobieszczyk *Chapter 3 Susceptibility to Shallow Landsliding Modeled for the Oakland-Berkeley Area, Northern California by Kevin M. Schmidt and Steven Sobieszczyk *Chapter 4 Landslide Hazard Modeled for the Cities of Oakland, Piedmont, and Berkeley, Northern California, from a M=7.1 Scenario Earthquake on the Hayward Fault Zone by Scott B. Miles and David K. Keefer *Chapter 5 Synthesis of Landslide-Hazard Scenarios Modeled for the Oakland-Berkeley Area, Northern California by Richard J. Pike The plates consist of: *Plate 1 Susceptibility to Deep-Seated Landsliding Modeled for the Oakland-Berkeley Area, Northern California by Richard J. Pike, Russell W. Graymer, Sebastian Roberts, Naomi B. Kalman, and Steven Sobieszczyk *Plate 2 Susceptibility to Shallow Landsliding Modeled for the Oakland-Berkeley Area, Northern California by Kevin M. Schmidt and Steven Sobieszczyk *Plate 3 Susceptibility to Shallow Landsliding Modeled for the Cities of Oakland and Piedmont Northern California by Kevin M. Schmidt and Steven Sobieszczyk *Plate 4 Seismic Landslide Hazard Modeled for the Cities of Oakland, Piedmont, and Berkeley, Northern California by Scott B. Miles and David K. Keefer III The relative hazard for each of several landslide scenarios is presented as a geospatial database. This publication includes ARC/INFO (Environmental Systems Research Institute, http://www.esri.com) version 8.1.2 grids and associated tables and four text files of FGDC-compliant metadata for each grid.

Scientific Investigations Report↗

USGS2025

Characterizing the scale of regional landslide triggering from storm hydrometeorology

Rainfall strongly affects landslide triggering; however, understanding how storm characteristics relate to the severity of landslides at the regional scale has thus far remained unclear, despite the societal benefits that would result from defining this relationship. As mapped landslide inventories typically cover a small region relative to a storm system, here we develop a dimensionless index for landslide-inducing rainfall, A * , based on extremes of modeled soil water relative to its local climatology. We calibrate A * using four landslide inventories, comprising over 11 000 individual landslides over four unique storm events, and find that a common threshold can be applied to estimate regional shallow-landslide-triggering potential across diverse climatic regimes in California (USA). We then use the spatial distribution of A * , along with topography, to calculate the landslide potential area (LPA) for nine landslide-inducing storm events over the past 20 years, and we test whether atmospheric metrics describing the strength of landfalling storms, such as integrated water vapor transport, correlate with the magnitude of hazardous landslide-inducing rainfall. We find that although the events with the largest LPA do occur during exceptional atmospheric river (AR) storms, the strength of landfalling atmospheric rivers does not scale neatly with landslide potential area, and even exceptionally strong ARs may yield minimal landslide impacts. Other factors, such as antecedent soil moisture driven by storm frequency and mesoscale precipitation features within storms, are instead more likely to dictate the patterns of landslide-generating rainfall throughout the state.

California↗