Engineering Geology seminars

This presentation introduces the first range-scale Deep-Seated Gravitational Slope Deformation (DSGSD) inventory in North America, focusing on the Sawatch Range of central Colorado. Through geomorphic mapping, field campaigns, and InSAR displacement analysis, we identified and characterized 39 previously unreported DSGSD. We analyzed this inventory to reveal the governing mechanisms that condition slopes for DSGSD development and to compare it with the global DSGSD inventory. Site-specific surveys of the South Mt. Massive and Mt. Jones DSGSDs result in interpretive cross sections that relate surface morphology to subsurface geological parameters and highlight how Sawatch DSGSDs form and evolve in unique ways. Furthermore, we discuss the implications of this work to the broader context of Rocky Mountain DSGSD. Widespread Deep-Seated Gravitational Slope Deformations Across the Sawatch Range, CO, Evans (2026), USGS Landslide Hazard Seminar, 09 September 2026.

The leaky barrel hillside hydrology metaphor—a straightforward “water in – water out” linear reservoir idealization originally applied to landslide studies more than 30 years ago by USGS scientists Ray Wilson and Gerry Wieczorek—remains useful despite (or maybe because of) its age and simplicity, especially for regional hazard forecasting applications potentially covering exceptionally large areas. The presentation will include a contextual overview of hindcasting (i.e., back-calculating) vs forecasting and the value of simple models for decision support, offer a new analytical solution for finite-duration rainfall pulses applied to examples from the Santa Cruz Mountains and Ohio River Valley, propose a rational expression for the originally empirical leaky barrel drainage coefficient, show how a leaky barrel model can be integrated into a factor of safety equation in a computationally efficient probabilistic approach amenable to spatially distributed (e.g., GIS-ish) applications, and finally show how the solutions used as input debris flow runout models.

Precipitation-triggered geohazards, including landslides, debris flows, flooding, erosion, and scour, present growing challenges as hydroclimatic extremes intensify. This presentation describes an integrated framework that combines physics-based probabilistic hazard modeling with holistic, multimodal monitoring to support detection, forecasting, prioritization, and management of geohazard risk. The framework incorporates InSAR, optical imagery, lidar, and field observations within a structured escalation pathway that links regional-scale screening with targeted investigation and decision support. Particular emphasis is placed on integrating monitoring and modeling into a self-improving system in which observations inform model refinement and models guide monitoring priorities. Current applications, implementation lessons, and future directions are discussed, including climate-informed forecasting and the development of scalable approaches that can be transferred across a wide range of geohazards and infrastructure settings. Towards an Integrated and Holistic Framework for Precipitation-Triggered Geohazard Risk Management, Kozacı (2026), 12 August 2026.

Hillslope mass wasting can have an outsized impact on both long-term landscape evolution and short-term hazards. Inputs of coarse sediment can shield river beds, alter local flow hydraulics, and impede fish passage. This talk focuses on the Fraser Canyon in British Columbia, a 375 km reach of the Fraser River where the 2018 Big Bar Landslide temporarily blocked the river and created a hydraulic barrier to salmon migration. I will examine the history of landsliding in the Fraser Canyon, evaluate hillslope morphology and valley connectivity to identify areas susceptible to future river-impacting landslides, and explore how mass wasting influences local river hydraulics within the canyon. These case studies indicate that boundary conditions at the upstream end of river networks affect downstream hillslopes, prompting questions of how drainage divide migration, incision into underlying bedrock, and valley widening impact landslide activity.

Landslides remain a major global hazard, with thousands of events each year posing significant impacts to human life, infrastructure, and ecosystems. While advanced constitutive models enable detailed slope-stability analyses at the single-hillslope scale, a critical gap persists in assessing landslide hazards at the community scale. Existing regional-scale models often struggle to balance physical rigor, predictive accuracy, and computational efficiency. They rely either on empirical approaches with limited physical basis or on mechanistic formulations that rely on major simplifying assumptions. This study presents CRISIS (Coupled Regional Rainfall-Induced and Seismic Slope Instability Simulations), a physics-based regional landslide prediction framework. It couples a pseudo-3D slope-stability formulation with a transient three-dimensional groundwater flow model. CRISIS operates in back-analysis and forward-prediction modes, integrating multi-scale topographic, geotechnical, hydraulic, and hydrological data. Back-analysis of both failed and stable slopes from prior events generates high-resolution spatial estimates of shear strength. These estimates are iteratively refined and used for forward prediction of landslide location, size, depth, and timing under future triggering events. Results reveal a strong geospatial connection between hillslope location and dominant failure mechanisms, emphasizing that landslide initiation is inherently geospatial and governed by coupled surface–subsurface processes. Application of the framework to Hurricane Maria in Puerto Rico, where over 70,000 landslides were triggered, demonstrates close agreement between predicted and observed landslide locations, sizes, and timing. The broader vision of this work is to advance regional characterization, assessment, and mitigation of cascading hazards through data-model integration.

A currently quiescent stratovolcano, Mount Shasta, California, still poses a significant hazard to nearby communities thanks to impactful non-eruptive debris flows that can occur throughout the year. In this work, we have built a more complete record of debris flow occurrence using monitoring campaigns and research into historical newspaper records; analyze debris flow frequency and triggering in the context of regional weather and climate patterns; and forecast the future of debris flow hazards at Mount Shasta. This topic is timely because of its relevance to the ongoing efforts to create up-to-date, usable, and relevant hazards assessments at United States Volcanoes, as well as a need expressed by local land managers for debris flow data. Ultimately, this work will not only enhance our understanding of debris flow occurrence at Mount Shasta, but will also aid stakeholders in land planning, hazard mitigation, and preparedness.

Rivers grow by moving their drainage divides. Drainage divide migration can be (1) gradual, and widely distributed, such that each stream grows headward by similar amounts, or (2) rapid, and narrowly focused, such that a single stream grows at the expense of its neighbors and carves a gorge. Do rivers share the wealth? Or is most of the water and attention grabbed by just a few? This talk describes patterns of drainage divide migration, downstream river incision, and bedrock landslide occurrence in two landscapes developed in gently-dipping sedimentary rock. First, we quantify drainage divide migration rates across a retreating escarpment within cuesta landscapes of southwestern Germany. Rates indicate that river growth is localized along mainstem rivers, which have reversed their flow direction and extended headward at rates ~10-1000 fold faster than long-term rock uplift and river incision rates. Growing mainstem rivers carve gorges into underlying stratigraphy, which includes erosionally-susceptible evaporites, marls, and swelling claystones, leading to a variety of slope failures and interesting geomorphic phenomena. Halfway across the globe, a similar story is taking shape. Rivers of northwestern Arizona are growing and connecting across a series of sedimentary basins that were previously isolated by basin and range tectonism. Rivers integrate across these basins by a combination of filling, spilling, and headward erosion. As rivers grapple across water-stressed landscapes, the winners incise deeper into diverse packages of syntectonic basin stratigraphy. Landslide inventory mapping aided by newly available aerial lidar data and 1:24000 scale geologic mapping reveals associations between landslides and incision through swelling claystones deposited in these Neogene basins. Intersections between both factors and existing infrastructure are shown. These case studies indicate that boundary conditions at the upstream end of river networks affect downstream hillslopes, prompting questions of how drainage divide migration, incision into underlying bedrock, and valley widening impact landslide activity.

We investigated meteorological controls on seasonal deep-seated motion of the Barry Arm landslide, a ~500 Mm³ slope instability with tsunamigenic potential in Prince William Sound, Alaska. Using ground-based synthetic aperture radar, we identified periods of deep-seated displacement, and combined airborne ice-penetrating radar with a glacier melt model driven by local meteorological data to evaluate the role of Cascade Glacier, which covers much of the area contributing groundwater to the landslide. We show that an over-deepened section of Cascade Glacier adjacent to the most active part of the landslide likely acts as a transient reservoir that routes meltwater to the landslide and that deep-seated landslide motion initiated only when modeled glacier discharge exceeded a distinct threshold.

We quantify slow-moving landslide kinematics across northern California using a 14-day L-band ALOS-2 ScanSAR InSAR time series. After systematically extracting and cleaning the displacement time series, we analyze deformation of 437 landslides across a ∼300 x 400 km area and group time series by relative velocity changes to identify anomalously fast motions. We test associations with external drivers (PGA, precipitation) and landslide attributes (slope, aspect ratio, area). Shaking from the 2022 event shows the strongest association with faster sliding rates. For slides that experienced higher PGA and increased velocities, a piecewise model yields recovery to within ~10% of pre-event rates in ~1.3 years. Using two earthquakes of similar magnitude and location, we demonstrate that rupture dynamics shape the spatial distribution of triggering and supply rare regional constraints on onset and recovery.

For more than a decade, the U.S. Geological Survey (USGS) has provided stakeholders and land managers with postfire debris-flow hazard information to assist them in considering important questions about postfire debris flows, such as “Where will they happen?”, “When will they happen?”, or “How big will they be?” Alongside assessing postfire debris-flow hazards for hundreds of burned areas to date, USGS and partners have identified additional aspects of these hazards that are not well addressed by existing predictive frameworks, such as developing rainfall thresholds for partially recovered conditions, or considering how susceptibility to postfire debris flows might be modified by regional differences in topography or rainfall climatology. This talk will discuss recent work to address these challenges by 1) developing a new method to track the evolution of debris-flow likelihood and rainfall thresholds with time and recovery after fire, and 2) calibrating new regional models to improve prediction of debris-flow likelihood and rainfall thresholds across the western United States.

This presentation introduces NASA’s Observational Products for End-Users from Remote Sensing Analysis (OPERA) project and its suite of freely available satellite-derived products. The talk will provide an overview of the OPERA project and products, then demonstrate how these products can be used for landslide detection, monitoring, and scientific research. Examples highlight how OPERA observations enable identification of active landslides, characterization of spatial patterns of motion, and tracking of temporal changes relevant to landslides.

Postfire debris flows pose a hazard to human life, property, and infrastructure when they travel from steep source areas to urbanized alluvial fans or other developed areas. Existing methods for rapid (< 1 week) postfire debris-flow hazard assessment document the increase in the likelihood and size of debris flows as the magnitude of high-intensity rain necessary to initiate debris flows increases but do not indicate the extent of downstream debris-flow runout. Although many models for the simulation of debris-flow motion are available, there is no established approach for using these models to delineate locations susceptible to postfire debris-flow runout that (1) is feasible to use at the spatial scale of an entire fire; (2) is appropriate for runout onto unconfined areas; (3) reproduces observed relations between runout and rainfall intensity; and (4) characterizes inherent uncertainty in runout, even without spatiotemporally variable rainfall. We propose and evaluate a method for generating postfire debris-flow runout hazard maps that has all the above qualities. Selection of case studies prioritized events triggered by a range of rainfall intensities, locations within and outside of southern California, and observed runout onto unconfined topography. Qualitative and quantitative assessment of performance for four events indicate that simulation results broadly match observations albeit with some discrepancies at a scale larger than structure or land parcel level (approximately 20-m by 20-m). The method may be used to identify potentially hazardous areas immediately following a fire and to provide approximate runout forecasts when a storm is imminent.

Shallow landslides typically involving just the soil mantle constitute both a primary process driving landscape evolution and a significant geologic hazard. Theory for and empirical documentation of shallow landslides generally assumes that the elevated pore pressures that destabilize soils arise from runoff just within the soil. In many landscapes, however, it has been recognized that groundwater emerging from underlying weathered bedrock can generate destabilizing pore pressures. Here, we develop a coupled hydrologic and slope stability model that explicitly explores how a conductive bedrock weathering zone guides storm runoff and localizes shallow landslides across a watershed. Our findings suggest that first-order variations of deep CZ can provide physical explanations for variations observed in the susceptibility, magnitude, and timing of shallow landslides, and that CZ structure may be inferred from patterns and timing of landsliding.

Regional-scale (>500 km2) landslide risk reduction models often suffer from their reliance on difficult-to-obtain data, such as inventories of past landslide locations or geomechanical properties of the hillslopes. However, over regional scales, these data are often sparse, inconsistent, and nonrepresentative, which can lead to biased model outputs. In this talk, I will present two recent studies that help overcome these challenges. First, I will share a method of assessing shallow landslide susceptibility based on a morphometric analysis of the landscape’s topography. Despite having no knowledge of past landslide locations, the morphometric approach can better characterize landslide potential over contrasting data-driven models that are generally used for assessing regional-scale landslide susceptibility. Second, I will present a Bayesian statistical comparison of common metrics used to predict rainfall-triggered landsliding across disparate regions of the United States. I will show that parsimonious leaky-bucket models, whose only inputs are a drainage constant and estimates of precipitation, can better distinguish landslide-triggering rainfall from non-landslide-triggering rainfall compared to traditional rainfall metrics or more complex models. The leaky-bucket model had the best performance across vastly different environments within the United States, suggesting that it may be used universally to enhance regional-scale landslide risk reduction efforts.

In the past decade, several fatal landslides have impacted Southeast Alaska, highlighting the need to advance our understanding of regional geomorphic and atmospheric controls on triggering events and runout behavior. A large and long runout landslide on Wrangell Island, with area in the top 0.5% of >14,760 slides mapped in the Tongass National Forest, initiated during an atmospheric river event in November 2023 and traveled >1 km downslope, causing six fatalities. We used field observations, sequential airborne lidar, geotechnical analyses, and climate data to characterize the geomorphic, hydrologic, and atmospheric conditions contributing to the landslide. Rainfall intensities recorded at the Wrangell airport were modest (~1-yr recurrence interval), but rapid snowmelt and drainage from a ridgetop wetland may have contributed to rapid saturation of the landslide. Although strong winds were recorded, we did not observe extensive windthrow, which may downgrade its contribution to slope failure. The landslide mobilized a steep, thick (>4 m) wedge of colluvium that accumulated below a resistant bedrock ledge and entrained additional colluvial deposits as it traveled downslope across cliff-bench topography. The substantial entrainment resulted in an unusually large width, extensive runout, and low depositional slope as the landslide terminated in the coastal environment. Our results suggest that the sequencing of rain- and snow-dominated storms, geologic controls on post-glacial colluvium production and accumulation, and ridgetop hydrology contributed to landslide initiation and mobility. Advances in post-glacial landscape evolution models, frequent lidar acquisition, and additional climate data are needed to inform regional landslide hazard assessment.

Hurricane Helene devastated western North Carolina and parts of surrounding Tennessee and Virginia. A stalled front over the Blue Ridge prior to landfall of the hurricane resulted in cumulative rainfall totals of 20–30 inches from Sept. 25–27, 2024. This triggered numerous landslides and devastating flooding, and has changed the landscape of the Blue Ridge and mountain communities. This mapping and assessment of the landslides was conducted as part of the USGS Landslide Assessments, Situational Awareness and Event Response Research (LASER) and in cooperation with the North Carolina Geological Survey Landslide Hazard Program. Mapping efforts focused on the northernmost area heavily impacted from the storm: parts of Watauga, Avery, and Ashe County, NC, and parts of Johnson County, TN. Initial observational descriptions of the landslides are presented. Landslides mapped are separated into three type occurrences, hyperconcentrated earth flows, debris flows, and modified slope failures. Earth flows occurred on steep grassed slopes and consisted of soil with a mixture of vegetated clumps, saprolite, and rock. The landslide tracks were 10–338 m long, and scarp widths of 10–30 m that often cut down 1–2 m to bedrock. Earth flows often occurred in clusters, and some merged down slope. Debris flows had longer tracks, 96–1085 m, and consisted of a mixture of soil, rock, trees, vegetation, and other debris. Head scarps were 10–114 m wide and cut down through 1–3 m of colluvium to bedrock. Bedrock structures controlling the failures included joints, fractures, and foliation. Seven debris flows on Howards Creek initiated on steep slopes with aspect and slope close to the orientation of the foliation in bedrock (330/20–40° NE). Modified slope failures included landslides that initiated on road cuts, road embankments, steep cut slopes, and other slopes modified by construction (e.g., failed drainages or septic fields). Although the slope modification was important to initiate these slides, some localized along preexisting bedrock (saprolite) structures. Collectively, the impact of landslides from Hurricane Helene highlights the importance of basic geologic mapping and landslide assessment to build robust datasets to better understand and model the occurrence of landslides and strengthen our planning and rebuilding of mountain communities.

On February 6, 2023, a Mw 7.8 and Mw 7.5 earthquake doublet struck along the East Anatolian Fault Zone in Türkiye, triggering over 3,600 coseismic landslides. Roughly a month later, a rare atmospheric river event delivered up to 183 mm of rainfall in just 20 hours to the earthquake impacted region. This extreme precipitation induced additional landslides, debris flows, and flooding. In our research, we conduct a probabilistic landslide hazard assessment using the open-source Landlab earth surface modeling library, integrating both seismic and climatic drivers. The model incorporates earthquake legacy effects, representing post-seismic slope weakening, and simulates shallow landslide susceptibility using a Monte Carlo implementation of the infinite slope stability theorem informed by remote sensing datasets. I will present three key analyses: (1) modeling hydrologic response to the AR event and mapping landslide probability with and without earthquake legacy effects; (2) examining how the sequence and combination of extreme events alter landslide hazard; and (3) demonstrating how using historic climate data can effectively replicate post-seismic landslide hazard maps that use real-time data, offering an approach for seasonal hazard forecasting in tectonically active and climate-sensitive regions.