Geophysics seminars

Frank Paul presents early findings from the Karakoram Anomaly Cross-ECV project. The research combines satellite Earth observations with climate data to improve glacier mass-balance modelling in a region where measurements are sparse and glaciers are changing rapidly. The talk examines how these complementary records can help monitor Karakoram glacier dynamics.

Atmospheric gravity waves arise from processes including flow over mountains, moist convection and geostrophic imbalance. They connect atmospheric layers, influence tropospheric jet streams and play a major dynamical role in the stratosphere and mesosphere. Yet much of their spectrum is unresolved by typical climate models, and observations provide limited constraints. Aditi Sheshadri presents research combining observations, high-resolution simulations and data-informed methods to understand their effects on climate variability and improve their representation in global models. Attend online via Zoom. The colloquium runs from 11:30 to 13:00 India Standard Time.

Abyssal marine turbidites provide some of the longest and most spatially extensive records of subduction zone earthquake recurrence globally; however, correlation of these deposits over long distances and interpretation of synchronous emplacement requires both an understanding of the turbidite generating systems and precise dating. Here, we present an integrated suite of high-resolution bathymetry, subbottom profiles, and sediment cores from combined autonomous underwater vehicle, remotely operated vehicle, and ship-based studies at a key paleoseismic site in the southern Cascadia subduction zone. We demonstrate how widespread, earthquake-triggered landslides on the lower slope deposit discrete, proximal mass transport deposits (MTDs) that grade offshore into complex, interfingered abyssal turbidites, which correspond to records of megathrust earthquake history. We propose accretion and oversteepening of thrust folds on the lower slope both preconditions the slope to fail and provides a perpetual source of unstable material to fail during every earthquake cycle. Furthermore, we suggest the periodic and pervasive landsliding indicates coseismic deformation of the outer accretionary wedge during megathrust rupture.

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.

The 2025 Matai’an landslide in eastern Taiwan represents the largest landslide event ever recorded in the region and initiated a cascading hazard sequence involving landslide-dam formation and repeated dam-breach floods. In this talk, I will demonstrate how seismic observations and remote sensing can be integrated to track landslide processes from pre-failure deformation to post-failure hazard evolution. I will also present a seismic-based monitoring framework capable of detecting landslides in near real time, estimating their size, and identifying landslide-dam formation, providing a practical approach for early warning of downstream flood hazards.

This talk focuses on cascading river hazards in Taiwan generated by landslides triggered by earthquakes and tropical cyclones. Drawing on case studies from Typhoon Morakot and the 2024 Hualien earthquake, I explore how sediment pulses move through river systems, reshaping channels and sustaining hazard long after the initial event. Together, these examples show how extreme events can produce lasting and evolving impacts in steep landscapes.

Volcanic edifice flank collapses are low-frequency, high-magnitude events that can rapidly mobilize tens of km3 of material and transport it large distances (>10 km) from the edifice. In ocean basins, these failures induce secondary hazards through the generation of tsunamis that can impact both neighboring and distal coastlines. These high-risk, far-reaching events have historically generated significant damage and loss of life, such as the 1792 collapse of the Mayuyama dome (Japan) that led to ~15,000 fatalities, and recently the 2018 collapse of Anak Krakatau (Indonesia) that resulted in ~440 deaths. Globally, there are 400–800 oceanic and coastal volcanic edifices with the potential for future collapses and associated tsunamis. Although previous studies have evaluated edifice collapse potential at both single volcanoes and over entire arcs, a global assessment of the edifices that are most capable of producing a tsunami-generating collapse is incomplete, in part because of remote locations and lack of detailed investigations. Building on previous studies, we develop a multi-component weighting procedure to rank the potential for edifice flank collapse and tsunami generation using three criteria: 1) edifice morphology; 2) satellite-derived estimations on the extent of hydrothermal alteration; and 3) 3D slope-stability analysis of potential collapses. We test this approach on oceanic and coastal volcanic edifices from the Marianas, Aleutians, Indonesia, and Philippines. After describing the results and relative ranking of edifices with the highest potential for collapse, we discuss implications for future tsunami hazard assessment.

Granular materials compose some of the most complex natural systems on Earth, governing the dynamics of hillslope creep, rock avalanches, landslides, debris flows, and concentrated pyroclastic density currents. Despite their prevalence, the mechanics of these granular systems remain highly enigmatic. To link external observations to internal states, we utilize particle-resolved numerical methods. By simulating both gravity-driven and fluid-destabilized granular beds, we track the fundamental grain-scale processes that govern macroscopic failure. We find that the entire lifespan of a granular flow—from the static state through yielding, fluidization, and final arrest—can be continuously mapped using two distinct probes: one isolating boundary stress fluctuations, and another measuring internal kinematic and structural evolution. We then validate this internal volumetric probe using optical Particle Image Velocimetry (PIV) data from scaled laboratory experiments, demonstrating how these numerical insights may be directly applied to remote geophysical monitoring.

This talk will examine the use of logarithmic spirals and planar or bi-planar geometries to estimate failure surface shapes and volumes of previously documented bedrock landslides. We present an inventory of large rock slides and rock avalanches for which pre- and post-event topography data are available, examine failure surface shapes using post-event topographic data, and evaluate the suitability of different geometries for approximating bedrock landslide failure surfaces and volumes.

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.