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Geology topics

Richard M. Iverson

Publications and source records attributed to Richard M. Iverson.

At least 19 recordsLinked to original sources
USGS2024

Numerical modeling of debris flows: A conceptual assessment

Real-world hazard evaluation poses many challenges for the development and application of numerical models of debris flows. In this chapter we provide a conceptual overview of physically based, depth-averaged models designed to simulate debris-flow motion across three-dimensional terrain. When judiciously formulated and applied, these models can provide useful information about anticipated depths, speeds, and extents of debris-flow inundation as well as debris interactions with structures such as levees and dams. Depth-averaged debris-flow models can differ significantly from one another, however. Some of the greatest differences result from simulation of one-phase versus two-phase flow, use of parsimonious versus information-intensive initial and boundary conditions, use of tuning coefficients versus physically measureable parameters, application of dissimilar numerical solution techniques, and variations in computational speed and model accessibility. This overview first addresses these and related attributes of depth-averaged debris-flow models. It then describes model testing and application to hazard evaluation, with a focus on our own model, D-Claw. The overview concludes with a discussion of outstanding challenges for development of improved debris-flow models and suggestions for prospective model users.

Book chapter↗
USGS2022

Modeling the dynamics of lahars that originate as landslides on the west side of Mount Rainier, Washington

Large lahars pose substantial threats to people and property downstream from Mount Rainier volcano in Washington State. Geologic evidence indicates that these threats exist even during the absence of volcanic activity and that the threats are highest in the densely populated Puyallup and Nisqually River valleys on the west side of the volcano. However, the precise character of these threats can be difficult to anticipate. To help predict depths and rates of possible lahar inundation in the area, this report presents the results of simulations of hypothetical future lahars that originate high on the west side of Mount Rainier and travel downstream into the Puyallup and Nisqually River valleys. Many of the results portrayed as still images in the figures of this report are also available as animated files that can be accessed at the web address provided in the figure captions. We simulated eight scenarios, including worst-case scenarios in which the simulated lahars are similar in size and mobility to the approximately 260 million cubic meter (Mm 3 ; 340 million cubic yard) Electron Mudflow lahar that descended from Mount Rainier and inundated the Puyallup River valley about 500 years ago. The other six scenarios place the worst-case scenarios in perspective by simulating lahars that originate from the same source areas but have smaller volumes or lesser mobilities. We perform our simulations using an open-source software package that we developed called D-Claw. The numerical model composing the kernel of D-Claw solves a system of five hyperbolic partial differential equations that describe the depth-averaged dynamics of static or flowing grain-fluid mixtures interacting with three-dimensional topography. In D-Claw, the volume fraction occupied by solid grains is a dependent variable that can freely evolve, enabling simulation of landslide liquefaction and of lahar interaction with static bodies of water. The latter feature facilitates a seamless simulation of a lahar in the Nisqually River valley entering Alder Lake reservoir. In the event of an approximately 260 Mm 3 high-mobility lahar originating on the west side of Mount Rainier, our results point to two areas of pronounced hazard. One area, comprising the densely populated lowlands of Orting, Washington, and environs, could be inundated by lahars originating from either the Sunset Amphitheater or Tahoma Glacier headwall areas. In the worst-case scenario we consider for the Orting lowlands, which involves a 260 Mm 3 high-mobility lahar originating from a landslide in the Sunset Amphitheater, a flow front approximately 4 meters deep and traveling about 4 meters per second reaches the Orting lowlands about 1 hour after the onset of slope failure. After passing through the Orting lowlands, the simulated lahar slows down and comes to rest in the valleys surrounding Sumner and Puyallup. A second area of pronounced hazard is the stretch of the Nisqually River valley beginning in Mount Rainier National Park and extending downstream to Alder Lake reservoir and Alder Dam. This area would be substantially affected in the worst-case scenario that involves a 260 Mm 3 high-mobility lahar originating from the Tahoma Glacier headwall area—the locality identified by a previous study as the sector of Mount Rainier most prone to large-scale gravitational collapse. The simulated lahar passes through the area of Ashford, Washington, within about 20 minutes of the onset of slope failure and reaches the head of Alder Lake within about 50 minutes. The lahar ultimately displaces enough reservoir water to cause overtopping of the 100 meter (330 foot) tall Alder Dam, but consequences of such dam overtopping are not addressed in this report.

Washington↗
USGS2021

When hazard avoidance is not an option: Lessons learned from monitoring the postdisaster Oso landslide, USA

On 22 March 2014, a massive, catastrophic landslide occurred near Oso, Washington, USA, sweeping more than 1 km across the adjacent valley flats and killing 43 people. For the following 5 weeks, hundreds of workers engaged in an exhaustive search, rescue, and recovery effort directly in the landslide runout path. These workers could not avoid the risks posed by additional large-scale slope collapses. In an effort to ensure worker safety, multiple agencies cooperated to swiftly deploy a monitoring and alerting system consisting of sensors, automated data processing and web-based display, along with defined communication protocols and clear calls to action for emergency management and search personnel. Guided by the principle that an accelerating landslide poses a greater threat than a steadily moving or stationary mass, the system was designed to detect ground motion and vibration using complementary monitoring techniques. Near real-time information was provided by continuous GPS, seismometers/geophones, and extensometers. This information was augmented by repeat-assessment techniques such as terrestrial and aerial laser scanning and time-lapse photography. Fortunately, no major additional landsliding occurred. However, we did detect small headscarp failures as well as slow movement of the remaining landslide mass with the monitoring system. This was an exceptional response situation and the lessons learned are applicable to other landslide disaster crises. They underscore the need for cogent landslide expertise and ready-to-deploy monitoring equipment, the value of using redundant monitoring techniques with distinct goals, the benefit of clearly defined communication protocols, and the importance of continued research into forecasting landslide behavior to allow timely warning.

Washington↗
USGS2021

Using high sample rate lidar to measure debris-flow velocity and surface geometry

Debris flows evolve in both time and space in complex ways, commonly starting as coherent failures but then quickly developing structures such as roll waves and surges. These processes are readily observed but difficult to study or quantify because of the speed at which they evolve. Many methods for studying debris flows consist of point measurements (e.g., flow height or basal stresses), which are inherently limited in spatial coverage and cannot fully characterize the spatiotemporal evolution of a flow. In this study, we use terrestrial lidar to measure debris-flow profiles at high sampling rates to examine debris-flow movement with high temporal and spatial precision and accuracy. We acquired measurements during gate-release experiments at the U.S. Geological Survey debris-flow flume, a unique experimental facility where debris flows can be artificially generated at a large scale. A lidar scanner was used to record repeat topographic profiles of the moving debris flows along the length of the flume with a narrow swath width (∼1 mm) at a rate of 60 Hz. The high-resolution lidar profiles enabled us to quantify flow front velocity of the debris flows and provided an unprecedented record of the development and evolution of the flow structure with a sub-second time resolution. The findings of this study demonstrate how to obtain quantitative measurements of debris-flow movement. In addition, the data help us to quantitatively define the development of a saltating debris-flow front and roll waves behind the debris-flow front. Such measurements may help constrain future modeling efforts.

Environmental and Engineering Geoscience↗
USGS2021

Channel-amphitheatre landforms resulting from liquefaction flowslides during rapid drawdown of glacial Lake Fraser, British Columbia, Canada

Unusual channel-amphitheatre landforms are present in Late Pleistocene–early Holocene, subaqueous fan and delta deposits in the glacial Lake Fraser basin, central British Columbia. The lake formed during the decay of the last Cordilleran Ice Sheet and drained ~11,500 years ago during a large outburst flood. The fronts of a delta and two subaqueous fans consisting of silt to fine sand are marked by branching networks of wide, nearly flat channels that terminate upstream in digitate, steep-walled amphitheatres. We propose that these channel-amphitheatre landforms formed by liquefaction flowslides that were induced by the rapid drawdown of glacial Lake Fraser during the outburst flood. Similar geomorphic forms, which we believe also to be associated with rapid drawdowns of large Late Pleistocene–early Holocene lakes, occur elsewhere in North America. A recent tailings dam failure and an intentional breaching of a 100-year-old hydroelectric dam provide insights into the processes responsible for the landforms. By using geomechanical analysis, we show how rapid lake drawdown can trigger liquefaction flowslides in deposits of silt to fine sand. The novelty of our approach lies in combining geomechanical reasoning with geomorphic analogues to understand histories of ancient glacier-dammed lakes and of the glacial lake outburst floods that are sourced from them.

British Columbia↗
USGS2020

Measuring basal force fluctuations of debris flows using seismic recordings and empirical green's functions

We present a novel method for measuring the fluctuating basal normal and shear stresses of debris flows by using along‐channel seismic recordings. Our method couples a simple parameterization of a debris flow as a seismic source with direct measurements of seismic path effects using empirical Green's functions generated with a force hammer. We test this method using two large‐scale (8 and 10 m 3 ) experimental flows at the U.S. Geological Survey debris‐flow flume that were recorded by dozens of three‐component seismic sensors. The seismically derived basal stress fluctuations compare well in amplitude and timing to independent force plate measurements within the valid frequency range (15–50 Hz). We show that although the high‐frequency seismic signals provide band‐limited forcing information, there are systematic relations between the fluctuating stresses and independently measured flow properties, especially mean basal shear stress and flow thickness. However, none of the relationships are simple, and since the flow properties also correlate with one another, we cannot isolate a single factor that relates in a simple way to the fluctuating forces. Nevertheless, our observations, most notably the gradually declining ratio of fluctuating to mean basal stresses during flow passage and the distinctive behavior of the coarse, unsaturated flow front, imply that flow style may be a primary control on the conversion of translational to vibrational kinetic energy. This conversion ultimately controls the radiation of high‐frequency seismic waves. Thus, flow style may provide the key to revealing the nature of the relationship between fluctuating forces and other flow properties.

Journal of Geophysical Research Earth Surface↗
USGS2020

Reconstructing the velocity and deformation of a rapid landslide using multiview video

Noncontact measurements of spatially varied ground surface deformation during landslide motion can provide important constraints on landslide mechanics. Here, we present and test a new method for extracting measurements of rapid landslide surface displacement and velocity (accelerations of approximately 1 m/s 2 ) using sequences of stereo images obtained from a pair of inexpensive, stationary 4K video cameras with nominal frame rates of 29.97 Hz. The method combines elements of Structure from Motion with those of optical flow to extract data on 3‐D evolution of the ground surface during slope failure. We apply the method to an experiment at the U.S. Geological Survey debris‐flow flume in which a high‐speed, liquefying landslide was triggered by gradually adding water to a 6‐m 3 prism of loosely packed sediment on a 31° slope. Strip‐scanning lidar measurements made during the experiment corroborate our video‐based measurements, but the latter encompassed the entire landslide surface and were much lower in cost. Our video‐based measurements enabled computation of depth‐integrated landslide dilation/contraction rates. The range of computed rates was within the ranges inferred from independent measurements of evolving pore water pressures and reasonable estimates of the hydraulic permeability of the sediment. Dilation and contraction rates play a crucial role in landslide mechanics. The dilation and contraction we observe contradict the incompressible flow assumption used in many studies that have employed noncontact methods to infer landslide properties.

Oregon↗
USGS2020

Landslide disparities, flume discoveries, and Oso despair

Landslide dynamics is the branch of science that seeks to understand the motion of landslides by applying Newton's laws. This memoir focusses on a 40‐year effort to understand motion of highly mobile—and highly lethal—landslides such as debris avalanches and debris flows. A major component of this work entailed development and operation of the U.S. Geological Survey debris flow flume, a unique, large‐scale experimental facility in Oregon. Experiments there yielded new insights that informed development of mathematical models that were aimed not only at explaining landslide dynamics but also at evaluating landslide and debris flow hazards. The most sophisticated of these models, called D‐Claw, found its first practical application during investigations of the 2014 Oso, Washington, landslide disaster. That event provided indelible lessons about the utility and sociology of science in the real world.

Washington↗
USGS2019

Basal stress equations for granular debris masses on smooth or discretized slopes

Knowledge of basal stresses is essential for analyzing slope stability and modeling the dynamics and erosive potential of debris flows and avalanches. Here we derive and test new algebraic formulas for calculating the shear stress τ and normal stress σ at the base of variable‐thickness granular debris masses in states of static or dynamic equilibrium on slopes. The formulas include a lateral pressure coefficient κ , but use of a fixed value κ = 0.7 yields predictions of σ that on average err by less than 3% and of τ that on average err by less than 13% in matching basal stresses measured in six large‐scale experiments involving wet debris masses with varying geometries and compositions. Much larger prediction errors result from use of infinite‐slope or shallow‐debris approximations. Specialized versions of the new formulas apply if basal topography is discretized and represented by a “staircase” function in a digital elevation model. Use of these formulas to assess static limiting equilibrium conditions shows that the apparent basal Coulomb friction angle ϕ tread of debris that engages friction acting on the horizontal surfaces (or “treads”) of a staircase sloping at an angle θ is generally described by tan ϕ tread = tan ( ϕ − θ )+ κ tan θ , where ϕ is the true basal friction angle of the same debris in contact with a uniformly sloping bed. Differences between the values of ϕ and ϕ tread can greatly influence the results of numerical simulations that use unsmoothed digital elevation model topography to calculate the stability or dynamics of debris masses on slopes.

Journal of Geophysical Research-Earth Surface↗
USGS2019

Valid debris-flow models must avoid hot starts

Debris-flow experiments and models commonly use “hot-start” initial conditions in which downslope motion begins when a large force imbalance is abruptly imposed. By contrast, initiation of natural debris flows almost invariably results from small perturbations of static force balances that apply to debris masses poised in steep channels or on steep slopes. Models that neglect these static balances may violate physical law. Here we assess how the effects of hot starts are manifested in physical experiments, analytical dam-break models, and numerical models in which frictional resistance is too small to satisfy static force balances in debris-flow source areas. We then outline a numerical modeling framework that avoids use of hot starts. In this framework an initial static force balance is gradually perturbed by increasing pore-fluid pressure that may trigger the onset of debris motion. Subsequent increases in pore-fluid pressure, driven by debris motion, may then reduce the debris frictional strength, leading to high flow mobility.

Conference Paper↗
USGS2019

Seamless numerical simulation of a hazard cascade in which a landslide triggers a dam-breach flood and consequent debris flow

Numerical simulations of hazard cascades downstream from moraine-dammed lakes commonly must specify linkages between models of discrete processes such as wave overtopping, dam breaching, erosion, and downstream floods or debris flows. Such linkages can be rather arbitrary and can detract from the ability to accurately conserve mass and momentum during complex sequences of events. Here we describe an alternative methodology in which we use high-resolution lidar topography and 2-D, two-phase conservation laws to seamlessly simulate all stages of a hazard-cascade that culminates in a debris flow. Our simulations employ our depth-integrated numerical model D-Claw to evaluate hazards from prospective breaching of a moraine dam that impounds Carver Lake on the eastern flank of South Sister volcano in central Oregon, USA. We simulate a “worst-case scenario” sequence of events that begins with a hypothetical 1.6 million m3 landslide that originates near the summit of South Sister and enters Carver Lake. Wave generation and displacement of lake water then leads to dam overtopping, breach erosion, and a downstream debris flow that funnels into Whychus Creek and eventually reaches the community of Sisters, Oregon, about 20 km away. Notably, our simulations predict that much of the debris is directed away from Sisters as a result of natural avulsion and flow diversion that occurs near the head of a low-gradient alluvial fan upstream from Sisters. Consequently, predicted hazards to downtown Sisters are less severe than those predicted by 1-D shallow-water simulations of a Carver Lake dam breach that were performed in the 1980s.

Conference Paper↗
USGS2019

Real-time monitoring of debris-flow velocity and mass deformation from field experiments with high sample rate lidar and video

Debris flows evolve in both time and space in complex ways, commonly starting as coherent failures but then quickly developing structures such as roll waves and surges. This process is readily observed, but difficult to study or quantify because of the speed at which it occurs. Many methods for studying debris flows consist of point measurements (e.g., of flow height or basal stresses), which are inherently limited in spatial coverage and fail to fully capture the spatiotemporal evolution of a flow. In this study, we use a terrestrial lidar to measure debris-flow profiles at high sample rates to examine debris-flow movement with high temporal and spatial precision and accuracy. We acquired measurements during gate-release experiments at the USGS debris flume, a unique experimental facility where debris flows can be simulated at a large scale. In this study, the laser scanner was placed at the bottom of the steep flume and recorded topography of the entire flume bed and debris flow at a rate of 60 Hz along a very narrow profile (~1mm in width), providing a detailed, two-dimensional cross-section of the debris flow through time. The high-resolution profiles enable us to quantify flow front and surge velocities of the debris flow and provide an unprecedented record of the development and evolution of the flow structure over time. The profiles also preserve a record of the highly variable deposition pattern of the debris flow on a downstream fan with a time resolution of hundredths of a second. In addition, video imagery from the experiment was used to track debris flow movement through time. By acquiring high-resolution topographic data and video imagery during a controlled experiment, we have been able to obtain unusually complete quantitative measurements of debris-flow movement. Such measurements may help constrain future modeling efforts.

Conference Paper↗
USGS2019

Overcoming barriers to progress in seismic monitoring and characterization of debris flows and lahars

Debris flows generate seismic signals that contain valuable information about events as they unfold. Though seismic waves have been used for along-channel debris-flow and lahar monitoring systems for decades, it has proven difficult to move beyond detection to more quantitative characterizations of flow parameters and event size. This is for two primary reasons: (1) our limited understanding of how the radiated wavefield relates to debris flow characteristics and dynamics, and (2) difficulties quantifying the effects of heterogeneous shallow earth structure on the observed wavefield. The latter issue, essentially our inability to sufficiently separate seismic path effects from source information, is a barrier to improving our understanding of the first issue. We review the progress that has been made toward establishing the theory, models and methods required to use seismic observations to make quantitative measurements of flows and summarize the practical, social, and scientific barriers to progress. We discuss some specific ongoing efforts to overcome some of these barriers, with a focus on how we are using large-scale seismic experiments at the U.S. Geological Survey debris-flow flume to develop methods for directly measuring path effects and to develop and validate theoretical debris flow seismicity models.

Conference Paper↗
USGS2018

Discussion of “Case study: Oso, Washington, landslide of March 22, 2014-Material properties and failure mechanism” by Timothy D. Stark, Ahmed K. Baghdady, Oldrich Hungr, and Jordan Aaron

The original paper discusses factors that may have contributed to the occurrence and long runout of a disastrous landslide near the community of Oso, Washington, on March 22, 2014. The paper reinforces a prior finding that the long runout likely resulted from liquefaction of wet colluvium that was rapidly loaded by landslide debris impinging from upslope ( Iverson et al. 2015 ). However, the original paper proposes a landslide geometry and chronology that differ from those presented in previous reports, and these differences have implications for interpreting the landslide’s mechanics. The paper also includes factual errors as well as misrepresentations that result from selective inclusion and exclusion of findings previously reported by others. The purposes of this discussion are to place the original paper in context and to rectify some of its mistakes.

Washington↗
USGS2018

Discussion of “Oso, Washington, landslide of March 22, 2014: Dynamic analysis” by Jordan Aaron, Oldrich Hungr, Timothy D. Stark, and Ahmed K. Baghdady

The original paper under discussion states that it “explains the spectacular mobility of the 2014 Oso landslide.” It addresses this objective by using two versions of the DAN model to compute the distribution of deposits produced by the landslide. The main purpose of this discussion is to demonstrate that the authors’ model is incapable of explaining the Oso landslide’s mobility—even though the model can be tuned to mimic the landslide’s distribution of deposits. An ancillary purpose is to contrast the authors’ model with the Oso landslide model of Iverson et al. (2015) and Iverson and George (2016), and to rebut false statements that the authors made about that model.

Washington↗
USGS2018

Discussion of “Shallow water hydro-sediment-morphodynamic equations for fluvial processes” by Zhixian Cao, Chunchen Xia, Gareth Pender, and Qingquan Liu

The original paper concerns the formulation and use of depth-integrated equations of motion to model the dynamics of shallow flows that entrain or deposit bed material. A recurring theme of the original paper is the authors’ criticism of related theoretical results published by Iverson and Ouyang ( 2015 ). This discussion explains why that criticism is misguided.

Journal of Hydraulic Engineering↗
USGS2017

Distributed shear of subglacial till due to Coulomb slip

In most models of the flow of glaciers on till beds, it has been assumed that till behaves as a viscoplastic fluid, despite contradictory evidence from laboratory studies. In accord with this assumption, displacement profiles measured in subglacial till have been fitted with viscoplastic models by estimating the stress distribution. Here we present a model that illustrates how observed displacement profiles can result from till deformation resisted solely by Coulomb friction. Motion in the till bed is assumed to be driven by brief departures from static equilibrium caused by fluctuations in effective normal stress. These fluctuations result from chains of particles that support intergranular forces that are higher than average and that form and fail at various depths in the bed during shearing. Newton’s second law is used to calculate displacements along slip planes and the depth to which deformation extends in the bed. Consequent displacement profiles are convex upward, similar to those measured by Boulton and colleagues at Breidamerkurjökull, Iceland. The model results, when considered together with the long-term and widespread empirical support for Coulomb models in soils engineering, indicate that efforts to fit viscoplastic flow models to till displacement profiles may be misguided.

Journal of Glaciology↗