Journal of Geophysical Research: Earth Surface最新文献

Flood hazards along alluvial rivers vary over time due to changes in both flow regime and channel morphology; however, their millennial-scale histories are difficult to study from incomplete and poorly dated alluvial stratigraphies. Thus, the role of external forcings (e.g., climate) in the magnitude of alluvial channel dynamics remains poorly understood. We developed a record of overbank flows of the Tolt River in Washington from a continuous 6,100-year sediment record obtained from a 33-m deep lake with an outlet dammed by alluvium. Overbank flows from the adjacent river result in fine laminations preserved in the lake sediment. Multi-century periods of overbank flows with fine (<2 mm; ca. annual) laminations account for 36% of the last 6,100 years. The only event recorded in the lake during the last 900 years is dated by ²¹⁰Pb-verified varves to a historic atmospheric river event in December 1867. Tree-ring and radiocarbon-dated alluvial surfaces upriver from the lake are consistent with a significantly aggraded channel during silt periods in the lake. Although a sediment slump in the lake dates to a known earthquake, there is little other linkage between earthquake history and alluvial history. However, regional paleoclimate, local fire history, and landslide ages suggest that the continuous periods of overbank flows were sustained by aggradation from sediment input after fires and during dry climate periods. The lake record indicates an alternation of incision and aggradation and a much more dynamic channel history than observed over the last several decades following channel modification and dam development.

Improving our ability to relate postfire debris-flow volume to rainfall characteristics, terrain attributes, and fire severity is critical for quantifying postfire sediment yields from steep landscapes and predicting changes in debris-flow hazards following fire. This is especially true in the Southwest United States (US) (Arizona and New Mexico), where fire activity has increased in recent decades. In this study, we present a database of 54 postfire debris-flow volumes that we collected across the Southwest between 2010 and 2021. We use these data to develop a multiple linear regression model for postfire debris-flow volume based on peak 30-min rainfall intensity, watershed area greater than 23°, and a soil burn severity variable. We further propose a model that utilizes only rainfall and terrain variables, as well as a model that requires only terrain attribute and fire-severity variables. These models are beneficial in scenarios where there are data limitations. We compare these new models with others developed in the western US to explore differences in the factors that control debris-flow volume across geographic regions. We find that the models introduced here more accurately predict postfire debris-flow volume in the Southwest relative to existing models. We also find that models that include sub-hourly rainfall intensity perform better than those that do not, revealing the benefits of high-resolution rainfall data for constraining postfire debris-flow volume. Results improve our ability to forecast postfire debris-flow volume in the Southwest and provide insights into relationships between rainfall intensity, terrain attributes, fire severity, and debris-flow volume.

Estimating flow velocities is key to assessing hazards associated with debris flows. One approach to post-event velocity estimation is the superelevation method, which uses debris-flow mudlines to measure the cross-channel surface inclination, or superelevation, produced by centripetal forces acting on the flow in a bend. Flow velocities are then calculated using a subjective parameterization of the forced vortex equation modified to include a debris-flow specific correction factor. Subjective parameterization of this equation leads to substantial variability and uncertainty in the resulting flow velocities. We present an analysis of the reliability of the superelevation method using a large UAV-based data set of 14 debris flows with front velocities of ∼0.8–6.5 m s⁻¹ and cross-channel surface inclinations of ∼0.6–8.5°, as well as a validation for a single debris flow measured using high-resolution, high-frequency 3D lidar data fused to video imagery. The validation event indicates that when the flow surface inclination can be measured directly, the forced vortex equation produces excellent results without needing a correction factor for Froude numbers ranging from 0.7 to 1.5. This finding indicates that the main challenge with the superelevation method lies in obtaining accurate measurements of superelevation from the mudlines, and that a correction factor may serve to compensate for measurement difficulties rather than variable flow properties. For very small and highly subcritical flows, the superelevation method may generate a large overestimation of flow velocities.

Drainage density is a fundamental landscape feature that determines the length scale for hillslope sediment transport and results from the competition of diffusive hillslope and advective stream incision processes, whose efficiencies are known to vary with rock type but are notoriously difficult to quantify. Here, we present a comprehensive analysis of a catchment in semi-arid Central Chile, where landscapes with different drainage densities, but equal tectonic and climatic conditions, have formed on three neighboring granitoid plutons (a monzogranite and two diorites). We combined topographic analysis of a 1-m digital elevation model with ¹⁰Be-derived denudation rates to estimate stream erosivity and soil diffusivity in the different landscapes. We find that the higher drainage density in the monzogranite is primarily due to higher stream erosivity, whereas soil diffusivity is similar between rock types. Remote sensing data from Landsat imagery confirm field observations of higher vegetation cover in the diorites, especially with regard to deeper-rooted shrubs, which may result in increased infiltration. Based on geochemical and compositional analyses, we link vegetation differences to a relatively higher abundance of plant-essential elements in the diorite bedrock. Additionally, the monzogranite's composition and crystal grain size supports more intense physical weathering and leads to a smaller observed hillslope grain size, which increases its erodibility. We conclude that subtle differences in composition and grain size can have a significant impact on stream erosivity and drainage density. Our results demonstrate the importance of taking lithology into account when interpreting fluvial networks and topographic metrics in slowly eroding landscapes.

Plio-Quaternary climatic changes are considered to be a key driver of landscape evolution, but many unresolved questions remain, such as the extent of the impact of major climatic shifts such as the Mid-Pleistocene Transition (MPT). Various geochronological methods are available to infer changes in surface processes over the Plio-Quaternary, and Terrestrial Cosmogenic Nuclides (TCN) have proven to be one of the most efficient tools to reconstruct paleo-denudation. Implementing these approaches requires very specific conditions, such as well-preserved and extensive sediment sequences. Developing alternative methods to document the evolution of denudation is thus of major interest to retrieve information on the evolution of denudation in places where recent detrital sediment records are absent. We explore the evolution of landscape erosion over a $��\sim �$1 Ma timescale in an intra-cratonic setting, the Espinhaço mountain range (Brazil), with a new data set of detrital cosmogenic nuclide concentrations (²⁶Al–¹⁰Be). We observe a systematic disequilibrium in the ²⁶Al/¹⁰Be ratio, which we interpret as resulting from the combination of soil mixing and a significant increase in the intensity of surface processes, close to the MPT. We discuss the different scenarios with respect to available local and global data concerning the relationships between climate evolution and erosion over this time period. Our results have important implications for the interpretation of the denudation rates derived from TCN concentrations under steady states assumption, in landscapes with low erosion rates, which have a long memory for surface processes history.

Mouth bar formation is critical for channel avulsions and progradation of river deltas. The morphology of mouth bars results from different hydrodynamic forcings such as river jets, tides, and wind waves. Here we study the asymmetry of mouth bars due to alongshore currents. Adopting a numerical model, we study how alongshore propagating tides and net alongshore currents cause asymmetric mouth bar formation. The results indicate that alongshore propagating tides shift the depocenter of the mouth bar in the direction of the alongshore currents during peak ebb. Net alongshore currents shift the depocenter to its down-current side. The main channels are oriented in the opposite direction of peak flood flows (with tides) or in the direction of the net alongshore currents (without tides). Systems highly influenced by alongshore tidal flows tend to form more and wider distributary channels which are oriented toward the direction of the alongshore ebb flows. With increased river discharge and sediment influx, the number of bifurcations and channels increases while the mouth bar is less asymmetric. We developed a predictor showing that the mouth bar asymmetry is directly proportional to alongshore currents divided by river jet velocities and the width of the river mouth. Our findings provide insights into the evolution of river deltas and contribute to the management of mouth bars and channels.

In recent years, Synthetic Aperture Radar Interferometry (InSAR) has become widely utilized for slow-moving landslide monitoring due to its high resolution, accuracy, and extensive coverage. By integrating data from various orbits/platforms and monitoring sources, one-dimensional (1-D) line-of-sight (LOS) InSAR measurements can be explored to infer three-dimensional (3-D) movements. However, inconsistencies in observation times among different orbits and monitoring sources pose challenges in accurately capturing dynamic 3-D movements over time (referred to as 4-D). In this study, we propose a novel method, termed KFI-4D that incorporates spatiotemporal constraints into the traditional Kalman filter. This enhancement transforms the underdetermined problem of 4-D movement acquisition into a dynamic parameter estimation problem, enabling precise monitoring of landslide movements. The KFI-4D method was evaluated using both synthetic data sets and real data from the Hooskanaden landslide, demonstrating an improvement exceeding 50% in root mean square errors (RMSEs) compared to conventional methods. Additionally, the high-resolution characteristics of InSAR-derived 4-D movements allow for the analysis of strain invariants, providing insights into block interactions and landslide dynamics. Our findings reveal that strain invariants effectively indicate the distribution and activity of landslide blocks and slip surfaces as well as their response to triggers. Notably, abnormal signals identified in strain invariants prior to the catastrophic event at Hooskanaden suggest potential for early warning of landslides. The future integration of data from advanced satellites, such as NISAR, ALOS4 PALSAR3, and Sentinel-1C, is expected to further enhance the KFI-4D method's capabilities, improving temporal resolution and early warning potential for landslide monitoring.

The western region of the wide Thwaites Glacier terminus is characterized by a near-vertical calving front. The grounding line at this western calving front (WCF) rests on a relatively high ridge, behind which exists a reverse-sloping bed; retreat of the grounding line into this over-deepening basin could therefore expose deep calving faces that may be subject to ice-cliff failure. Here, we use the 3D Helsinki Discrete Element Model to identify the factors that control the calving dynamics in this location. We then focus on the ability of mélange to influence these dynamics given the wide embayment in which Thwaites Glacier terminates. We find that calving along the WCF is currently influenced by ice flow across the grounding line and consequent longitudinal tensile stress and rift formation. Calving is slowed in simulations that are initiated with a highly constricted mélange, with a thicker mélange suppressing calving entirely. We liken the constrained simulations to a scenario in which mélange piles behind a large grounded iceberg. In a future which may see calving become a more dominant control on the retreat of Thwaites Glacier, this type of blockage will be necessary for robust force chains to develop and transmit resistive forces to the terminus. The ability of the mélange to hinder calving at this location will be determined by the presence and rigidity of binding land-fast sea ice and iceberg keel depths. Therefore, it is necessary to represent calving, mélange and sea ice in a single framework to predict the fate of Thwaites Glacier.