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The geomorphic evolution of the upper Indus River that traverses across the southwest (SW) edge of Tibet, and the Ladakh and Zanskar ranges, was examined along a ~350-km-long stretch of its reaches. Based on the longitudinal river profile, stream length gradient index, and river/strath terraces, this stretch of the river is divided into four segments. Valley fill river terraces are ubiquitous, and strath terraces occur in the lower reaches where the Indus River cuts through deformed Indus Molasse. Optically stimulated luminescence ages of river/strath terraces suggest that valley aggradation occurred in three pulses, at ~52, ~28, and ~16 ka, and that these broadly coincide with periods of stronger SW Indian summer monsoon. Reconstructed longitudinal river profiles using strath terraces provide an upper limit on the bedrock and provide incision rates ranging from 1.0±0.3 to 2.2±0.9 mm/a. These results suggested that rapid uplift of the western syntaxes aided by uplift along the local faults led to the formation of strath terraces and increased fluvial incision rates along this stretch of the river.

The fluvial geomorphology and stratigraphy on the middle Snake River at Bancroft Springs, Idaho, provide evidence for numerous episodes of Snake River aggradation and incision since the Bonneville Flood at ca. 18 ka. A suite of seven terraces ranging from 20–1 m above modern bankfull elevation records multiple cut-and-fill cycles during the latest Pleistocene and Holocene in response to local base-level controls, variations in sediment supply, and hydroclimate change. Radiocarbon and luminescence dating show that the ages of fluvial aggradation generally coincide with increased sediment supply and likely wetter hydroclimate during onset of the Younger Dryas stadial (ca. 13.2 ka), deglaciation and termination of the Younger Dryas stadial (ca. 11.3 ka), Early Holocene cooling (ca. 8.8 ka), and Neoglacial (ca. 4.5, 2.9, 1.1 ka). Six intervening periods of incision and channel stability may also reflect either reduced sediment supply, drier hydroclimate, or both. The terrace chronology can be correlated to a variety of local and regional paleoclimate proxy records and corresponds well with periods of continental- and global-scale rapid climate change during the Holocene. The fluvial record demonstrates the geomorphic response and sensitivity of large river systems to changes in hydroclimate variability, which has important implications for inferring paleoenvironmental conditions in the region.

During its 6,300-km course from the Tibetan Plateau to the ocean, the Yangtze River is joined by two large lakes: Dongting Lake and Poyang Lake. We explain why these lakes exist. Deglaciation forced the ocean adjacent to the Yangtze mouth to rise ∼120 m. This forced a wave of rising water surface elevation and concomitant bed aggradation upstream. While aggradation attenuated upstream, the low bed slope of the Middle-Lower Yangtze River (∼2 × 10−5 near Wuhan) made it susceptible to sea level rise. The main stem, sourced at 5,054 m above sea level, had a substantial sediment load to “fight” against water surface level rise by means of bed aggradation. The tributaries of the Middle-Lower Yangtze have reliefs of approximately hundreds of meters, and did not have enough sediment supply to fill the tributary accommodation space created by main-stem aggradation. We show that the resulting tributary blockage likely gave rise to the lakes. We justify this using field data and numerical modeling, and derive a dimensionless number capturing the critical rate of water surface rise for blockage versus nonblockage.

Permafrost, a critical global cryospheric component, supports subarctic boreal forests but is frequently disturbed by wildfires, an important driver of permafrost degradation. Wildfires reduce vegetation, organic layers, and surface albedo, leading to active layer thickening and ground subsidence. Recent studies using interferometric synthetic aperture radar (InSAR) have confirmed the rapid and extensive post‐fire permafrost degradation, and have largely focused on short‐term impacts. However, the longer‐term post‐fire permafrost deformation, potentially persisting for decades, remains poorly understood due to limited data. Here, we applied InSAR in North Yukon to detect deformation signals across multiple fire scars in the past five decades. Using a chronosequence (space‐for‐time substitution) approach, we summarize a continuous trajectory of post‐fire permafrost evolution: (a) an initial degradation stage, characterized by abrupt subsidence up to 50 mm/year and gradually slowing over the first decade, with cumulative subsidence exceeding 100 mm locally; (b) an aggradation stage from approximately 15 to 30 years after fire, marked by ground uplift reaching 25 mm/year before gradually declining, compensating for the earlier subsidence; and (c) a stabilization stage beyond three to four decades, where permafrost nearly recovers to pre‐fire conditions with indistinguishable deformation between burned and unburned areas. Notably, the rarely‐reported uplift phase appears closely related to vegetation regeneration and fire‐greening feedback that provide thermal protection, suggesting a critical mechanism of permafrost recovery. These findings provide new insights into the resilience of boreal‐permafrost systems to wildfires and also underscore the importance of long‐term InSAR monitoring in understanding permafrost responses to wildfires under climate change. Plain Language Summary Permafrost plays an important role in global climate systems and is closely associated with the circum‐Arctic boreal forest environments. While wildfires are common disturbances of sub‐arctic boreal forests. Wildfires remove insulating vegetation and organic layers, allowing more heat to reach the ground, leading to permafrost thaw and ground subsidence. Currently, many studies have shown how permafrost degrades soon after wildfires, but little is known about what happens over the following decades. In this study, we used satellite radar technology to monitor ground deformation in North Yukon, Canada, across areas that burned recently to nearly five decades ago. We found that permafrost typically follows three stages after wildfire: initial subsidence over the first decade, uplift over the next 15–30 years as permafrost recovers, and finally a recovered phase when burned areas behave similarly to undisturbed ground. A key discovery is that the ground can recover to pre‐fire condition two to three decades after a fire, owing to vegetation regrowth that helps the ground stay frozen again. These findings suggest that, in cold sub‐arctic boreal forest regions like North Yukon, permafrost can recover after wildfires, showing resilience, but long‐term monitoring is essential as climate change and wildfires continue to intensify. Key Points Interferometric synthetic aperture radar is applied to study long‐term post‐fire permafrost deformation in North Yukon by chronosequence Wildfires cause permafrost degradation and ground subsidence, but recovery with ground uplift can occur over decades Permafrost may recover to pre‐fire conditions in three decades due to the vegetation regeneration that helps ground ice aggradation

Outburst floods generated by dam breaches associated with debris flow may have long-lasting effects on the formation and development landscape and the safety of human beings, increasing the difficulty of disaster prevention and mitigation. However, little was considered about channel aggradation contributing downstream damage of outburst flood. Therefore, we investigated a debris flow dam’s breaching and flooding process triggered by a 50-year heavy rainfall occurring on 17th June 2020 in Danba, China. The 6-m dam and a concomitant 1.04 × 106 m3 barrier lake were formed by a tributary debris flow blocking the Xiaojin river. We used the dam breach overtopping and two-dimensional hydrodynamic models to simulate the whole process. The dam breach event persisted for 4.5 h with an outburst flood peak discharge of 823.5 m3/s, equal to a 20-year flood. It was noted that numerous sediments of approximately 5 × 106 m3 were transported to the downstream channel, elevating the main channel bed and the terrace by 10–15 m and 2–5 m, respectively. Averaged transportation efficiency of an outburst flood is 1269.73 times greater than a 20-year seasonal flood. We simulated representative seasonal floods and outburst floods based on the pre-beach river geometry, which shows that previous channel capacity is sufficient to convey seasonal floods and the outburst flood. However, the outburst flood could easily submerge terraces and living land using after-breach geometry. Due to river aggradation lifting river elevation, deposited riverbed promotes sediment and flood evolute to living land, resulting in amplified damage. Additionally, we collected 59 dam breaches and demonstrated that local riverbed slopes could increase more than 100 times. During dam breaches, the sharp slope plays a key role in high sediment transportation efficiency. This study can promote understanding the formation and development of channel aggradation triggered by outburst flood and provide more reasonable considerations for disaster prevention and mitigation triggered by outburst flood hazard chain.

Sea-level rise, subsidence, and reduced fluvial sediment supply are causing river deltas to drown worldwide, affecting ecosystems and billions of people. Abrupt changes in river course, called avulsions, naturally nourish sinking land with sediment; however, they also create catastrophic flood hazards. Existing observations and models conflict on whether the occurrence of avulsions will change due to relative sea-level rise, hampering the ability to forecast delta response to global climate change. Here, we combined theory, numerical modeling, and field observations to develop a mechanistic framework to predict avulsion frequency on deltas with multiple self-formed lobes that scale with backwater hydrodynamics. Results show that avulsion frequency is controlled by the competition between relative sea-level rise and sediment supply that drives lobe progradation. We find that most large deltas are experiencing sufficiently low progradation rates such that relative sea-level rise enhances aggradation rates—accelerating avulsion frequency and associated hazards compared to preindustrial conditions. Some deltas may face even greater risk; if relative sea-level rise significantly outpaces sediment supply, then avulsion frequency is maximized, delta plains drown, and avulsion locations shift inland, posing new hazards to upstream communities. Results indicate that managed deltas can support more frequent engineered avulsions to recover sinking land; however, there is a threshold beyond which coastal land will be lost, and mitigation efforts should shift upstream.

This paper proposes a novel approach for generating 3-dimensional complex geological facies models based on deep generative models. It can reproduce a wide range of conceptual geological models while possessing the flexibility necessary to honor constraints such as well data. Compared with existing geostatistics-based modeling methods, our approach produces realistic subsurface facies architecture in 3D using a state-of-the-art deep learning method called generative adversarial networks (GANs). GANs couple a generator with a discriminator, and each uses a deep convolutional neural network. The networks are trained in an adversarial manner until the generator can create “fake” images that the discriminator cannot distinguish from “real” images. We extend the original GAN approach to 3D geological modeling at the reservoir scale. The GANs are trained using a library of 3D facies models. Once the GANs have been trained, they can generate a variety of geologically realistic facies models constrained by well data interpretations. This geomodelling approach using GANs has been tested on models of both complex fluvial depositional systems and carbonate reservoirs that exhibit progradational and aggradational trends. The results demonstrate that this deep learning-driven modeling approach can capture more realistic facies architectures and associations than existing geostatistical modeling methods, which often fail to reproduce heterogeneous nonstationary sedimentary facies with apparent depositional trend.

In the active tectonic setting of Aotearoa/New Zealand, large earthquakes are a relatively frequent occurrence and pose particular threats to infrastructure and society in Westland, on the west coast of South Island. In order to better define the medium- and long-term (annual to decadal) implications of these threats, existing dendrochronological data were supplemented by several hundred tree-ring analyses from 14 hitherto unstudied living tree stands in five catchments; these were combined to compile a regional picture of the location, extent, and timing of major prehistoric reforestation episodes on the floodplains of the area. These episodes correspond well with known dates of large earthquakes in the area (ca. 1400, ca. 1620, 1717 and 1826 AD), and their extents are thus interpreted to reflect the sediment deliveries resulting from coseismic landsliding into mountain valleys, and their reworking by rivers to generate widespread avulsion, aggradation, floodplain inundation and forest death. This regional aggradation picture can underpin anticipation of, and planning for, the medium- to long-term societal impacts of future major West Coast earthquakes. The source location of the next major earthquake in the region is unknown, so any of the Westland floodplains could be affected by extensive, up to metre-scale river aggradation, together with avulsion and flooding, in its aftermath, and these could continue for decades. Re-establishment and maintenance of a functioning economy under these conditions will be challenging because roads, settlements and agriculture are mostly located on the floodplains. The differences in floodplain vegetation between prehistoric and future episodes will affect the rapidity and distribution of aggradation; response and recovery planning will need to consider this, together with the impacts of climate changes on river flows.

In the present work, we investigate the post-glacial aggradation of three tributary valleys draining the left hydrographic basin of the Tiber River in central Rome: the Murcia, Caffarella, and Grottaperfetta valleys. We describe the Upper Pleistocene–Holocene stratigraphic record of the alluvial successions occurring in the Caffarella Valley through the core data collected in a dedicatedly performed 35 m deep borehole. We provide seven 14C age constraints to the sediment aggradation which allow us to make a comparison with the Grottaperfetta and Murcia valleys, for which we present previously unpublished borehole data, and with the Tiber River Valley investigated in the previous literature. In particular, we highlight the effects of a mid-Holocene (5200–3800 yr BP) erosional phase, partially overlapping with the global 4.2 ka cooling/drying event, and we discuss the possible occurrence of a sea level fluctuation linked with this paleoclimatic event which has not been detected so far by other sedimentary records. Finally, we provide evidence for the widespread occurrence of a 6th century BCE (2550–2450 yr BP) overflooding phase that was previously observed only in the eastern portion of the Tiber River Valley in central Rome, which we suggest may be originated by concurrent intensive deforestation activity in central Italy.

Northwestern Alaska has been highly affected by changing climatic patterns with new temperature and precipitation maxima over the recent years. In particular, the Baldwin and northern Seward peninsulas are characterized by an abundance of thermokarst lakes that are highly dynamic and prone to lake drainage like many other regions at the southern margins of continuous permafrost. We used Sentinel-1 synthetic aperture radar (SAR) and Planet CubeSat optical remote sensing data to analyze recently observed widespread lake drainage. We then used synoptic weather data, climate model outputs and lake ice growth simulations to analyze potential drivers and future pathways of lake drainage in this region. Following the warmest and wettest winter on record in 2017/2018, 192 lakes were identified as having completely or partially drained by early summer 2018, which exceeded the average drainage rate by a factor of ∼ 10 and doubled the rates of the previous extreme lake drainage years of 2005 and 2006. The combination of abundant rain- and snowfall and extremely warm mean annual air temperatures (MAATs), close to 0 ∘C, may have led to the destabilization of permafrost around the lake margins. Rapid snow melt and high amounts of excess meltwater further promoted rapid lateral breaching at lake shores and consequently sudden drainage of some of the largest lakes of the study region that have likely persisted for millennia. We hypothesize that permafrost destabilization and lake drainage will accelerate and become the dominant drivers of landscape change in this region. Recent MAATs are already within the range of the predictions by the University of Alaska Fairbanks' Scenarios Network for Alaska and Arctic Planning (UAF SNAP) ensemble climate predictions in scenario RCP6.0 for 2100. With MAAT in 2019 just below 0 ∘C at the nearby Kotzebue, Alaska, climate station, permafrost aggradation in drained lake basins will become less likely after drainage, strongly decreasing the potential for freeze-locking carbon sequestered in lake sediments, signifying a prominent regime shift in ice-rich permafrost lowland regions.