Abstract We investigate experimental observations of megaripple formation and migration near a shore‐parallel nearshore breaker bar. Experiments were conducted in the 2D Large Wave Flume at the O.H. Hinsdale Wave Research Laboratory at Oregon State University, USA. We observed that irregular megaripple‐scale bedforms in the landward bar trough initially migrated offshore and later migrated onshore as the wave breaking pattern changed. Offshore migration was associated with spilling‐dominant conditions, whereas onshore migration began during the transition toward plunging‐dominant conditions and continued after plunging became dominant. The offshore migration of these bedforms near the landward bar trough was estimated to represent approximately 10% of the total volumetric growth of the bar during the experiment. Additionally, megaripples on the seaward side of the breaker bar migrated onshore, also transporting sediment toward the bar. This migration was estimated to represent an additional 10% of the total volumetric growth. Overall, in this 2D large‐scale laboratory experiment, a first‐order estimate of form‐related sediment transport associated with megaripple migration indicates that it may represent up to 20% of the total volumetric growth of the shore‐parallel breaker bar during periods of active migration under high‐energy wave conditions.
Abstract Open bedrock fractures are common features in unstable rock slopes and alter subsurface thermal conditions of fractured rock masses through convective air ventilation and atmospheric exchange. These processes are particularly relevant in cold mountain environments, where variations in ground temperature affect rock mass stability and may allow for the occurrence of localized permafrost. Here, we investigate fracture‐atmosphere interaction systems in the Stampa unstable rock slope (Norway) by combining remote sensing, field mapping, continuous temperature and airflow monitoring, and radon and thoron surveys. In total, 79 temperature anomalies were identified and classified as: (a) cold vents and fractures during summer, with mean annual air temperatures (MAATs) generally below 0°C (down to −1.65°C), and (b) warm vents during winter, characterized by MAATs ranging from 2.62 to 5.27°C. Radon and thoron concentrations within fracture openings vary widely (8 to about 15,000 Bq m −3 ), reflecting differences in ventilation rates, fracture connectivity and volumes. Monitoring at vents shows that airflow direction and intensity are primarily controlled by temperature gradients between the subsurface and atmosphere, while strong winds can significantly affect ventilation and gas concentrations. We identified four types of fracture‐atmosphere interaction systems: reversible and seasonal chimney ventilation, local convection in deep fractures, and cold‐air trapping in shallow fractures. These processes generate spatial heterogeneity in the rock thermal regime and can maintain frozen conditions far below regional permafrost limits. Our results demonstrate that fracture‐controlled ventilation plays a key role in shaping the thermal regime of unstable rock slopes and influences rock mass stability in mountain environments.
Abstract Meandering rivers are ubiquitous on Earth and other planetary surfaces, yet generating dynamically active meandering channels that can sustain meandering patterns for multiple flow cycles without introduced external disturbances remains challenging in laboratory conditions. Here, we use flume experiments to investigate how a synthetic cohesive surface layer, representing increased erosion resistance (associated with vegetation, biofilms, organic matter, and fine sediment) can reorganize an initially braided sand‐bed under an initial bed slope of approximately 1.6%. In the absence of cohesion, the channel maintained a multithread braided morphology. Following the introduction of surface cohesion to the floodplain and riverbanks, the system transitioned through wandering and single‐thread meandering states while remaining morphodynamically active, with continued bend migration, bend regeneration, and seven chute cutoffs. Quantitative classification using the channel count index and sinuosity confirms this transition from the initial braided toward more organized wandering and meandering configurations. Surface cohesion reduced the active channel area, and erosion and deposition rates, while localized bank erosion and channel migration continued. These results show that increased surface erosion resistance can suppress distributed channel and floodplain reworking without eliminating channel mobility, offering a vegetation‐independent mechanism for developing and maintaining dynamically active sinuous channels on Earth and other planetary surfaces.
Abstract Using the BISICLES ice sheet model, we explore the Antarctic Ice Sheet's response over the 22nd century under two climate scenarios. In the return scenario , climate forcing is returned to present‐day levels (2015) in either 2050 or 2100 and then held constant until 2200. In the stabilization scenario , climate forcing is held at 2050 or 2100 levels through to 2200. Results are highly climate model dependent, with larger differences between models than between return and stabilization scenarios, but show that returning the climate cannot prevent significant losses from Antarctica over the next two centuries due to committed changes and the possibility of ice sheet instabilities already being under way. The timing of returning the climate is important, with substantially different Antarctic responses between returning the climate in 2050 versus 2100. If the climate is returned in 2050, sea level contributions are generally lower than under stabilization scenarios. However, if returning is delayed until 2100, under high emissions, the return scenarios produce higher sea level contributions than stabilization scenarios, as increased surface mass balance in the warmer stabilization scenarios offsets some of the dynamic losses. Despite this, dynamic losses appear to accelerate and may eventually negate this initial offset, indicating that beyond 2200, returning in 2100 could eventually be more effective. Our results suggest that a large scale climate intervention may not be a complete solution to mitigating sea level contribution from the ice sheet nor reverse it on multi‐century timescales.
Abstract Wakes from finite, bank‐attached vegetation patches are common along channel margins, yet comparisons between canopy states of the same patch remain limited. Bank vegetation is not a static roughness element: the same patch can shift between emergent and submerged hydraulic states through biomass change, flow‐induced bending, or stage rise. This study examined a controlled representation of that transition by holding depth, discharge, and patch planform fixed while reducing effective canopy height through stem truncation, a configuration most analogous to dieback, biomass loss, or bending rather than pure stage rise. A rigid, fixed‐bed bank‐attached patch was tested as an emergent canopy and as a stem‐truncated, overtopped canopy with a submergence ratio of 2.1 and a lower frontal area index. Velocimetry across 12 cross‐sections showed that the emergent wake retained a laterally organized, depth‐spanning structure through 12.5 patch widths; extrapolated threshold crossings placed recovery at 16–19 patch widths. In the stem‐truncated case, velocity and Reynolds stress fields in the measured lower flow showed concurrent lateral and canopy‐top exchange signatures and faster cross‐sectional homogenization. The inferred near‐bed shear stress field indicated broader near‐bank sheltering and a more persistent edge‐stress band in the emergent case, with integrated excess shear about 4.5 times that of the stem‐truncated case. In this tested configuration, the depth‐spanning state maintained a longer downstream zone of altered momentum and stress, whereas the stem‐truncated, overtopped state compressed the low‐stress region and shortened the edge‐stress band.
