Geomorphology最新文献_第6页

A drumlin field at Fláajökull, Iceland: New insights from till shearing using magnetic fabrics

IF 3.1 2区地球科学 Q2 GEOGRAPHY, PHYSICAL

Geomorphology

Pub Date : 2025-01-09 DOI: 10.1016/j.geomorph.2025.109604

William R. Jacobson

The drumlins at Fláajökull, a non-surge-type glacier, Iceland provide the opportunity to investigate a modern drumlin-forming environment. Field observations indicate that the drumlins were formed sub-marginally along with an end moraine between the time period of 1966–1995. The fact that the drumlins did not extend beyond the end moraine, suggests that they were formed during this period. The Fláajökull drumlins consist of glaciofluvial outwash or till in their cores and have been streamlined with basal till. The Boulton hypothesis specifies that drumlin formation is driven by strain gradients in the glacier bed caused by hydrologic heterogeneity. This hypothesis was tested by measuring the anisotropy of magnetic susceptibility (AMS) of 457 till samples from two drumlins in the glacier forefield. In the first drumlin, two end member states of strain indicated that the basal till was sheared on the up-glacier side of the ridge (toward the overdeepened basin) and compressed on the down-glacier end with upward extrusion. These fabrics were likely formed in a recessional push-moraine on the drumlin surface. AMS fabrics in the other drumlin indicate that the tills were sheared in directions 10° and 12° northwest of the drumlin long axis; however, in one case the fabric was precisely sheared along the drumlin axis. Shear plane orientations conform to the drumlin morphology and were observed in both the drumlin core and the overlying basal till carapace in relation to the drumlin long axis. Shearing azimuths at the stoss end of the drumlin indicate some tendency for divergence suggesting higher basal resistance in the bed. New observations of hydrometer tests indicate that the Fláajökull tills are texturally similar to basal till from the Múlajökull drumlin field in central Iceland and the Horicon till, a late Wisconsin-age basal till from the Green Bay Lobe of the Laurentide Ice Sheet. In addition, ring-shear calibrations on the Horicon till provide a basis for estimating the state of strain for the tills at Fláajökull.

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引用次数: 0

Turbulent structures at the bottom of the Gobi desert boundary layer and their impact on aeolian sand transport and dust emission

IF 3.1 2区地球科学 Q2 GEOGRAPHY, PHYSICAL

Geomorphology

Pub Date : 2025-01-09 DOI: 10.1016/j.geomorph.2025.109593

Linhao Liang , Shaoxiu Ma , Weimin Zhang , Lihai Tan , Weiqi Liu , Atsushi Tsunekawa

The Gobi Desert (GD) is one of the mixed sand-gravel desert surfaces in the arid regions of northwest China, where turbulent convection develops vigorously and is one of the major dust sources in Asia. However, the turbulence structures at the bottom of the GD boundary layer and its impact on sand transport and dust emission are poorly understood. In this paper, based on field systematic measurements of two different wind directions dust storm events in the GD, the classified turbulence structures within 0.4 m of the GD boundary layer and its influence on the sand transport rate and dust emission flux are investigated using the quadrant analysis method. We found that the classified turbulent structures at the bottom of the GD boundary layer contributes >90 % of the Reynolds shear stress, ∼50 % of the sand transport rate, and ∼70 % of the dust emission flux with a time frequency of 54 %–55.8 %. The turbulent structures over GD surface are less affected by wind direction and the turbulent flow is more conducive to dust emission and diffusion than the sand transport. The height of the monitoring point affects the time share of different behaviors in the turbulent structure, where outward interactions (Q1:

u^{'} > 0, w^{'} > 0

) and ejections (Q2:

u^{'} < 0, w^{'} > 0

) are the most frequent behaviors at the bottom of GD boundary layer, accounting for >60 % of the total time frequency in classified turbulent structures. The streamwise fluctuation wind speed (

u^{'} > 0

) plays an important role in the sand transport in the GD boundary layer, and the positive vertical pulsation component (

w^{'} > 0

) is more favorable to the diffusion and transport of dust. The GD boundary layer classified turbulence structures are distinctly different from flat surfaces such as sandy desert and farmland, exhibiting turbulent behaviors similar to that of water flowing over gravel riverbeds.

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引用次数: 0

Influence of faults on landslide formation and distribution: Insights from the Hanwang Fault Zone in the Qinling-Daba Mountains, China

IF 3.1 2区地球科学 Q2 GEOGRAPHY, PHYSICAL

Geomorphology

Pub Date : 2025-01-09 DOI: 10.1016/j.geomorph.2025.109603

Wenbo Zheng , Yanbo Cao , Wen Fan , Xin Liang , Shaoqing Yuan , Qianyi Guo , Jikai Zhang

Faults contribute significantly to the formation and distribution of landslides, especially in the highly faulted Qinling-Daba mountain region. Yet, evidence of the long-term and regional dependency influence of active faults on landslides is limited. In particular, in-depth knowledge is still lacking regarding their specific mechanisms, influence range, and detailed interaction processes. This study focuses on Hanwang Town, a region in the Qinling-Daba Mountains with extensively developed fault structures and frequent geological hazards. Detailed field survey data, photogrammetry, UAV technology, point cloud analysis software, laboratory experiments, and SBAS-InSAR technology were utilized to quantify the relationship between the Hanwang Fault Zone and distributed landslides with various formation patterns. The results reveal that the Hanwang Fault Zone primarily affects regional geological hazards by influencing the geometric and mechanical properties of rock masses and changes in topography. Specifically, the critical threshold distance of the Hanwang Fault damage zone is approximately 2.2 ± 0.3 km. Geological hazards are linearly distributed along the fault zone. The joint density of rock masses shows a strong negative correlation with their distance from the fault zone. The mechanical properties of rock masses rapidly decline due to fragmentation, affecting slope stability. Furthermore, the application of SBAS-InSAR technology has enabled the identification of differential uplift and subsidence rates in the vicinity of the fault zone, which has been identified as contributing factors in the formation of hydrogeological structures that are conducive to the occurrence of geological hazards. This study not only reveals the dynamic influence of the Hanwang Fault Zone but also provides an in-depth analysis of the development characteristics and damage mechanisms of geological hazards under the control of the fault zone based on typical cases. The findings open new perspectives for understanding the complex relationship between fault zones and geological hazards, providing scientific and technical support for disaster risk management and sustainable development strategies.

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引用次数: 0

Submarine geomorphology and processes: From coast to deep abyssal plains

IF 3.1 2区地球科学 Q2 GEOGRAPHY, PHYSICAL

Geomorphology

Pub Date : 2025-01-07 DOI: 10.1016/j.geomorph.2025.109592

Ziyin Wu

引用次数: 0

The ‘management perimeter’: A proposal for effective conservation of geomorphosites

IF 3.1 2区地球科学 Q2 GEOGRAPHY, PHYSICAL

Geomorphology

Pub Date : 2025-01-06 DOI: 10.1016/j.geomorph.2025.109591

Andrea Ferrando , Francesco Faccini , Paola Coratza , Emmanuel Reynard

Geomorphosites, i.e. geosites with geomorphological interest, have a great spatial variability. Geomorphological heritage is visible at all scales, thus the area of a geomorphosite may include a single landform, groups of landforms, up to larger portions of a landscape. However, in many cases, landforms and processes included in the area of a geomorphosite interact with other processes acting outside of it. Therefore, the evolution and eventual degradation of the geomorphosite can be affected by active processes outside its perimeter, be they natural or anthropogenic. This poses an issue in geoconservation and geoheritage management – the perimeter of the site may be not enough to ensure its conservation and prevent it from degradation. In this paper the identification of a second perimeter, called the ‘management perimeter’ (MP), is proposed for each geomorphosite. The MP is delineated on a geomorphological basis, by individuating the active processes which influence the evolution of the geomorphosite, and including the whole area on which they act. Thus, the extent of the MP depends on the intrinsic characteristics of the geomorphosite and the surrounding geomorphological context. The methodology was tested on two study areas: the Liguria region (North-western Italy), and the Hérens valley (Valais canton, Switzerland), which are characterised by very different geomorphological settings, thus they permit to apply the methodology on a wide variety of geomorphosites. The identification of a MP based on geomorphological evidence could allow for effective conservation and management. The results of this research highlight the systemic dimension of geomorphology and geomorphosites, and emphasise how a systemic look has great significance when dealing with the issues of geoconservation.

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引用次数: 0

Interaction between climatic conditions, water- and sediment-fluxes in an alpine basin: Long-term monthly and seasonal analysis

IF 3.1 2区地球科学 Q2 GEOGRAPHY, PHYSICAL

Geomorphology

Pub Date : 2025-01-02 DOI: 10.1016/j.geomorph.2024.109590

Riccardo Rainato, Giacomo Pellegrini, Mario Aristide Lenzi, Lorenzo Picco

Mountain basins are sites where complex interactions among climatic, geological, geomorphic, and ecological conditions can unfold. These interplays can be reflected in the erosion processes, and in the water and sediment fluxes released along the stream network, which can be highly variable in time and space. To investigate the relationships between temperature, precipitation, runoff, and sediment fluxes at monthly and seasonal scales in an Alpine basin, this work analyzed a long-term (January 1987–September 2018) field dataset produced in the Rio Cordon basin (eastern Italian Alps). The monthly variability revealed that higher precipitation occurred in summer (i.e., June–August). However, the runoff peaked in May generated by the snowmelt process. The total sediment load exhibited two peaks in May and September, somewhat reflecting the pattern of the monthly peak of water discharge. The monthly correlation analysis proved that temperature and precipitation weakly influenced the variables investigated, while the peak of water discharge was a good predictor of sediment fluxes observed. At the seasonal scale, temperature influenced snowmelt and summer dynamics, while precipitation showed the highest correlations in autumn. The hysteresis patterns obtained by the relationships between the averaged peak of water discharge and sediment loads (suspended load and bedload) highlighted the succession of high transport efficiency months and months characterized by supply-limited conditions. Such dynamics appeared strongly influenced by a single month, i.e., September 1994, when a large and infrequent flood affected the study basin. September 1994 resulted in a breakpoint in the mass curve built by relating cumulated runoff and cumulated total load, inducing a change in the long-term trend observed until then. Specifically, about 8 years of intensified sediment load were noted, a period during which the Rio Cordon experienced frequent streamed reworking and release of fine material. These findings demonstrated how alpine basins can respond to large and infrequent events, which can be expected more frequently due to climate change, providing important insights into areas such as soil erosion control, river basin management and hazard assessment.

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引用次数: 0

Back-analysis of the 2000 Yigong dam breach flood morphodynamics: Challenges and promises

IF 3.1 2区地球科学 Q2 GEOGRAPHY, PHYSICAL

Geomorphology

Pub Date : 2025-01-02 DOI: 10.1016/j.geomorph.2024.109588

Yunlong Lei , Marwan A. Hassan , Giorgio Rosatti , Luigi Fraccarollo , Daniel Zugliani , Xudong Fu , Chunhong Hu

Landslide Dam-Break Outburst Floods (LDBOF) are among the most devastating natural hazards, significantly altering downstream river morphologies. The challenge of collecting field data, compounded by the inaccessibility of such events and the risk of equipment loss, hampers our understanding and capability to issue timely warnings. The 2000 Yigong event in China is one of the most significant recorded modern LDBOF occurrences, yet it suffered from sparse data collection. In our study, we have compiled a dataset that includes open-source elevation data, literature-based records, satellite-derived flood inundation extents, and direct field observations. We utilized a hydro-morphodynamic model to simulate the 2000 Yigong event. Comparisons of the simulated lake emptying, dam breaching, flood inundation, bank erosion, and channel infilling with field observations and similar studies indicate that our results are reasonable. Our analysis of the bed evolution during the event revealed it could be divided into two stages influenced by the flow dynamics and primarily by the sediment supply from the dam breach. In the initial stage, the breach development was transport-limited, resulting in intense erosion of dam material, which caused widespread aggradation in the downstream river channel over a distance of around 12 km. In the latter stage, the flow became sediment-supply-limited, redistributing the previously deposited sediments in the downstream reach. This process involved eroding sediment in the broader valley near the dam and depositing it downstream, creating an aggradation area. The aggradation ceased when the river reached a narrow valley, where the transported sediment load balanced with transport capacity, halting further aggradation downstream. The local valley characteristics significantly influenced flow hydraulics and subsequent bed evolution. Furthermore, our findings contribute to interpreting field observations, including forming new channels, deposition on bars, and the varying textures of bar surfaces from coarse near the dam to finer further downstream. We advocate for expanded data collection to advance the study of LDBOF events and enhance hazard mitigation efforts.

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引用次数: 0

Decoding Late Quaternary faulting through marine terraces and MIS 5.5 tilted tidal notches: Insights from central Mediterranean Sea (NW Sicily, Italy)

IF 3.1 2区地球科学 Q2 GEOGRAPHY, PHYSICAL

Geomorphology

Pub Date : 2024-12-31 DOI: 10.1016/j.geomorph.2024.109587

Mauro Agate , Fabrizio Antonioli , Francesco Caldareri , Stefano Devoto , Maurizio Gasparo Morticelli , Attilio Sulli , Nicolò Parrino , Stefano Furlani

This study investigates the recent tectonic evolution of coastal landscapes, focusing on integrating fossil tidal notches and fossil marine terraces as tools for coastal tectonic studies in the Capo Rama promontory (central Mediterranean, southern Italy, NW Sicily). These geomorphological features are crucial for understanding the tectonic forcings that shape coastal landscapes (e.g. active faulting or regional uplift), especially in the context of the high resolution topographic and morphometric data available today. This research addresses a significant gap in the current understanding of the combined use of these markers to study the evolution of the coastal landscape and its tectonic drivers. The aim is to elucidate the interplay between coastal geomorphology and tectonics in areas with elusive tectonic activity (i.e., regions deforming at a rate lesser than 1 mm/yr), hosting previously undetected seismogenic sources and, for that reason, assumed as having low seismic hazard. Employing a multidisciplinary approach, the study integrates surveys conducted along the emerged and submerged coastline with analytic/statistical morphometric analyses and fault modelling. This methodology offers a comprehensive view of the elevation and distribution of MIS 5.5 littoral deposits and coastal geomorphological markers such as marine terrace inner edges and tidal notches. Key findings reveal substantial elevation differences in these markers, varying between +34 and +1.9 m above sea level along a north-south transect, highlighting an active seaward tilting in the study area. Such tilting is related to the Quaternary deformation of a previously unknown buried fault crossing the study area. Achieved outcomes allowed exploring the integration of tidal notches and marine terraces' inner edges as geomorphological markers for coastal tectonic analyses. Moreover, this study lays foundations for future research, enabling a more detailed understanding of the hypothesized buried fault, and its contributions to the understanding of the active faulting processes in the southern Tyrrhenian region.

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引用次数: 0

Paleoenvironmental interpretation of sinkhole sediments on a flat low-lying carbonate platform, a case study from Chassahowitzka River, west-central Florida

IF 3.1 2区地球科学 Q2 GEOGRAPHY, PHYSICAL

Geomorphology

Pub Date : 2024-12-31 DOI: 10.1016/j.geomorph.2024.109589

Philip Edward van Beynen, Ping Wang

After rapid increases in ocean volumes during the early Holocene, sea levels rose more slowly from the mid- to late-Holocene. The flat shelf of the eastern Gulf of Mexico meant even small rises in sea level shifted the coastline inland many kilometers. The impact of this transgression on the karst environments of western Florida is not well known. Here we investigate how one Floridian location responded to changing climate from the mid- and late-Holocene. Chassahowitzha River, representing one of many west-central Florida rivers, is spring fed and discharges into the Gulf of Mexico. Sinkholes along this river have the potential to preserve complete and un-disturbed sedimentary records. Three sediment cores were collected from a sinkhole complex just north of the river. All three cores contain their sedimentary record down to the limestone bedrock. Ten radiocarbon dates were used to create the core chronologies. Interpretation of paleoenvironmental changes is based on sediment grain size analysis, microphotography, loss-on-ignition organic carbon contents and identification of microfossils in the sediments. Prior to 7 ka BP, sediments are dominated by quartz sand followed by an organic-rich layer ending at 6 ka BP. We interpret the organic sediments as the onset of a freshwater wetland/marsh environment along the river. Most of the marsh sediments are deposited between 7 and 6 ka BP when the coastline was 30 kms seaward. Next, there is a 3.8 kyr gap in deposition as demonstrated by the radiocarbon chronology. This hiatus could have been caused by changes in sea level, periods of aridity, draining of the sinkhole lakes or the development of the sinkhole complex. After this interval the sedimentary record is characterized by inorganic deposits which contain an abundance of microfossils. The topmost sediments of each core were interspersed with discrete shell layers which may be indicative of extreme storm events.

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引用次数: 0

Effects of islands on sediment transport in a narrow strait: Strengthening or choking?

IF 3.1 2区地球科学 Q2 GEOGRAPHY, PHYSICAL

Geomorphology

Pub Date : 2024-12-29 DOI: 10.1016/j.geomorph.2024.109585

Xingmin Liu , Yongzhi Wang , Lulu Qiao , Yi Zhong , Hongbing Miao

Straits are important pathways for material exchange in the ocean, and understanding the dynamics of these conduits is critical for quantifying regional and global sediment balances. Many straits contain complex island chains, yet little is understood about the role of these mid strait islands in controlling hydrodynamics and sediment dynamics. We examine the impact of island distribution on sediment transport in the Bohai Strait using in-situ observations and numerical modeling. Observations of water level, velocity, and suspended-sediment concentration around an archipelago in the Bohai Strait demonstrated that increases in water velocity and sediment flux were generated by Island topography. The model results showed that the distributions of current and sediment transport in the Bohai Strait were mainly controlled by the barotropic gradient force, and the presence of islands increased the sea level height difference across the axis of the strait. This change in sea level height enhanced the current velocity between islands, improved the efficiency of suspended sediment transport, and thus increased suspended sediment transport. Altering the width/average depth ratios of the channel and distributions of islands affected the total suspended sediment flux. Through many numerical experiments, we proposed a simple parametric equation, hoping to provide some reference for the simulation of sediment transport in complex topography.

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引用次数: 0