Mass-wasting Processes Research Articles

Global survey of paleo-bedforms on Mars

Sedimentary processes on Mars have contributed to a plethora of landforms, both ancient and modern. Many of these are aeolian- or fluvial-formed constructs that meet the morphologic criteria for dunes and ripples but are clearly lithified and part of the rock record. This study conducted a survey of Mars using data returned from the High Resolution Imaging Science Experiment (HiRISE) to characterize the spatial distribution, origin, and geologic context of these preserved ancient bedforms, termed here as paleo-bedforms. The most compelling class include organized groups of 2–80-m-tall, crescentic to transverse features spaced at 100–1000 m wavelengths at Apollinaris Sulci, Valles Marineris, and other low-latitude sites. These morphologies along with superposed craters, boulders, and fractures led to the interpretation that these are highly lithified, friable, and partially eroded ancient aeolian dunes. In addition to lithified dunes, other remnants of ancient bedforms include examples in which the dune was completely removed, leaving a shallow depression in a crescentic outline as dune cast pits. The most widespread occurrences of paleo-bedforms show crest-to-crest wavelengths (10–80 m), heights (∼1–4 m), and morphologies consistent with lower-order bedforms of megaripples or transverse aeolian ridges. Paleo-megaripple fields in Arcadia Planitia, Hellas Planitia, Terra Sirenum, and other locations exhibit a progression of degraded morphologies, with crests showing signs of rounding, pitting, or fracturing, while heights and slopes are diminished due to erosion. Most rare are the paleo-bedforms in the fluvial bedform class at Lethe Vallis and Holden crater, as they occur along the path of proposed ancient flooding events. More enigmatic paleo-bedform candidates occur concentrated along the steep Valles Marineris and Noctis Labyrinthus wall slopes. These intermediate-sized, arcuate landforms that resemble transverse climbing dunes are heavily cratered, but they may align perpendicular or oblique to the local gradient, perhaps formed by wall slope winds and slope creep.The bedforms are unlike most ancient terrestrial aeolian or fluvial bedform systems, which are typically preserved only as truncated members of stratigraphic sections. Episodes of burial and exhumation by various geologic units (e.g., the Medusae Fossae Formation, pyroclastic units, lava flows, dust) are notable, whereas other bedforms appear to have been stabilized and partially lithified in place without burial. Ongoing agents of mass wasting, aeolian abrasion, and cryo-driven processes have contributed to the exhumation, erosion, and weathered appearance of paleo-bedforms, and a spectrum of degradation states was observed. Collectively, we report a diverse variety of ancient sedimentary bedforms preserved across Mars, with implications about paleoclimates and landscape evolution on Mars.

The complex interaction between channel–levee systems and mass transport complexes in the Pliocene–Quaternary Rakhine Basin, offshore Myanmar

Channel–levee systems (CLSs) and mass transport complexes (MTCs) are prevalent in deep-water basins, yet their interplay remains enigmatic. This study uses high-resolution 3D seismic data to investigate the architecture of CLSs and MTCs, aiming to explore how CLSs influence the distribution of MTCs in the Rakhine Basin, Bay of Bengal. Two models are built to illustrate the interaction between CLSs and MTCs. In the first model, large-scale aggradational CLSs created unfilled relief in their overbank environments, which acted as spatially confined topography for subsequent mass-wasting deposits. In this model, the interaction between large-scale CLSs and confined MTCs controls the distribution of confined MTCs. In the second model, laterally migrating CLSs do not create such prominent topographic relief in their overbank environments. This characteristic renders them inconsequential in influencing the distribution of subsequent mass-wasting processes. Consequently, spatially extensive MTCs develop within unconfined settings. This configuration gives rise to lithological traps, which might be common and represent potential drilling targets on continental margins. This study could contribute to a better understanding of the interplay between CLSs and MTCs and have some enlightenment on looking to provide some insight into the search for lithological traps in the Rakhine Basin.

A Comprehensive Assessment of Submarine Landslides and Mass Wasting Processes Offshore Southern California

AbstractIt is critical to characterize submarine landslide hazards near dense coastal populations, especially in areas with active faults, which can trigger slope failure, subsequent tsunamis, and damage seabed infrastructure during earthquake shaking. Offshore southern California, numerous marine geophysical surveys have been conducted over the past decade, and high‐resolution bathymetric and subsurface data now cover about 60 percent of the total region between Point Conception and the United States‐Mexico border from the California coast out to the base of Patton Escarpment ∼200 km offshore. In a comprehensive compilation and interpretive mapping effort, we find evidence of seafloor failure throughout offshore southern California with nearly 1,500 submarine landslide‐related features, including 63 discrete slide deposits with debris and >1,400 slide‐related scarps. In our analysis, we highlight new mapping of submarine landslides in Catalina Basin, the Del Mar slide, the San Gabriel slide complex, and the 232 km2 San Nicolas slide, the largest area of any known submarine landslide mass offshore southern California. Analysis of the spatial distribution of submarine landslide features suggests that most mapped slide features are located relatively near coastal sediment sources, particularly during sea‐level lowstand conditions, which underscores the importance of sediment supply and sediment accumulation on low‐gradient slopes as failure preconditioning processes. Tectonically driven uplift at shelf edges and along basin flanks is another key preconditioning factor, and our results also suggest that earthquakes along active faults trigger mass wasting, especially for repeated, small‐scale failures on tectonically steepened slopes.

Estimating surface water availability in high mountain rock slopes using a numerical energy balance model

Abstract. Water takes part in most physical processes that shape mountainous periglacial landscapes and initiation of mass-wasting processes. An observed increase in rockfall activity in high mountain regions was previously linked to permafrost degradation, and water that infiltrates into rock fractures is one of the likely drivers of processes related to thawing and destabilization. However, there is very little knowledge of the quantity and timing of water availability for infiltration into steep rock slopes. This knowledge gap originates from the complex meteorological, hydrological, and thermal processes that control snowmelt, as well as challenging access and data acquisition in extreme alpine environments. Here we use field measurements and numerical modeling to simulate the energy balance and hydrological fluxes on a steep high-elevation permafrost-affected rock slope at Aiguille du Midi (3842 m a.s.l, France), in the Mont Blanc massif. Our results provide new information about water balance at the surface of steep rock slopes. Model results suggest that only ∼ 25 % of the snowfall accumulates in our study site; the remaining ∼ 75 % is likely transported downslope by wind and gravity. The snowpack thickness was found to decrease with surface slopes between 40 and 70∘. We found that among all water fluxes, sublimation is the main process of snowpack mass loss at our study site. Snowmelt occurs between spring and late summer, but most of it may not reach the rock surface due to refreezing and the formation of an impermeable ice layer at the base of the snowpack, which was observed at the field site. The annual snowmelt that is available for infiltration (i.e., effective snowmelt) is highly variable in the simulated years 1959–2021, and its onset occurs mostly between May and August and ends before October. By applying the model to a range of altitudes, we show that effective snowmelt is the main source of water for infiltration above 3600 m a.s.l.; below, direct rainfall on the snow-free surface is the dominant source. This change from snowmelt- to rainfall-dominated water input leads to an abrupt, nonlinear increase in water availability at altitudes below 3600 m a.s.l and may point to higher sensitivity of permafrost-affected rock slopes to climate change at these altitudes.

Multi-Sensor and Multi-Scale Remote Sensing Approach for Assessing Slope Instability along Transportation Corridors Using Satellites and Uncrewed Aircraft Systems

Rapid slope instabilities (i.e., rockfalls) involving highway networks in mountainous areas pose a threat to facilities, settlements and life, thus representing a challenge for asset management plans. To identify different morphological expressions of degradation processes that lead to rock mass destabilization, we combined satellite and uncrewed aircraft system (UAS)-based products over two study sites along the State Highway 133 sector near Paonia Reservoir, Colorado (USA). Along with a PS-InSAR analysis covering the 2017–2021 interval, a high-resolution dataset composed of optical, thermal and multi-spectral imagery was systematically acquired during two UAS surveys in September 2021 and June 2022. After a pre-processing step including georeferencing and orthorectification, the final products were processed through object-based multispectral classification and change detection analysis for highlighting moisture or lithological variations and for identifying areas more susceptible to deterioration and detachments at the small and micro-scale. The PS-InSAR analysis, on the other hand, provided multi-temporal information at the catchment scale and assisted in understanding the large-scale morpho-evolution of the displacements. This synergic combination offered a multiscale perspective of the superimposed imprints of denudation and mass-wasting processes occurring on the study site, leading to the detection of evidence and/or early precursors of rock collapses, and effectively supporting asset management maintenance practices.

Late Holocene volcanic stratigraphy and eruption chronology of the dacitic Young Doña Juana volcano, Colombia

We present the late Holocene eruption history of the poorly known Doña Juana volcanic complex, in SW Colombia, which last erupted in the twentieth century. This represents a case study for potentially active volcanism in the rural Northern Andes, where tropical climate conditions and a fragmented social memory blur the record of dormant volcanoes. We reconstructed the volcanic stratigraphy of the central-summit vent area by integrating new mapping at 1:5000 scale with radiocarbon ages, sedimentology analysis, and historical chronicles. Our results revealed cyclic transitions from lava-dome growth phases and collapse to explosive Vulcanian and possibly subplinian phases. Pyroclastic density currents were generated by dome collapse producing block-and-ash flows or by pyroclastic fountain/column collapse and were rapidly channelized into the deeply incised fluvial valleys around the volcano summit. The pyroclastic density currents were ∼4−10 × 106 m3 in volume and deposited under granular flow− or fluid escape−dominated depositional regimes at high clast concentrations. In places, more dilute upper portions reached a wider areal distribution that affected the inhabited areas on high depositional terraces. The coefficient of friction (ΔH/L) is higher for block-and-ash flows and dense lava−bearing fountain/low-column-collapse pyroclastic density currents compared to pumice-bearing, column-collapse pyroclastic density currents. Associated mass-wasting processes included syneruptive and intereruptive debris flows, with the last one documented in 1936 CE.

Mapping and classification of heavy rainfall-induced hazards in the Petrich town area (SW Bulgaria)

The torrential catchments located on the northern slopes of Belasitsa Mountain (SW Bulgaria), in the area of Petrich town were affected by an intense rainfall event in December 2021 that triggered a cascade of hazard processes like floods, landslides, debris flows/floods that caused major damage to the road network, properties, and buildings, showing the urgent need to take hazard and risk assessment and mitigation measures. For assessment purposes, we perform field and UAV-based analysis, and mapping of the affected areas, the geomorphological changes after the flooding event, and the different types of identified mass-wasting processes. We also investigated the effects of early December 2021 heavy rain on a regional scale.

Integration of Remote Sensing and Offshore Geophysical Data for Monitoring the Short-Term Morphological Evolution of an Active Volcanic Flank: A Case Study from Stromboli Island

The Sciara del Fuoco (SdF) collapse scar at Stromboli is an active volcanic area affected by rapid morphological changes due to explosive/effusive eruptions and mass-wasting processes. The aim of this paper is to demonstrate the importance of an integrated analysis of multi-temporal remote sensing (photogrammetry, COSMO-SkyMed Synthetic Aperture Radar amplitude image) and marine geophysical data (multibeam and side scan sonar data) to characterize the main morphological, textural, and volumetric changes that occurred along the SdF slope in the 2020–2021 period. The analysis showed the marked erosive potential of the 19 May 2021 pyroclastic density current generated by a crater rim collapse, which mobilized a minimum volume of 44,000 m3 in the upper Sciara del Fuoco slope and eroded 350,000–400,000 m3 of material just considering the shallow-water setting. The analysis allowed us also to constrain the main factors controlling the emplacement of different lava flows and overflows during the monitored period. Despite the morphological continuity between the subaerial and submarine slope, textural variations in the SdF primarily depend on different processes and characteristics of the subaerial slope, the coastal area, the nearshore, and “deeper” marine areas.

Water evacuations in remote tourist regions: evaluating case studies from natural hazards in North Patagonian lakes, Argentina.

The remote North Patagonian region is a sparsely populated territory and a world famous tourist destination located on the leeward side of the Andes Mountains. Recent disasters triggered by various types of geoenvironmental hazards (including volcanic eruptions, mass-wasting processes and extreme weather events) heavily disrupted ground transport networks in a region with already limited territorial accessibilities. All these catastrophes prompted the need to evacuate or assist a number of secluded visitors, locals and livestock extemporaneously on board of coastguards and tourist passenger-ships from the shores of the many glacial lakes that make up part of the regional attraction. Despite the recurrence of these types of events, water evacuations in the region continue to be spontaneous, improvised and hazardous procedures. This contribution reconstructs and assesses a number of recent local-scale cases of lake evacuations and assistances from a number of Patagonian urban centers, rural areas and tourist sites. For each case study, we systematically elaborated on the prime components of an evacuation process, which enabled us to recognize key achievements, failures and conditioning factors for managing emergencies via water transport, most of them inherent to the studied region. Some of the complexities to emerge from case studies referred to: complex hazard-related scenarios; limited ground-based accessibilities and risk of isolation; various inter- and intra-organizational issues, incidental to natural reserves and tourist regions; a wide range of particular demographic features; and the availability and vulnerability of water transport resources. We suggested fundamental and replicable recommendations for developing water evacuation plans, also identifying forthcoming problems to solve in order to improve the management of emergencies through this alternative means of transport.Electronic supplementary materialSupplementary material (Appendix 1) is available in the online version of this article at 10.1007/s11629-021-7207-3

A 1.5 Ma Marine Record of Volcanic Activity and Associated Landslides Offshore Martinique (Lesser Antilles): Sites U1397 and U1399 of IODP 340 Expedition

The products of eruptive and mass-wasting processes that built island arc volcanoes are better preserved in marine deposits than on land. Holes U1397A and U1399A drilled during IODP Expedition 340 provide a 1.5 Ma record of the volcanic history of Martinique. 14C dating and δ18O patterns are used to reconstitute the chronostratigraphy of tephra, volcaniclastic turbidites, and mass-wasting events (traced by debris avalanches, debrites, and duplication and deformation of pre-existing sediments), leading to a new volcanic history of Montagne Pelée and Pitons du Carbet volcanoes. The top 50 m of core U1397A provides a continuous high-resolution sedimentation record over the last ∼130 ka. The sedimentation record deeper than 50 m in core U1397A and in the whole core U1399A is discontinuous because of the numerous sliding and deformation events triggered by debris avalanches related to flank collapses. Three successive activity periods are identified since ∼190 ka: the “Old Pelée” until 50 ka, the “Grand Rivière” (50–20 ka), and the “Recent Pelée” (20 ka—present day). The first two periods have the highest volcanic deposition rates offshore but very little outcrop on land. The whole magmatic activity of Mt Pelée comprises silicic andesites, but mafic andesites were also emitted during the whole “Grand Rivière.” At ∼115 ka, a major flank collapse (“Le Prêcheur”) produced a debris avalanche and submarine landslide that affected sea floor sediments by erosion and deformation up to ∼70 km from the shore. The Pitons du Carbet volcano was active from 1.2 Ma to 260 ka with numerous large flank collapses at a mean rate of 1 event every 100 ka. The average deposition rate of tephra fall offshore is much less than that at Mt Pelée. Our data show that correlations between the timing of large landslides or emission of mafic magmas and rapid sea level rise or lowstands suggested by previous studies are not systematic. The reconstituted chronostratigraphy of cores U1397A and U1399A provides the framework necessary for further studies of the magma petrology and production rates and timing of the mechanisms triggering flank collapses and related submarine landslides of Mt Pelée and Pitons du Carbet.

Permafrost Base Degradation: Characteristics and Unknown Thread With Specific Example From Hornsund, Svalbard

Permafrost degradation is one of the most pressing issues in the modern cryosphere related to climate change. Most attention is paid to the degradation of the top of the active permafrost associated with contemporary climate. This is the most popular issue because in the subsurface part of it there is usually the greatest accumulation of ground ice in direct relation to the changes taking place. The melting of ground ice is the cause of the greatest changes related to subsidence and other mass-wasting processes. The degradation of the subsurface permafrost layer is also responsible for the increased emission of CO2 and methane. However, this is not a fully comprehensive look at the issue of permafrost degradation, because depending on its thickness, changes in its thermal properties may occur more or less intensively throughout its entire profile, also reaching the base of permafrost. These changes can degrade permafrost throughout its profile. The article presents the basic principles of permafrost degradation in its overall approach. Both the melting of the ground ice and the thermal degradation of permafrost, as manifested in an increase in its temperature in part or all of the permafrost profile, are discussed. However, special attention is paid to the degradation characteristics from the permafrost base. In the case of moderately thick and warm permafrost in the zone of its sporadic and discontinuous occurrence, this type of degradation may particularly contribute to its disappearance, and surficial consequences of such degradation may be more serious than we expect on the basis of available research and data now. A special case of such degradation is the permafrost located in the coastal zone in the vicinity of the Hornsund Spitsbergen, where a multidirectional thermal impact is noted, also causing similar degradation of permafrost: from the top, side and bottom. Especially the degradation of permafrost from the permafrost base upwards is an entirely new issue in considering the evolution of permafrost due to climate change. Due to the difficulties in its detection, this process may contribute to the threats that are difficult to estimate in the areas of discontinuous and sporadic permafrost.

Volcano-sedimentary processes at Las Derrumbadas rhyolitic twin domes, Serdán-Oriental Basin, Eastern Trans-Mexican Volcanic Belt

Abstract The eruption of the c. 10 km 3 rhyolitic Las Derrumbadas twin domes about 2000 years ago generated a wide range of volcano-sedimentary deposits in the Serdán-Oriental lacustrine basin, Trans-Mexican Volcanic Belt. Some of these deposits have been quarried, creating excellent exposures. In this paper we describe the domes and related products and interpret their mode of formation, reconstructing the main phases of the eruption as well as syn- and post-eruptive erosional processes. After an initial phreatomagmatic phase that built a tuff ring, the domes grew as an upheaved plug, lifting a thick sedimentary pile from the basin floor. During uplift, the domes collapsed repeatedly to form a first generation of hetero-lithologic hummocky debris avalanche deposits. Subsequent dome growth produced a thick talus and pyroclastic density currents. Later, the hydrothermally altered over-steepened dome peaks fell to generate second-generation, mono-lithologic avalanches. Subsequently, small domes grew in the collapse scars. From the end of the main eruptive episode onwards, heavy rains remobilized parts of the dome carapaces and talus, depositing lahar aprons. The Las Derrumbadas domes are still an important source of sediments in the basin, and ongoing mass-wasting processes are associated with hazards that should be assessed, given their potential impact on nearby populations.

Tree-ring stable isotopes indicate mass wasting processes at Radicofani in the upper Orcia Valley (Tuscany, Italy)

Tree-ring carbon (C) and oxygen (O) stable isotope (SI) chronologies spanning the period 1983–2012 were analysed at three Pinus nigra Arn. sites located in the upper Orcia Valley (Tuscany, Italy) in a badlands landscape. The goal of the study was to determine the extent to which tree-ring stable isotopes (SI) can serve as a proxy for mass wasting processes. To this end, we applied an established dual-isotope model to detect physiological changes between trees growing at three sites, one along the upper border of a well-studied shallow landslide, one on the landslide, and one in a stable area, as control. We further analysed whether trees at the three sites showed different δ18O responses to climate and to precipitation δ18O. Tree-ring δ13C and δ18O variations and trends revealed impairments of the photosynthetic process at the landslide site. We found that trees growing on the landslide show signs of reduced photosynthetic capacity since the onset of the landslide in 1993, whereas since 2000, while producing compression wood during periods of landslide activity, the trees show trends of higher average maximum net photosynthesis. The correlation analysis performed between the SI chronologies and the climatic variables revealed that the climatic signals at the site located on the landslide are masked by growth stress induced by the mass wasting processes. The most distinct differences in climate responses between sites were found in tree-ring δ13C in response to mean temperature and to mean temperature range, and in tree-ring δ18O in response to precipitation δ18O. Our research confirms that it is possible to reconstruct mass-wasting processes on forested slopes and to date geomorphological events by considering the trees' physiological conditions as recorded by stable C and O isotopes in tree rings, and by comparing affected with unaffected sites.

Geological and geomorphological influences on a recent debris flow event in the Ice-scoured Mountain Quaternary domain, western Scotland

Debris flows in settings that have experienced net glacial erosion within the UK's Ice-scoured Quaternary domain are the result of a complex interaction of a range of geological and geomorphological factors. On the 11th of August 2016 a rainfall-triggered debris flow deposited 100 t of sediment onto local road and rail infrastructure blocking transport between town of Fort William and port of Mallaig in north-west Scotland. The debris flow occurred in an ice-scoured setting, where current 1:50,000-scale geological maps suggest that little or no sediment is expected on the valley slopes. In this study, we show how weathering and mass-wasting processes have interacted with bedrock structures to fill localised depressions with sediment on the upper parts of the slope. The intense rainfall event of August 2016 caused the destabilisation of this localised sediment, with eventual failure along bedrock joint surfaces resulting in two debris flows. This study demonstrates the combination of processes that can result in thick accumulations of sediment on slopes that are otherwise generally lacking in superficial sediment cover. These sediment accumulations have the potential to pose a significant landslide hazard in areas that might previously have been thought of as lower susceptibility. The research illustrates a need to improve understanding and representation of sediment thickness and distribution on hill slopes – particularly those that show an absence of superficial deposits at the scale of currently available geological maps.

Characterization of a landslide-triggered debris flow at a rainforest-covered mountain region in Brazil

Debris flows represent great hazard to humans due to their high destructive power. Understanding their hydrogeomorphic dynamics is fundamental in hazard assessment studies, especially in subtropical and tropical regions where debris flows have scarcely been studied when compared to other mass-wasting processes. Thus, this study aims at systematically analyzing the meteorological and geomorphological factors that characterize a landslide-triggered debris flow at the Pedra Branca catchment (Serra do Mar, Brazil), to quantify the debris flow’s magnitude, peak discharge and velocity. A magnitude comparison with empirical equations (Italian Alps, Taiwan, Serra do Mar) is also conducted. The meteorological analysis is based on satellite data and rain gauge measurements, while the geomorphological characterization is based on terrestrial and aerial investigations, with high spatial resolution. The results indicate that it was a large-sized stony debris flow, with a total magnitude of 120,195 m3, a peak discharge of 2146.7 m3 s−1 and a peak velocity of 26.5 m s−1. The debris flow was triggered by a 188-mm rainfall in 3 h (maximum intensity of 128 mm h−1), with an estimated return period of 15 to 20 years, which, combined with the intense accumulation of on-channel debris (ca. 37,000 m3), indicates that new high-magnitude debris flows in the catchment and the region are likely to occur within the next two decades. The knowledge of the potential frequency and magnitude (F–M) can support the creation of F–M relationships for Serra do Mar, a prerequisite for reliable hazard management and monitoring programs.

Mass-wasting processes input in proximal metalliferous sediments: A case study of the Pobeda hydrothermal fields

Metalliferous sediments associated with oceanic hydrothermal systems contain various amounts of metals of a dual origin: from suspended particulate matter of an overlying plume and from weathered massive sulfide edifices. This study investigates the influence of the latter component on metal enrichment in sediments proximal to sulfide bodies for the Pobeda hydrothermal fields of the Mid-Atlantic Ridge (MAR). This region consists of three separate venting fields Pobeda-1, 2, and 3 located at different depth levels in the MAR rift valley. Hydrothermal precipitates within the site occur as massive sulfide edificies and metalliferous sediments. Detailed mineralogical and geochemical analysis of all these components revealed that a significant amount of hydrothermally-derived material in the sediments derives from overlying plume particulate superimposed by mass wasted oxidized sulfides from the nearest edifices. This last component is mostly abundant in the sediments of the deepest Pobeda-2 field, which complicates using bulk geochemistry to decipher the history of hydrothermal activity there. For the two remaining fields, Pobeda-1 and Pobeda-3, a reconstruction of vent discharge history indicates that it began almost simultaneously at the time interval recorded in core sediments. However it waned steadily at the Pobeda-3 field, whereas at Pobeda-1 field it exhibited a significant decrease in intensity and then a reverse movement upward until recently.

Repeated degradation and progradation of a submarine slope over geological timescales

ABSTRACTSubmarine slopes prograde via accretion of sediment to clinoform foresets and degrade in response to channel or canyon incision or to mass-wasting processes. The timescales over which progradation and degradation occur, and the large-scale stratigraphic record of these processes, remain unclear due to poor age constraints in subsurface-based studies and areally limited exposures of exhumed systems. We here integrate 3D seismic reflection and borehole data to study the geometry and origin of ancient slope canyons developed in late Mesozoic strata of the Måløy Slope, offshore Norway. Slope degradation and canyon incision commenced during the late Kimmeridgian, coincident with the latter stages of rifting. Later periods of canyon formation occurred during the Aptian to Albian and the Albian to Cenomanian, during early post-rift subsidence. The canyons are straight, up to 700 m deep, and 10 km wide on the upper slope and die out downdip onto the lower slope. The canyons trend broadly perpendicular to and crosscut most of the rift-related normal faults, although syn-filling fault growth locally helped to preserve thicker canyon-fill successions. The headwalls of the oldest (late Kimmeridgian) canyons are located at a fault-controlled shelf edge, where younger canyons overstep this fault, which was inactive when they formed, extending across the paleo-shelf. Downslope, Aptian to Albian canyons either erode into the older, late Kimmeridgian to Barremian canyon fills, forming a complicated set of unconformities, or in the case of the Albian to Cenomanian canyons, die out into correlative conformities. Boreholes indicate that the canyon bases are defined by sharp, erosional surfaces, across which we observe an abrupt upward shift from shallow- to deep-marine facies (i.e., late Kimmeridgian canyons), or deep marine to deep marine facies (Aptian to Albian and Albian to Cenomanian canyons). Missing biostratigraphic zones indicate the canyons record relatively protracted periods (c. 2–17 Myr) of structurally enhanced slope degradation and sediment bypass, separated by > 10 Myr periods of deposition and slope accretion. The trigger for slope degradation is unclear, but it likely reflects basinward tilting of this tectonically active margin, enhanced by incision of the slope by erosive sediment gravity flows. The results of our study have implications for the timescales over which large-scale slope progradation and degradation may occur on other tectonically active slopes, and the complex geophysical and geological record of these processes. We also show that canyon formation can cause large volumes of margin-derived sediment to bypass proximal sub-basins within rifted terranes, an important process not currently captured by marine rift-basin tectono-stratigraphic models.

Fragipan Horizons: Definition, Properties, Genesis, and Influence on Soil Behavior

Many Missouri forest soils exhibit fragipans, which influence soil productivity, ecosystem services and land management. Fragipan bearing soils tend to occur where loess thickness is moderate (1 to 2 meters) or where the soil profile exhibits evidence of mass wasting of weathered limestone residuum. Consensus is consolidating around the self-weight collapse of loess and residuum after repeated wetting and desiccation. The use of gravel as an indicator of parent material differences and its correlation with fragipan development is not perfectly aligned, thus although most fragipans do exhibit a bisequal soil profile, the placement of the lithologic discontinuity is difficult given mass wasting, eluviation-illuviation, side slopes, and other soil processes that contribute to increasing the bulk density and conferring strength. Fragipan genesis is evolving; however, research involving Ecosystem Site Descriptions are a fusion of a land parcel’s soil properties, vegetational community, hydrology, and climate to guide land management. Ecological Site Descriptions associated with fragipan bearing soils are necessary, especially when making land management decisions.

Organic debris and allochthonous coal in Quaternary landforms within a periglacial setting (Longyearbyen Mining District, Norway) - A multi-disciplinary study (coal geology-geomorphology-sedimentology)

High volatile bituminous coal C and B is currently exploited at Spitsbergen-Svalbard, Norway. Several coal seams formed during the Palaeocene, of which some were reworked by mass wasting (MW), (glacial)-fluvial (GF) and coastal-marine wave-dominated (WM) processes under periglacial conditions during the Quaternary. This supergene alteration resulted in different landforms and deposit bearing four different types of depositional environments in Svalbard: (1) Invisible floral and faunal remains, (2) visible floral remains, (3) drift wood, (4) coal placers s. The subaerial slow- and fast-moving MW was accompanied by chemical weathering giving rise to jarosite coatings indicative of acidic meteoric solutions, whereas the remaining subaquatic processes operated under neutral to slightly alkaline conditions. Fast-moving MW and WM are productive processes, whereas GF ones are destructive with regard to coal accumulation. The most efficient tools to study the origin of the OM-bearing coarse-grained deposits are the morphology and orientation of bioclasts while the LER/HER (= low exothermic / high exothermic reaction) ratio is used for finer-grained OM-bearing sediments. The maceral analysis revealed that the landforms accounted for by GF and WM were emplaced as a result of geogenic and anthropogenic processes and aged younger than 1900 CE, while MW is Quaternary and true geogenic. Driftwood is cast in the role of a marker for coal-bearing (fluvial-) marine environments different in age and rank of coalification. With this in mind it is an excellent tool to drawn the boundary in paralic settings between the marine and fluvial impact. In conclusion, coal fragments are markers for short-term, periodical and fast landform-building processes, whereas siliciclasts from the host and bedrock are markers for long-term and episodical geomorphological and sedimentological supergene alteration.

Multidisciplinary approach to sediment connectivity between debris-flow channel network and the Dolra River, Mazeri Valley, Southern Caucasus, Georgia

The Mazeri Valley in the southern Caucasus Mountains, Georgia, is characterized by a highly dynamic landscape with several active mass-wasting processes. The spatial and temporal dynamics of these geomorphic processes have, over time, resulted in the formation of large cones and fans. In this context, the coupling between the hillslope and the channel plays a fundamental role in controlling the catchment sediment dynamics. The sediment produced at higher altitudes on hillslopes may occasionally reach the debris-flow channel network, and downstream propagation may have significant effects on the fluvial environment and create potential hazards for the population and infrastructure. In this regard, we report a tree-ring-based chronology of the debris-flow activity on a large cone to shed light on sediment connectivity and better understand the coupling between the main debris-flow channel and a bedload river in this remote area under global climate change and glacial retreat. The 161 sampled trees demonstrated the appearance of 12 significant events over the last 65 years, with all of the events involving possible sediment input into the stream system of the Dolra River. These successional events, with a return interval of 5.4 years, have partially destabilized the fluvial system and locally induced a switch in the channel style to a braided channel. Surficial sedimentary characteristics, such as morphometric indices, have enabled the discrimination between sediments from the debris-flow activity and river dynamics (alluvium inputs). Finally, most of the reconstructed event-years are characterized by at least one month of above-average rainfall.