Coarse Debris Research Articles

A conceptual model for the formation of ramparts on Martian impact crater ejecta

Mars Orbiter Laser Altimeter (MOLA) elevation measurements for 23 different impact craters and 12 different long runout landslides show rampart ridges on Martian fluidized ejecta flows are higher relief than those on Martian landslides. We propose a conceptual model to explain this height difference that is based on the effects of the impact and ejecta emplacement process on the development of ejecta ramparts. Our model explains the relatively high relief of the distal ramparts as well as the particle size distribution that is inferred from thermal inertia measurements. In this model, impact events produce ejecta curtains that advance radially at increasingly higher velocity outward excavating and roughening the surface as they impact. This produces an inertia-driven, ground-hugging ejecta flow composed of primary and secondary ejecta. This flow moves rapidly across the surface following closely behind the impacting ejecta curtain. The ejecta curtain continuously adds impact-generated debris to the flow front that includes large particles, some of which are overridden by the flow, but some accumulate at the flow front. These particles are pushed forward at the flow front as a high-friction “dam” with the accumulating material growing into a relatively high rampart as the ejecta curtain adds more large particles to it. In addition, the impact-roughened surface cause substantial vibrations and shear in the flows moving behind the ejecta curtain. This roughness results in kinetic sieving in the flows that brings large particles to the surface and transports them to the flow front where some are also overridden or accumulate to add the ones already at flow front. We propose that these processes combine to produce the observed high ejecta ramparts. The relatively high velocity of the ejecta flows pushes the load of coarse-grained debris to the top of even high developing ramparts. When the flow halts, it drains back from the accumulated coarse debris at the flow front, leaving a high rampart dominantly composed of large particles.

Two stages of subsidence and its formation mechanisms in Mid-Late Triassic Ordos Basin, NW China

Based on a large number of newly added deep well data in recent years, the subsidence of the Ordos Basin in the Mid-Late Triassic is systematically studied, and it is proposed that the Ordos Basin experienced two important subsidence events during this depositional period. Through contrastive analysis of the two stages of tectonic subsidence, including stratigraphic characteristics, lithology combination, location of catchment area and sedimentary evolution, it is proposed that both of them are responses to the Indosinian Qinling tectonic activity on the edge of the craton basin. The early subsidence occurred in the Chang 10 Member was featured by high amplitude, large debris supply and fast deposition rate, with coarse debris filling and rapid subsidence accompanied by rapid accumulation, resulting in strata thickness increasing from northeast to southwest in wedge-shape. The subsidence center was located in Huanxian–Zhenyuan–Qingyang–Zhengning areas of southwestern basin with the strata thickness of 800–1 300 m. The subsidence center deviating from the depocenter developed multiple catchment areas, until then, unified lake basin has not been formed yet. Under the combined action of subsidence and Carnian heavy rainfall event during the deposition period of Chang 7 Member, a large deep-water depression was formed with slow deposition rate, and the subsidence center coincided with the depocenter basically in the Mahuangshan–Huachi–Huangling areas. The deep-water sediments were 120–320 m thick in the subsidence center, characterized by fine grain. There are differences in the mechanism between the two stages of subsidence. The early one was the response to the northward subduction of the MianLüe Ocean and intense depression under compression in Qinling during Mid-Triassic. The later subsidence is controlled by the weak extensional tectonic environment of the post-collision stage during Late Triassic.

Near-IR Spectral Observations of the Didymos System: Daily Evolution Before and After the DART Impact Indicates that Dimorphos Originated from Didymos

Ejecta from Dimorphos following the DART mission impact significantly increased the brightness of the Didymos–Dimorphos system, allowing us to examine subsurface material. We report daily near-IR spectroscopic observations of the Didymos system using NASA’s IRTF that follow the evolution of the spectral signature of the ejecta cloud over 1 week, from 1 day before the impact. Overall, the spectral features remained fixed (S-type classification) while the ejecta dissipated, confirming that both Didymos and Dimorphos are constructed from the same silicate material. This novel result strongly supports binary asteroid formation models that include the breaking up of a single body due to rotational breakup of kilometer-wide bodies. At impact time +14 and +38 hr, the spectral slope decreased, but the following nights presented an increasing spectral slope that almost returned to the preimpact slope. However, the parameters of the 1 μm band remained fixed, and no “fresh”/Q-type-like spectrum was measured. We interpret this as follows. (1) The ejecta cloud is the main contributor (60%–70%) to the overall light during the ∼40 hr after impact. (2) Coarser debris (≥100 μm) dominated the ejecta cloud, decreasing the spectral slope (after radiation pressure removed the fine grains ≤10 hr after impact). (3) After approximately 1 week, the ejecta cloud dispersed enough to make the fine grains on Didymos’s surface the dominant part of the light, increasing the spectral slope to the preimpact level. (4) A negligible amount of nonweathered material was ejected from Dimorphos’s subsurface, suggesting that Dimorphos was accumulated from weathered material ejected from Didymos’s surface.

Torrential Hazards’ Mitigation Measures in a Typical Alpine Catchment in Slovenia

Different sediment-related disasters due to torrential hazards, such as flash floods, debris flows, and landslides, can occur in an Alpine torrential catchment. When protecting infrastructure and human lives, different structural and non-structural protection measures can be used to mitigate permanent and future risks. An overview of the mitigation measures constructed near the Krvavec ski resort in northwest Slovenia (Central Europe) is presented. In May 2018, an extreme debris flood occurred in this area, causing significant economic damage. After the May 2018 event, different field investigations (i.e., geological and topographic surveys) and modeling applications (e.g., hydrological modeling, debris flow) have been conducted with the purpose of preparing the required input data for the design of protection measures against such disasters in future—due to climate change, more disasters are expected to happen in this torrential watershed. The mitigation includes the restoration of local streams, the construction of a large slit check dam for sediment retention, the construction of several smaller check dams and the construction of 16 flexible net barriers with an estimated ~8000 m3 retention volume for controlling in-channel erosion in steep torrential streams. Additionally, in order to observe and monitor potential future extreme events, an extensive monitoring system has been established in the investigated area. This monitoring system will cover measurements of flexible net corrosion, the estimation of concrete abrasion at check dams, periodical geodetic surveys using small drones (UAV), hydro-meteorological measurements using rainfall gauges and water level sensors. The recent extreme floods of August 2023 also hit this part of Slovenia, and this combination of technical countermeasures withstood the event and prevented large amounts of coarse debris from being transported to the downstream section and devastating infrastructure, as was the case in May 2018 during a less extreme event. Therefore, such mitigation measures can also be used in other torrential catchments in the Alpine environment.

Clay mineral and Nd, Pb, and Sr isotope provenance of a MIS 4-3 sediment record from the Lomonosov Ridge, central Arctic Ocean

Modern techniques for detrital mineral provenance were applied to sediment core 96/12-1pc from the Lomonosov Ridge in the central Arctic Ocean. The techniques include quantitative clay mineralogy analysis combined with determination of Nd, Pb, and Sr isotopes from clay fraction. The clay mineral assemblage and the isotope signatures depict distinct changes during the Marine Isotope Stage (MIS) 4-3 transition corresponding to the Middle Weichselian deglaciation. This transition is characterised by a homogenous, 48 cm thick, dark grey, silty clay layer with a distinctive IRD concentration, forming a prominent marker bed for the central Arctic Ocean sediments. The elevated smectite and kaolinite contents in the transitional interval are possible weathering products of the Siberian basaltic rocks, such as the Putorana Plateau, feeding the shelves of the Kara Sea and the western Laptev Sea. The Nd and Sr isotope values are compatible with input from the basaltic rocks and fall within the isotopic range of sediments from these shelves. The abrupt changes in the Nd, Pb and Sr isotopic data from the distinct grey layer attributed to the MIS 4-3 transition likely mark a pronounced deglaciation event. An increase in coarse debris in the grey layer indicates a change in the sedimentation regime with a strong iceberg rafting component. This change may also be related to a sudden release of meltwater from a large ice-dammed lake in the northern Siberia.

Heat Transfer Analysis of Core Melt Contact with a CANDU Calandria

In a severe accident in a CANDU reactor, disassembly of the core could produce a bed of coarse debris at the bottom of the calandria that would eventually transition into a pool of molten corium. During this process, it may be possible for small amounts of molten core material to contact the calandria wall. The transient heat flow through a calandria wall suddenly contacted by molten Zr or corium is analyzed with a finite element model. Ablation of the wall at its inner surface and the temporary increase in heat flux through its outer surface are calculated for various boundary conditions. Model calculations are compared to observations of the ablation and temperature of a stainless steel plate sprayed by prototypic corium in the Cesium Aerosol Generation-4 or CAGE-4 experiment.

Steel Baffles as a Rockfall Protection Measure for Mountainous Urban Settings

A form of steel baffles, which is made of steel poles encased in concrete and embedded into the ground, are introduced in this article. This type of protective installation is to be located on previously identified/designed catchment at multiple levels up the hillslope to fence off large fallen boulders during landslides or rockfalls. These baffles are intended to serve as added-on protection to filter barriers (array of baffles) that have recently gained popularity as a means of filtering out coarse debris. The aforementioned protective devices are to be installed in strategic positions close to unstable rocks (noting that the velocity of impact can be much reduced at the upstream end of the rockfall trajectory). The proposed design involves only a simple hollow steel section, which is embedded into the ground. The installation process involves manually excavating a hole in the ground to accommodate the baffle, followed by backfilling with concrete. A straightforward calculation method, which is found on the established principles of structural dynamics and soil mechanics, has been developed to determine the section sizes and embedment depths for a given impact scenario. Based on the presented design procedure, a set of design charts have been developed for expediting the design and analysis process. The presented calculation methodology based on use of design charts have been validated by comparison with data generated by LS-DYNA simulations.

Hydrological, thermal and chemical influence of an intact rock glacier discharge on mountain stream water

Rock glaciers are the most prominent permafrost-related mountain landforms. This study investigates the effects of the discharge from an intact rock glacier on the hydrological, thermal and chemical dynamics of a high-elevation stream in the NW Italian Alps. Despite draining only 39 % of the watershed area, the rock glacier sourced a disproportionately large amount of discharge to the stream, with the highest relative contribution to the catchment streamflow occurring in late summer - early autumn (up to 63 %). However, ice melt was estimated to be only a minor component to the discharge of the rock glacier, due to its insulating coarse debris mantle. The sedimentological characteristics and internal hydrological system of the rock glacier played a major role in its capability to store and transmit relevant amounts of groundwater, especially during the baseflow periods. Besides the hydrological influence, the cold and solute-enriched discharge from the rock glacier significantly lowered the stream water temperature (especially during warm atmospheric periods) as well as increased the concentrations of most solutes in the stream. Furthermore, in the two lobes forming the rock glacier, different internal hydrological systems and flowpaths, likely driven by different permafrost and ice content, caused contrasting hydrological and chemical behaviours. Indeed, higher hydrological contributions and significant seasonal trends in solute concentrations were found in the lobe with higher permafrost and ice content. Our results highlight the relevance of rock glaciers as water resources, despite the minor ice melt contribution, also suggesting their potential, increasing hydrological importance in the light of climate warming.

The normal impact stiffness of a debris-flow flexible barrier

This paper proposes a normal oriented impact stiffness of a three-supporting cable flexible barrier under a small pretension stress to estimate the structural load behaviour, and employs two categories of small-scale debris flows (coarse and fine) to explore the stiffness evolution through physical model experiments with high-speed photography and load sensing. Results suggest that the particle-structure contact is essential to the normal load effect. Coarse debris flow performs more frequent particle-structure contact and exerts evident momentum flux, while fine debris flows with few physical collisions impart much smaller one. The middle-sited cable that receives only tensile force from vertical equivalent cable-net joint system exhibits indirect load behaviour. The bottom-sited cable shows high load feedback due to the sum of direct contact of debris flow and tensile forces. The relationship between impact loads and maximum cable deflections can be explained by power functions according to quasi-static theory. The impact stiffness is not just affected by the particle-structure contact but by the flow inertia and particle collision effect. Savage number Nsav and Bagnold number Nbag manage to depict the dynamical effects on the normal stiffness Di. Experiments indicate that Nsav has positive linear correlation with the nondimensionalization of Di, whilst Nbag has positive power correlation with the nondimensionalization of Di. This idea is an alternative scope for the study on flow-structure interaction and may contribute to the parameter identification in numerical simulation of the debris flow-structure interaction and the optimization of the design standardization.

UNDERWATER CANYONS OF THE SOUTHWESTERN OUTSKIRTS OF SOUTHERN BAIKAL AS PRESUMABLE TRANSITERS OF TECHNOGENIC MATERIALS TO THE ABYSSAL SURFACE

Numerous publications by domestic and foreign authors deal with a significant role of underwater canyons in transit of loose material from the littoral to the abyssal surfaces of the seas. Lake Baikal fully corresponds in its hydrodynamic and bathymetric parameters to sea water basins, and the Baikal canyons are similar in their morphological and morphometric factors to sea canyons. A digital elevation model of the southwest underwater tip of the lake, generated based on a large array of bathymetric data, allowed identifying clearly defined valleys of the Shamanka and Slyudyanka canyons. The data obtained during the study of the canyon-valley area, carried out using special geophysical measuring instruments – Kongsberg EM710S multibeam echosounder and Knudsen CHIRP 3260 profilograph, – and analysis of the published materials showed a rather high degree of confindness of coarse debris to the canyon valleys and alluvial fans which implies their significant role in sediment transit. It has been shown that high seismicity of the Baikal basin and active wave conditions give rise to the formation of movable loose sediment masses and to the occurrence of gravity flows in the canyon valleys. Climate changes over the last decades contribute also to permafrost decomposition in the Baikal basin and to new-sediment transport into the lake. It is implied that an intensive development of the coastline leads to the coastal accumulation of a large amount of industrial and municipal contaminants which can move through the canyons to different distances into the lake water area. To date, there is no definite answer to the question about an actual role of underwater canyons in the transit of technogenic wastes to the abyssal lake surface. This requires organized large-scale specialized fieldwork with the use of high-precision geological-geophysical measuring instruments, and systematic sampling and thorough analysis of the bottom material.

Sedimentation and geomorphology of the Ruoergai Basin outlet reach at the source of the Yellow River: Response to the late quaternary glacial debris flow damming events

Fluvial terraces in the source of the Yellow River suggest that Ruoergai Basin was connected with the lower reach after ∼10 ka, much younger than the uplift chronology of the Tibetan Plateau. In this study, the geomorphology and sedimentation of the Cairima–Ningmute River at the exit of the Ruoergai Basin were investigated. Combined with the optically stimulated luminescence dating of the sediments, the reconstructed fluvial geomorphology processes are as follows: During ∼50–20 ka, coarse debris such as moraines and glacial mudflows from the Anyemaqen Shan and Xiqing Shan were unloaded to the Maqu valley in the bottleneck reach of the Ruoergai Basin outflow, causing river blockage and lake formation in the upper Ruoergai Basin; during ∼20–12 ka, the headward erosion of the river accelerated from the downstream to the upstream and the barrier dam eroded, forming terraces; since ∼12 ka, the Yellow River has cut through the Ruoergai Basin and has developed two levels of terraces based on lacustrine sediments. Our results suggest that glacial debris flow from the Anyemaqen Shan extensively accumulated at the basin-canyon bottleneck during the last glacial period, and when the amount of sediment accumulation exceeded the amount of river erosion, damming events occurred. The glacial-interglacial cycles during the Quaternary might generate repeated damming and cut-through of the Ruoergai Basin. The Ruoergai Basin should be connected with the lower reach before ∼50 ka.

Evolution of sediment gravity flows in response to early Carboniferous subduction and closure of the West Junggar Basin, China

This study describes and characterises the spatial distribution and evolution of Carboniferous deep-water sediment gravity flows and their associated deposits in the West Junggar region of north-western China. It uses a combination of outcrop sections, cores and seismic profiles to define nine lithofacies associated with a different sediment gravity flow types, including turbidity currents, debris flows, hyperpycnal flows and supercritical flows. The subduction and closure of the remnant West Junggar Ocean basin demonstrated variable palaeogeographical characteristics and configurations during different periods of the Carboniferous. Fossil assemblages and zircon dating data indicate that the target strata have completely recorded the evolution of the Western Junggar remnant ocean in the Carboniferous. The basin evolution is divided into the stable ocean basin stage, the slow subduction and filling stage and the fast subduction and filling stage. Active faulting and varying slope gradients affected the occurrence and types of sediment gravity flows during each stage. Tectonic and seismic activities associated with subduction caused continental slope instabilities and basinward transport of sediment by gravity flows with active faults on the continental slope triggering sediment gravity flows. At the beginning of subduction, the ability of gravity flows to transport coarse debris was limited owing to the shallow gradient of the continental slope. Sediment transport via gravity flows was dominated by sandy debris flows, muddy debris flows, turbidity currents and less frequent flood-controll3ed hyperpycnal flows. As the basin entered the fast subduction and filling stage, the slope gradient steepened and the frequency of active thrust faulting increased, which triggered high-density turbidity currents and supercritical flows. Additionally, the warm and humid paleoclimate led to the development of hyperpycnal flows during the fast-filling stage. This study demonstrates the importance of understanding the character and distribution of sediment gravity flows and associated deposits, especially, the implications for the hydrocarbon industry.

Simulating two-phase debris flows in HEC-RAS at Hummingbird Creek, British Columbia, Canada

Debris flows are typically modelled as a single homogeneous surge due to lack of data to support more complex model development and due to lack of time and funding for the practitioner and the communities they aim to support. Coarse debris flows are typically characterized by a coarse front, followed by a muddy slurry, that is then followed by a hyperconcentrated flow phase with lesser sediment concentrations. Presented herein is the modelling for a debris flow hazard assessment for Hummingbird Creek, British Columbia, Canada. Model calibration best matched the observed debris flow deposit when the coarse front and hyperconcentrated flow were modelled separately in two phases allowing for separate flow rheologies to be used for the front and the tail of the debris flow, and allowing for deposition between phases. Further research is needed to understand when simulation of two-phase flow may be most representative, particularly when no calibration data is available.

Effects of the coupling between slope morphology and bottom currents on flow erosion and sedimentation at the Dongsha Continental Margin, South China Sea

Abstract The Dongsha Continental Margin (DCM) projects seaward and is situated in the path of bottom currents coming through the only deep-water exchange passage, the Luzon Strait between the South China Sea (SCS) and the western Pacific Ocean. This provides an opportunity to observe the different interaction between the two wings of the convex margin and the bottom currents, and help understand the corresponding implications for provenance, debris transportation, and sedimentation in such an environment. The convexity of the DCM causes its eastern flank to shrink against upcoming bottom currents and internal solitary waves (ISWs), producing a funneling effect and forming strong erosion grooves or strips, remnant seamounts, and large seafloor coarse debris dunes. The concavity of the western flank induces the expansion of bottom currents that flow around the plateau, resulting in a depositional zone with weak erosion that mainly interacts with bottom currents and gravity flow. The strong erosion on the DCM caused by the bottom current forms the primary provenance of the deep-water environment, while the nepheloid layer that entraps the fine debris of the gravity flow that derives from Taiwan and that is transported by the bottom current is the secondary provenance. The different coupling patterns between the bottom currents and the two flanks determine the different modes of debris transportation and deposition. Debris eroded by the currents is mainly transported by the gravity flow on the eastern flank while sweeping of the outer shelf and upper slope by eddy currents, progradation of the gravity flow, and reworking by the bottom current mainly occur on the western flank. Two types of morphological breaks, namely, continental slope break and bottom-current slope break, have developed on the DCM. They control the evolution of the flow regime of the multi-layer bottom currents and the gravity flow of the DCM as well as the effects of erosion and deposition. These two types of slope breaks are coupled and form an area in front of Dongsha Island with the highest deposition rate in the SCS.

Vegetal Undercurrents-Obscured Riverine Dynamics of Plant Debris.

Much attention has been focused on fine‐grained sediments carried as suspended load in rivers due to their potential to transport, disperse, and preserve organic carbon (OC), while the transfer and fate of OC associated with coarser‐grained sediments in fluvial systems have been less extensively studied. Here, sedimentological, geochemical, and biomolecular characteristics of sediments from river depth profiles reveal distinct hydrodynamic behavior for different pools of OC within the Mackenzie River system. Higher radiocarbon (14C) contents, low N/OC ratios, and elevated plant‐derived biomarker loadings suggest a systematic transport of submerged vascular plant debris above the active riverbed in large channels both upstream of and within the delta. Subzero temperatures hinder OC degradation promoting the accumulation and waterlogging of plant detritus within the watershed. Once entrained into a channel, sustained flow strength and buoyancy prevent plant debris from settling and keep it suspended in the water column above the riverbed. Helical flow motions within meandering river segments concentrate lithogenic and organic debris near the inner river bends forming a sediment‐laden plume. Moving offshore, we observe a lack of discrete, particulate OC in continental shelf sediments, suggesting preferential trapping of coarse debris within deltaic and neritic environments. The delivery of waterlogged plant detritus transport and high sediment loads during the spring flood may reduce oxygen exposure times and microbial decomposition, leading to enhanced sequestration of biospheric OC. Undercurrents enriched in coarse, relatively fresh plant fragments appear to be reoccurring features, highlighting a poorly understood yet significant mechanism operating within the terrestrial carbon cycle.

Characteristics of the Impact Pressure of Debris Flows

AbstractDebris flows are common geological hazards in mountainous regions worldwide. Predicting the impact pressure of debris flows is of major importance for hazard mitigation. Here, we experimentally investigate the impact characteristics of debris flows by varying the concentrations of debris grains and slurry. The measured impact pressure signal is decomposed into a stationary mean pressure (SMP) and a fluctuating pressure (FP) through empirical mode decomposition. The SMP of low frequency is caused by the thrusting of bulk flow while the FP of high frequency is induced by the collision of coarse debris grains, revealed by comparing the features of impact pressure spectra of pure slurries and debris flows. The peak SMP and the peak FP first increase and then decrease with the slurry density. The basal frictional resistance is reduced by the nonequilibrium pore‐fluid pressure for debris flows with low‐density slurry, which can increase the flow velocity and impact pressures. In contrast, the viscous flow of high‐density slurry tends to reduce the flow velocity. The peak SMPs are well predicted by the Bernoulli equation and are related to the hydrostatic pressure and Froude number of the incident flow. The peak FPs depend on the kinetic energy and degree of segregation of coarse grains. The maximum degree of segregation occurs at an intermediate value of slurry density due to the transition of flow regime and fluid drag stresses. Our results facilitate predicting the impact pressures of debris flows based on their physical properties.

Non-negligible role of dead organic matter in a rainforest remnant in Northeast Brazil

Abstract Dead organic matter represents an essential reservoir of carbon, especially that allocated in standing dead trees, coarse woody debris, and fine litter, playing a pivotal role in nutrient cycling and habitat provisioning. However, necromass is frequently disregarded in forest assessments. Here, we aimed to perform the first assessment of multiple necromass compartments in the Atlantic Forest of Northeast Brazil, providing a basis for future integrative studies related to necromass in this region. We registered 17 standing dead trees in 0.5 hectare and 239 logs of coarse woody debris. Necromass had 3.9 Mg.ha-1 of standing dead trees, 54.24 Mg.ha-1 of coarse woody debris and 7.2 Mg.ha-1 of litter. We indicate that standing dead trees and coarse debris were mostly in the intermediate and final stages of decomposition. Leaves were the dominant component of litter, and drier months had more litterfall. Finally, we highlight that assessing standing dead trees and coarse woody debris adds 25.6% on top of aboveground tree mass, improving information about organic matter storage in rainforest ecosystems. Our findings emphasize that the necromass compartment must be considered in forest assessments, also including small pieces of coarse woody debris, which could inform better practices of forest management.

Heinrich Stadial aridity forced Mediterranean-wide glacier retreat in the last cold stage

Throughout the last cold stage, the North Atlantic region was punctuated by abrupt climate shifts and atmospheric processes propagated their effects to adjacent continents. During Heinrich Stadials, the ocean was chilled by icebergs calved from the great ice sheets. The impact of multiple temperature and precipitation regime changes on Late Pleistocene mountain glaciers and landscape development is poorly understood. Here we analyse 1,118 cosmogenic exposure ages—spanning the last 100,000 years—from glacial landforms on three continents across the Mediterranean. We evaluate their geomorphological context and stratify the record by depositional setting and geographical region. The database includes 300 dated moraines. We show that, despite cold temperatures, Heinrich Stadial aridity caused negative glacier mass balance and repeatedly stalled glacier growth across the Mediterranean. In contrast, relatively warm and humid climates between Heinrich Stadials favoured positive glacier mass balance, resulting in region-wide glacier growth and moraine formation. Our analysis supports climate model simulations of repeated and widespread Heinrich Stadial aridity in the Mediterranean basin during the last cold stage. Heinrich Stadials also saw enhanced supply of coarse debris from valley sides. The cumulative geomorphological impact of these climate shifts saw the largest moraines form at the culmination of the glacial cycle. Mountain glacier growth around the Mediterranean repeatedly stalled during cold, dry Heinrich Stadials, according to an analysis of cosmogenic isotope-dated glacial landforms from across the region.

Polymer Identification and Specific Analysis (PISA) of Microplastic Total Mass in Sediments of the Protected Marine Area of the Meloria Shoals.

Microplastics (MPs) quantification in benthic marine sediments is typically performed by time-consuming and moderately accurate mechanical separation and microscopy detection. In this paper, we describe the results of our innovative Polymer Identification and Specific Analysis (PISA) of microplastic total mass, previously tested on either less complex sandy beach sediment or less demanding (because of the high MPs content) wastewater treatment plant sludges, applied to the analysis of benthic sediments from a sublittoral area north-west of Leghorn (Tuscany, Italy). Samples were collected from two shallow sites characterized by coarse debris in a mixed seabed of Posidonia oceanica, and by a very fine silty-organogenic sediment, respectively. After sieving at <2 mm the sediment was sequentially extracted with selective organic solvents and the two polymer classes polystyrene (PS) and polyolefins (PE and PP) were quantified by pyrolysis-gas chromatography-mass spectrometry (Pyr-GC/MS). A contamination in the 8–65 ppm range by PS could be accurately detected. Acid hydrolysis on the extracted residue to achieve total depolymerization of all natural and synthetic polyamides, tagging of all aminated species in the hydrolysate with a fluorophore, and reversed-phase high performance liquid chromatography (HPLC) (RP-HPLC) analysis, allowed the quantification within the 137–1523 ppm range of the individual mass of contaminating nylon 6 and nylon 6,6, based on the detected amounts of the respective monomeric amines 6-aminohexanoic acid (AHA) and hexamethylenediamine (HMDA). Finally, alkaline hydrolysis of the residue from acid hydrolysis followed by RP-HPLC analysis of the purified hydrolysate showed contamination by polyethylene terephthalate (PET) in the 12.1–2.7 ppm range, based on the content of its comonomer, terephthalic acid.

Mapping Soil Burn Severity at Very High Spatial Resolution from Unmanned Aerial Vehicles

The evaluation of the effect of burn severity on forest soils is essential to determine the impact of wildfires on a range of key ecological processes, such as nutrient cycling and vegetation recovery. The main objective of this study was to assess the potentiality of different spectral products derived from RGB and multispectral imagery collected by unmanned aerial vehicles (UAVs) at very high spatial resolution for discriminating spatial variations in soil burn severity after a heterogeneous wildfire. In the case study, we chose a mixed-severity fire that occurred in the northwest (NW) of the Iberian Peninsula (Spain) in 2019 that affected 82.74 ha covered by three different types of forests, each dominated by Pinus pinaster, Pinus sylvestris, and Quercus pyrenaica. We evaluated soil burn severity in the field 1 month after the fire using the Composite Burn Soil Index (CBSI), as well as a pool of five individual indicators (ash depth, ash cover, fine debris cover, coarse debris cover, and unstructured soil depth) of easy interpretation. Simultaneously, we operated an unmanned aerial vehicle to obtain RGB and multispectral postfire images, allowing for deriving six spectral indices. Then, we explored the relationship between spectral indices and field soil burn severity metrics by means of univariate proportional odds regression models. These models were used to predict CBSI categories, and classifications were validated through confusion matrices. Results indicated that multispectral indices outperformed RGB indices when assessing soil burn severity, being more strongly related to CBSI than to individual indicators. The Normalized Difference Water Index (NDWI) was the best-performing spectral index for modelling CBSI (R2cv = 0.69), showing the best ability to predict CBSI categories (overall accuracy = 0.83). Among the individual indicators of soil burn severity, ash depth was the one that achieved the best results, specifically when it was modelled from NDWI (R2cv = 0.53). This work provides a useful background to design quick and accurate assessments of soil burn severity to be implemented immediately after the fire, which is a key factor to identify priority areas for emergency actions after forest fires.