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Compilation of (a) the geochronology of the CAF system Guanillos since MIS 4 e including age estimates from CAF Mamilla e and its deduced evolution. Principally internal errors ( 10 Be exposure dating) or 1s-uncertainties (other methods) are shown for age constraints. The outliers (GUA-24, -58, -59, and -61) are not considered. (1) Mean ages were calculated from multiple age datings of the same depositional event (same layer). (b) Selected spectral, textural, and gravelometric proxies of post-depositional fan surface alteration plotted against age of the morphostratigraphic units; spectral: mean Pleiades spectral ratios R/B and NIR/B, textural: mean Vector Ruggedness Measure (VRM) for the nano-(l ¼ 45 cm) and micro-scale (l ¼ 195 cm), gravelometric (restricted to bright clasts of the fraction 39e256 mm, based on a-axes): geometric mean x
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Hyperarid coasts develop under relatively high air humidity and abundant sea salt aerosols, resulting in physical and chemical weathering processes that distinctly differ from those present in inland deserts. However, neither the geomorphic effects of the weathering processes nor the timescales on which they alter depositional surfaces are sufficie...
Citations
... Accelerated Holocene incision as a response to changing climate has been described for various Peruvian rivers (Abbühl et al., 2010;Viveen et al., 2019Viveen et al., , 2021. In addition, studies on alluvial fans in the United States, Spain, and Chile have shown that Holocene marine transgression may also have triggered incision in a fan (Harvey, 2002;Walk et al., 2022). In these cases, just like in Lima, the onshore fan gradient was steeper than the offshore gradient. ...
A complete, fluvial stratigraphic record for the last glacial period of the Western Andes in Peru is not available due to preservation issues and spatial variability in sedimentation. Deposits are typically restricted to incomplete records of fluvial terraces or localised occurrences of alluvial fans and landslides. These landforms are thought to have formed under a regime of climate cyclicity controlling increases in precipitation. Because of the fragmented preservation of these deposits, as well as dating uncertainties, it remains unclear if orbital climate cycles, such as the precession cycle, or suborbital cycles, such as the wet Heinrich events, are driving Andean sedimentation. In this paper, we try to answer this question through a sedimentological–stratigraphical analysis of a much more complete sedimentary sequence than usually found in the region. We present the results of a grain size analysis of 5000 clasts and 13 new luminescence ages of a 52‐m‐long, stratigraphic section of the Lima fluvial fan in Peru. Bayesian age–depth modelling resulted in a robust chronostratigraphic framework and derived sedimentation rates. The stratigraphic record registered sedimentation from 121.7 ± 4 to ka. Three major sedimentation periods occurred between 121.7 to , 87 ± 1 to , and to ka. These periods registered various unconformities and coarsening–fining upward sequences which chronologically correlate to suborbital pluvial periods, recognised from speleothems and lake records, that drove fluvial deposition. They also correlate with the timing of other recognised sedimentation events throughout the Western Andes. Marine regression resulted in fan progradation and not in incision. The Lima fan stratigraphy represents therefore the most complete, last glacial fluvial record for the Peruvian Western Andes to date and it highlights the potential of fluvial fans as recorders of suborbital climate variability.
... [ 8 , 9 ]), and larger-scaled landforms (e.g. Alluvial fans, [10] ) as well as landscapes (e.g. [11][12][13][14][15] ). ...
The U.S. Geological Survey (USGS) has published a guideline to improve the quality of digital photogrammetric reconstructions created with the widely used Agisoft Metashape Professional software. The suggested workflows aim at filtering out low-quality tie points from the tie point cloud to optimize the camera model. However, the optimization procedure relies on an iteratively performed trial-and-error approach. If manually performed, the time expenditure required from the operator can be significant and the optimization process can be affected by the degree of diligence that is applied.
To minimize the time expenditure and attentiveness required from the operator and to provide a framework for an improved reproducibility of camera model optimization workflows, we present here a python script serving as an extension for Agisoft Metashape Professional (tested on version 2.1.0) that automatizes the iterative point filtering procedure proposed by the USGS. As a result, the entire processing cycle can be performed largely unattended.
•A graphical user interface allows to individually adjust important camera model optimization parameters.
•Main tie point cloud quality measures can be directly assessed.
•The reproducibility of the automated camera model optimization as tested in this study generally is above 99%.
... Fuentes et al., 2022) and traces of humidity related surface alterations have been found (e.g. Walk et al., 2022) even under such life-threatening conditions. These environments allow the study of life and surface evolution and potential relationships under extreme water limitation (Dunai et al., 2020). ...
The importance of water vapor in arid and hyperarid regions motivates a comparative study in the Atacama and Namib deserts, a natural laboratory to test the role of topography in present-day climate. Based on ERA5 reanalysis evaluated by satellite and ground-based instruments, we focus on the climatological water vapor seasonal cycle and interannual variability offshore the deserts, distinguishing between the free troposphere (FT) and the marine boundary layer (MBL) moisture. In the Namib, moisture variability is strongly controlled by air mass transport. For example, between austral fall and winter, an easterly continental warm and cloud-free air mass settles over the coast, reducing the MBL height to a few hundred meters and decreasing humidity. In summer, the easterly winds are also present, bringing moisture from the center of the continent to the FT of the Namib, along with clouds and rainfall. This feature is intensified during the cold phase of ENSO (La Niña). In contrast, the Andean Cordillera blocks any air mass exchange between the continent and the MBL, allowing the development of stable southerly winds along the coast that transport cold air over warmer waters due to the early westward turn of the Humboldt Current. This induces a strong coupling between SST and MBL moisture, which is enhanced by a permanent stratocumulus cloud cover. In addition, the FT remains drier than the Namib for most of the year due to the predominance of westerly dry air in the region. ENSO is not correlated with the MBL moisture offshore Atacama, and it is the local SST that plays a major role in modulating interannual moisture variability. Only in winter, ENSO seems to impact the FT by increasing the moisture transport from the mid-latitudes during the warm phase (El Niño). We hypothesize that the differences in moisture seasonality and its controlling mechanisms are strongly related to differences in topography and the resulting circulation patterns. Furthermore, similar moisture transport and variability may have been part of a Paleo-Atacama when its topography was similar to the present-day Namib Desert.
... One of the most important soil components is clay fraction which is considered the finer part of soil fractions with an average diameter of less than 0.002 mm, and because of this size it possesses a higher specific surface area and according to that clay exhibits as a most active fraction with or without organic matter (Walk et al., 2022). The results in Table 6 showed the percentage of clay minerals in studied soil pedons which display that montmorillonite (from the smectite group) is the dominant clay mineral that belongs to 2:1 clay minerals (phyllosilicates) which ranged between (38-45)%, followed by mica ranged (23-32) % followed by chlorite (15-18)% followed by kaolinite (1:1) ranged (9-12)% followed by less mineral content Mica-Smectite mixed layer which ranged (2-7)%, these results support the assumption of the activity of chemical weathering in this area where the stages of weathering include the transformation of mica minerals to montmorillonite passing in the middle stage of weathering which is the formation of interstratified mixed layer minerals (Kalinin et al., 2021;Rozanov et al., 2017;Yousefifard et al., 2015). ...
A 59 km2 area of soil transect called Al-Band Hills in the eastern part of Misan governorate, south of Iraq was studied. The objective of this study was to understand the behavior of minerals and features of chemical weathering in the transect area soils that developed on fluvial and water-loaded sediments, to fulfill this objective, three soil pedons were selected one of them at the top of Hills and second in the middle and third Pedon in the bottom of the Hill. The results showed that Al-Band Hills located in semi-arid soils in the east of Misan governorate, south of Iraq are characterized by a low and middle intensity of chemical weathering. In an alkaline environment according to its carbonate minerals richness, with a low amount of precipitation, the intensity, and type of silicate minerals weathering is restricted not only by the climate but by the chemical conditions of the soil solution. According to this study's findings, the intensity of weathering of present soil pedons is mostly inherited from the parent rocks which is transferred by the action of water movement from northern areas from Turkey and Iran which belongs to the Quaternary. This study will give clear sights into the geomorphological and geochemical processes that happen in studied soils in semi-arid regions and show the possibility of using weathering features in carbonate and alkali sediments.
... Furthermore, the environmental conditions at the coast significantly differ from those further inland due to the direct vicinity to the sea acting as a source of moisture and minerals. In case of the Atacama Desert, the coast receives precipitation up to one order of magnitude higher than the interior (Houston, 2006;Fick and Hijmans, 2017), and is characterized by a higher air humidity and more frequent occurrence of fog events (Cereceda et al., 2002(Cereceda et al., , 2008Schween et al., 2020;Walk et al., 2022), which enables the growth of specially adapted Loma vegetation (Schulz, 2009;Schulz et al., 2011). In addition, the coast receives much more atmospheric salts mainly due to sea spray (Rech et al., 2003;Wang et al., 2014). ...
... In addition, the coast receives much more atmospheric salts mainly due to sea spray (Rech et al., 2003;Wang et al., 2014). Accordingly, Walk et al. (2022) showed that the processes and rates of weathering are specific for the coast and comprise the formation of weathering rinds and clast breakdown dominantly by salt weathering. This ultimately results in fully developed desert pavements on a Late Pleistocene timescale. ...
... Coastal Cliff, which presents the prominent western flank of the Coastal Cordillera, a narrow, mostly ~1 to ~3 km wide coastal plain hosts a lowaltitude environment characterized by distinct climatic and geomorphological processes (e.g., Cereceda et al., 2008;Hartley et al., 2005;Walk et al., 2020Walk et al., , 2022. To investigate the processes and timescales of soil formation in a coastal desert environment, we selected a single, laterally unconfined CAF located in the western south-central Atacama Desert, ~2 km south of the small town Paposo (25.03 • S/70.47 • W). ...
... The depositional landforms primarily respond to external forcings (e.g., tectonics, climate, and base-level change) that typically dominate the evolution of alluvial fans (Waters et al., 2010;Fidolini et al., 2013;Davis et al., 2021). Mapping and dating alluvial fans are critical to disentangle the response of geomorphic evolution to external forcings and highlight the need for analytical tools that can quickly determine the spatial distributions and the relative ages of different morphostratigraphic units (Stock et al., 2013;Harvey, 2018;Walk et al., 2022). Among techniques that have been used for such purpose, remote sensing techniques (Frankel and Dolan, 2007;Zhang and Guo, 2013;Regmi et al., 2014;D'Arcy et al., 2018;Su et al., 2020a) and in-situ dating techniques (Le Béon et al., 2010Béon et al., , 2012Porat et al., 2010;Duehnforth et al., 2017) are the most promising. ...
... Among techniques that have been used for such purpose, remote sensing techniques (Frankel and Dolan, 2007;Zhang and Guo, 2013;Regmi et al., 2014;D'Arcy et al., 2018;Su et al., 2020a) and in-situ dating techniques (Le Béon et al., 2010Béon et al., , 2012Porat et al., 2010;Duehnforth et al., 2017) are the most promising. Previous studies have shown that the extent of alluvial fans can be mapped by morphological parameters (e.g., surface texture, surface relief, and gravel size) (Frankel and Dolan, 2007;Regmi et al., 2014;Brooke et al., 2018;D'Arcy et al., 2018;Purinton and Bookhagen, 2020;Walk et al., 2022). In particular, surface roughness is a universal time-dependent geomorphic feature within arid environments that decreases when there are no perturbations (e.g., hydrological events) that renew the alluvial fan surface (Frankel and Dolan, 2007;Regmi et al., 2014). ...
... Such datasets can capture fine features of alluvial surfaces at the meters to centimeters scale (Frankel and Dolan, 2007;Haas et al., 2014;Mushkin et al., 2014;Regmi et al., 2014), but the cost to obtain high-resolution data is high, especially over large areas (i.e., tens of kilometers) (Schwendel and Milan, 2020). (b) Spectral characterization from multispectral satellite images is also a powerful index to map alluvial fans in hyperarid regions based on surface mineralogy (Meer et al., 2014;D'Arcy et al., 2018;Walk et al., 2022). However, it requires either the calibration of ground measurements or high-resolution satellite images with a spatial resolution of meters (Walk et al., 2022). ...
Despite recent advances in mapping and dating alluvial fans, due to the availability of high-resolution remote sensing data and Quaternary dating techniques, quantifying surface features in remote sensing data remains a challenge. Surface roughness is a time-dependent feature under stable conditions, which indicates the relative age of alluvial fans in a hyperarid environment. Although surface roughness can be quantitatively inferred from remote sensing data, determining surface roughness in a uniform index remains a complex problem. Here, we used the normalized backscatter intensity (NBI) from high-resolution ALOS PALSAR data to quantify alluvial fan surface roughness, which is further used to quantitatively map alluvial fans. We established a robust power-law relation between the NBI value (R) and the in-situ age (T) as measured with independently dated alluvial fans. Based on the R-T relation, it can be further to apply the R measurement to T estimates as old as ∼540 ka with an average uncertainty of ∼25% on a regional scale. The NBI value, independent of atmospheric conditions and sensitive to surface roughness variability, is an effective criterion for quickly distinguishing alluvial fans and performing age estimation. We propose that insolation weathering is an important physical weathering pattern in the Dead Sea area, which mainly controls the surface roughness in this hyperarid region.
Debris flows typically originate in mountainous watersheds. At the base of these watersheds and where not truncated by a higher order stream or discharging into a body of still water, repeated debris-flow deposition often forms semi-conical debris-flow fans. To mitigate debris-flow hazards, it is important to identify debris flow-prone watersheds and to understand their dynamics. This chapter reviews the morphology, sedimentology and dynamics of debris-flow watersheds and associated fans. Debris flow-generating watersheds are generally smaller and steeper than those dominated by floods and debris floods, and host less well-developed drainage networks. They can be roughly categorized into transport-limited systems (in which each hydroclimatic event producing high discharge triggers debris flows due to an abundance of sediment and high recharge rates) or supply-limited systems (in which debris-flow activity is limited by sediment availability and corresponding slow recharge rates). Debris-flow fans have typical lengths of 0.5–10 km and slopes of 5–15° and develop through spatio-temporal shifts of the locus of deposition through avulsion. Their surface topography and stratigraphy consist of stacked and amalgamated lobe, levee, and channel deposits, with sediment of mud to boulder grade. They provide archives of past flow processes and sediment supply indicative of past climate and environmental change. However, our ability to interpret debris-flow successions is still limited by relatively poor knowledge of how catchment geology and flow properties and composition affect resulting depositional features, from bed scale to fan scale. Recent field-based, experimental, and numerical advances on these topics are starting to fill this knowledge gap.
Soils in hyper‐arid climates, such as the Chilean Atacama Desert, show indications of past and present forms of life despite extreme water limitations. We hypothesize that fog plays a key role in sustaining life. In particular, we assume that fog water is incorporated into soil nutrient cycles, with the inland limit of fog penetration corresponding to the threshold for biological cycling of soil phosphorus (P). We collected topsoil samples (0–10 cm) from each of 54 subsites, including sites in direct adjacency (<10 cm) and in 1 m distance to plants, along an aridity gradient across the Coastal Cordillera. Satellite‐based fog detection revealed that Pacific fog penetrates up to 10 km inland, while inland sites at 10–23 km from the coast rely solely on sporadic rainfall for water supply. To assess biological P cycling we performed sequential P fractionation and determined oxygen isotope of HCl‐extractable inorganic P (d18O_HCl-Pi). Total P (P t ) concentration exponentially increased from 336 mg kg ⁻¹ to a maximum of 1021 mg kg ⁻¹ in inland areas ≥10 km. With increasing distance from the coast, soil d18O_HCl-Pi values declined exponentially from 16.6‰ to a constant 9.9‰ for locations ≥10 km inland. Biological cycling of HCl-Pi near the coast reached a maximum of 76%–100%, which could only be explained by the fact that fog water predominately drives biological P cycling. In inland regions, with minimal rainfall (<5 mm) as single water source, only 24 ± 14% of HCl‐P i was biologically cycled. We conclude that biological P cycling in the hyper‐arid Atacama Desert is not exclusively but mainly mediated by fog, which thus controls apatite dissolution rates and related occurrence and spread of microbial life in this extreme environment.
Reservoirs have become an important component in the worldwide river sediment flux. Reservoirs prevent downstream sediment transport and have become a major sediment sink. In this study, sediment deposition during the last 115 years in the Urft Reservoir in western Germany is reconstructed. The Urft Reservoir is the oldest reservoir in the Eifel Mountains and was almost completely drained in 2020. This enabled a detailed mapping of the lake bottom using an unmanned aerial system and the computation of a high-resolution digital surface model. Topographic maps with a nominal resolution of 1:1000 from the time prior to the construction of the dam (around 1900) were used to construct a pre-reservoir elevation model. A digital elevation model of difference (DoD) was calculated from these two datasets for the reservoir floor (0.72 km²). Based on the DoD, a net sediment accumulation of 1.16 × 10^6 m³ was calculated alongside a propagated volume error of 6.91 × 10^5 m³, resulting in a mean accumulation of 1.54 m. Conservative vertical error propagation results in an average level of detection (LoD) of 1.8 m. In contrast, the comparison of the DoD with 47 cores in the upper part of the reservoir showed a mean difference of −0.11 m, indicating a high, independently assessed accuracy of the DoD. Three depositional hotspots were identified in the reservoir. One is close to the Urft dam where very fine sediments are draped across the pre-reservoir topography. Two areas are related to reservoir management. Sediment deposition in the Urft Reservoir has been comparably low in comparison to other regions globally, resulting in a 3.25% ± 1.93% loss of reservoir volume between 1905 and 2020. To analyse the effect of strong flooding events, a subset of the reservoir was analysed after an extreme event in July 2021, but accumulation did almost entirely not exceed the LoD.
