A terrestrial brine-seepage analog for Martian slope streaks near Salar de Pedernales in the Atacama Desert, Chile

Martian slope streaks are elongated down-slope, low-albedo surface features that currently form within sub-annual time scales in the high-albedo (“dusty”) regions of equatorial Mars. These km-scale streaks, which can persist up to several decades on the Martian surface, present one of the most enigmatic and dynamic suites of active surface features on present-day Mars. Two categories of explanations remain in debate regarding their nature: 1) “Dry” formation models, in which surface darkening is associated with mass wasting processes, such as dust avalanches; and 2) “Wet” formation models, in which surface darkening is associated with transient wetting of the surface by either seepage of sub-surface brines or deliquescence of atmospheric moisture. Here, we report recently discovered dark slope streaks that occur in the high Atacama Desert in Chile and display a close geomorphic resemblance to the Martian streaks. Field examination of the Atacama slope streaks revealed that they formed through down-slope seepage of groundwater brines sourced from the Salar de Pedernales located 500 m away. Chemical and mineralogical analyses demonstrate that salts deposited from the Pedernales brines combined with detrital input from soils/dust are responsible for surface darkening in the Atacama case. Field-based spectral measurements in the 0.4-2.5 micron wavelength range compare to those obtained from orbit for the Martian slope streaks. In addition, high-resolution topography derived from drone imagery revealed that the Atacama streaks are rougher than their surroundings at the decimeter-scale roughness of the entire hillslope they occur on. A similar distinction was previously established between Martian slope streaks and their surrounding slopes, although on Mars these roughness variations appear to occur at lower-range sub-centimeter scales. Our study of the unique Atacama slope streaks may support “wet” formation as a viable hypothesis for some of the Martian slope streaks.Fil: Mushkin, Amit. Geological Survey of Israel; IsraelFil: Sletten, Ronal. University of Washington; Estados UnidosFil: Trombotto, Dario Tomas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Jigjidsurengiin, Batbaatar. University of Washington; Estados UnidosFil: Amit, Rivka. Geological Survey of Israel; IsraelFil: Halevy, Itay. Weizmann Institute Of Science.; IsraelFil: Morag, Navot. Geological Survey of Israel; IsraelFil: Gillespie, Alan R.. University of Washington; Estados UnidosThe Geological Society of America: Connects 2021OregonEstados UnidosThe Geological Society of Americ

Toward the detection of permafrost using land-surface temperature mapping

Permafrost is degrading under current warming conditions, disrupting infrastructure, releasing carbon from soils, and altering seasonal water availability. Therefore, it is important to quantitatively map the change in the extent and depth of permafrost. We used satellite images of land-surface temperature to recognize and map the zero curtain, i.e., the isothermal period of ground temperature during seasonal freeze and thaw, as a precursor for delineating permafrost boundaries from remotely sensed thermal-infrared data. The phase transition of moisture in the ground allows the zero curtain to occur when near-surface soil moisture thaws or freezes, and also when ice-rich permafrost thaws or freezes. We propose that mapping the zero curtain is a precursor to mapping permafrost at shallow depths. We used ASTER and a MODIS-Aqua daily afternoon land-surface temperature (LST) timeseries to recognize the zero curtain at the 1-km scale as a "proof of concept. " Our regional mapping of the zero curtain over an area around the 7000 m high volcano Ojos del Salado in Chile suggests that the zero curtain can be mapped over arid regions of the world. It also indicates that surface heterogeneity, snow cover, and cloud cover can hinder the effectiveness of our approach. To be of practical use in many areas, it may be helpful to reduce the topographic and compositional heterogeneity in order to increase the LST accuracy. The necessary finer spatial resolution to reduce these problems is provided by ASTER (90 m).Fil: Batbaatar, Jigjidsurengiin. University of Washington; Estados UnidosFil: Gillespie , Alan R.. University of Washington; Estados UnidosFil: Sletten, Ronald S.. University of Washington; Estados UnidosFil: Mushkin , Amit. University of Washington; Estados UnidosFil: Amit, Rivka. Geological Survey Of Israel; IsraelFil: Trombotto, Dario Tomas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Liu , Lu. University of Washington; Estados UnidosFil: Petrie, Gregg. University of Washington; Estados Unido

A terrestrial brine-seepage analogue for Martian slope streaks near Salar de Pedernales in the Chilean Atacama desert

Martian slope streaks are elongated down-slope, low-albedo surface features that currently form within sub-annual time scales in the high-albedo (dusty) regions of equatorial Mars. These km-scale streaks, which can persist up to several decades on the Martian surface, present one of the most enigmatic and dynamic suites of active surface features on present-day Mars. Two categories of explanations remain in debate regarding their nature: 1) Dry formation models, in which surface darkening is associated with mass wasting processes, such as dust avalanches; and 2) Wet formation models, in which surface darkening is associated with transient wetting of the surface by either seepage of sub-surface brines or deliquescence of atmospheric moisture. Here, we report recently discovered dark slope streaks that occur in the high Atacama Desert of Chile and display a close geomorphic resemblance to the Martian streaks. Field examination of the Atacama slope streaks revealed that they formed through down-slope seepage of a groundwater brine sourced from the Salar de Pedernales located 500 m away. Chemical and mineralogical analyses demonstrate that salts deposited from the Pedernales brines combined with detrital input from soils/dust are responsible for surface darkening in the Atacama case. Field-based spectral measurements in the 0.4-2.5 micron wavelength range and high-resolution topography derived from drone imagery compare between the spectral and textural characteristics of the Martian and Atacama streaks. Our study of these unique terrestrial streak analogs supports the wet formation hypothesis as a viable hypothesis for some of Martian slope streaks.Fil: Mushkin, Amit. Geological Survey Of Israel; Israel. University of Washington; Estados UnidosFil: Sletten, Ronal. University of Washington; Estados UnidosFil: Trombotto, Dario Tomas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Batbaatar, Jigjidsurengiin. University of Washington; Estados UnidosFil: Amit, Rivka. Geological Survey Of Israel; IsraelFil: Halevy, I.. Weizmann Institute of Science; IsraelFil: Morag, N.. Geological Survey Of Israel; IsraelFil: Gillespie, Alan R.. University of Washington; Estados UnidosConferencia de la Sociedad Geológica y la Asociación Israelí de RecursosJerusalemIsraelIsrael Geological Societ

Frequency of boulders transport during large floods in hyperarid areas using paleoflood analysis: an example from the Negev desert, Israel

Tuesday, 12 October 2021Direct measurements of boulder entrainment in desert wadis are not available. The 2004 flood (peak discharge - 470 m3 s-1; recurrence interval - 120 years) in the hyperarid, ungauged Nahal Hatzera, ephemeral stream (45 km2 ), in the Negev Desert, transported and deposited 0.85-1.5 m concrete boulders and slabs detached from infrastructure upstream and natural boulders. EDM and drone air-photographic surveys documented the geometry of the study reach and the location of boulders. Analyses of flood slackwater deposits established a paleoflood record of 23 floods with peak discharges of 200-760 m3 s-1, during the last 600 years. 1-D HEC-RAS hydraulic analysis provided water surface profiles, discharges and hydraulics, long the study reach and velocity, shear stress and stream power for each boulder. MAX program and Pearson 3 distribution were used for flood frequency analysis. Most of the concrete boulders were deposited in the sub-critical backwater of channel constrictions where velocities were 1.5-2.1 m s1. The largest boulders were deposited in super-critical flow where velocity was 8-9.2 m s-1. The alluvial channel enables to transport these concrete boulders, reflecting the unstable, active sandy layer of the channel bed over which the boulders moved. The maximum flood shear stress and stream power characterize medium-large floods with return period of 20-120 years and not for the largest floods, as expected. Boulders <2.1 m and weighing <15 tonnes can be transported at least once in 120 years. The shear stress and stream power indicate that the moderate-large floods are the most geomorphically effective floods rather than the largest floods in Nahal Hatzera basin. Nevertheless, the 'geomorphic effectiveness' of the 2004 flood ¿ a typical desert flash flood, was small based on the minor changes along the channel and banks indicating that their resistance thresholds were not exceeded and energy expenditure was mainly on boulders entrainment and transport

Linking coarse silt production in asian sand deserts and quaternary accretion of the Chinese Loess Plateau

The Chinese Loess Plateau (CLP) is a large, spatially well defined and persistent zone of loess accumulation developed near the fluctuating northwest margin of the East Asian monsoon. Many studies have analyzed its loess sediments to provide insights into paleoclimatic conditions. Although spatial and temporal variations in the grain sizes of CLP sediments are fundamental to this effort, controversy over the origin of the dominant coarse quartz silt has limited interpretations. Reexamination of the spatial pattern of grain-size distribution across the CLP and a field-scale experiment conducted in the Gobi Desert revealed a genetic association between the coarse silt fraction of the loess and primary production of coarse silt through eolian abrasion of sand in the proximal Mu-Us, Tengger, and Badain Jaran sandy deserts. Our results demonstrate the effectiveness of eolian abrasion of quartz sand in primary coarse silt production in Central Asia and identify this process as the most consistent with the well-recognized systematic northwest-southeast depositional pattern of the CLP. We suggest that only abraded coarse quartz grains transported short distances by long-term persistent eolian activity can build up thick loess sequences to form a massive and spatially well defined loess plateau. These results decouple the production and transport of coarse silt and finer silt and clay particles, which have a more distant and wider provenance, changing the constraints on previous paleoclimatic reconstructions.</p

Frequency of boulders transport during large floods in hyperarid areas using paleoflood analysis – An example from the Negev Desert, Israel

Direct measurements of boulder entrainment in desert wadis are not available. The 2004 flood (peak discharge – 470 m s; recurrence interval – 120 years) in the hyperarid, ungauged Nahal Hatzera ephemeral stream (45 km), transported and deposited 0.85–2.1 m concrete boulders and slabs detached from infrastructure upstream and natural boulders. EDM and drone air-photographic surveys documented the geometry of the study reach and the location of boulders. Analyses of flood slackwater deposits established a paleoflood record of 23 floods with peak discharges of 200–760 m s, during the last 600 years. 1-D HEC-RAS hydraulic analysis provided water surface profiles, discharges and hydraulics, along the study reach and velocity, shear stress and stream power for each boulder. MAX program and Pearson 3 distribution were used for flood frequency analysis. Most of the concrete boulders were deposited in the sub-critical backwater of channel constrictions where velocities were 1.5–2.1 m s. The largest boulders were deposited in super-critical flow where velocity was 8–9.2 m s. The alluvial channel enabled to transport these concrete boulders, reflecting the unstable, active sandy layer of the channel bed over which the boulders moved. The maximum flood shear stress and stream power characterize medium-large floods with return period of 20–120 years and not for the largest floods, as expected. Boulders about 2.1 m and weighing about 15 t can be transported at least once in 120 years. The shear stress and stream power indicate that the moderate-large floods are the most geomorphically effective floods rather than the largest floods in Nahal Hatzera basin. Nevertheless, the ‘geomorphic effectiveness’ of the 2004 flood – a typical desert flash flood with high peak and short duration, was small based on the minor changes along the channel and banks indicating that their resistance thresholds were not exceeded and energy expenditure was mainly on boulders entrainment and transport.The authors wish to thank the Royal Geographical Society Thesiger-Oman International Fellowship UK, for fund no. THES03/16, to P.A

Linking coarse silt production in Asian sand deserts and Quaternary accretion of the Chinese Loess Plateau

The Chinese Loess Plateau (CLP) is a large, spatially well defined and persistent zone of loess accumulation developed near the fluctuating northwest margin of the East Asian monsoon. Many studies have analyzed its loess sediments to provide insights into paleoclimatic conditions. Although spatial and temporal variations in the grain sizes of CLP sediments are fundamental to this effort, controversy over the origin of the dominant coarse quartz silt has limited interpretations. Reexamination of the spatial pattern of grain-size distribution across the CLP and a field-scale experiment conducted in the Gobi Desert revealed a genetic association between the coarse silt fraction of the loess and primary production of coarse silt through eolian abrasion of sand in the proximal Mu-Us, Tengger, and Badain Jaran sandy deserts. Our results demonstrate the effectiveness of eolian abrasion of quartz sand in primary coarse silt production in Central Asia and identify this process as the most consistent with the wellrecognized systematic northwest-southeast depositional pattern of the CLP. We suggest that only abraded coarse quartz grains transported short distances by long-term persistent eolian activity can build up thick loess sequences to form a massive and spatially well defined loess plateau. These results decouple the production and transport of coarse silt and finer silt and clay particles, which have a more distant and wider provenance, changing the constraints on previous paleoclimatic reconstructions. © 2013 Geological Society of America

Frequency of boulders transport during large floods in hyperarid areas using paleoflood analysis – An example from the Negev Desert, Israel

Direct measurements of boulder entrainment in desert wadis are not available. Also, estimating the hydraulic conditions and frequency of natural boulders transport is difficult because their presence cannot be related to their arrival date, discharge or any other hydraulic parameter. The 2004 flood (peak discharge of 470 m3 s-1; recurrence interval &gt;100 years) in the ungauged Nahal Hatzera ephemeral stream (45 km2), transported and deposited concrete boulders and slabs detached from infrastructure upstream as well as natural boulders, 0.85-1.5 m in size, at the outlet of the Makhtesh Hatzera Erosion Cirque (MHEC). Geometrical survey and a drone air-photographic survey documented the geometry of the study reach and the location of boulders. Accumulations and analyses of flood slackwater deposits along the study reach established a paleoflood record of 23 floods with peak discharges of 200-760 m3 s-1 during the last 600 years (radiocarbon ages). Step back-water hydraulic analysis using the 1-D HEC-RAS program, provided water surface profiles to show the hydraulics along the study reach and assigned a peak discharge to the 2004 flood using the clear high water marks of the flood, as well as to the paleoflood-related sedimentary units. The hydraulic program also provided velocity, shear stress and stream power for each boulder at its specific location along the study reach and within the cross section. The Max program was used for flood frequency analysis (FFA) of the paleoflood record. The results indicate that most of the concrete boulders were deposited in the sub-critical backwater of channel constrictions where velocities were 1.5-2.1 m s-1. The largest boulders, were deposited in super-critical flow where velocity was 8-9.2 m s-1. For the sandy alluvial bed of the Nahal Hatzera channel, maximum shear stresses of 250-900 N m-2 are available to transport a range of concrete boulders sizes (0.85-1.5 m), reflecting the unstable, active sandy layer of the channel bed over which the boulders moved. The mobile boulders probably were deposited on the falling limb of the flood and actually represent conditions of dis-entrainment. The FFA analysis and resulting peak discharges provide maximum depositional hydraulic values for return periods of 10-1000 years: velocities 7.1-9.8 m s-1, shear stress - 310-507 N m-2 and stream power - 2500-4972 N m-1 s-1. The frequency of the 2004 flood, based on the FFA, indicates that boulders up to 2.1 m and weighing up to 15 tonnes can be transported at least once in 120 years. The geomorphic effectivity of this typical desert flash flood was small based on it's qualitative properties - high peak, short duration and the small visible changes along the course of the channel and banks indicating that surface and channel resistance thresholds were not exceeded

Validation of ASTER Emissivity Retrieval Using the Mako Airborne TIR Imaging Spectrometer at the Algodones Dune Field in Southern California, USA

Validation of emissivity (&epsilon;) retrievals from spaceborne thermal infrared (TIR) sensors typically requires spatial extrapolations over several orders of magnitude for a comparison between centimeter-scale laboratory &epsilon; measurements and the common decameter and lower resolution of spaceborne TIR data. In the case of NASA&rsquo;s Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) temperature and &epsilon; separation algorithm (TES), this extrapolation becomes especially challenging because TES was originally designed for the geologic surface of Earth, which is typically heterogeneous even at centimeter and decameter scales. Here, we used the airborne TIR hyperspectral Mako sensor with its 2.2 m/pixel resolution, to bridge this scaling issue and robustly link between ASTER TES 90 m/pixel emissivity retrievals and laboratory &epsilon; measurements from the Algodones dune field in southern California, USA. The experimental setup included: (i) Laboratory XRD, grain size, and TIR spectral measurements; (ii) radiosonde launches at the time of the two Mako overpasses for atmospheric corrections; (iii) ground-based thermal measurements for calibration, and (iv) analyses of ASTER day and night &epsilon; retrievals from 21 different acquisitions. We show that while cavity radiation leads to a 2% to 4% decrease in the effective emissivity contrast of fully resolved scene elements (e.g., slipface slopes and interdune flats), spectral variability of the site when imaged at 90 m/pixel is below 1%, because at this scale the dune field becomes an effectively homogeneous mixture of the different dune elements. We also found that adsorption of atmospheric moisture to grain surfaces during the predawn hours increased the effective &epsilon; of the dune surface by up to 0.04. The accuracy of ASTER&rsquo;s daytime emissivity retrievals using each of the three available atmospheric correction protocols was better than 0.01 and within the target performance of ASTER&rsquo;s standard emissivity product. Nighttime emissivity retrievals had lower precision (&lt;0.03) likely due to residual atmospheric effects. The water vapor scaling (WVS) atmospheric correction protocol was required to obtain accurate (&lt;0.01) nighttime ASTER emissivity retrievals