Ground Ice Research Articles

Identification of candidate martian maars in Arena Colles and Nephentes/Amenthes with extension to maars as a proxy for past ground water/ice depths

Maar craters represent the top of a volcanic construct produced by subsurface explosive interactions between ground water/ice and rising magma. Recent comprehensive studies of terrestrial maars have established the commonality of complex maar crater geometries composed of overlapping circular components with a single near continuous outer rim. These distinctive geometries, and the availability of high spatial resolution visible imagery on Mars, provide an opportunity to identify and evaluate candidate maars on Mars. This study evaluated 49 closed depressions in Arena Colles and Nephentes/Amenthes based on their proximity to pitted cones of proposed volcanic origin. Across the two regions, 13 candidate maars were recognized for their similarity to terrestrial maars in absence of any exclusionary characteristics related to other formation processes such as butterfly ejecta around binary craters. The recognition of maars on Mars would provide additional proxies for the presence and range of depths for ground water and ice at the time of eruption. The diameter of the multiple overlapping circular components in maar craters can be used to provide first order estimates of the depths of the underlying diatreme as a proxy for depth of explosions and thus presence of water in the subsurface. Estimates based on the circular components of the 13 candidate maars recognized here indicate that water/ice depths at the time of formation would be between 0.6 and 4 km.

Review article: Retrogressive thaw slump characteristics and terminology

Abstract. Retrogressive thaw slumps (RTSs) are spectacular landforms that occur due to the thawing of ice-rich permafrost or melting of massive ground ice, often in hillslope terrain. RTSs occur in the Arctic, the subarctic, and high mountain (Qinghai–Tibet Plateau) permafrost regions and are observed to expand in size and number due to climate warming. As the observation of RTSs is receiving more and more attention due to their important role in permafrost thaw; impacts on topography; mobilization of sediment, carbon, nutrients, and contaminants; and their effects on downstream hydrology and water quality, the thematic breadth of studies increases and scientists from different scientific backgrounds and perspectives contribute to new RTS research. At this point, a wide range of terminologies originating from different scientific schools is used, and we identified the need to provide an overview of variable characteristics of RTSs to clarify terminologies and ease the understanding of the literature related to RTS processes, dynamics, and feedbacks. We review the theoretical geomorphological background of RTS formation and landform characteristics to provide an up-to-date understanding of the current views on terminology and underlying processes. The presented overview can be used not only by the international permafrost community but also by scientists working on ecological, hydrological, and biogeochemical consequences of RTS occurrence and by remote-sensing specialists developing automated methods for mapping RTS dynamics. The review will foster a better understanding of the nature and diversity of RTS phenomena and provide a useful base for experts in the field but also ease the introduction to the topic of RTSs for scientists who are new to it.

The cryostratigraphy of thermo-erosion gullies in the Canadian High Arctic demonstrates the resilience of permafrost

Abstract. Thermo-erosion gullies (TEGs) are one of the most common forms of abrupt permafrost degradation. They generally form in ice-wedge polygonal networks where the interconnected troughs can channel runoff water. Although TEGs can form within a single thawing season, it takes them several decades to stabilize completely. While the inception of TEGs has been examined in several studies, the processes of their stabilization remain poorly documented, especially the cryostructures that form following permafrost aggradation in stabilizing TEGs. For this study, we investigated the impacts of two TEGs in the Canadian High Arctic (Bylot Island, NU, Canada) on ground ice content, cryostratigraphic patterns, and geomorphology to examine permafrost recovery following thermal erosion in ice-wedge polygonal tundra. We sampled 17 permafrost cores from two TEGs – one still active (since 1999) and one stabilized (> 100 years old) – to describe the surface conditions, interpret the cryostratigraphic patterns, and characterize the state of permafrost after TEG stabilization. Although the TEG caused discernable cryostratigraphic patterns in permafrost, ground ice content and thaw front depth in the TEGs were comparable to measurements made in undisturbed conditions. We also noted that, once stabilized, TEGs permanently (at the Anthropocene scale) alter landscape morphology and hydrological connectivity. We concluded that, although the formation of a TEG has profound effects in the short and medium term (years to decades) and leaves near-permanent geomorphological and hydrological scars in periglacial landscapes, in the long term (decades to centuries), High Arctic permafrost can recover and return to geocryological conditions similar to those pre-dating the initial disturbance. This suggests that, in stable environmental conditions undergoing natural variability, permafrost can persist longer than the geomorphological landforms in which it forms.

Insights into permafrost aggradation and thawing: A case study of Zonag Lake on the Qinghai–Tibet Plateau using SAR interferometry

AbstractLakes on the Qinghai–Tibet Plateau (QTP) are important indicators of climate change. The water level and area of Zonag Lake have increased sharply since 2000, and the west lake bottom area was exposed after an outburst of flood in September 2011. The drained basin was exposed to the cold environment, causing rapid permafrost forming. In this paper, time‐series synthetic aperture radar interferometry (InSAR) was utilized to monitor the surface deformation of the drained basin using Sentinel‐1A images within a 4‐year period (2017–2020). This research focused on characterizing the spatial and temporal dynamics of ground deformation and exploring changes in the permafrost base around the drained basin based on the deformation information. The experimental results revealed spatially variable ground deformation, with long‐term deformation rates ranging from −78.3 mm/year to 72.8 mm/year and seasonal amplitudes of 0–14 mm. Subsidence was prominent in the lakeshore, the thermokarst region and the slope drainage area, indicative of the thawing of ice‐rich permafrost. Conversely, uplift was concentrated in the exposed unconsolidated sediment region, with a maximum displacement of 110 mm over the nearly 4‐year observation period, suggesting ground ice aggradation. The uplift information was used to estimate the change in the permafrost base in the drained basin, yielding a maximum value of 4 m. The estimated permafrost base change closely aligned with simulated results, with an error of 0.28 m. This study demonstrates the capability of InSAR in monitoring permafrost stability and improving the understanding of the dynamic permafrost formation process.

GEOCHEMISTRY OF GROUNDWATERS AND SURFACE WATERS, AND GROUND ICE OF THE OKA PLATEAU, EASTERN SAYAN (RUSSIA)

The study area is located in the Eastern Sayan hydrogeological folded area. The objects of the study were groundwaters, surface waters and ground ice in the Sentsa River basin on the Oka Plateau. Cold and thermal groundwaters are associated with Proterozoic and Paleozoic metamorphic and igneous rocks. Their discharge as springs occurs in the river valleys along fault zones. Ground ice was studied in mineral frost mounds (lithalsas) composed of clays, clayey silts and silts of lacustrine-alluvial and fluvioglacial genesis. It has been established that thermal and cold groundwaters have HCO3 Ca-Na compositions, river and lake waters, as a rule, have HCO3 Ca-Na compositions, and ground ice melts – HCO3, SO4-HCO3 and NH4-HCO3 Ca. Thermal waters are largely enriched in Li, Be, B, Si, Mn, Ga, Ge, Se, As, Br, Rb, Sr, Cs, Ba and all REE relative to river and rain waters, and have the highest values of trace elements enrichment factor (EFREE). The latter shows that atmospheric precipitation participates in the formation of the composition of groundwaters (cold and thermal) and surface waters. The specificity of the geochemistry of ground ice is determined by the composition of precipitation, the injection of ice-forming groundwater from taliks, the interaction in the water-rock system, and the presence of organic matter in unconsolidated sediments. The participation of river water and groundwater in the formation of the frost mound ice core is also evidenced by similar values of stable isotopes (δ18O, δD) in surface water, groundwater and ground ice. The 3He/4He ratio points to a possible influx of mantle helium into thermal waters, and δ13С points to the magmatic and thermometamorphic mechanisms of carbon dioxide accumulation in thermal waters. The 87Sr/86Sr ratio in travertines indicates a significant contribution of intrusive rocks to the formation of fluid composition.

Effectiveness evaluation of cooling measures for express highway construction in permafrost regions based on GPR and ERT

Global warming and human activities are accelerating the degradation of permafrost on the Qinghai-Tibet Plateau (QTP), leading to significant settlement and cracking issues in the local express highway infrastructures. In response, the Gonghe-Yushu Express Highway (GYE) on the east edge of the QTP incorporated extensive cooling measures during its construction to enhance embankment stability. Despite these efforts, field investigations have disclosed that embankment diseases persist across various sections, including those with implemented cooling measures. This study focuses on a specific test and demonstration section of the GYE, employing a suite of cooling measures to assess their engineering effectiveness. Utilizing a combination of multi-time ground-penetrating radar (GPR) and electrical resistivity tomography (ERT) detection, alongside on-site disease investigations and temperature monitoring, this research comprehensively evaluates the efficacy of different cooling interventions. Findings indicate that although cooling measures generally curb permafrost degradation in areas with ice-rich and ice-saturated soils, they fall short in sections with massive ground ice. Of the six cooling measures examined in the demonstration section, ventilation duct embankments emerge as the most effective, whereas crushed-rock layer embankments rank as the least. The study further reveals that the combined use of XPS insulation boards and two-phase closed thermosyphons inadequately addresses the issue of central heat accumulation in broad-width express highways, reducing uneven settlement issues but aggravating longitudinal cracking. Comparative analysis of on-site surveys and monitoring data suggests that regular application of GPR and ERT techniques can proficiently assess the performance of cooling measures.

No deceleration signs in the permafrost ground subsidence four years after the 2019 fire in Northwest Territories, Canada

Abstract The circum-arctic permafrost environment is often disturbed by wildfires but could also show resilience to these disturbances. However, the increased frequency and extent of wildfires, coupled with unprecedented hot weather, have introduced greater uncertainties in the post-fire permafrost dynamics. We need to address emerging questions, e.g., How will permafrost respond to the joint effect of hot anomalies and wildfires? To what extent will post-wildfire deformation evolve? How will permafrost resilience to wildfires vary? Utilizing Interferometric Synthetic Aperture Radar (InSAR) time series analysis, we investigated the post-wildfire ground deformation around a 2019 fire scar in the lower Mackenzie Valley, Northwest Territories, Canada, where dramatic heat anomalies and severe wildfires have been recorded in recent years. The resilience of permafrost to wildfires appears to be weakened by the continuous and rapid warming after the fire, as evidenced by the year-on-year acceleration in subsidence rates. Such acceleration was never reported by previous findings that typically observed deceleration in subsidence rates four to five years after wildfires. The deformation along the line of sight (LOS) of the satellite demonstrates significant permafrost degradation induced by wildfires and exacerbated by climate warming, and the cumulative subsidence was detected up to 25 cm in the LOS direction in the upland areas and up to 10 cm in the lowland areas four years after the fire. The difference in deformation magnitude could be attributed to local factors, including ground ice, topography, and vegetation. Our study highlights the increasingly severe threat to circum-arctic permafrost due to the combined effects of wildfires and extreme heat anomalies.

Advances in InSAR Analysis of Permafrost Terrain

ABSTRACTDifferential interferometric synthetic aperture radar (InSAR) is a remote sensing technique for measuring surface displacements with precision down to millimeters, most commonly from satellites. In permafrost landscapes, InSAR measurements can provide valuable information on geomorphic processes and hazards, including thaw subsidence and frost heave, thermokarst, and permafrost creep. We first review recent progress in InSAR data availability, InSAR processing and uncertainty analysis methods relevant to permafrost studies. These technical advances have contributed to our understanding of surface deformation in flat and sloping terrain in polar and mountainous regions. We emphasize two emerging trends. First, InSAR increasingly enables insight into the mechanisms, controls, and drivers of permafrost landscape dynamics on subseasonal to decadal time scales. Second, InSAR observations in conjunction with models enable novel ways to infer subsurface parameters, such as near‐surface ground ice content and active layer thickness. We anticipate that in the coming decade, InSAR will mature into a widely used operational tool for monitoring, modeling, and planning across rapidly changing permafrost landscapes.

Мониторинг развития Дуплетного объекта взрыва газа С22 на полуострове Ямал по данным дистанционного зондирования Земли

The paper presents a comprehensive study of the C22 gas blowout Doublet object formed in 2023 in the central part of Yamal peninsula carried out with the use of remote sensing (RS) data and unmanned aerial vehicle (UAV). The object is situated 12.7 km south of the Bovanenkovo field. The uniqueness of the C22 crater lies in its location — 230 m from a similar, widely-known C2 object exploded in 2012, which is why the C22 object is named ‘Doublet’. Based on RS data the researchers have determined that within August 23 and September 3, 2023 the C22 permafrost heaving mound (PHM) exploded. According to ArcticDEM data for the period 2011-2023, the features of changes in the size of C22 PHM have been studied, including an abnormally high average growth rate of 44 cm/year three years before its explosion, which can serve as one of the criteria for identifying explosive PHM objects. The UAV data of May 14, 2024 has resulted in building a 3D model, which displays a partially snow-covered cavity in a ground ice massif. The depth of the cavity from the crater parapet is at least 28.5 m, the diameter of the crater neck is about 13 m. In the lower part, the cavity widens to 26 m and additionally extends by at least 8 m in the NNW direction at an azimuth of about 341°, which is consistent with the direction of the faults of the Bovanenkovo field identified by seismic exploration data. The bottom of the cavity has an elliptical shape with the size from 26×33 m to 26×41 m. The study is interdisciplinary and is included in the list of critical technologies for the prevention and reduction of risks of natural and man-made emergencies.

Local Excitation of Kagome Spin Ice Magnetism Seen by Scanning Tunneling Microscopy.

The kagome spin ice can host frustrated magnetic excitations by flipping its local spin. Under an inelastic tunneling condition, the tip in a scanning tunneling microscope can flip the local spin, and we apply this technique to kagome metal HoAgGe with a long-range ordered spin ice ground state. Away from defects, we discover a pair of pronounced dips in the local tunneling spectrum at symmetrical bias voltages with negative intensity values, serving as a striking inelastic tunneling signal. This signal disappears above the spin ice formation temperature and has a dependence on the magnetic fields, demonstrating its intimate relation with the spin ice magnetism. We provide a two-level spin-flip model to explain the tunneling dips considering the spin ice magnetism under spin-orbit coupling. Our results uncover a local emergent excitation of spin ice magnetism in a kagome metal, suggesting that local electrical field induced spin flip climbs over a barrier caused by spin-orbital locking.

Cryosphere degradation in a changing climate

AbstractOver the last few decades, the instrumental climate record shows a progressive global warming. As one of the most sensitive elements of the Earth's climate system, the cryosphere is significantly affected by this trend. As a result, its various components are readjusting in a situation of disequilibrium with the climate through a series of dynamics. These include the thinning and retreat of glaciers that may lead to the formation of new lakes; the thawing of ground ice, leading to the deformation of terrain; the reduction of snow cover; and the occurrence of mass movements that threaten populations and infrastructures. This Special Issue contains 23 scientific papers with case studies that explore the above issues in the Arctic, Antarctic and high mountain regions.

Iceberg ploughmarks and glacial lineations on Jan Mayen Ridge: Evidence for past iceberg and possible ice-shelf grounding in deep water

Jan Mayen Ridge, south of the isolated island of Jan Mayen (71°N 8°W), is located strategically near the centre of the Polar North Atlantic and surrounded by deep-water seas. Examination of about 4,100 km2 of multibeam bathymetric data allowed identification of 1700 chaotic seafloor depressions at 300–1000 m modern water depth and two sets of lineations at 400–600 m and 750–900 m deep. The chaotic depressions are interpreted as ploughmarks produced as iceberg keels impinged on a sedimentary seafloor. The deepest ploughmarks reach 1010 m depth. Multi-keel ploughmarks indicate the presence of tabular icebergs of minimum widths 0.5–2.3 km. Ploughmark orientations were W/E and SW/NE on the northern and southern ridge, respectively, suggesting that deep-keeled icebergs drifting across Jan Mayen Ridge were probably calved mainly from short floating tongues at the margins of full-glacial Greenland ice streams. The mapped seafloor lineations are morphologically similar to mega-scale glacial lineations and flutes formed by soft-sediment deformation beneath active ice. They are interpreted to indicate the possible grounding of glacier ice on Jan Mayen Ridge. Their W-E orientation precludes ice flow from a full-glacial Jan Mayen ice cap. A possible interpretation is that they may represent grounding of a large floating ice shelf probably fed by ice from the Greenland Ice Sheet during one of the very large pre-Weichselian glaciations of the Quaternary. Whereas these lineations at 70°N do not provide direct evidence for a huge ice-shelf complex flowing southwards from the Arctic Ocean, the general climatic conditions required to form and maintain large ice shelves suggest that the development of an Arctic Ocean ice shelf at some point during Quaternary full-glacials remains a possibility.

Effect of surficial geology mapping scale on modelled ground ice in Canadian Shield terrain

Abstract. Ground ice maps at small scales offer generalized depictions of abundance across broad circumpolar regions. In this paper, the effect of surficial geology mapping scale on modelled ground ice abundance is examined in the Slave Geological Province of the Canadian Shield, a region where the geological and glacial legacy has produced a landscape with significant variation in surface cover. Existing model routines from the Ground ice map of Canada (GIMC) were used with a 1:125 000-scale regional surficial geology compilation and compared to the national outputs, which are based on surficial geology at a 1:5 000 000 scale. Overall, the regional-scale modelling predicts much more ground ice than the GIMC due to greater representation of unconsolidated sediments in the region. Improved modelling accuracy is indicated by comparison of the outputs to empirical datasets due to improved representation of the inherent regional heterogeneity in surficial geology. The results demonstrate that the GIMC significantly underestimates the abundance and distribution of ground ice over Canadian Shield terrain. In areas with limited information on ground ice, regional-scale modelling may provide useful reconnaissance-level information to help guide the field-based investigations required for planning infrastructure development. The use of current small-scale ground ice mapping in risk or cost assessments related to permafrost thaw may significantly influence the accuracy of outputs in areas like the Canadian Shield, where surficial materials range from bedrock to frost-susceptible deposits over relatively short distances.

20-year permafrost evolution documented through petrophysical joint inversion, thermal and soil moisture data

This study investigates the ground characteristics of the high altitude (3410 m a.s.l.) permafrost site Stockhorn in the Swiss Alps using a combination of surface and subsurface temperature, soil moisture, electrical resistivity and P-wave velocity time series data including a novel approach to explicitly quantify changes in ground ice content. This study was motivated by the clear signal of permafrost degradation visible in the full dataset at this long-term monitoring site within the PERMOS (Permafrost Monitoring Switzerland) network. Firstly, we assess the spatio-temporal evolution of the ground ice and water content by a combined analysis of all available in situ thermal (borehole and ground surface temperature), hydrological (soil moisture) and geophysical (geoelectric and seismic refraction) data over two decades (2002–2022) regarding the driving factors for the spatially different warming. Secondly, we explicitly quantify the volumetric water and ice content and their changes in the subsurface from 2015 to 2022 using a time-consistent petrophysical joint inversion scheme within the open-source library pyGIMLi. The petrophysical joint inversion scheme has been improved by constraining the rock content to be constant in time for six subsequent inversions to obtain consistent changes in ice and water content over the monitoring period based on jointly inverted resistivity and traveltime data. All different data show a warming trend of the permafrost. The ice content modeled from the petrophysical joint inversion has decreased by about 15 vol.% between 2015 and 2022. Changes in ice content are first observed in the lower, south-facing part of the profile. As a result, resistivity and P-wave velocity have been decreasing significantly. Permafrost temperatures measured in the boreholes have increased between 0.5 °C and 1 °C in 20 years. Our study shows the high value of joint and quantitative analysis of datasets comprising complementary subsurface variables for long-term permafrost monitoring.

Identifying ice wedges in ground-penetrating radar data from the Cold Regions Research and Engineering Laboratory permafrost tunnel, Fox, Alaska

The warming of Alaska’s permafrost has been leading to thawing within its discontinuous permafrost. This can cause ice wedges to melt, resulting in thermokarst formations such as sinkholes and landslides, which are causing damage to Alaskan infrastructure. To avoid developing further infrastructure in areas containing ice wedges, it is necessary to improve methods of detecting subsurface ground ice. Ground-penetrating radar (GPR) is a nonintrusive remote sensing method of locating and characterizing permafrost and other subsurface features that are not evident on a cut face or surface. When applied to the detection of ice wedges at the Cold Regions Research and Engineering Laboratory permafrost tunnel in Fox, Alaska, a few identifying features have been observed which corresponded with prior research. We first use GPR reflections of areas along the tunnel walls holding known ice wedges to verify the identifying features of an ice wedge within GPR data. We use these reflections as test data to identify possible ice wedges in locations where they were not observed on the tunnel walls.

Seawater Intrusion in the Observed Grounding Zone of Petermann Glacier Causes Extensive Retreat

AbstractUnderstanding grounding line dynamics is critical for projecting glacier evolution and sea level rise. Observations from satellite radar interferometry reveal rapid grounding line migration forced by oceanic tides that are several kilometers larger than predicted by hydrostatic equilibrium, indicating the transition from grounded to floating ice is more complex than previously thought. Recent studies suggest seawater intrusion beneath grounded ice may play a role in driving rapid ice loss. Here, we investigate its impact on the evolution of Petermann Glacier, Greenland, using an ice sheet model. We compare model results with observed changes in grounding line position, velocity, and ice elevation between 2010 and 2022. We match the observed retreat, speed up, and thinning using 3‐km‐long seawater intrusion that drive peak ice melt rates of 50 m/yr; but we cannot obtain the same agreement without seawater intrusion. Including seawater intrusion in glacier modeling will increase the sensitivity to ocean warming.

Water accumulation unrelated to ice segregation near the freezing front during soil freezing: Implications for frost heave in high-speed railway embankments and ground ice formation

Investigating water migration in frozen ground is crucial for understanding the hydrothermal dynamics of frozen soil, which is central to frozen soil engineering (e.g., frost heave) and permafrost environments (e.g., ground ice formation). Previous studies have mostly focused on water migration related to ice segregation in frost-susceptible soils, but less on water migration that is independent of ice segregation in non-frost-susceptible soils. Using a novel layer-scanning method based on the nuclear magnetic resonance (NMR) techniques, the water migration dynamic was observed during the freezing of non-frost-susceptible loess under different drainage conditions (with or without water drainage). Results showed an apparent phenomenon of water migration to the freezing front (TFF) (layer L7) (i.e., water accumulation that is independent of ice segregation) occurred in the early freezing stage of non-frost-susceptible soils under no draining water conditions. The traditional water migration mode is related to ice segregation, a new water migration (including upward and downward) mechanism was proposed to reveal this water accumulation unrelated to ice segregation at TFF. The water accumulation at the freezing front is independent of ice segregation, and is attributed to 9% volume expansion due to pore ice formation in the frozen zone, causing water migration downward TFF; while the decrease of the pore volume of the unfrozen zone (being compressed) accounts for the water migration upward TFF. Investigation into whether ice segregation exists and different modes of water migrations (depending on ice segregation or not) will be greatly helpful for exploring the mechanisms of micro frost heave in the high-speed railway embankments and the thick-layered ground ice formation.

Rate of permafrost thaw and associated plant community dynamics in peatlands of northwestern Canada

Abstract The most rapid climate warming is occurring in northern, permafrost environments. Peatlands of these regions are particularly sensitive to climate warming, with the high ground ice content of peat plateaux resulting in the formation of collapse scars as ground temperatures warm. To quantify the rates of permafrost thaw and associated vegetation changes, we sampled the plant and lichen communities in transects spanning actively thawing collapse scar margins at sites from mid‐Boreal to Low Subarctic conditions, within Canada's Northwest Territories. Seventeen transects were sampled in 2007/08 and 14 of these were resampled 10 years later. The rate of lateral permafrost thaw of collapse scar margins ranged from −6 to 63 cm year−1 (mean: 22.0 cm ± 4.7 cm year−1 (SE)); variability was high and no trends with respect to latitude or temperature gradients were detected. Plant communities displayed a clear gradient from lichen‐ and ericaceous shrub‐dominated peat plateaux, to collapse scars primarily characterized by Sphagnum mosses and graminoids. Both space‐for‐time (distance from collapsing margin) and direct measurement of 10‐year changes showed a successional sequence following permafrost thaw; floating mat communities characterized by Sphagnum riparium or S. balticum proceeded to lawn communities of S. angustifolium and, finally, to hummock communities with Mylia anomala or S. fuscum. This successional sequence was associated with increased water table depth and lower soil water content in plant communities farther from the actively collapsing front, illustrating that peat growth above the water table was driving plant community successional changes. The most rapid plant community succession occurred in recently thawed environments as peat growth propelled the ground surface above the water table while the slowest succession occurred in the collapse scar hummock communities located farthest from the actively collapsing peat plateau margin. Synthesis. In just 10 years, significant vegetation change was detected, in association with both permafrost thaw and subsequent plant community succession. These changes occurred across a broad climatic and latitudinal gradient, from mid‐Boreal to Low Subarctic and have implications for wildlife, global C cycle and indigenous communities who depend on this landscape for harvesting, spiritual and cultural practices.

A global map of gullied hillslopes on Mars

The distribution of gullies on Mars has been used to support different modes of formation involving CO2, H2O or entirely dry processes. We mapped the extent of gullied hillslope using a global mosaic of ConTeXt camera (CTX) at 6 m/pixel and High Resolution Imaging Science Experiment (HiRISE) browse products at ∼3 m/pixel. Our new global catalog of gullied hillslopes allows for quantitative, area-based analysis of gullies both at global and regional scale, which was not possible with point-based or more localized previous datasets. We analyzed aspect and gradient information derived from MOLA topography for every mapped gullied hillslope. We have confirmed the trends identified in previous works, which are that the mean gradient of gullied hillslopes is lower than 30°, the angle of repose of dry material on Mars, and that the preferred aspect of gullied hillslopes is latitude-dependent, with a shift between pole-facing to equator-facing happening around 40° in both hemispheres. We established a hierarchy of factors that can explain the global distribution of gullied hillslopes: Latitude is the strictest control because gullies are constrained between 26°-83°S and 28°-76°N. The availability of steep slopes is a strong control over gully distribution, and we observed that gullied hillslopes aspect reflects the orientation of large regional reliefs, which implies that hillslope aspect is less of a factor than the hillslope gradient in explaining gully distribution. We analyzed the correlation of gully distribution with a subsurface water ice consistency map, and we found that gullies are preferentially distributed on areas with some ground ice rather than no ice at all. We identified for the first time a bias toward an east-facing trend for southern hemisphere gullies poleward of ∼40° of latitude. We also linked our gullied hillslopes dataset with a global crater morphometry dataset: 63% of the gullied area on Mars is found in craters, and we find that the area covered by gullies in a given crater is positively correlated with the depth and diameter ratio of this crater.Our observations point toward a complex interplay between local slope, insolation, and thermal properties of the substrate to explain the spatial distribution of the current population of gullies. Finally, we have assessed the very high resolution (sub-meter) imagery coverage of gullies to be 36% and that the repeated coverage reaches 21% of gullies, hence this would need expanding to better understand the spatial trends in active gullies.

Retrogressive thaw slump susceptibility in the northern hemisphere permafrost region

AbstractMean annual temperatures in the Arctic and subarctic have increased in recent decades, increasing the number of permafrost hazards. Retrogressive thaw slumps (RTSs), triggered by the thawing of ground ice in permafrost soil, have become more common in the Arctic. Many studies report an increase in RTS activity on a local or regional scale. In this study, the primary goals are to: (i) examine the spatial patterns of the RTS occurrences across the circumpolar permafrost region, (ii) assess the environmental factors associated with their occurrence and (iii) create the first susceptibility map for RTS occurrence across the Northern Hemisphere. Based on our results, we predicted high RTS susceptibility in the continuous permafrost regions above the 60th latitude, especially in northern Alaska, north‐western Canada, the Yamal Peninsula, eastern Russia and the Qinghai‐Tibetan Plateau. The model indicated that air temperature and soil properties are the most critical environmental factors for the occurrence of RTSs on a circumpolar scale. Especially, the climatic conditions of thaw season were highlighted. This study provided new insights into the circumpolar susceptibility of ice‐rich permafrost soils to rapid permafrost‐related hazards like RTSs and the associated impacts on landscape evolution, infrastructure, hydrology and carbon fluxes that contribute to global warming.