Crater Degradation Research Articles

A Mechanistic Model and Experiments on Bedrock Incision and Channelization by Rockfall

AbstractRockfall and rock avalanches are common in steep terrain on Earth and potentially on other planetary bodies such as the Moon and Mars. Since impacting rocks can damage exposed bedrock as they roll and bounce downhill, rockfall might be an important erosive agent in steep landscapes, even in the absence of water. We developed a new theory for rockfall‐driven bedrock abrasion using the ballistic trajectories of rocks transported under gravity. We calibrated this theory using laboratory experiments of rockfall over an inclined bedrock simulant. Both the experiments and the model demonstrate that bedrock hillslopes can be abraded by dry rockfall, even at gradients below the angle of repose, depending on the bedrock roughness. Feedback between abrasion and topographic steering of rockfall can produce channel‐like forms, such as bedrock chutes, in the absence of water. Particle size has a dominant influence on abrasion rates and runout distances, while the hillslope angle has a comparatively minor influence. Rockfall transport is sensitive to bedrock roughness; terrain with high friction angles can trap rocks creating patches of rock cover that affect subsequent rockfall pathways. Our results suggest that dry rockfall can play an important role in eroding and channelizing steep, rocky terrain on Earth and other planets, such as crater degradation on the Moon and Mars.

Variation of crater morphological parameters in the landing area of Tianwen-1: relationships with the geological environment and climate change

The Zhurong rover of the Tianwen-1 mission successfully landed in the southern part of the Utopian Planitia and the northern region of the dichotomy boundary. Craters within a ~ 134 km2 region surrounding the Zhurong rover were identified and divided into seven degradation classes based on their preservation states and morphological details. Assessing how craters have degraded over time provides insight into local surface processes and then speculates on the climate evolution of the study area. The small depth/diameter (d/D) of craters in the study area may be caused by the rapid filling of sediments or by impact processes occurring in poorly cohesive weathering layers, and may also be associated with the volatile material alteration. As time went by, the process of crater degradation is nonlinear, and the degradation rate of the fresh crater in the study area at the initial stage of degradation may be as high as 0.2 m/Myr. The calculated surface erosion rate for the study area is ~ 10–2–10–3 m/Myr, indicating that the erosion of the Martian surface since the Middle Amazonian occurred in the dry environment dominated by wind-sand erosion.Graphical

Lunar Impact Craters: New Perspectives From Full‐Polarimetric Analysis of Chandrayaan‐2 Dual‐Frequency SAR Data

AbstractWith the availability of the full‐polarimetry data from Chandrayaan‐2 Dual‐frequency Synthetic Aperture Radar (DFSAR) for the first time, the lunar impact craters are studied for comprehensive characterization, which was earlier limited due to hybrid‐polarimetry based observations. In conjunction with the conventional Circular Polarization Ratio (CPR), we explore the unique full‐polarimetric parameters such as Single‐bounce Eigenvalue Relative Difference and T‐Ratio which are sensitive to surface roughness and dielectric constant, respectively. We studied the polarimetric behavior of a total of 115 nos. of impact craters within a specific size range (∼1–25 km diameter) belonging to different categories viz. fresh, degraded, polar and non‐polar anomalous craters. Our results confirm that both kinds of non‐polar and polar anomalous craters overall hold centimeter‐decimeter scale surface roughness similar to the exterior of the fresh craters, which mainly leads to the anomalous nature of the craters. Our analysis indicates possible control of the crater degradation process on the change in the radar scattering behavior of the studied lunar craters. The crater degradation causes a reduction in the surface roughness and dielectric property (density) of the scatterers present in various craters leading to a change in the radar scattering behavior. Alongside, water ice, if at all present admixed into the regolith in the polar anomalous craters, is not in the form of dominant scatterers that can influence the radar signature. However, the occurrence of relatively higher CPR values in smooth low dielectric crater interiors supports the possibility of the presence of water ice in some of the studied polar anomalous craters belonging to Pre‐Imbrian to Imbrian lunar geological periods.

Slopes of Lunar Crater Size‐Frequency Distributions at Copernican‐Aged Craters

AbstractCraters on the lunar surface can provide valuable information about the timing and sequence of surface‐forming processes on the Moon. A commonly used method for age determination is the analysis of the crater size‐frequency distribution (CSFD) to which a production function (PF) is fitted that represents the size‐frequency distribution of the impactors. However, the commonly used PF of Neukum (1983) is valid for crater diameters between 10 m and 300 km. Neukum et al. (2001, https://doi.org/10.1007/978-94-017-1035-0_3) revised the PF for crater diameters of 100 m–200 km. However, it is suggested to also be valid for the diameter range of 10 m–300 km as well. To assess whether we can extend a PF to craters ≤10 m in diameter, we investigated the slopes of the CSFDs of small craters formed on ejecta of young Copernican‐aged craters Giordano Bruno, Moore F, North Ray, and South Ray. A PF for smaller diameters would allow dating of young geological units, which are typically small, and would reduce the statistical error in age determinations, since smaller craters are more abundant. However, small craters are strongly influenced by geological factors, such as target properties, crater degradation, and secondary craters. For craters between 10 and 20 m we obtain a steeper CSFD slope than Neukum's proposed −3 slope (cumulative), whereas for craters ≤10 m the slope is about −3. We conclude that the PF of Neukum (1983) provides a reasonable CSFD slope for smaller craters, although it was not developed for this crater diameter range.

Geology of the Neruda quadrangle (H13), Mercury

ABSTRACT We present the first geological map of the Neruda Quadrangle (H13), Mercury. H13 is in Mercury’s southern hemisphere between latitudes 22.5°S–65°S, and longitudes 90°E–180° covering a total area of just under 5 million km², equivalent to 6.5% of the planet’s surface. Map digitisation was carried out at scales between 1:300,000 and 1:700,000 for final presentation at 1:3,000,0000, from end-of-mission data products from NASA’s MESSENGER mission. We distinguish three main photogeologic plains units: intercrater, intermediate, and smooth plains. We also distinguish all craters and their materials ≥ 20 km in diameter based on their degradation state. We have completed two versions of the map, one using a three-class crater degradation scheme and one using a five-class crater degradation scheme. In addition, specific geological units were charted for the Rembrandt impact basin. This map has been constructed to provide context and targets for the ESA-JAXA BepiColombo mission to Mercury.

“The spatial distributions of degraded craters and valley networks on Mars as a function of elevation: Their implications for Noachian climate”

Cold and dry models of Noachian Mars postulate that the Noachian epoch characterized a hyperarid and frigid world dominated by low-latitude cold-locked icefields. This ice caps supposedly protected underlying substrates and topography of the Southern Highlands from erosional degradation. I test the Late Noachian Icy Highlands (LNIH) hypothesis by mapping small distribution of both degraded and fresh [2–4] km diameter craters, crater depth and infilling of the smallest [2–5] km craters, valley network (VN) and inverted channels within an area of interest (AOI) representing over 1.1 × 107 km2 of the Noachian Southern Highlands utilizing Environmental Systems Research Institute (ESRI) ArcMap, clipped exclusively to Noachian terrain. Crater degradation results from this study do not show preferential preservation of fresh craters at elevation. Also, crater rim – crater floor (km) depth values show greatest erosion at elevations >1 km purported LNIH Equilibrium Line Altitude (ELA). VN and inverted channels likewise give evidence for net precipitation and erosion at elevation and net deposition and water transport below the global dichotomy at 0 km and extinction at −2.78 km. VN distribution patterns also requires an intertropical convergence zone (ITCZ). I propose that my results are most consistent with emerging PMGCMs incorporating atmospheric collision-induced-absorption (CIA) of CO2 and H2, bypassing the Faint Young Sun Paradox. I propose that statistical evidence derived from geomorphological features on Mars should be used as boundary conditions for future Mars global climate models.

Morphological characteristics of impact craters with diameters of 5–20 km on the Moon

The morphology of impact craters on the Moon plays an important role in understanding impact cratering process, surface and subsurface properties, and their evolutions. In this study, we systematically analyzed the depth, rim height, slope, and rock abundance of 15,135 impact craters between 5 and 20 km in diameter on the Moon, covering the simple and simple-to-complex transitional crater regimes. We found that the decline rates of inner average slopes of mare craters are generally larger than those of non-maria craters and that the degradation rate of inner upper wall slopes around rim crest is not uniform, which decreases rapidly when the depth/diameter ratio (d/D) lies in 0.25–0.15 but slowly when d/D is in 0.15–0.05. However, we found that there is no difference in crater rim height between different terrains (e.g., maria and highlands). In addition, we also found the decrease in rock abundance is more rapid than the ejecta infilling of the crater floor, especially for large simple craters. Moreover, we investigated the diameter-dependent morphological features of fresh craters in different terrains and revised the onset of transitional crater diameters based on the 180 freshest craters. We found that crater initial depth depends on target properties (e.g., strength and porosity) whereas that the degradation rate of the crater depth is independent of terrains. Furthermore, we found that the power-law relations for depth and diameter of fresh simple craters are d = 0.293D0.865 (mare), d = 0.297D0.884 (highland), d = 0.221D0.959 (north pole) and d = 0.209D0.981 (south pole). The onsets of transitional crater diameters are ∼14.2 km (mare), ∼15.7 km (highland), ∼16.6 km (north pole), and ∼ 16.8 km (south pole). These morphological characteristics and their differences in different terrains suggest that target properties (e.g., strength, layering, and porosity) affect the formation and degradation of larger simple and transitional craters.

Improvement of Lunar Surface Dating Accuracy Utilizing Crater Degradation Model: A Case Study of the Chang’e-5 Sampling Area

Taking the Chang’e-5 (CE-5) sampling area as an example, this study carried out an investigation on improving the crater size-frequency distribution (CSFD) dating accuracy of lunar surface geologic units based on the crater degradation model. We constructed a three-parted crater degradation model, which consists of the diffusion equation describing crater degradation and equations describing the original crater profile for small craters (D < 1 km) and larger craters (D ≥ 1 km). A method that can improve the accuracy of CSFD dating was also proposed in this study, which utilizes the newly constructed degradation model to simulate the degradation process of the craters to help determine the crater degradation process and screen out the craters suitable for CSFD analysis. This method shows a good performance in regional dating. The age determined for the CE-5 sampling area is 2.0 ± 0.2 Ga, very close to the 2.03 ± 0.004 Ga of isotopic dating result of the returned sample. We found that the degradation state of the craters simulated by our constructed degradation model is highly consistent with the real existing state of the craters in terms of their topographic, geomorphological, and compositional (e.g., FeO) features. It fully demonstrates that the degradation model proposed in this study is effective and reliable for describing and distinguishing the degradation state of craters over time due to the cumulative effects of small craters. The proposed method can effectively distinguish between diffusively degraded (which conform to the degradation model) and non-diffusively degraded (which do not conform to the degradation model) craters and improve the CSFD accuracy through the selection of the craters. This not only provides an effective solution to the problem of obtaining a more “exact” frequency distribution of craters, which has long plagued the practical application of the CSFD method in dating the lunar surface but also advances our understanding of the evolutionary history of the geologic units of the study area. The results of this work are important for the in-depth study of the formation and evolution of the moon, especially for lunar chronology.

Assessment of Morphology and Degradation of Craters in and Around Gale Crater, Mars Using High Resolution Stereo Camera (HRSC) Images

Assessment of Morphology and Degradation of Craters in and Around Gale Crater, Mars Using High Resolution Stereo Camera (HRSC) Images

Topographic Diffusion Revisited: Small Crater Lifetime on the Moon and Implications for Volatile Exploration

AbstractCrater degradation and erosion control the lifetime of craters in the meter‐to‐kilometer diameter range on the lunar surface. A consequence of this crater degradation process is that meter‐scale craters survive for a comparatively short time on the lunar surface in geologic terms. Here, we derive crater lifetimes for craters of <∼200 m in diameter by analyzing existing functional expressions for crater population equilibrium and production. These lifetimes allow us to constrain the topographic degradation needed at different scales to explain when craters become undetectable on equilibrium surfaces. We show how topographic degradation can be treated as a process of anomalous (scale‐dependent) topographic diffusion and find large differences in effective diffusivities at different scales, consistent with a wide range of evidence besides equilibrium behavior. Understanding the range of morphology of meter‐scale craters is particularly relevant for future exploration of the lunar surface with rovers. We illustrate expectations for the d/D distribution of small lunar craters on surfaces with negligible regional‐scale slopes. Our results imply that if volatiles are found in preserved <4 m craters and were delivered after crater formation, the volatiles must have been emplaced in the last ∼50 Ma. Given the rates of surface evolution we infer, the most likely emplacement time for any volatiles discovered at or near the surface in the interior of fresh, small craters may be much younger than this upper limit.

Degradation of the Lunar Surface by Small Impacts

The surfaces of airless bodies like the Moon are bombarded by a steady stream of small impactors that lead to erosion of the topography over time. However, the rate of degradation from small impacts, a key parameter in interpreting the ages of present-day lunar surface features, is not well constrained. Here we demonstrate, using a numerical mass transport model, that impact erosion is a nonlinear diffusion process, in contrast to past studies of crater degradation that have assumed that the downslope mass flux of ejecta is linearly proportional to hillslope gradient. Nonlinearity is a consequence of the asymmetric shape of ejecta blankets on sloped surfaces, and as a result, the degradation rate on steep slopes is over 40% greater than on nearly flat surfaces. Using measurements of the morphology and formation rate of small primary and secondary craters, the kilometer-scale lunar landscape diffusivity is computed and compared to the value inferred from topographic profiles of degraded craters. We show that the abundance of decameter-scale craters forming on the Moon over the past decade is consistent with small impacts dominating the erosion of the lunar landscape, but only if the primary size−frequency distribution remains steep down to the submillimeter scale.

Population of Degrading Small Impact Craters in the Chang’E-4 Landing Area Using Descent and Ground Images

The landing camera (LCAM) of Chang’e-4 lander provides a series of low (46 cm/pixel) to high (2.3 cm/pixel) resolution images, which are suitable for centimeter-scale craters. In this paper, we analyze the degradation of those small-sized craters to provide detailed information on the local geological evolution of the lunar surface. From the mosaicked descent image, 6316 craters were extracted and classified into four degradation levels based on their morphology on the image: fresh, slightly degraded, moderately degraded, and severely degraded. The ground terrain camera (TCAM) image and the DEM of the Yutu-2 panoramic camera (PCAM) validate the crater degradation levels from a qualitative and quantitative perspective, respectively. The results show that the smaller the size of the craters, the more easily they are degraded. The crater populations in equilibrium in the four study areas indicate that the cumulative size–frequency distribution (SFD) slope is different from previous research results, and the smaller the craters, the more difficult to reach an equilibrium state (for craters smaller than a given size, the production rate is exactly balanced by the removal rate), which may be due to secondary cratering and surface resurfacing caused by the burial of ejecta from neighboring craters.

Constraining the formation of paleolake inlet valleys across crater rims

Impact crater lakes with an inlet valley were common on Mars during past epochs. However, it has not been established exactly how impact craters with initially high-standing rims were breached by an inlet. We investigated four potential mechanisms for inlet valley breach formation: (1) rim erosion, (2) depositional rim burial, (3) drainage head erosion, and (4) overflow. We used remote sensing measurements to assess the relative likelihood of these mechanisms for 39 crater paleolake inlet systems, keeping in mind that either a single mechanism or multiple mechanisms may have occurred. Our findings indicate that crater degradation associated with (1) rim erosion and/or (2) depositional rim burial played an important role in establishing connections between exterior fluvial systems and crater interiors, especially during the late Noachian - early Hesperian valley network era. Isolated fluvial valleys, interpreted to post-date the main valley network era, breached craters in a wider range of degradation states compared to valley network-fed craters. Interestingly, in many cases, these younger systems accomplished a comparable magnitude of fluvial erosion via drainage head erosion and across crater rims as the valley network inlets, despite differences in broader landscape dissection. This finding suggests fluvial activity was able to accomplish comparable geomorphic work during later periods of Mars' history, at least locally. Our catalog of analyzed paleolakes includes Jezero crater, and so our work provides broader context for in situ rover analyses at this site.

Degradation at theInSightLanding Site,Homestead Hollow, Mars: Constraints From Rock Heights and Shapes

AbstractRock shapes and heights around theInSightlander are examined to refine the degradation history of the 27 m‐diameterHomestead hollow. Results document decreasing average exposed rock height and increasing percentage of rocks where height comprises the short axis from outside to within the hollow and support prior models of ejecta deflation accompanied by hollow infilling. We estimate 0.3 m of deflation at the current rim that is realistic compared to rock relief, original ejecta thickness, and predicted aeolian contributions to infilling. We also find that shapes of embayed basalt rocks outside the hollow appear platy, bladed, and elongate in a triangular form factor plot, and more discoidal and bladed in an axes ratio plot. By contrast, expected shapes based on terrestrial studies of basalt rocks are mostly compact, compact platy, compact bladed, compact elongated, platy, bladed, and elongate in triangular form factor plots, and equant with lesser, but significant disc‐ and blade‐shaped rocks in axes ratio plots. We find addition of 10 cm to the heights of rocks near the hollow rim, to account for continued partial embedding in ejecta, yields the best match between observed and expected rock shapes. Exposure of small ejecta rocks in the hollow supports degradation rates of 10−4 m/Myr during most of hollow history. Results indicate that deflation from ejecta accompanied by downwind deposition in the hollow can account for the current degraded form of the crater. Our approach is a new tool for characterizing small crater degradation on regolith‐covered lava plains on Mars.

Insight into martian crater degradation history based on crater depth and diameter statistics

Impact craters are widely used to investigate the geologic history of planetary surfaces. Their morphology bears clues on past surface processes that affected it such as erosion, sedimentary deposit and volcanic processes and their density is widely used to date planetary surfaces.In this study we propose to combine crater Density and morphology into a single representation, Crater Size and Depth Frequency Distribution (CSDFD) that offers a snapshot not only at the age but also at the obliteration history of the crater population. Using simple models, we interpreted the CSDFD in term of crater obliteration rates. This methods can be applied on any body featuring impact craters. We present here the results obtained on Mars, using a global crater database.The obliteration rates obtained from CSDFD are consistent with known geologic history of Mars. Reaching thousands of m/Gy during Noachian and rapidly dwindling as soon as 3.5 Gy. Moreover, our method highlighted an continuous activity of Northern Lowlands surface during Amazonian we interpret to be linked with the formation of the vastitas borealis formation. This study offer a continuous vision in time and space of Martian obliteration history.

Impact crater degradation, Oxia Planum, Mars

ABSTRACT The main goal of the European Space Agency (ESA) and Roscosmos ExoMars rover mission is to collect samples from the near-subsurface of Mars. The rover will look for any physical or chemical evidence of ancient life in the near subsurface. This map shows the distribution of impact craters at this proposed landing site in Oxia Planum on Mars. The map records 1199 impact craters > 500 m in diameter in a 5.0° × 2.5° region around Oxia Planum. The impact craters are symbolised based on the way different aspects of their morphology have degraded since their formation. The distribution of degradation and burial morphologies of impact craters can be used to determine where burial and erosion processes have occurred. Because the formation of impact craters is well constrained, occurs instantly and with a predictable flux, future studies could use this knowledge and our dataset to constrain when these events occurred.

The relationship between thermal inertia and degradation state of craters in areas of low surface dust cover on Mars

On Mars, impact craters that are proximal can exhibit vastly different thermal inertia values on their rims, even where the target lithology appears to be the same. Degradation of crater rims produces fine-grained regolith over time through comminution, and we investigated whether this process affects crater rim thermal inertia in regions with low dust cover. We used a series of regression analyses to test for correlations between crater rim thermal inertia and rim irregularity, an indicator of degradation state, in three martian study locations. The results of these analyses support the interpretation that crater rim thermal inertia is a function of crater degradation state in all three study areas. Therefore, rim thermal inertia could be used as a quick way to estimate impact crater degradation states and relative ages in areas on Mars with low dust cover and similar target properties. In contrast, crater rim thermal inertia in regions with high dust cover is a function of the amount of dust mantling the crater rims.

The Lunar Mare Ring‐Moat Dome Structure (RMDS) Age Conundrum: Contemporaneous With Imbrian‐Aged Host Lava Flows or Emplaced in the Copernican?

AbstractRing‐moat dome structures (RMDSs) are small circular mounds of diameter typically about 200 m and ∼3–4 m in height, surrounded by narrow, shallow moats. They occur in clusters, are widespread in ancient Imbrian‐aged mare basalt host units and show mineralogies comparable to those of their host units. Based on these close associations and similarities, a model has been proposed for the formation of RMDS as the result of late‐stage flow inflation, with second boiling releasing quantities of magmatic volatiles that migrate to the top of the flow as magmatic foams and extrude through cracks in the cooled upper part of the flow to produce the small RMDS domes and surrounding moats. In contrast to this model advocating a contemporaneous emplacement of RMDSs and their host lava flows, a range of observations suggests that the RMDS formed significantly after the emplacement and cooling of their host lava flows, perhaps as recently as in the Copernican Period (∼1.1 Ga to the present). These observations include: (a) stratigraphic embayment of domes into post‐lava flow emplacement impact craters; (b) young crater degradation age estimates for the underlying embayed craters; (c) regolith development models that predict thicknesses in excess of the observed topography of domes and moats; (d) landform diffusional degradation models that predict very young ages for mounds and moats; (e) suggestions of fewer superposed craters on the mounds than on the adjacent host lava flows, and (f) observations of superposed craters that suggest that the mound substrate does not have the properties predicted by the magmatic foam model. Together, these observations are consistent with the RMDS formation occurring during the period after the extrusion and solidification of the host lava flows, up to and including the geologically recent Late Copernican, that is, the last few hundreds of millions of years of lunar history. We present and discuss each of these contradictory data and interpretations and summarize the requirements for magma ascent and eruption models that might account for young RMDS ages. We conclude with a discussion of the tests and future research and exploration that might help resolve the RMDS age and mode of emplacement conundrum.

A New Method to Evaluate and Modify Chang’E-2 Microwave Radiometer Low-Frequency Data Constrained From Diviner Thermal Measurements

Microwave emission is influenced by regolith thermophysical properties that can reveal the geological evolution of the Moon. Lunar near-surface microwave emission has been systematically investigated by the microwave radiometer (MRM) onboard Chinese Chang’E-2 (CE-2) lunar satellite. However, recent work showed that global calibration issues were causing discrepancies between CE-2 observations and theoretical simulations at 3.0- and 7.8-GHz channels, which influences data interpretations and applications. In this study, we use a new method to improve thermal models by employing the bolometric brightness temperature and thermophysical property of subsurface structure derived from high quality and repeated coverage Diviner data. The derived subsurface temperatures make it possible for us to improve the accuracy of microwave brightness temperature ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T_{B}$ </tex-math></inline-formula> ) simulation within 70°N/S latitudes. We evaluate the MRM data quantitatively by comparing the global <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T_{B}$ </tex-math></inline-formula> between modeled values and CE-2 observations (i.e., offset values) at different local times (LTs) and latitudes. The results show that offset values of the two channels vary significantly with LT, especially near 06:00 and 18:00. However, the 7.8-GHz channel presents greater (~12k in average) calibration uncertainties than the 3.0-GHz channel. In addition, the offset of both the two channels becomes complex at high latitudes but presents an obvious north–south asymmetry. Finally, we modify the MRM data according to different offsets at different LTs and latitudes. The modified global <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T_{B}$ </tex-math></inline-formula> maps provide us a new view to characterize the lunar near-surface thermal environment, especially for low- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T_{B}$ </tex-math></inline-formula> spots that are related to the elevated rock abundance and crater degradation.

A Noachian Proglacial Paleolake on Mars: Fluvial Activity and Lake Formation within a Closed-source Drainage Basin Crater and Implications for Early Mars Climate

Abstract A 54 km diameter Noachian-aged crater in the southern highlands of Mars contains unusually well preserved inverted fluvial channel networks and lacustrine deposits, all of which formed completely inside the crater. This “closed-source drainage basin” (CSDB) crater is distinct from previously documented fluvially breached or groundwater-fed crater basin lakes on Mars. We compare our observations to previously established models of crater degradation, fluvial incision, and topographic inversion on Mars to assess the most likely origins of the water that formed the fluvial and lacustrine features. We favor top-down melting of a cold-based glacier as the source of water in the CSDB crater, which would represent the first examples of proglacial fluvial channels and lakes found on Noachian Mars.