# Morphological Mapping and Dating of Recent Ice-Rich Deposits on Alba Mons, Mars

Léo Scordia, Noé Le Becq, Susan J. Conway

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Léo Scordia, Noé Le Becq, Susan J. Conway. Morphological Mapping and Dating of Recent Ice-Rich Deposits on Alba Mons, Mars. 56th Lunar and Planetary Science Conference, LPI, Mar 2025, The Woodlands (Texas), United States. hal-05395655

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## MOPHOLOGICAL MAPPING AND DATING OF RECENT ICE-RICH DEPOSITS ON ALBA MONS, MARS.
L. Scordia¹, N. Le Becq¹, S.J. Conway¹. ¹Laboratoire de Planétologie et Géosciences, Nantes, France (noe.le-becq@univ-nantes.fr).

**Introduction:** Assessing the nature and distribution of water ice in the mid-latitudes of Mars is fundamental for the understanding of the planet's recent climate history [1], and for characterizing ice reservoirs as a resource for future human exploration [2].

Impact craters are ideal locations to search for ice-rich deposits as their pole-facing slopes act as cold-traps, favoring the deposition and preservation of the ice [3, 4]. Numerous works have already identified ice-rich deposits in mid-latitude craters, such as [5] with a global map of concentric crater fill (CCF), or other studies on small-scale viscous flow features (VFF) in craters, such as small glacier-like forms (GLF) [6, 7] and lobate debris aprons (LDA) [8]. More recently, Sinha & Vijayan [9] reported lobate ice-rich deposits on pole-facing crater slopes in the Alba Mons region and dated them to between 10 and 100 Ma. Also, Schiff et al. [10] studied the texture of similar deposits on the slopes of the Alba Mons caldera and observed an ice-rich mantle superimposing these deposits, interpreted as younger and showing a “hummocky” texture with few superimposed craters.

In this study, we focus on the hummocky texture identified by [10] and search for deposits with similar textures within the craters identified by [9]. The objective is to explore the distribution of these hummocky upper deposits (UD) and compare to the distribution of VFFs [11] and to the large-scale patterns in atmospheric circulation models [1] in order to understand the complex deposition chronology of these ice-rich deposits.

**Datasets and approach:** The UD were mapped using the ~5 m/pix MurrayLab CTX mosaic [12] in the Alba Mons region, from 27° to 62°N and 79° to 142°W. We selected craters larger than 1 km that have sufficient data quality to investigate the surface texture in the database from [9]. For each crater, we looked for the hummocky texture to identify the upper deposits and classified them based on their termination style. Hummocky deposits with a lobate margin and steep termination, lying directly on the crater floor were classified as type 1 UD, and those with a concave termination smoothly transitioning into an underlying lower icy deposit (LD), such as CCF or LDA, as type 2 UD (Fig. 1). For each crater with an identified UD, we noted the morphology of the host crater (diameter, depth, rim, ejecta) as well as that of the deposit itself (ridges, texture, stratigraphy) using available images from the High-Resolution Imaging Science Experiment

(HiRISE) and the Colour and Stereo Surface Imaging System (CaSSIS). We then created a density map with a resolution of 160 km in order to compare the number of craters with UD depending on their type, and the number of craters with VFF from [11], normalized by the total number of craters >1km referenced in [13]. Finally, we counted the superimposed craters on two UD with HiRISE in order to plot the crater size-frequency distributions (CSFD) and estimate their age [14].

<figure><img src="image_2.png" /><figcaption>**Fig. 1:** CTX images showing craters with UD. **A**- Crater with a type 1 UD with a steep termination (blue arrow) (92°36′W 42°50′N). **B**- Crater with a type 2 UD smoothly transitioning (red arrow) into a LD with a higher crater density (108°1′W 36°50′N).</figcaption></figure>

**Results:** From the 346 craters in [9], 280 have sufficient data quality to be analyzed. We find 43 craters with type 1 UD and 237 craters with type 2 UD. These craters are located between 30° and 50°N and type 1 UD
are located slightly further north than type 2 UD (Fig. 2). The normalized distribution reveals a higher concentration of UD on the south-eastern flank of Alba Mons. Type 1 UD in this area are smaller, their hummocky texture is more pronounced, and their termination appears less steep than those further north.

**Comparison with climate models.** By comparing the distribution of UD with a map of the modeled surface water-ice accumulation at 35° obliquity [1], we find that the area where UD are concentrated corresponds to the northern part of a zone of maximum water ice accumulation in the model (between 20 and 40°N and from -110 to -90°E). The last time Mars had an obliquity of 35° was between 10 and 5 Ma [15].

**Headwall erosion.** We found that pole-facing UD are systematically associated with enhanced upslope erosion on the headwall of the crater [16]. This is illustrated in Fig. 3 where the southern wall of the crater has a sharp crest below which there is a jumble of disorganized rocks, that sometimes appear on top of the UD. Conversely, on the opposite wall with no UD, there is a more rounded crest with spurs of bedrock below and superimposed small craters on the talus slope. The lateral extent of the eroded headwall corresponds exactly to the lateral extent of the UD below it.

**Age estimations.** For the two UD with available HiRISE images, we find ages of 4.5±2 Ma and 8.8±4 Ma. This is broadly consistent with the ages obtained by [9] which range from 10 Ma to 100 Ma and probably differ because [9] dated both UD and LD together.

**Conclusion:** We have mapped hummocky textured ice-rich deposits present on the pole-facing slopes of craters, in the Alba Mons region. These deposits are sometimes alone in the crater (type 1 UD), or overly older deposits such as CCF or LDA (type 2 UD). Our dating suggests they are characteristic of a very recent episode of glaciation on the surface of Mars. Two UDs have been dated at 4.5±2 Ma and 8.8±4 Ma, which corresponds to the last time Mars had an average obliquity of 35°. There is a higher density of UD on the south-eastern flank of Alba Mons, an area already

identified in climate models as favoring ice accumulation during periods of high obliquity [1]. Moreover, we find a very strong spatial correlation between the presence of these ice-rich deposits and erosion of the crater headwall. We are investigating whether this erosion is linked to periglacial processes or liquid water films at the base of the ice. Our results provide additional constraints for climate model simulations for recent glaciations on Mars.

**Acknowledgments:** Authors have been financially supported by the French Space Agency - CNES and by INSU-CNRS via an International Research Center (IRC) set up with the University of Arizona.

**References:** [1] Madeleine et al. (2009) *Icarus*, **203**. [2] Morgan et al. (2021) *Nature Astron*, **5**. [3] Forget et al. (2006) *Science*, **311**. [4] Lange et al. (2023) *JGR*, **128**. [5] Levy et al. (2010) *Icarus*, **209**. [6] Souness et al. (2012) *PPG:EE*, **36**. [7] Hubbard et al. (2014) *The Cryosphere*, **8**. [8] Head et al. (2010) *EPSL*, **294**. [9] Sinha & Vijayan (2017) *PSS*, **144**. [10] Schiff et al. (2022) *Icarus*, **383**. [11] Levy et al. (2014) *JGR*, **119**. [12] Dickson et al. (2024) *ESS*, **11**. [13] Robbins & Hynek (2012) *JGR*, **117**. [14] Hartmann & Daubar (2016) *MPS*, **52**. [15] Laskar et al. (2004) *Icarus*, **170**. [16] Conway et al. (2018) *Icarus*, **318**.

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**Fig. 3:** HiRISE image ESP_085734_2220 of a 2.5 km crater with a type 1 UD (A) showing the exposed bedrock on the equator-facing slope (B) and erosion of the headwall on the pole-facing slope (C). Blue arrow indicates the UD lateral extent. Red arrow indicates the eroded headwall lateral extent.

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**Fig. 2:** Map of craters with UD. Type 1 UD are shown in blue, and Type 2 UD are shown in red. Gray points are the craters hosting VFF from [14], but with no visible UD. MOLA colorized elevation ranges from 6800 m (white) to -2500 m (light blue).