the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Cirque-like alcoves in the northern mid-latitudes of Mars as evidence of glacial erosion
Abstract. While glacial remnants in the form of viscous flow features in the mid-latitudes of Mars are considered to be cold-based in the present-day, an increasing amount of geomorphic evidence suggests that at least some flow features were previously wet-based or had a mixed thermal state (polythermal) at during their evolution. Many of the viscous flow features known as glacier-like forms have been observed to emerge from alcoves that appear similar to cirques on Earth. Terrestrial cirques are typically characterized by a concave basin connected to a steep backwall. Cirques are expected to form from depressions in mountainsides that fill with snow/ice and over time support active glaciers that deepen the depressions by wet-based glacial erosion. To assess which alcoves on Mars are most “cirque-like”, we mapped a population of ~2000 alcoves in Deuteronilus Mensae, a region in the mid-latitudes of Mars characterized by mesas encompassed by glacial remnants. Based on visual characteristics and morphometrics, we refined our dataset to 386 “cirque-like alcoves”, which is five times the amount of glacier-like forms in the region, and used this to assess the past extent and style of glaciation on Mars. Using high resolution imagery, we find geomorphic evidence for glacial occupation associated with the cirque-like alcoves, including crevasse-like features, surface lineations, polygonal terrain, and moraine-like ridges. We propose that the cirque-like alcoves with icy remnants similar to rock glaciers on Earth represent a late stage of glacier-like form evolution. We also outline stages of cirque-like alcove evolution, linking a potential early stage of cirque-like alcoves to gully activity. On a population-wide scale, the cirque-like alcoves have a south to southeastward aspect bias, which may indicate a requirement for increased insolation for melting to occur and a connection to gullies on Mars. While the alcoves also have similarities to other features such as landslide scarps and amphitheater-headed valleys, the cirque-like alcoves have unique morphologies and morphometrics that differentiate their origin. Assuming warm-based erosion rates, the cirque-like alcoves have timescales consistent with both glacier-like forms and other viscous flow features like lobate debris aprons, whereas cold-based erosion rates would only allow the older timescales of lobate debris aprons. We propose that based on the geomorphic features and southward aspect, cirque-like alcove formation is more consistent with warm-based glaciation.
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Status: final response (author comments only)
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RC1: 'Comment on egusphere-2023-2568', Joseph Levy, 18 Feb 2024
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AC2: 'Reply on RC1', An Li, 03 Aug 2024
We are grateful to the reviewer for their detailed comments on the manuscript. Following their suggestions, we have modified the manuscript with improvements. Attached is our response to the reviewer.
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EC1: 'Reply on AC2', Frances E. G. Butcher, 20 Aug 2024
Dear authors,
Thank you for your responses to reviewer 1. I have attached comments on your response document, including where references are made to editorial recommendations. I have also provided some additional suggestions on some other topics of discussion raised.
I hope these will be useful for your preparation of a revised manuscript.
Many thanks
Frances Butcher
Associate Editor
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EC1: 'Reply on AC2', Frances E. G. Butcher, 20 Aug 2024
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AC2: 'Reply on RC1', An Li, 03 Aug 2024
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RC2: 'Comment on egusphere-2023-2568 by Rishitosh Sinha', RISHITOSH Sinha, 18 May 2024
This paper explores the formation of cirque glaciers in glaciated terrains, typically forming in bowl-shaped depressions with flat floors and steep headwalls, primarily originating from the accumulation of snow and ice avalanching from upslope areas. The authors apply this concept to identify similar cirques on Mars, suggesting that cirques deepen through wet-based glacial erosion. Their detailed morphometric analysis is commendable, particularly in relating gullies with cirques, aligning with the proposal that gully heads serve as initiation points for cirques on Earth. However, there is one major point that requires clarification to enhance the paper's clarity.
In lines 314-317, the authors reference works by Costard et al. (2002), Williams et al. (2008, 2009), and Dickson et al. (2023b), suggesting that gully formation on Mars may be driven by meltwater resulting from increased insolation during high obliquity excursions. Later, in lines 450-452, they propose that gully incision might also be influenced by CO2 or dry mass wasting. It is unclear which gully formation mechanism the authors prefer in their work to relate to the formation of cirque-like alcoves. Can gullies formed by CO2 ice sublimation or dry mass wasting be considered initiation points for cirque-like alcoves, or is this specific to gullies formed by meltwater generation linked to higher obliquity excursions?
This distinction is crucial if the authors use it to link the early stages of cirque-like alcoves to gully activity, explaining the southward bias in the aspect of cirque-like alcoves, and gully heads as initiation points for cirque-like alcoves. The authors must address the two distinct thoughts on gully formation on Mars: one linking gully formation to meltwater and the other proposing a dry origin. For the sake of clarity and the readers' understanding, the authors should make this part clear in the paper.
Currently, the concepts appear mixed. Initially, the authors relate slope orientation preferences based on latitude, higher obliquity excursions, and insolation-driven meltwater generation with both gullies and cirque-like alcoves (e.g., lines 673-681). They also suggest that gullies can initiate through sediment flow assisted by either liquid water or CO2 ice sublimation. These are two different concepts, and the authors have mixed them. Please clarify this distinction and accordingly revise the paper.
My other concern, which would come alongside papers’ revision, is that the authors have to present evidence that can substantiate the relationship between ice meltwater and gully formation on Mars. A lot of papers published during the last decade have provide vital inputs regarding the role of CO2 ice sublimation as the main driver for gully formation on Mars. So the authors would have to present evidence for the role of water if they wish to relate meltwater driven gullies as the initiation point for cirque-like alcoves.
Citation: https://doi.org/10.5194/egusphere-2023-2568-RC2 -
AC1: 'Reply on RC2', An Li, 08 Jul 2024
We thank the reviewer for their comments on the connection between gullies and cirque-like alcoves. We agree with the reviewer that the manuscript would benefit from further clarity in areas. We outline these changes in the attached document.
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AC1: 'Reply on RC2', An Li, 08 Jul 2024
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