Cirque-like alcoves in the northern mid-latitudes of Mars as evidence of glacial erosion

Abstract. Viscous flow features known as glacier-like forms on Mars have been observed emerging from alcoves that resemble cirques on Earth. However, many alcoves exist without associated glacier-like forms, and these features have never been studied or categorized at a regional population scale. On Earth, cirques form when depressions on mountain slopes accumulate snow, which gradually compacts into glacial ice. As the glacier flows downhill, it deepens the depression through erosion. Most of this erosion is driven by wet-based glaciers, although cold-based glaciers can also contribute to some headward and sidewall retreat. Here, we present evidence that cirque-like alcoves on Mars, similar to terrestrial cirques, are shaped by glacial erosion. To assess which alcoves on Mars are most “cirque-like”, we mapped a regional population of ∼ 2000 alcoves in Deuteronilus Mensae (40–48° N, 16–35° E), a region in the mid-latitudes of Mars characterized by mesas surrounded by glacial remnants. Based on visual characteristics and morphometrics, we refined our dataset to 434 “cirque-like alcoves” – nearly six times the amount of glacier-like forms in the region – and used this to better understand the potential contribution of glaciation to landscape evolution in Deuteronilus Mensae, Mars. High-resolution imagery reveals geomorphic evidence for past glacial occupation of these cirque-like alcoves, including flow features, linear terrain, moraine-like ridges, mound-and-tail terrain, polygonal terrain, rectilinear-ridge terrain, and washboard terrain, as well as an ice-rich mantling unit. Most cirque-like alcoves face south to southeast, similar to gullies poleward of 40°. One possibility to explain this trend is that southward facing cirque-like alcoves in the northern mid-latitudes formed when conditions were more favorable for ice accumulation during periods of high obliquity. Using wet-based glacial erosion rates, assuming a mean annual temperature of 0 °C (compared to present-day temperatures of ∼-63 °C), the timescales for Martian cirque-like alcove formation align with both the estimated ages of glacier-like forms (millions to tens of millions of years) and other viscous flow features such as lobate debris aprons (hundreds of millions of years). In contrast, using a temperature assumption of −50 to −68 °C, cold-based erosion rates are only consistent with the older ages of lobate debris aprons. By mapping cirque-like alcoves at a large scale for the first time, we expand the catalog of features attributed to glacial erosion on Mars. Future work is needed to specify the timing of the formation of cirque-like alcoves and whether their formation required warm-based erosion.