CONSTRAINTS ON PAST GLACIATION IN THE MID-LATITUDES OF MARS THROUGH MORPHOMETRIC ANALYSIS OF A LARGE-SCALE POPULATION OF ALCOVES

While glaciation on Mars is typically considered to be cold-based, recent work suggests more widespread wet-based glaciation than previously expected. On Earth, cirque erosion typically requires liquid water at the base of the glacier and cirque morphometrics are useful paleoenvironmental indicators. Cirques are typically characterized by a concave basin connected to a steep backwall and 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. While select alcoves have been interpreted as cirques in multiple locations on Mars, we assess a large-scale population of alcoves as potential cirques across Deuteronilus Mensae (40-48ºN, 16-35ºE), a region in the mid-latitudes of Mars characterized by mesas encompassed by glacial relicts from previous glaciations. Excluding filled alcoves with mapped glacier-like forms, we map a total of 1952 alcoves using Context Camera images and High Resolution Stereo Camera digital elevation models. We apply the Automated Cirque Metric Extraction tool (Spagnolo et al. 2017) in ArcMap to calculate 16 metrics such as length (L), width (W), elongation (L/W), depth (H), area, elevation, and aspect. To evaluate alcoves shaped by glacial versus non-glacial processes, we define seven classes of alcoves but focus on four: simple, compound, complex, and staircase; for this work we exclude alcoves in the crater, fluvial, and branching classes. We use subcategories to define any type of debris within the alcoves, ranging from boulders to layers. We refine our dataset to 1524 potential cirques by retaining only alcoves with a ratio of L/W between 0.5-4.25, which correspond to cirques mostly eroded by ice-action on Earth (Barr & Spagnolo 2015). We use power exponents of logarithmic regressions of size as (LWH)^1/3 versus L, W and H to determine relative directional growth and which erosional processes dominate, such as periglacial processes, headwall recession, or subglacial deepening. We find compound alcoves have the most isometric growth like cirques, though width increases faster than length and height for all four classes. Building from these alcove morphometrics, we differentiate the alcoves most likely influenced by glacial erosion in Deuteronilus Mensae on Mars.