Debris-covered Glaciers within the Arsia Mons Fan-shaped Deposit: Implications for Glaciation, Deglaciation and the Origin of Lineated Valley Fill

Introduction: Recent MOC and THEMIS data have shed new light upon intriguing flow-like features on Mars including viscous flow-like features [1], lobate debris aprons [2], concentric crater fill, lineated valley fill, and features interpreted as rock glaciers or debris-covered glaciers [3,4,5,6]. These features are distributed over lowto mid-latitudes and all appear to have experienced flow due to the presence of volatiles. Here we consider debris-covered glaciers – features that consist of a relatively pure glacier ice core covered by a thin (sub-m to m scale) layer of debris. A debris cover typically develops from rockfall or direct atmospheric dust deposition in the accumulation zone of the glacier and/or through sublimation of ice in the ablation zone, resulting in a surficial lag deposit of supraglacial and englacial debris. Using new data, we assess the origin of these features at Arsia Mons. We also consider how this interpretation may provide insight into processes of glaciation and deglaciation on Mars, and discuss its application to other areas containing candidate deposits of glacial origin. Arsia Mons Smooth Facies: The Arsia Mons shield volcano has an 180,000-km fan-shaped deposit present on its west-northwestern flank (Fig. 1). Our previous work suggests that this fan-shaped deposit represents the depositional remains of a large cold-based glacier that formed on the westnorthwestern flank in the late Amazonian [5, 9]. One of the three main facies (smooth facies; Fig. 1) was interpreted as debris-covered rock glaciers [5]. These features consist of 20 to 100-km-long, broad, lobate plains, hundreds of meters thick with concentric ridges near the margins [5].