Steep topographic scarps often dissect the terrain at the transition from the southern
cratered uplands towards the northern lowlands. At their base, well-defined flow fronts
with convex-upward surfaces extend into the low-lying plains [43]. These lobate debris
aprons have been attributed to gelifluction and/or frost creep [46]. The water
content in this mixture of rock and ice might be derived from the atmosphere [44], or
from ground ice by sapping or scarp collapse [45]. Where flow fronts from opposing
walls collide, e.g., in valleys, linear ridges and grooves cover the whole valley floor.
This so-called lineated valley fill resembles terrestrial median moraines on glaciers