THE FORMATION OF YARDANGS IN THE WESTERN MEDUSSA FOSSAE FORMATION

Yardangs are aerodynamically shaped landforms that represent the remnants of eroded deposits by the wind. On earth they occur in scales of meters to kilometers long and in dry, arid environments with little or no precipitation. In the Medusa Fossae Formation, they occur within different levels of deposition. The Medusa Fossae has been studied extensively and is thought to be a large deposition of windblown ash from a nearby eruption. Massive yardang fields have etched the landscape of this formation from tens of meters to tens of kilometers long. The abrasive material carves out large ridges and slowly carves away more and more sediment to create fleets of these structures. Yardangs show the direction of the prevailing winds by the way they are pointing. They have a very steep side on the windward side and a gentler sloping side on the back. The yardangs in the vicinity of the volcano, Apollinaris Patera (9° S, 174.4° E) only occur in two areas, to the northwest and east of the volcano. The yardangs to the northwest of Apollinaris occur on top of the Medussa Fossae and indicate a wind direction from the south west. Yardangs east of Appollinaris occur stratigraphically younger than those of the northwest and indicate a more southerly wind direction. There is evidence for multiple periods of deposition for the MFF as evidenced by the change in yardang orientation and the covering of the yardangs themselves as discussed by Mandt et. al.(2008). These two different occurrences of yardangs suggest that there was a long period of deposition and a wind direction change over time on this part of Mars.