MASS WASTING FEATURES ON AND RELATED TO APOLLINARIS PATERA

The isolated Martian shield volcano Apollinaris Patera (8.6°S, 174°E) is Hesperian in age and has been built largely through explosive volcanism. Subsequently, much of the volcano’s edifice appears to consist of weak, easily erodible pyroclastic deposits that have undergone mass wasting; the most prominent evidence of mass wasting is the presence of a scarp at the base of the volcano. Here we focus on two locations on the western flank of Apollinaris that appear to have experienced mass wasting: 1) the middle of the western flank and 2) a blocky terrain west of the volcano’s basal scarp. Topographically, Apollinaris’ western flank is about 10° steeper than the rest of the volcano, making it likely that mass wasting could occur here.

Magnified CTX satellite images of the slump block show that it possesses buried, block-like features on the landform. The surface of the block appears dry and undulatory with traces of other shapes including ridges and smooth hills towards the toe of the block. Using the program JMARS to plot elevation versus distance data, a total volume of the slump block was estimated to be 725,186 km³. The volume of the main body, secondary toe, and partial toe were estimated separately for accuracy. An estimate for the main body of the slump block is 657, 020 km³, being 26.6 km in length, 1900 km in height, and 13 km in width. The secondary toe is about 51,336 km³, being 13.8 km in length, 1550 km in height, and 2.4 km in width. The partial toe is about 16, 830 km³, being 9 km in length, 850 km in height, and 2.2 km in width. Considering age relationships, we suggest this mass wasting occurred after cessation of volcanism. The landslide deposit and blocky terrain bordering the western flank is striped with troughs. We used bidirectional rose diagrams to determine if the deposit formed from a landslide. The diagrams showed no dominant trends in the troughs’ orientations. Magnified MOC images show that the blocky terrain west of the volcano looks similar to the material in the slump block. We found, by using bidirectional rose diagrams, that the formation of this blocky terrain is structurally controlled. Two dominant orientation trends of these troughs at 90° and 130° demonstrate the blocky terrain is a result of structural control. We conclude that the landslide deposit and block terrain likely formed following the cessation of volcanism.