Morphology and geological structure of the western part of the Olympus Mons volcano on Mars from the analysis of the Mars Express HRSC imagery

The images of the western part of Olympus Mons and adjacent plains acquired by the HRSC camera onboard the Mars Express spacecraft were studied. The morphology, topography, and color of the surface were investigated. The surface age was determined by the frequencies of impact craters. The examination of the HRSC images combined with an analysis of the MOC imagery and MOLA altitude profiles have shown that the Olympus Mons edifice, at least in its western part, is composed of not only lavas but also of sedimentary and volcanic-sedimentary rocks consisting of dust, volcanic ash, and, probably, H2O ice that precipitated from the atmosphere. These data also indicate that glaciations, traces of which are known on the western foot of Olympus Mons (Lucchitta, 1981; Milkovich and Head, 2003), probably also covered the gentle upper slopes of the mountain. It is probable that the ice is still there, protected from sublimation by a dust blanket. Confirming (or rejecting) its presence is a challenge for the scheduled radar sounding with the MARSIS instrument mounted on the Mars Express spacecraft as well.