Phreato-magmatic dike–cryosphere interactions as the origin of small ridges north of Olympus Mons, Mars

Using images from the Mars Orbiter Camera, we have identified several linear ridges located 10–60 km north of the volcano Olympus Mons, Mars, at the edge of the Olympus Mons aureole materials. These ridges appear to be made of unconsolidated material by virtue of the many dust avalanche scars seen on their upper slopes. Based upon their morphology (several ridges have crater-like central depressions) and superposition relationships, the ridges appear to have formed very recently and post-date the formation of the youngest lava flows spilling over the northern escarpment of Olympus Mons. Several possible origins for the ridges, including an eolian, periglacial, or depositional origin have been considered, but we favor a ridge origin by a series of small explosive eruptions initiated by the intrusion of a dike into a volatile-rich substrate. To explore this process, we develop a numerical model for dike intrusion into a volatile-rich substrate that yields plausible dike widths between 2.4–3.5 m. The total volume of a single ridge system is ∼65×106 m3, and we calculate that it may have taken only a few minutes to form. Viable solutions only exist when the thicknesses of the ice-rich layer is less than ∼1000–2000 m. This strongly suggests that the ice-rich region is limited in its vertical extent to a value of this order.