Some Martian volcanic features as viewed from the Viking orbiters

Abstract

The plains to the south and southwest of Arsia Mons are composed of elongate lava flows, many of which appear to originate at a reentrant in the Arsia Mons edifice. Individual flows can be traced for up to 300 km. Their widths range from 5–6 km close to Arsia Mons to 40–60 km at distances greater than 400 km from the volcano. The age of the flows, as indicated by the number of superposed impact craters, increases systematically with increasing distance from Arsia Mons. The length of the flows varies with altitude of the vent: the higher the vent, the shorter the flow. The distribution of vents on Arsia Mons and Pavonis Mons suggests the presence of deep-seated fractures trending NW-SE and NE-SW. Flows on the flanks of Olympus Mons extend far beyond the basal scarp, an indication of a much larger size for the volcano than was formerly believed. Around the basal scarp are numerous lobate features interpreted as landslides. Several types of flows are recognized on the flanks of Alba Patera. These include tube-fed flows, sheet flows, and tube-channel flows. The different types of flows are believed to indicate different eruption rates of a low-viscosity lava similar to basalt in its Theological properties.