Lava flows at Arsia Mons, Mars: Insights from a graben imaged by HiRISE

HiRISE has imaged a graben wall on the western flank of Arsia Molls volcano, Mars. This graben is similar to-3 x 16 km in plan-view size and is oriented almost perpendicular to the general volcano slope. We have identified 1318 individual sub-horizontal layers, which we interpret to be lava flows, in the 885 m high, nearly vertical, eastern wall of this graben. The average and median outcrop widths of each layer are 149 and 85 m, respectively. No layers extend > 1.72 km across the width of the section, arguing against these being either areally-extensive ash or paleo-glacial deposits, which has implications for the reoccurrence interval of glacial events and/or the long-term magma production rate of the volcano. Measurements (N = 118) made at a 100-m spacing across the width of the section reveal that there are, on average, 17.3 layers at each location. This implies an average layer thickness of similar to 51 m. Locally, however, as many as 7 layers call be counted within a 70 m-high part of the section, implying, if these layers are indeed lava flows, that Arsia Molls occasionally erupted flows that were only similar to 10 m thick. (C) 2008 Elsevier Inc. All rights reserved.