The Formation of the Kilometer-sized Flows in Chryse Planitia (Mars)

Abstract

Introduction: High-resolution images show the presence of kilometer-sized flows (KSFs) on Mars. Most of KSFs are associated with well-known volcanic centers, hence they have been interpreted as lava flows [1,2]. However, some KSFs occur in regions where such link is not obvious and  processes related to sedimentary volcanism have been proposed as an alternative [3-7]. A remarkable example of such KSF was reported by Komatsu et al. [6,8] at the southern margin of Chryse Planitia (19.16°N; 322.71°E). Later thirty-five similar KSFs (e.g., Fig. 1a) have been observed in the region [7]. KSFs typically feature three morphological elements: a) a central depression from which channel(s) originate(s), b) leveed channel(s), c) a distal portion of the fading channel where the material is deposited forming terminal lobes.Brož et al. [7] proposed that the KSFs resulted from low viscosity mud extrusions that propagate through extensive networks of channels that gradually lose their transport energy. As initial studies were based on Context Camera (CTX) images (~5-6 m/px, [9]) and HiRISE images (~30 cm/px; [10]), they lacked topographic resolution to support these hypotheses. Currently, six KSFs are covered by HiRISE stereo pairs. Using established methods [11], we generated seven Digital Elevation Models (DEMs) with a ground sampling of 1-2 m/px to obtain additional insights about their origin.Observations: Studied KSFs show a topographically well-defined “source” area displaying circular, semicircular or elongated map-view outline (Figs. 1, 2a). Three source areas are situated on relatively flat plains and are surrounded by ~hundred(s) of meter-wide elevated rims (Fig. 2a). The other source areas are superposed on higher elevation/inclined pre-existing surfaces with laterally less extensive rims (Fig. 1). The elevation difference between source area floors and the rims ranges from 10 to 20 m. The elevation of the source area floors is the same as that of the flat plains beyond the elevated margins on which KSFs are superposed. The margins of all studied source areas are breached, enabling any extruded fluid to flow out. The presence of elevated mounds (