AN ENIGMATIC LANDFORM ON MARS: THE ZEPHYRIA FLUCTUS SOURCE AREA

For more than a decade, imaging data from the Mars Reconnaissance Orbiter (MRO) have revolutionized our understanding of geologic processes on the Red Planet. The ability to image relatively large (>1,500 km²) areas at ~6 m/pixel with the Context Camera (CTX), and then follow-up with more detailed (~25 cm/pixel) investigations with the High Resolution Imaging Science Experiment (HiRISE), has identified many new geologic features and geomorphic processes. The ability to collect stereo CTX and HiRISE images has enabled digital elevation models (DEMs) to be produced and has further enhanced this understanding.

This approach is illustrated through analysis of a HiRISE-derived DEM produced for the source area of a 37 km-long flow called Zephyria Fluctus, a distinctive flow deposit southwest of Cerberus Fossae on Mars. Discovered from a single CTX image, the flow source (0.35^oN, 155.17^oE) is a ~20 m deep, ~12 x 1.5 km wide, depression cut in a yardang within the Medusae Fossae Formation. However, the source area does not resemble any known volcanic vent on any planet so that the origin of the flow is enigmatic. The source area is characterized by multiple inward-dipping ridges interpreted to be products of waves of sediment erupted from the center of the depression. The curvature of these waves suggests multiple sources along a central fissure. Three clusters of numerous small cones (~2 – 8 m high) exist on the source floor and on the NE rim are interpreted to be mud volcanoes.

The origin of the Zephyria Fluctus flow has broad implications for recent (late Amazonian) geologic activity on Mars. Wilson and Mouginis-Mark (2014; Icarus 233, pp. 268 – 280) showed that the flow could well be a mud flow, but there are strong morphologic similarities between this (possible) mud flow and other flows within the Cerberus Fossae region which have previously been interpreted as volcanic flows. Getting the interpretation right has significant implications for the thermal history of Mars (if lava flows) or the availability of near-surface water (if mud flows). It is expected that additional stereo data from CTX, HiRISE and the Colour and Stereo Surface Imaging System (CASSIS) instrument on the Trace Gas Orbiter now in orbit around Mars will reveal additional fascinating geologic problems on Mars.