Influence of clay minerals on the slope angles and its implication for subsurface water in Mars

An internal frictional angle is determined from a frictional coefficient, which is largely influenced by clay minerals. Most mineral exhibit a constant frictional coefficient μ=0.6-0.85, whereas clay minerals are characterized by a markedly lower frictional coefficient 0.1 at presence of water (e.g. Behnsen and Faulkner, 2012; Moore and Lockner, 2004). Since a slope angle is roughly equivalent to an internal frictional angle, it is considered that slope angles are affected to become smaller by presence of clay minerals including water. Clay minerals are widely recognized on Mars (Ehlmann and Edwards, 2014) by infrared spectroscopic tools. We focus on a slope angle of Martian topography and research the areas where clay minerals are reported.

We focus on rootless cones which have young formation age and a wide range of distribution on Mars. They are also seen in Iceland and Hawaii on the Earth. It has been proposed that rootless cones are formed by interaction between lava and water, e.g. water bearing strata and river-bed sediments (Thorarinsson, 1953). Cones' shape and components vary with their formation environment (Hamilton et al., 2010) and cones have diverse slope angles. We are going to analyze slope angles of these topography to test presence of clay minerals near a surface layer of Mars.