How the wind turns
A piece of Mars: The two shadowed hills in the upper part of this frame (497×373 m or 1631×1224 ft across) rest on a flat plain covered in large ripples. On the plain the ripples are aligned north-south, formed perpendicular to a wind blowing from the east (right). But those hills block the wind and turn it, so that the ripples between the hills change direction. This is how windblown landforms can be used as wind vanes in remote places (like on Mars). (HiRISE ESP_037188_1835, NASA/JPL/Univ. of Arizona)
