Dead end tributaries

Dead end tributaries

. All of the deep tributaries of Nirgal Vallis have blunt ends and steep walls, with no indication of erosion between them. These characteristics suggest an origin by collapse into cavities that were eroded by underground streams rather than surface rivers. This Viking image is 60 thousand meters across. (Courtesy of Michael Carr and NASA.)

Copyright 2010, Professor Kenneth R. Lang, Tufts University