A FRAMEWORK FOR ANALYZING YARDANG MORPHOMETRY ON EARTH AND MARS

Yardangs are streamlined bedrock ridges that form in friable substrates and parallel to unidirectional winds in arid regions on Earth, Mars, and other bodies. Their formation by a dynamic fluid creates diverse morphologies that require a systematic measurement methodology in order to characterize the factors influencing their evolution. This work presents a measurement framework that describes yardangs in the Medusae Fossae Formation, Mars, and the Puna region of Argentina, Earth with four points for each yardang and tests this measurement framework for exceptions in those settings.

Current models of yardang evolution interpret their boat-shaped morphology as being due to erosion by local variations in airflow. These variations are caused and perpetuated by the prow-shaped protuberances on the upwind section of most yardangs. With this initial point established, three other points are necessary to describe the yardang shape: the back point and the two wide points on each side of the yardang. The back point is defined for an isolated yardang as the region where separated flows have become completely reattached to the substrate and vortices have dissipated. This was field identified in the Puna by the lowest downwind ridge, which was found to consistently correspond in imagery to the backmost topographic expression of the yardang. The length of the yardang is defined as the distance between front and back points, and the width is defined as the sum of the distances between the two side points and the line running between the front and back points. These definitions provide flexibility for parameterizing asymmetric yardangs and those influenced by other features upwind or across from them. The spacing is described by the orthogonal distance between each side point of a yardang and a line parallel to the length of an adjacent yardang projected from its nearest side point.

These morphometric and spacing parameters will be used to characterize the erosive maturity and appearance of entire yardang fields. However, yardang morphologies that are less discrete require modification or exemption from this framework. Yardangs with multiple prows can be described using more than four points. Other yardangs lack discrete boundaries and would be better characterized using automated image analysis rather than manual parameterization.