What is a Yardang?
A "yardang" is a streamlined, teardrop-shaped ridge carved out of a cohesive material by strong winds coming from one main direction. Yardangs form when the wind is acting a rock unit with variable strength, for example, when a hardened layer caps a softer layer. These wind erosional features form parallel to one another and are separated by a trough. The highest point of the yardang is the side that the wind is blowing from (windward) and it tends to be steep and blunt. The formation slopes down in the direction that the wind is traveling and tapers to a point.
What is a Volcanic Rootless Cone?
A rootless cone is a volcanic landform that resembles a volcanic crater. However, there is not an actual vent from which lava erupts. These volcanic features form when lava explosively interacts with waters. The interaction produces steam explosions and produces porous material that builds up in a crater-like form.
Our work found that when the wind removed rock to form the yardangs, it may have exposed a porous material that was filled with ice. These exposed areas are called wind blown aprons. When the lava flowed over these aprons, it heated up the ice being stored in the rock and resulted in steam explosions! So, the presence of these volcanic rootless cones can suggest the present of ground ice on Mars during the lava flow event.