Small scarps on the surface of Mercury

The low-altitude MESSENGER images reveal that Mercury’s small scarps often occur in clusters, collections of several small scarps with a common orientation (three white arrows).  As the small scarps grow in length and height from continued contraction or shrinking of the crust, the clusters of small faults merge together and form a larger fault.  With enough contraction the clusters of small fault scarps can grow to become large-scale scarps that are hundreds of kilometers long and hundreds to thousands of meters high.