section_path: Physical characteristics/Surface geology/Compressional features
section_name: Compressional features
paragraph_text: Compressional features
  
  An unusual feature of Mercury's surface is the numerous compression folds, or rupes, that crisscross the plains. These exist on the Moon, but are much more prominent on Mercury. As Mercury's interior cooled, it contracted and its surface began to deform, creating wrinkle ridges and lobate scarps associated with thrust faults. The scarps can reach lengths of 1,000 km (620 mi) and heights of 3 km (1.9 mi). These compressional features can be seen on top of other features, such as craters and smooth plains, indicating they are more recent. Mapping of the features has suggested a total shrinkage of Mercury's radius in the range of ~ 1–7 km (0.62–4.35 mi). Most activity along the major thrust systems probably ended about 3.6–3.7 billion years ago. Small-scale thrust fault scarps have been found, tens of meters in height and with lengths in the range of a few kilometers, that appear to be less than 50 million years old, indicating that compression of the interior and consequent surface geological activity continue to the present.