What are ruined lunar craters?
Ruined craters are ones that have been formed in the early stages of the Moon’s history but have been devastated subsequently by later volcanic eruptions and crustal disturbances. The outlines of some of the heavily ruined craters are barely recognizable.
What are lunar clefts?
A lunar cleft has the appearance of a river bed on Earth. This is a mere coincidence since there is no water on the Moon and appearances can be deceptive. One of the impressive clefts, the great Heroclotus Valley clefts, is 500 m deep and winds impressively like a river gorge across the plain.