So we’ve moved deeper into the smooth plains in the Hokusai quadrangle of Mercury and whenever these plains that are made from lava flows become particularly deep they are able to bury impact craters completely and here’s an example of one. You might be able to make out this faint ring, which shows that an impact crater that’s maybe 100 km across or more has been buried by volcanic lavas. and around the edge the ring is picked out by things called ‘wrinkle ridges’, these little slight folds in the landscape all around, marking where the impact crater rim originally was.