This photo shows the Hadley Rille on the southeast edge of Mare Imbrium. It is fairly well known because Apollo 15 landed there (see next image). The rille begins at the curved gash in the bottom left corner, and is clearest in the rectangular, mare-floored valley shown here. In the upper left, it gets much shallower and it slowly fades out of sight in Palus Putredinis. In all, the rille is over 75 miles (120 km) long. It is up to 5000 feet (1500 m) across and is over 950 feet (300 m) deep in places. It formed nearly 3.3 billion years ago . In contrast, lava channels on Hawaii are usually under 6 miles (10 km) long and are only 150 - 300 feet (50-100 m) wide. This contrast in channel size probably reflects (1) differences in the volume of erupted lava and (2) the difference in gravity. Note -- The bright bumps surrounding Hadley are peaks of the Montes Apenninus. These mountains mark the edge of the impact basin holding Mare Imbrium. They rise from 6000 to 15,000 feet (1800 - 4500 m) above the mare. (Apollo 15 image M-1135, arrow marks landing site of Apollo 15. Image taken from NASA SP-469, Geology of the Terrestrial Planets)
