This oblique photo shows the crater Alphonsus on the eastern edge of Mare
Nubium. Note the five dark patches along the crater floor edge. Each of
these patches has a central pit. Three are located along clear fracture
trends. Also, most of these pits are also elongated or irregular in
shape. Thus, they are unlikely to be small impact craters. Instead, they
probably mark the sites of small vulcanian eruptions.
Note: The long corkscrew-like pole pointing into the image from the left
is part of the Apollo Orbiter.
(Apollo 16 image M-2478, looking southwards.)