Mare Humorum
This image shows Mare Humorum and the western edge of Mare Nubium. Mare
Humorum is a small circular mare on the lunar nearside. It is about
275 miles (~440 km)
across. The mountains surrounding Mare Humorum mark the edge of an old
impact basin. This basin has been flooded and filled by mare lavas. These
lavas also extend past the basin rim in several places. In the upper right
are several such flows which extend northwest into southern Oceanus
Procellarum. Note the large fractures arcing around Mare Humorum on the
right. These fractures are believed to mark a bending of the lunar surface
due to the weight of Mare Humorum. Such a sinking of the mare may also
explain the two large, partly flooded craters that
seem to slope into Mare Humorum.
(Earth-based telescopic photo from the Consolidated Lunar Atlas)