Geological Chronicle
Mare Undarum (Latin for 'Sea of Waves') is an irregular lunar mare spanning 243 kilometers across the eastern near side of the Moon at 7.5° N, 68.7° E. The mare lies directly north of Mare Spumans and east of the crater Firmicus, occupying an outer structural trough between the third and fourth rings excavated by the Mare Crisium impact. Unlike circular maria that fill deep basin floors, Undarum formed when volcanic lavas flooded elevated highland topography, producing isolated patches and dark ribbons that follow the contours of the underlying crust.
The surrounding highland terrain dates to the Nectarian period, while the basalt fill erupted during the Imbrian period. Because the lava sheets were relatively thin, the pre-existing topography remains visible beneath the dark basalt. The lava settled into valleys between raised ridges, producing the characteristic wave-like bands that give the mare its name. The crater Dubyago borders the southern margin of the mare, while Condorcet P lies on the northeastern edge. Geological surveys have identified five lunar domes within Undarum, marking low volcanic vents where effusive eruptions took place.
In the 1830s, German astronomer Johann Heinrich von Mädler mapped Mare Undarum and observed periodic changes in the appearance of its dark streaks under varying solar illumination angles, leading him to suggest that vegetation might be growing on the lunar surface. Spacecraft observations later confirmed the volcanic origin of the dark material. In 1972, the Apollo 17 crew photographed oblique views of Mare Undarum during lunar orbit, and NASA's Lunar Reconnaissance Orbiter later mapped its basalt flows and volcanic domes in detail.