Volcanism on the Moon
By Robert Wickman
Cones and Domes
While there are no large volcanoes on the Moon, a few
smaller volcano-like features have been recognized. These features are
mostly fairly small. Few are more than a few thousand feet (few hundred
meters) high, or more
than 6 to 10 miles (10 to 15 km) across. They are also somewhat irregular in
most are not very striking in appearance. Few show any large central pit
or vent structures, but many do have very small central pits or craters.
These lunar constructs resemble small cinder cones and volcanic domes on
the Earth. However, such cones and domes may form differently on the Earth
and Moon. On the Earth, cinder cones form when small explosive eruptions
pile up pieces of lava around a central vent. On the Moon, however, such
eruptions will throw things much further, leaving little to pile up near
the vent. Instead of a volcanic cone, such lunar eruptions should form a
broad, thin layer around the central vent (a dark mantling deposit).
Similarly, lava domes on Earth form from very thick, pasty lavas. Basaltic
lavas are more liquid, and tend to form broad, flat lava flows. On the
Moon, most of the domes and cones appear to be made of basalts. Thus, they
can not have formed like Earth domes from thick, non-basaltic lavas.
Instead, the lunar domes/cones may mark places where the erupted basalts
were just barely molten.