Dark Mantling Deposits
Although the mare formed from large effusive lava flows, there is some
evidence for explosive volcanism on the Moon. In places, the lunar surface
is covered by dark layers of material. The largest of these areas are near
the edges of the lunar mare. They cover many thousands of square
kilometers. They also include a range of knobs and other highland
features. Thus, because lavas only flow downhill, these units can not be
lava flows. Instead, they seem to mark areas where a thin layer has been
draped over an older surface. Apollo 17 brought back samples from one such
unit. They contain many small spheres of orange and black glass. These
spheres probably formed from small drops of lava that cooled very quickly.
Such droplets are thrown out of an eruption when bubbles of gas burst near
the surface. Due to the size of the dark mantle deposits, however, some of
these spheres may have been thrown hundreds of kilometers. Thus, despite
the low gravity and lack of air on the Moon, some of lunar eruptions must
have been quite violent. They may have resembled Hawaiian fire fountains,
but on a much larger scale. There are also many smaller dark mantling
units on the Moon. Most of these features are only a few kilometers in
diameter. They are almost always located near the mare or in large crater
floors. Many also lie along clear fault lines. Since most have a small
central pit or crater, they are likely sites for small volcanic
explosions. Some of these small eruptions may have released gases from
shallow lunar intrusions.
Map of Dark Mantling Deposits
Sinus Aestum
Crater Alphonsus
Eruption Styles