This figure shows two styles of volcanism that might leave dark
mantling units. (1) Strombolian eruptions feature bubbly, frothy magmas,
and spatter large volumes of magma over large distances. Thus, such
eruptions may have formed the largest dark mantle deposits on the Moon.
(2) Vulcanian eruptions tend to be smaller than strombolian eruptions.
They feature short explosions of gas and rocks. Because gases need to
build up near the vent, they do not involve large volumes of magma. They
also are somewhat episodic. Thus, vulcanian eruptions are more likely to
form the smaller patches of dark materials on the Moon. They also are
more likely to open up a recognizable central pit or vent structure.
In the figure, red depicts new lavas in an eruption, blue represents old,
colder lavas, and purple denotes mixtures of old and new lava.
(figure modified from Wilson and Head (1981) J. Geophys. Res, vol. 86)