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INTRODUCTION

MARE

SINUOUS RILLES

DARK MANTLING DEPOSITS

DOMES AND CONES




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Volcanism on the Moon

By Robert Wickman

Dark Mantling Deposits


Map of Dark Mantling Deposits Sinus Aestum
Crater Alphonsus Eruption Styles

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.