Geology Home Page physical geology historical geology planetary gems
Roger Weller, geology instructor
by Patrick Ransford
Volcanism is the next major geologic force on the moon. Elements such as
uranium, potassium, and thorium reheated areas of the lower crust and upper
mantle, which created a series of melts. The melts were less dense then the
surrounding rock which caused it to rise to the surface. These massive impacts
sent faults deep into the moon’s surface that made pipes for the rising lava.
The mantle underneath that created “basins” which are artificial hollow place
containing water, rose closer to the surface, making it a shorter path to the
Lunar lavas generally erupted from narrow openings, which poured out and ponded into the lower plains. When it erupted on an inclined surface, the lava could flow downhill and even create river like channels. On the moon these formations are called “sinuous rilles”. Some may even run up to several hundred kilometers before pouring out their lava onto lower surfaces. This process of flooding results in large, flat lava sheets that covered the basins. Lava was thicker in the center of the basin and thinner toward the edges. Since lava is heavier than the surrounding crustal rock, it compresses the bedrock underneath. The thicker areas which would be in the middle did this more than the thinner less heavy lava on the sides. This made the center sink as the outer areas remained raised.
Lunar volcanism, which are also called lunar “domes” are smooth sided with low levels of incline. This is because lunar lava has a low viscosity. Most of the lunar domes are 5-20 km across, which also have a small pit crater. The Marius Hills region contains a large number of lunar domes. Some of the domes in this region are very steep sided.
Dark mantling, were formed by which they describe as a fire fountain. This is when lava is in the moons mantle and under a lot of pressure, and as in rises to the surface this pressure allows trapped gasses to escape. These gasses that they thought to be carbon monoxide or dioxide act as propellant’s shooting the lava very high above the lunar surface. As it is high it cools down creating dark glassy beads. These beads as they fall to the surface create large patches of “dark mantling”. You could even see these threw small telescopes.
Volcanism on the moon is different in many ways from
volcanism on earth. On earth it is an ongoing process. On the moon, volcanism is
3 to 4 billion years old compared to earths at most 100,000 years. The oldest
rock on earth is about 3.9 billion years old, and the oldest sea floor basalts
is 200 million years old. The moon is considered a “dead planet” because no
evidence shows recent volcanic or geologic activity. Earths volcanoes occur
within long linear mountain chains, also with very large, very old craters.
Lunar mare is found on one side of the moon that cover one third of the moon and
less than 2 percent of lunar on the two thirds. The primary factors that control
the volcanism on the moon appear to be surface elevation and the crustal
thickness of it.
Although a team of scientist from India that has claimed to have found evidence of a recent volcanic activity on the moon, using data from “NASA”. They say that according to central peak of Tycho crater has features of volcanic origins, indicating that the moon was active during the craters formation 110 million years ago. PRL researchers claim lava channels and flows of inner crustal materials were within Tycho were made as recently as 100 million years ago. Large boulders ranging in the size of 33 meters were spotted by LRO on Tycho central peaks. The researchers also hint that they may be volcanic in origin. Without further studies of this, it is hard for these scientists to determine the exact origin and age as well of these lunar formations that were found on the moon. The forces driving lava flow on the moon is very weak compared to the lava flow on earth, although they both flow and spread very easily. Debris on the moon from the explosive eruptions can be tossed much farther than on earth because of the low gravity. These eruptions on the moon should cause the lava to come out as a smooth flat service and not a cone like structure as earth’s lava creates. On the moon all lunar mare are bone dry which means there is no dissolved water, but on earth water is one of the most common gases in lavas. Water also plays a big role for driving very violent eruptions on earth. The moon without water will make it less likely to have violent explosive eruptions, which should make it to where the lava flows quickly and much smoother on the moon then it should on earth.
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3. Rare Lunar Vocalism
4. History of Lunar Vocalism
5. The Vocalism Blog