Volcanism on the Moon
Volcanism on the Moon is represented by the presence of volcanoes, pyroclastic deposits and vast lava plains on the lunar surface. The volcanoes are typically in the form of small domes and cones that form large volcanic complexes and isolated edifices. Calderas, large-scale collapse features generally formed late in a volcanic eruptive episode, are exceptionally rare on the Moon. Lunar pyroclastic deposits are the result of lava fountain eruptions from volatile-laden basaltic magmas rapidly ascending from deep mantle sources and erupting as a spray of magma, forming tiny glass beads. However, pyroclastic deposits formed by less common non-basaltic explosive eruptions are also thought to exist on the Moon. Lunar lava plains cover large swaths of the Moon's surface and consist mainly of voluminous basaltic flows. They contain a number of volcanic features related to the cooling of lava, including lava tubes, rilles and wrinkle ridges.
The Moon has been volcanically active throughout much of its history, with the first volcanic eruptions having occurred about 4.2 billion years ago. Volcanism was most intense between 3.8 and 3 billion years ago, during which time much of the lunar lava plains were created. This activity was originally thought to have petered out about 1 billion years ago, but more recent evidence suggests that smaller-scale volcanism may have occurred in the last 50 million years. Today, the Moon has no active volcanoes even though a significant amount of magma may persist under the lunar surface.
Impacts[edit]
Analysis of Moon magma samples retrieved by the Apollo missions indicate that volcanism on the Moon produced a relatively thick lunar atmosphere for a period of 70 million years between 3 and 4 billion years ago. This atmosphere, sourced from gases ejected from lunar volcanic eruptions, was twice the thickness of that of present-day Mars. It has been theorized, in fact, that this ancient atmosphere could have supported life, though no evidence of life has been found.[62] The ancient lunar atmosphere was eventually stripped away by solar winds and dissipated into space.[63]
Partial melting of the lunar mantle and the emplacement of Oceanus Procellarum flood basalts may have caused axial tilting of the Moon 3 billion years ago, during which time the lunar poles shifted 125 mi (201 km) to their modern positions. This polar wander is inferred from polar hydrogen deposits that are antipodal and displaced equally from each pole along opposite longitudes.[64]
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Recent activity[edit]
In 2014, NASA announced "widespread evidence of young lunar volcanism" at 70 irregular mare patches identified by the Lunar Reconnaissance Orbiter, some less than 50 million years old. This raises the possibility of a much warmer lunar mantle than previously estimated, at least on the near side where the deep crust is substantially warmer because of the greater concentration of radioactive elements.[65][66][67][68] Just prior to this, evidence has been presented for 2–10 million years younger basaltic volcanism inside the crater Lowell,[69][70] located in the transition zone between the near and far sides of the Moon. An initially hotter mantle and/or local enrichment of heat-producing elements in the mantle could be responsible for prolonged activities also on the far side in the Orientale basin.[71][72] There are currently no active volcanoes on the Moon, although moonquake data published in 2012 suggest that there is a substantial amount of magma under the lunar surface. The lack of active volcanism on the Moon may be due to the magma being too dense to rise to the surface.[73]
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