The Moon: Differences from Earth's Volcanism
Differences from Earth's Volcanism
Mt St. Helens' eruption in 1980
- Volcanism on the Earth is an ongoing process.
- All volcanism on the Moon ended over a billion years ago.
- Many of Earth's volcanoes are less than a few 100,000 years old.
- Most volcanism on the Moon occurred between 3 and 4 billion
- Because the Moon does not show any evidence for recent volcanic or
geologic activity, it is sometimes called a "dead" planet.
- Earth's volcanoes mostly occur within long linear mountain chains.
- Mountain chains like the Andes mark the edge of a plate.
- Mountain chains like the Hawaiian Islands mark past plate movements over
a mantle hotspot.
- In contrast, mare typically occur in the bottoms of very large, very old impact craters.
- Therefore, lunar mountain chains form the edges of these impact basins and
tend to surround the lunar mare.
- There is no evidence that any system of plate tectonics ever
developed on the Moon.
- Mare surfaces are very flat and smooth. This implies that mare lavas were very fluid.
- They could both flow very easily and spread out over large areas.
- The low gravity means that any rare explosive eruptions could throw debris further on the Moon than on the Earth.
- Eruptions on the Moon should spread lavas out into a
broad flat layer and not into the cone-shaped features seen on the
- This explains why large volcanoes are not seen on the
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