Volcanic Processes

Volcanism is another of these processes. Volcanoes are among the most spectacular, and dangerous, features on Earth. They typically form around mid-oceanic ridges, or subducting plates. Over the course of several thousand years, some volcanoes can build themselves up to quite impressive sizes. The rate at which volcanoes grow depends on which type it is. Stratovolcanoes can reach massive heights, some peaking at over 22,000 feet (in the Andes). Meanwhile shield volcanoes and cinder cones have much more modest heights. The lifespan of a volcano tends to be significantly shorter than that of a mountain, despite being formed in somewhat similar fashion. This is because of two main reasons. The first is that stratovolcanoes often self-destruct. During large eruptions, they will sometimes eject so much material that there isn’t enough material remaining to support the edifice of the volcano, causing it to collapse downward and form a caldera. Earthquakes and landslides can also trigger a volcano to erupt, as is what happened with Mount St. Helen in 1980. In geological terms, volcanoes are short-lived features with lifespans of usually around hundreds of thousands to a few million years.

The final process is impact cratering. Impact Cratering when a planet’s surface is excavated by being struck by a meteoroid. They leave behind very characteristic features. Here on Earth, they are much harder to recognize due to erosion on the planet’s surface. This isn’t the case on the moon, however, which explains why there are so many more to be found there. By comparison, about 80% of the Earth’s surface is less than 200 million years old whereas over 99% of the moon surface is over 3 billion years old. Scientists, about a decade ago, began to employ the help of NASA’s Lunar Reconnaissance Orbiter (LRO) to study the impact craters of the moon, which is hit in the same proportions over time as Earth. Using this knowledge, they were able to form a list of all lunar craters younger than a billion years old. They were then able to conclude that the Earth and moon have been struck about the same. However, up until 290 million years ago, the Earth had a much lower impact rate. Nobody is really sure of the reason why the impact rate has risen, although a popular belief is that more than 300 million years ago large collisions may have taken place in the asteroid belt between Mars and Jupiter, creating debris that could reach the inner solar system.

The geological processes change and mold features of the Earth daily. Some of these events, such as volcanic eruptions, can be seen and observed in real time. Others, however, like the shifting the of plate tectonics, happen as such a slow rate that observation over the course of years is needed before any real difference may be seen.

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