The set of processes and phenomena involved in volcanic activity is called volcanism [early 19th century: from volcano + -ism]. The study of volcanism and volcanoes is called volcanology [mid-19th century: from volcano + -logy], sometimes spelled vulcanology.

Plate tectonics

According to the theory of plate tectonics, Earth's lithosphere, its rigid outer shell, is broken into sixteen larger and several smaller plates.

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