What is volcanism in geology ?

Volcanism : definition

Volcanism is a fundamental geological phenomenon, which has participated in the life of our planet since its origin. This term includes all continental and underwater volcanic manifestations, the most spectacular being eruptions, the sometimes very violent setting up of volcanic rocks as well as earthquakes and hydrothermal manifestations (hot springs, geysers, acid lakes, solfataras, etc...) associated with them.

Magmas give rise to numerous volcanic rocks, which cover large areas on the earth and at the bottom of the oceans. The main volcanic rocks are basalts, andesites, trachytes and rhyolites.