4.S: Summary

Igneous rock is divided into two major groups: intrusive rock that solidifies from underground magma, and extrusive rock formed from lava that erupts and cools on the surface. Magma is generated from mantle material at several plate tectonics situations by three types of melting: decompression melting, flux melting, or heat-induced melting. Magma composition is determined by differences in the melting temperatures of the mineral components (Bowen’s Reaction Series). Volcanoes come in a wide variety of shapes and sizes, and are classified by multiple factors, including magma composition, and plate tectonic activity. Because volcanism presents serious hazards to human civilization, geologists carefully monitor volcanic activity to mitigate or avoid the dangers it presents.

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