Image credit: Scott Brande
Magma that rises to the surface of the earth may erupt in different styles, depending on such factors as chemical composition and abundance of dissolved gas, such as carbon dioxide (CO2) and water vapor. Two distinct eruption styles may be termed explosive (airborne) and liquid flow of lava on the land.
In the explosive eruption style, the sizes of particles that rapidly solidify may vary by many orders of magnitude, from microscopic and small yet visible particles of ash, to clods of airborne magma that rapidly cool into blocks and bombs.
The explosive nature of such eruptions also shatters the older rock of the pre-existing volcano, and perhaps large volumes of the 'country' rock (whatever it may be) surrounding the volcano.
Explosive events may result in a number of different types of igneous rock termed fragmental, for the mixture of debris produced by the high energy eruption.
In our simplified classification of the common igneous rocks, we will recognize only two types - tuff and volcanic breccia.
Watch this short video to learn how to distinguish tuff and volcanic breccia.