Figure 6: Components of a volcano

There are two main types of lavas:

1. Basic Lavas: These are the hottest lavas and are highly fluid. They are dark coloured like basalt, rich in iron and magnesium but poor in silica. They flow quietly and are not very explosive. They affect extensive areas, spreading out as thin sheets over great distances before they solidify. The resultant volcano is gently sloping with a wide diameter and forms a flattened shield or dome.

2. Acid Lavas: These lavas are highly viscous with a high melting point. They are light coloured, of low density and have a high percentage of silica. They flow slowly and seldom travel far before solidifying. The resultant volcano is therefore steep-sided. The rapid cooling of lava in the vent obstructs the flow of the outpouring lava, resulting in loud explosions throwing out many volcanic bombs or pyroclasts.

Note: Pyroclasts are any volcanic fragment that was hurled through the air by volcanic activity.