Acid lava is rich in silica. Silica, or silicon dioxide, is a compound that is abundant in the Earth's crust and is a major component of many types of lava. When lava is rich in silica, it is referred to as "acidic" because it has a high viscosity or thickness, and it tends to solidify quickly. This type of lava often erupts explosively and can produce volcanic ash and debris. Acidic lava is also associated with the formation of steep-sided volcanoes, such as those found in the Andes Mountains in South America. In contrast, lava that is low in silica is referred to as "basic" or "mafic," and it is often less viscous and less explosive than acidic lava.