Ohio Assessment for Educators (OAE) Integrated Science (024) Practice Exam

Which content in magma is primarily responsible for determining its viscosity and explosiveness?

1. Magnesium

2. Silica

3. Potassium

4. Calcium

The correct answer is: Silica

The viscosity and explosiveness of magma are primarily influenced by its silica content. Silica, or silicon dioxide (SiO2), plays a crucial role in determining how thick or fluid magma is. When there is a high concentration of silica in the magma, it tends to form a more viscous substance, which can lead to more explosive volcanic activity. This is because the high viscosity traps gases within the magma, and as pressure builds up, it can result in explosive eruptions when the magma eventually escapes. In contrast, magmas with lower silica content are generally more fluid, allowing gases to escape more easily and resulting in less explosive eruptions. This understanding of silica content is fundamental in volcanology and helps predict volcanic behavior. The other components, such as magnesium, potassium, and calcium, do not have the same direct impact on viscosity and explosiveness to the extent that silica does. Their roles may be significant in other geochemical properties or mineral formation, but in terms of magma viscosity and eruptive potential, silica is the key element.