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

What affects the explosiveness of an active composite volcano?

1. Temperature of lava

2. Silica and water content of the magma

3. Location of the volcano

4. Type of surrounding rock

The correct answer is: Silica and water content of the magma

The explosiveness of an active composite volcano is primarily influenced by the silica and water content of the magma. Higher silica content in magma leads to increased viscosity, meaning the magma is thicker and flows less easily. This increased viscosity can trap gases within the magma, preventing them from escaping easily. As gas builds up, pressure increases, ultimately leading to explosive eruptions when the pressure surpasses the strength of the surrounding rock. Additionally, the presence of water in the magma can further enhance explosiveness. Water vapor expands significantly when heated, adding to the pressure build-up and contributing to more volatile eruptions. In contrast to the other options, while temperature, location, and surrounding rock type can influence volcanic behavior and eruption characteristics, the direct relationship between the composition of the magma—specifically the silica and water content—and the explosiveness of an eruption is a key factor in understanding why certain composite volcanoes are more explosive than others.