Science Olympiad Dynamic Planet Practice Test

What is the main factor that contributes to the explosive nature of eruptions in stratovolcanoes?

1. Low viscosity of lava

2. High viscosity of lava

3. Frequent eruption cycles

4. Elevation of the volcano

The correct answer is: High viscosity of lava

The explosive nature of eruptions in stratovolcanoes is primarily attributed to the high viscosity of their lava. When magma rises from the Earth’s mantle to the surface, its composition and temperature greatly influence its viscosity. Stratovolcanoes typically produce magma that is rich in silica, which significantly increases the magma's viscosity. High-viscosity lava does not flow easily, creating a tendency for gas bubbles to become trapped within the magma. As the magma ascends towards the surface, the pressure from the volcano's gases can build up dramatically. When the pressure becomes too great, it can lead to a violent release of gas and magma, resulting in explosive eruptions. This contrasts with volcanoes that have low-viscosity lava, where gases can escape more easily, leading to less explosive eruptions. While factors like eruption cycles and elevation can influence volcanic activity, they do not directly determine the explosiveness of stratovolcano eruptions in the way that magma viscosity does.