What is a defining feature of composite volcanoes?

• A. They are primarily made of basaltic lava
• B. They have steep slopes and explosive eruptions
• C. They form exclusively at divergent boundaries
• D. They produce only minor volcanic gases

Answer: (B)

Composite volcanoes are characterized by their steep slopes and tendency for explosive eruptions. This specific feature comes from their formation process, where alternating layers of lava flows, ash, and other volcanic debris accumulate over time. Composite volcanoes typically erupt more violently than other types of volcanoes due to the viscosity of the magma involved, which is usually andesitic to rhyolitic in composition. The high viscosity causes gas to become trapped, leading to pressure build-up and explosive eruptions.

The other options, while related to volcanic activity, do not accurately describe composite volcanoes. For instance, basaltic lava is more characteristic of shield volcanoes due to its low viscosity, and divergent boundaries are typically associated with volcanoes that produce less explosive eruptions. Additionally, the statement regarding the production of only minor volcanic gases does not align with the behavior of composite volcanoes, which can emit significant amounts of gas during their eruptions. Therefore, the defining feature of steep slopes and explosive eruptions clearly identifies composite volcanoes.