Science Olympiad Dynamic Planet Practice Test

Which structure is typically formed from explosive eruptions?

1. Cinder cone

2. Shield volcano

3. Composite volcano

4. Caldera

The correct answer is: Composite volcano

Explosive eruptions are characterized by their violent release of gases and magma, leading to the formation of specific volcanic structures. Among these, composite volcanoes, also known as stratovolcanoes, are the most commonly associated with explosive eruptions. These volcanoes are built up from alternating layers of lava flow, ash, and other volcanic debris, creating steep profiles. The explosive nature of eruptions at composite volcanoes is largely due to the viscosity of their magma, which is typically andesitic to rhyolitic in composition. This high viscosity prevents gases from escaping easily, leading to increased pressure that culminates in explosive eruptions. When such eruptions occur, they can eject large amounts of ash and volcanic rock into the atmosphere, contributing to the layered structure characteristic of composite volcanoes. In contrast, cinder cone volcanoes primarily form from explosive eruptions but are generally smaller and have a one-time explosive event that leads to the buildup of volcanic ash and tephra around the vent. Shield volcanoes, on the other hand, are associated with non-explosive eruptions where low-viscosity basaltic lava flows spread out over large areas, resulting in broad, gently sloping structures. Calderas are large depressions formed after massive