Answer
Composite volcanoes, also known as stratovolcanoes, are composed of alternating layers of different materials that result from both explosive and effusive eruptions. These volcanoes are typically characterized by their steep-sided cone shape. The materials that compose composite volcanoes can be described as follows:
1. Lava Flows: Composite volcanoes consist of lava flows that are primarily composed of intermediate to high viscosity lava, such as andesite or dacite. These lava flows are usually thick and slow-moving, which contributes to the steepness of the volcano's slopes.
2. Pyroclastic Deposits: Composite volcanoes also have layers of pyroclastic deposits, which are fragmented materials ejected during explosive eruptions. These deposits include volcanic ash, lapilli (small volcanic fragments), and volcanic bombs (large, solidified lava fragments). The accumulation of these pyroclastic materials contributes to the overall structure of the volcano.
3. Volcanic Ash: Fine-grained volcanic ash, consisting of tiny glassy particles and rock fragments, is a common component of composite volcanoes. Ash can be ejected into the atmosphere during explosive eruptions and carried by wind for long distances, settling on the volcano's slopes and surrounding areas.
4. Volcanic Gases: Composite volcanoes release various gases during eruptions, including water vapor, carbon dioxide, sulfur dioxide, and others. These gases can be dissolved in the magma and released explosively during eruptions, contributing to the explosive nature of composite volcanoes.
The combination of these materials, including lava flows, pyroclastic deposits, volcanic ash, and volcanic gases, contributes to the composite nature of these volcanoes and influences their eruptive behavior.
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