Composite volcano

Definition

A composite volcano, also known as a stratovolcano, is a type of volcano characterized by its steep profile and layers of hardened lava, tephra, and volcanic ash. These volcanoes typically form at convergent tectonic plate boundaries, where an oceanic plate subducts beneath a continental plate, leading to explosive eruptions and the formation of a cone-shaped mountain. The interplay of explosive activity and lava flows gives composite volcanoes their distinct layered structure and significant height.

5 Must Know Facts For Your Next Test

1. Composite volcanoes are known for their violent eruptions due to the high viscosity of their magma, which traps gas until it is released explosively.
2. The layers of a composite volcano consist of alternating lava flows and deposits of tephra, creating a steep-sided structure that can reach heights over 3,000 meters.
3. Mount St. Helens in the United States and Mount Fuji in Japan are well-known examples of composite volcanoes, showcasing the typical features and eruptive styles.
4. These volcanoes often have crater summits formed during explosive eruptions, which can lead to caldera formation if the summit collapses after an eruption.
5. Composite volcanoes can produce pyroclastic flows, which are fast-moving currents of hot gas and volcanic matter that pose significant hazards to nearby areas.

Review Questions

• Compare and contrast composite volcanoes with shield volcanoes in terms of their formation and eruptive styles.
  • Composite volcanoes differ from shield volcanoes primarily in their shape and eruptive style. Composite volcanoes have steep profiles due to layers of explosive tephra and lava flows, while shield volcanoes have gentle slopes built up from low-viscosity lava that can flow long distances. In terms of eruptions, composite volcanoes tend to produce more explosive eruptions due to higher gas content in their viscous magma, whereas shield volcanoes typically exhibit effusive eruptions with less explosive activity.
• Discuss the role of tectonic settings in the formation of composite volcanoes and how they influence eruption types.
  • Composite volcanoes are commonly formed at convergent plate boundaries where an oceanic plate subducts beneath a continental plate. This tectonic setting leads to the melting of mantle rocks and the generation of magma rich in silica. The high viscosity of this magma results in explosive eruptions that can create significant hazards like pyroclastic flows and ashfall. Understanding these tectonic processes is crucial for predicting volcanic activity and assessing risks associated with composite volcanoes.
• Evaluate the potential hazards associated with composite volcanoes and their impact on surrounding communities.
  • Composite volcanoes pose several hazards to surrounding communities, including explosive eruptions that can eject large volumes of tephra into the atmosphere, resulting in ashfall that disrupts air travel and affects health. Pyroclastic flows can devastate areas near the volcano due to their speed and temperature. Additionally, lahars—volcanic mudflows caused by heavy rainfall mixing with loose volcanic material—can occur post-eruption, posing further risks. Understanding these hazards is essential for effective emergency planning and risk mitigation for communities living near these powerful natural features.

Related terms

Lava flow: The movement of molten rock (lava) that erupts from a volcano, which can vary in viscosity and speed depending on its composition.

Tephra: Fragmented material produced by a volcanic eruption, including ash, pumice, and volcanic rock fragments that can be ejected into the air.

Subduction zone: A region of the Earth's crust where one tectonic plate moves under another, often associated with volcanic activity due to the melting of the subducted plate.