Question

What type of boundary is associated with composite volcanoes? A) plates moving apart B) plates sticking and slipping C) plates moving together D) plates sliding past each other

Short answer

C) plates moving together.

Step-by-step solution

Understand Composite Volcanoes

Composite volcanoes, also known as stratovolcanoes, are characterized by a conical shape with steep sides. They are built up by many layers of hardened lava, tephra, pumice, and volcanic ash. These types of volcanoes are known for explosive eruptions.

Identify Plate Boundary Types

The four types of plate boundaries are: - Divergent: where plates move apart. - Convergent: where plates move together. - Transform: where plates slide past each other. - Sticking and slipping can occur at various boundaries, especially transform boundaries.

Link Composite Volcanoes to Plate Boundaries

Composite volcanoes are primarily associated with convergent plate boundaries. These occur where an oceanic plate subducts beneath a continental plate, leading to melting and volcanic activity.

Select the Correct Answer

Given that composite volcanoes form mainly at convergent boundaries due to subduction, the correct answer is C) plates moving together.

Key concepts

Convergent Plate Boundaries

At convergent plate boundaries, tectonic plates move towards each other. These boundaries are often the sites of intense geological activity. There are three main types of convergent boundaries: oceanic-continental, oceanic-oceanic, and continental-continental interactions.

• Oceanic-Continental Convergence: An oceanic plate slides beneath a continental plate due to subduction, creating a trench and volcanic arcs. This is where many composite volcanoes form.
• Oceanic-Oceanic Convergence: One oceanic plate is forced under another, forming volcanic island arcs.
• Continental-Continental Convergence: Neither plate subducts completely due to both being buoyant, creating mountain ranges instead of volcanoes.

The process of subduction causes the oceanic crust to melt as it descends into the mantle. The molten material, or magma, then rises, forming volcanoes like stratovolcanoes at the earth's surface.

Stratovolcanoes

Stratovolcanoes, also known as composite volcanoes, are large and steep volcanoes that can rise thousands of meters above their surroundings. They have a distinctive cone shape formed by repeated eruptions that deposit layers of lava, ash, and volcanic debris.

These volcanoes are primarily found at convergent plate boundaries, where an oceanic plate subducts under a continental plate. Their eruptions are notorious for being both explosive and dangerous, compared to other types of volcanoes.

The eruptions of stratovolcanoes often produce pyroclastic flows, which are fast-moving currents of hot gas and volcanic matter. These flows, along with lava, tephra, and volcanic bombs, add to the layers that form the stratovolcano's massive cone. Examples of famous stratovolcanoes include Mount St. Helens in the United States and Mount Fuji in Japan.

Explosive Eruptions

Explosive eruptions are a hallmark of stratovolcanoes, occurring when high-pressure gas is trapped within the viscous magma. This is typically due to higher amounts of silica in the magma, creating thicker lava that can clog the volcano's vent.

When pressure from the trapped gases becomes too great, a powerful eruption occurs, releasing massive amounts of ash, gas, and volcanic rocks. These eruptions can be extremely dangerous, causing widespread damage, igniting fires, and altering landscapes.

• Pyroclastic Flows: Fast-moving flows of hot ash, gas, and volcanic material.
• Lahars: Mudflows or debris flows triggered by volcanic activity, often occurring with snow or ice on volcanic peaks.
• Volcanic Ash Clouds: Fine particles of volcanic rock that can disrupt air travel and affect climate.

Understanding the explosive nature of these eruptions helps scientists predict potential hazards and mitigate risks associated with living near stratovolcanoes.