Plate Tectonics and Volcanoes

10.1 Volcanoes and Plate Tectonics Pt. 2

Convergent Boundary Volcanism

• Volcanoes form at convergent plate boundaries where slabs of oceanic crust subduct into the mantle.

• As a slab sinks deeper into the mantle, the increase in temperature and pressure drives water from the oceanic lithosphere.

• Once the sinking slab reaches a depth of about 100 to 150 km, this water reduces the melting point of hot mantle rock low enough for melting to begin.

• Magma migrates upward through the overlying plate, forming Volcanoes!

Multiple Choice

What is a convergent plate boundary?

• Where two tectonic plates move away from each other
• Where two tectonic plates slide past each other horizontally
• Where two tectonic plates are stationary and do not move
• Where slabs of oceanic crust subduct into the mantle.

Convergent Boundary Volcanism

• If the affected part of the overlying plate is made of oceanic lithosphere, the process produces a chain of volcanoes on the ocean floor.

• Eventually, these volcanic mountains grow large enough to rise above the surface.

• If that happens, the volcanoes are called a volcanic island arc.

Numerous volcanic island arcs, such as the Mariana islands, are found near subduction zones of the Pacific Ocean.

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Volcanic Island Arcs

Multiple Choice

What is a volcanic island arc?

• A chain of islands formed by erosion
• A series of islands formed by tectonic uplift
• A chain of volcanic mountains that grew large enough to rise abo

• A group of islands created by a volcanic eruption

• Together, the Mariana islands with other volcanoes bordering the Pacific, form the Ring of Fire.

• The Ring of Fire is the long belt of volcanoes that circles much of the Pacific Ocean.

Multiple Choice

What is the Ring of Fire?

• A famous rock band
• A type of spicy hot sauce
• The long belt of volcanoes that circles much of the Pacific Ocean.

• A popular jewelry store chain

• Volcanism may also occur at convergent plate boundaries where a slab of oceanic lithosphere is subducted under continental lithosphere.

• The result is a continental volcanic arc.

• Tungurahua and the other volcanoes of the Andes in South America form a continental volcanic arc.

• These volcanoes formed as the Nazca plate was subducted beneath the South American plate.​

Continental volcanic arc

Multiple Choice

What process formed the volcanoes of the Andes?

• Subduction
• Glacial movement
• Volcanic eruption
• Erosion

• Volcanic activity that occurs within a plate.

• Examples: Hawaii's Mount Kilauea and Yellowstone

Intraplate volcanism

• Most intraplate volcanism occurs where a mass of hotter-than-normal mantle material, called a mantle plume, rises toward the surface.

• As the plume nears the top of the mantle, decompression melting forms magma.

• The result may be a small volcanic region a few hundred kilometers across called a hot spot.

• More than 40 hot spots are known and most of these hot spots have lasted for millions of years.

​Hot spots on the map!

Multiple Choice

What three factors affect how magma forms?

• Heat, pressure, and the water content.

• Distance from the equator, ocean currents, and air pressure
• Wind speed, humidity, and altitude
• Color, shape, and size

Multiple Choice

What are the locations of volcanoes related to plate boundaries?

• At the center of tectonic plates
• At the equator
• In the middle of continents
• They form along convergent and divergent plate boundaries, as well as hot spots.

Multiple Choice

How is magma formed through decompression melting?

• By increasing the pressure on a rock, causing it to melt and form magma.
• When the temperature of a rock is decreased, causing it to melt and form magma.
• Through the process of erosion, causing the rock to melt and form magma.
• When the pressure on a rock is reduced, causing it to melt and form magma.